8.25 8 1/4 Rebuild and modification

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greymouser7

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I want to change the ring and pinion on my axle, install a rebuild kit, rebuild the sure grip unit in it, and add disk brakes from a Jeep Cherokee. Can I do this on my own? What tools/calibration equipment do I need? If not, what is a fair price for the axle rebuild? Thank you for your time and input!

1976 Volare road runner (360 E-58) axle -originally a 2.94 gear

I bought a 3.21 ring and pinion and a master rebuild kit.

going into a 1977 dodge aspen (with the volare's suspension), stick shift A833 O/D, with a 367ci engine
 
Ring and Pinion Gear Set Up Specs - Torque and Backlash

Chrysler Axles - Gear Setup Torque and Backlash Specs:


Off-Road Resources

IMG_0466 (Medium).JPG
 
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Custom 8 1/4 Rear-End Install - Project Build - Mopar Muscle Magazine
Installing An 8-1/4 Rearend To A Muscle Mopar


Written by Brad Ocock on March 1, 1999

Tom Rounds - photographer;

When it comes to making your car perform better, there’s always a set order for performance modifications; front-to-back. We all start under the hood (usually with carb/ intake/headers, often followed by a cam swap). For those who like to row their own, a performance shifter is installed, maybe a clutch; automatic guys modify the valve body and later install a high-stall converter. Last on the list has always been the rearend. A lot of post-muscle Mopars rolled off the line with a standard, “small” not- built-for-punishment 8 1/4-inch rear end. The 8-3/4 is far more popular by virtue of it’s easy to set-up drop-out carrier, ease of gear changes (need a different ratio? Just swap the carrier!), no C-clips, stout construction and, of course, the strength of a larger ring gear. If you really want strength on an unparalleled level, you can step up to the legendary Dana 60. Able to handle torque output on the scale of diesel locomotives, the Dana is the last word in rearend strength. During the halcyon days, all it took to get one as original equipment was checking off the right boxes.

If your current street stomper came equipped with an 8-1/4 rear, standard thinking goes something like this — If it ain’t broke, don’t fix it. When it breaks, upgrade to an 8-3/4 or Dana. We’ll build the engine and trans, but forget about the rearend. When it breaks, we call the car all kinds of nasty names, tow it home, yank the rear and replace it. Most project cars are high-mileage cars, but the engine and trans have at least been gone through, if not outright rebuilt. When’s the last time you even changed the fluid in the rearend? Then you get mad when the poor thing breaks after increased horsepower from the front of the car on top of years of neglect....
 
Truth be known, unless you’re building a big-block or a full-race small-block, that lowly 8-1/4 is good enough. There are some guys who prefer a totally built 8-1/4 in drag racing situations because it’s lighter and there’s less reciprocating mass, so more power hits the tires. And because they’re the “cheaper” rear ends, the parts to rebuild and upgrade them are less expensive. Finally — and this is the real selling point — it’s already under the car! You don’t have to pay for a new housing, it doesn’t have to be narrowed to fit, you already have brakes on it, even the spring perches are in the right place! The situation we were in with one of our projects was, we had the whole rearend and brake set-up already in the vehicle, but it was an open diff with a highway gear. We thought about replacing/upgrading it, but decided to work with what we had. The engine is going to be warmed over, and the 904 will be upgraded, but it’s a daily driver that probably won’t see much strip duty. We felt the “little” 8-1/4 would hold up nicely if rebuilt right the first time. We ordered a complete differential, ring and pinion, and rebuild kit from Ring & Pinion Service and a rearend girdle cover from LPW Racing Products (PN 301-10C, fits 8.2 and 8.3 Chrysler 8-1/4). If we were going to put the vehicle on the strip, and especially if we were going to run slicks, we’d have stayed with this rear but purchased aftermarket axles and a C-clip eliminator kit. We had Mike Mott at Pro Automotive Performance Center put together a stout little rear that will survive nicely under an average street car. Certainly less than a full swap and perhaps just right for our needs.
 
Chrysler 8.25 rebuild writeup - JeepForum.com

- new bearing kit. for the two carrier bearings and two pinion bearings. i didnt get new axle bearings because they were already brand new. it should also come with new ring gear bolts and some lock-tite and new races for your carrier and pinion bearings along with new washers and new pinion bolt.

-start by removing the differential cover and draining the oil.

-take off your wheels and drum brake shoes.

-remove your u-joint bolts i believe they were an 8mm? i could be wrong. once my driveshaft was no longer attached to the pinion. i slid it out from the transfer case and decided this would be a good time to grease up the slip joint. there was no grease left.

- since im rebuilding the differential there was no point in marking where the driveshaft lined up but heres the male end (Sticking out of the transfer case) and the female end(on the driveshaft) all greased up

-and again, since i was under there i decided to remove the rear SWAY bar since its like an appendix, theres just no need for it

-now you can remove the bolt in the center of housing that mounts to the pinion that attaches your u-joints to the rear driveshaft. its pretty big and i forgot the exact size. to remove it i had to clamp down the housing while i used an air wrench to unscrew the bolt.

-then take the housing off and sit it somewhere you wont forget it.

-reach around and hold the pinion inside the differential while u tap it out , i used a rubber hammer. the smaller pinion bearing should slide off also.

-get a large flathead screwdriver and pop your pinion oil seal out.

-nextly get a drive and hammer your inside and outside pinion races out(unless your rebuild kit didnt come with them)

- remove the old ring gear from the carrier, *the bolts are reverse threads*, just an important tip for you. i didnt know and snapped the bolts from the old ring gear, which didnt matter because i have a new one with a new set of bolts

-tap in your new races in place , i used a race setting tool because if you dont its alot harder to set them in place

- now this is when i removed the bearings from the carrier and the the pinion, you HAVE to use a special tool to get the bearings off i will try to get a picture of that tool
 
- new bearing kit. for the two carrier bearings and two pinion bearings. i didnt get new axle bearings because they were already brand new. it should also come with new ring gear bolts and some lock-tite and new races for your carrier and pinion bearings along with new washers and new pinion bolt.

-start by removing the differential cover and draining the oil.

-take off your wheels and drum brake shoes.

which required an air wrench and it clamps down underneath the bearings and as you tighten down the bolt, it pulls off the bearings.

the only reason you remove the old bearing from the old pinion is to have this shim, without it your new pinion will not set right with the new bearing.

- nextly you can put your new bearings on, i started with the inside pinion bearing. it would be wise to use a hydraulic press. sit your old race on top of the bearing the way it would sit in the differential so you dont damage the bearing as you press down on it.

make sure the shim is in between the bearing and pinion and most importantly while your pressing the bearing in , make sure you are pressing it evenly because if one side of the bearing starts going on faster, it could cause you a great headache when you ruin your new bearing.

-then the carrier bearings, sit the bearings on as they would sit (smaller side of the bearing facing outward, then sit the old races in place on the bearings. i pressed them both in at the same time like this

-start by holding the ring gear in place and starting a few of the reverse threaded bolts so they will pull it into place. pull the bolts back out and put them in one at a time after dabbing some loc-tite on them. they are very important bolts and are almost impossible to find. so be careful as you torque them down. i used a very small impact wrench and put it on the lowest setting.

-again since i had the jeep on the lift i decided now would be the time to drain the front differential which has never had its oil changed (my jeep has 110 k on it) so it was overdue. i also decided now would be the perfect time to get synthetic gear oil for my differentials. i chose mobil 1 synthetic 75w-90 gear oil

-i used a air tool with a wire wheel attachment to get rid of the gasket covering the rim of the differential and cover. the same was done to the 8.25 cover and differential. if you dont have an air tool like that a scraper putty knife or wire brush works fine as well.

-put new gasket on the diff cover and and bolt it back up and fill 'er up with some good synthetic.

-now comes the hard part of setting the new pinion and spider gears/carrier

pinion depth- pinion depth is the depth of the pinion in relation to the axle centerline, and is adjusted by adding or subtracting shims to move your pinion in or out. pinion depth is verified by tooth contact pattern. your ideal pattern is centered between the face and flank. pinion depth must be set properly to avoid unneccessary noise and even worse, gear failure
 
tools needed-

dial indicator

precision calipers or micrometer

gear marking paint and a clean brush

bearing pullers.

bearing press

10 or 12 inch spanner wrench

impact gun or breaker bar

pinion nut socket,ring gear bolt socket and main cap bolt socket.

center punch and oil drain pan and other misc. tools.
 
From GotDart, "
An open differential drives both wheels, but if one of the wheels looses traction then ALL the torque is directed to that one wheel that is spinning. This is what the majority of cars have. These are often refered to as a 'peg leg' rear end.

A limited slip differential is one that 'limits' the amount of torque applied to only one wheel. There are several implementations that accomplish this. One is to use spring loaded clutch discs, a typical example is the Eaton differential. Another way is to use cones instead of the clutches, the example for this is the Auburn differential. Mopar's marketing name for limited slip is 'Suregrip'. And all Suregrips fall into one of these two types of limited slip. Often times these limited slip differentials are called a 'posi', but that is incorrect

Next is the locking differential. This does not use traditional clutches, it use 'cogs' to positively lock the two axles yet still allows one axle to spin faster than the other in turns. This differential is correctly refered to as a 'posi' and the example of this is the Detroit Locker.

In full blown race cars a spool replaces the differential. This solidly locks the two axles together and does not allow either side to spin faster than the opposite side.

There is also a torque biasing differential that behaves similar to a limited slip. These are more common on FWD transaxles.

And there is also an aftermarket device called a Powertrax that can be added to an open differential to make it work similar to a limited slip. The sad thing is they cost as much or more than a true limited slip. However you don't have to disturb the gears to install it so it's easy for the backyard mechanic to set up."

from thread: Why a suregrip?
 
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From mbaird,"
the terms posi, suregrip, trac loc, etc. are more like brand names of the same thing. although there are some differences between certain units, ie clutch style vs. cone style etc.
mopars call them suregrips, chevy calls them posi's and ford calls them
trac loc's ((or limited slip))
 
From Ace, "
GotDart, your definition of the Powertrax is wrong. It locks the axles in straight line, allowing "differentiation" in turns, when the gears overrun:

"It works something like this: During typical driving conditions, a Lock-Right–enhanced differential allows your axles to turn at different speeds (or differentiate), much like an open or limited-slip differential gear set. It’s a bit clicky-sounding during sharp, low-speed cornering (when the meshed teeth overrun each other), but this is perfectly natural. Since the unit is spring-loaded, under straightline operation (both axles turning in unison) the axles are continually locked together. That’s the key to full power transfer to the rear wheels and a solid hole shot."

Full article here:

http://www.moparmusclemagazine.com/techarticles/91299/index.html

They are expensive, but not as expensive as a new suregrip/posi/whatever and are much stronger than any of those OEM-type solutions. I have two of them installed in 8.75 rears on my cars and couldn't be happier!"
 
Rodney had an 8 1/4 in the Demon and ran some 11's hangin the front tires in the air. He still has the UNbroken rear end.

@Bighead440 Please tell these guys the 8 1/4 is probably all they'll ever need.
 
Rear Axles: Chrysler 8 1/4" Rear Axle

Chrysler 8 1/4" Rear Axle

Chrysler Corporation's Spicer 8.25" rear was one of two differential types used in M-bodies, with the other being the weaker 7.25" unit. The 8.25" rear axle first appeared around 1969 in Plymouth Belvederes, Satellites and Dodge Coronets. The measurement refers to the size of the ring gear. This gear, which is turned by the pinion gear, changes the direction of the power being transmitted to it. The pinion gear is turned by the driveshaft. From 1973 on, the 8.25" rear was used in virtually every rear wheel drive car model produced by Chrysler through 1989 and in trucks and Jeeps through the 1990s. Some truck versions were designated as 8 3/8" or 8.375", but many internal parts interchanged with the 8.25" unit. It should be noted that all 8.25" rear axle assemblies DO NOT necessarily interchange across all models due to different widths.

Built by the Dana Corporation, the housing is cast iron with tubular steel axle tubes pressed and welded in to form a complete carrier and tube assembly. The gear assembly is accessed by removing an inspection cover having 10 bolts. 8.25" axles use either the "7260" or "7290" style U-joints. All 8.25" rears had 3" axle tubes with large bolt pattern (5 X 4.5" bolt circle) axles. Units with a 2.45:1 gear ratio have a special case that will not accept any other gear ratio. The axles are retained by a c-clip on either side. All axles were 27 spline until 1997 when they were upgraded to 29 spline.

Although the consensus among many Mopar enthusiasts is that a Sure-Grip (limited slip) equiped 8.25" rear is good for up to 500 crank horsepower, it fares much better in street applications than the strip, and in lighter cars than heavy cars. Open 8.25" differentials are more prone to fail at higher horsepower levels than Sure-Grip units. The 8.25" axle has considerable aftermarket support since it was so widely used in the 1970s for performance use.

7.25" To 8.25" M-Body Swap (Originally posted by Malcolm)

If you currently have a 7.25" axle, the 8.25" axle will drop right onto the spring perch pad centers perfectly, requiring no modifications. On early M-body 8.25" rears, the measurement from the outside of the left drum to the outside of the right is one inch narrower than the later M-bodies, but there should be no tire clearance problems. As I mentioned in the old Forum, I run 7 inch rims and 225/70 15's without any problems and there is room for larger tires.

You will need:
  • The donor 8.25" rear. The best bet for locating a sure-grip equipped unit at this point are any police, taxi or fleet cars (see Cop Car Information ). Good donors that will be more difficult to find are 1978 And 1979 LeBaron, Diplomat and Caravelle (Canada) Station Wagons. These cars were owned by families and are usually not punished as violently as former police or fleet cars. In most cases the axles are mint even if the bodies are rotted out (and the fake wood panelling is twisted by the sun). You can also hunt F-Bodies Aspen/Volare), older M-Bodies (Lebaron/Diplomat/Gran Fury) and J-Bodies (Cordoba/Imperial/Mirada) as they'll all drop right if you find the ratio you want.
  • If available, get the driveshaft from a donor vehicle with a wheelbase and transmission similar to yours, i.e. 2-door, 4-door or wagon. If the driveshaft is not available, you will have to take your present driveshaft to a driveshaft shop, (along with the measurement from the transmission to the new rear end) and have it shortened or lengthened accordingly, and re-balanced.

If your donor axle is from a cop car, it will have 11 inch drums, so just buy new 11 inch ones. If your donor axle has 10 inch drums, you should be able to re-use the brake drums, shoes and all associated brake hardware from your 7 1/4" axle.

It's also a lot safer to do a brake job on everything in the rear while you're at it. It would be smart to replace both the brake lines on the axle and the rear brake hose (from body to axle) while you're there. They're cheap and also easy to get at while the axle's out.

Great time to replace the rear shocks too if money permits. New axle U-bolts and a buddy to help you lift the axles out and in and you're all set.

If you find a 727 equipped 4 door M-body with the driveshaft in it, the front yoke will not fit your 904 transmission’s spline. In addition the wagons will have longer drive shafts, which require shortening and re-balancing.

TRW makes a greasable heavy duty U-joint (part # 20124) that takes a beating and is well advised if you're going to spell your name on the highway in twin streaks of rubber (spelling "Malcolm" used to take a while until I installed the 360). Back to the U-joint. The nipple is on the end of one of the caps not in the valley of the inner cross where you can't get a grease gun on. Note: NEAPCO (New England Axle Product Company) also has one with the zerk in one of the caps.

Factory axle dimensions (7.25" and 8.25"
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for all F/J/M cars:


  • Axle flange to flange: 54.34"
  • Perch center to perch center: 44.46"

Factory ratios offered down through the years include but are not limited to:

  • 2.26:1 - This ridiculously high ratio was found in later M-bodies.
  • 2.45:1 - This was the most common ratio for 1978-1979 M-bodies. It also appeared in many fleet cop cars through 1989.
  • 2.76:1
  • 2.94:1 - This was also common. Usually found in M-body police/taxi/fleet cars.
  • 3.23:1 - This highly desirable ratio was not so common in M-bodies.
  • 3.55:1
  • 3.91:1

Aftermarket gear ratios available include but are not limited to:

  • 2.25:1
  • 2.45:1
  • 2.76:1
  • 2.94:1
  • 3.07:1
  • 3.08:1
  • 3.21:1
  • 3.55:1
  • 3.73:1
  • 3.90:1
  • 3.91:1
  • 4.10:1
  • 4.11:1
  • 4.56:1

Photos below:

  • Front view of an older 8.25" rear in an A-body (Courtesy of Moparts member V194)
  • Rear view of an 8.25" rear found in later M-bodies (Courtesy of Farley's member Woodvark)
  • Exploded view diagram of the 8.25" rear (Courtesy Chrysler RWD Factory Service Manual)

Sources:
« Last Edit: January 30, 2010, 16:39:03 by Reggie »
 
If the 8.25" or 8-1/4" axle has a 2.45 gear only 2.45, 2.25 gears and those specific sure grip units work for that particular 8-1/4" axle
My 2.45 gear under Victoria should be perfect as I hit the streets and hwy's for some fun trip's and yes, sure grip for some fun at the track but still give my 360 Valiant backed by a full stacked 904 trans some fun gas millage (Rear came out of a 73 duster).

abody 66 7.jpg
 
Sure Grip Differential

The Sure-Grip differential design is basic and simple and consists of a two piece case construction and is completely interchangeable with the conventional differential and also the previous
type.
A conventional differential allows the driving wheels to rotate at different speeds while dividing the driving torque equally between them. This function is ordinarily desirable and satisfactory. However, the total driving torque can be no more than double the torque at the lower traction wheel. When traction conditions are not the same for both driving wheels, a portion of the available traction cannot be used.

The Sure-Grip differential allows the driving wheel with the better traction condition to develop more driving torque than the other wheel, so that the total driving torque can be significantly greater than with a conventional differential.
Sure-Grip is not a locking differential. In normal driving conditions the controlled internal friction is easily overcome during cornering and turning so that the driving wheels can turn at different speeds. Extreme differences in traction conditions at the driving wheels may permit one wheel to spin.
Sure-Grip has been engineered to perform its specialized functions with minimum effect on normal vehicle operations.
The cone clutch Sure-Grip differentials are similar to corresponding conventional differentials except for the incorporation of the helix-grooved cones that clutch the side gears to the differential case. The grooves assure maximum lubrication of the clutch surface during operation. The cones and side gears are statically spring preloaded to provide an internal resistance to differential action within the differential case itself. This internal resistance provides pulling power while under extremely low tractive conditions such as mud, snow or ice when encountered at one of the rear wheels.
During torque application to the axle, the initial spring loading of the cones is supplemented by the gear separating forces between the side gears and differential pinions which progressively increases the friction in the differential. It should be remembered that this differential is not a positive locking type and will release before excessive driving force can be applied to one wheel.
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Identification of Sure-Grip differential assembly can easily be made by lifting both rear wheels off the ground and turning them. If both rear wheels turn in the same direction simultaneously, the vehicle is equipped with a Sure-Grip Differential. Another means of identification is by removing the filler plug and using a flashlight to look through the filler plug hole to identify the type of differential case.
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(Chatter-Moan)
Noise complaints related to rear axles equipped with cone-clutch Sure-Grip should be checked to determine the source of the noise. If a vehicle ride check produces the noise in turns but not straight ahead, the probable cause is incorrect or dissipated rear axle lubricant. The following draining and flushing procedure has been established for the Sure-Grip Differential before it is removed from the vehicle and replaced.
CAUTION: When servicing vehicles equipped with Sure-Grip differentials do not use the engine to rotate axle components unless both rear wheels are off the ground. Sure-Grip equipped axles can exert a significant driving force if one wheel is in contact with floor and could cause the vehicle to move.

(1) With lubricant of rear axle assembly at operating temperature raise car on hoist so rear wheels are free to turn. Install jack stands.
(2) Remove axle cover and drain and discard lubricant. Rotate differential so hole in case is facing down. Wipe out all accessible areas of carrier. The purpose of draining and discarding this lubricant is to rid the axle of any solid particles or liquid contaminants that may be contributing to the noise condition.
(3) Scrape any gasket material from housing cover and thoroughly clean surface with mineral spirits or equivalent and dry completely. Apply a 1/16 inch to 3/32 inch bead of MOPAR Silicone Rubber Sealant, Part No. 4318025 or equivalent (See Figure 7 in Conventional Axle Section of this Group) along the bolt circle of the cover.
Allow sealant to cure while cleaning carrier gasket flange with mineral spirits or equivalent. Dry surface completely. Install cover on axle and torque cover screws to 35 ft. lbs. (47 N•m). Beneath one of the cover screws, install the ratio identification tag.
If for any reason cover is not installed within 20 minutes after applying sealant, old sealant should be removed and a new bead installed.
(4) Remove jack stands. Raise or lower hoist until vehicle is in a level position.
(5) Remove filler plug. Install 4 ounces (.1183 litres) of MOPAR Hypoid Gear Oil Additive Friction Modifier, Part No. 4318060 or equivalent in the axle. Refill axle to proper level with MOPAR Hypoid Lubricant, Part No. 4318058 or equivalent.
(6) Install filler plug. Lower vehicle.
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The Sure-Grip differential can be checked to determine if its performance is satisfactory without removing the differential and carrier assembly from the vehicle.

(1) Position vehicle on a hoist with engine off and the transmission selector lever in park if automatic or in low gear if manual.
(2) Attempt to rotate wheel by applying turning force with hands gripping tire tread area.
(3) If you find it extremely difficult, if not impossible to manually turn either wheel, you can consider the Sure-Grip differential to be performing satisfactorily. If you find it relatively easy to continuously turn either wheel the differential is not performing properly and should be removed and replaced. The Sure-Grip Differential and internal parts are serviced as a complete assembly only. Under no circumstances should the differential be removed and disassembled and reinstalled.
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CAUTION: During removal and installation of axle shafts, DO NOT rotate an axle shaft unless both are in position. Rotation of one axle shaft without the other in place may result in misalignment of the two spline segments with which the axle shaft spline engages, and will necessitate realignment procedures when shaft is installed.

conventional differential removal.
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(1) Clean the Sure-Grip differential assembly in a fast evaporating mineral spirits or a dry cleaning solvent and with exception of bearings, dry with compressed air.
(2) Inspect differential bearing cones, cups and rollers for pitting, spalling or other visible damage. If replacement is necessary, remove bearing cones from differential case using procedure outlined in conventional axle section of this group.
(3) Visually inspect differential case for cracks or other visible damage which might render it unfit for further service.
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(1) If during cleaning and inspection the differential bearings were found to be unfit for further use and were removed follow procedure outlined in conventional axle section of this group.
(2) On axles requiring ring gear to be installed on differential case, relieve the sharp edge of the chamfer on the inside diameter of the ring gear using an Arkansas stone (Fig. 3). This is very important, otherwise during the installation of ring gear on differential case, the sharp edge will remove metal from the pilot diameter of case, which can get imbedded between differential case flange and gear; causing ring gear not to seat properly.
(3) Heat the ring gear with a heat lamp or by immersing the gear in a hot fluid (water or oil). The temperature should not exceed 300 degrees Fahrenheit (149.0 degrees Celsius). DO NOT USE A TORCH. It is advantageous to use pilot studs equally spaced in three positions to align the gear to the case.
(4) Using new drive gear screws (left hand threads) insert through case flange and into drive gear.
(5) Position unit between brass jaws of a vise and alternately tighten each screw to 70 ft. lbs. (95 N•m) on all axles.
(6) Follow procedure outlined in conventional axle assembly for setting drive pinion depth of mesh, drive gear backlash adjustment and bearing preload adjustment.
 
03a03.jpg



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Follow the same procedure outlined under conventional differential installation.
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Multi-Purpose Gear Lubricant, as defined by the American Petroleum Institute GL-5 should be used in all rear axles with conventional differentials; MOPAR Hypoid Lubricant, Part No. 4318058 is an oil of this type and is recommended or equivalent.
In Sure-Grip Differentials 4 ounces (.1183 litres) of MOPAR Hypoid Gear Oil Additive Friction Modifier, Part No. 4318060 equivalent must be included with this fill.
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For normal passenger car service, periodic fluid level checks are not required. At each engine oil change however, a fluid level check is recommended When this check is performed with the car in a level position, supported by the suspension, the fluid level should be 1/4 inch (6.4 mm) below the filler plug opening.
When the fluid level check is made with the vehicle on a frame contact type hoist, with the axle hanging free, the fluid level should not be lower than the bottom of the filler plug opening.


CAUTION: Should the rear axle become submerged in water, the lubricant must be changed immediately to avoid the possibility of early axle failure resulting from contamination of the lubricant by water.
 
Installing A Powertrax Differential Unit - Mopar Muscle Magazine

Installing A Powertrax Differential Unit – Making Trax
Written by Steve Dulcich on March 1, 2002

Getting Your 8 1/4 Rear Hooked Up With The Power Trax No-Slip
Got horsepower? If you are going to do more than go up in smoke, you’re gonna need some traction to back it up. The conventional open differentials used in most passenger cars utilize side gears that are splined to the axleshafts and in constant mesh with the differential pinion (spider) gears. These spider gears turn freely on the pinion shafts, and act as idler gears when the rear wheels are turning at different speeds, such as around a corner. This cheap, simple, and effective way to provide differential action in a drive axle has been around for a century. For high performance applications there’s a drawback we’re all too familiar with-lay on the power, and the conventional differential sends the power to the wheel with the least amount of traction, producing a smoky one-legged burn-out.

Chrysler, like the other manufacturers in the musclecar years, was hip to this requirement, offering their Sure Grip limited-slip differential as an option. With a Sure Grip, the differential was equipped with a clutch mechanism to create locking action to the rear axles which increases as drive torque is applied to the differential. Unfortunately, the vast majority of passenger cars received conventional open differentials. Since the differential case serves as the carrier for the ring gear, installing an OE-style limited slip requires full disassembly of the rear, and the accompanying “setting-up” of the gear clearances and bearings.


Our ’69 Dart, originally a 273 car with a 7 1/4-inch rear, had been updated with a later A-Body 8 1/4-inch rearend. With its 5 on 4 1/2-inch wheel bolt pattern, availability, and greater torque handling capacity, it was a good swap. Unfortunately, this rear, like most, was a peg leg. With a built 318 up front, and a four-speed in the tunnel, dropping the hammer produced more tire smoke than acceleration. Considering the remedy, we weighed the options. The rear could be torn down and a new OE-style limited-slip case installed, but the down time and setup hassle made us put it off. Then we heard about the Powertrax.
 
The Powertrax unit is a no-slip retrofit differential designed to fit within the confines of the stock differential case. Make no mistake about it-the Powertrax is a locking differential which results in uncompromised torque splitting when locked, and then automatically unlocks when going around a corner in a normal manner. Simply put, it’s either locked or unlocked, and therein lies the caveat. There is a mechanical shift from locked to unlocked and back again. Around a corner, the differential will unlock to disengage the outside wheel under mild acceleration or disengage the inside wheel when coasting or braking. The rear and chassis will react to the change. With the Powertrax unit, extra care is required under certain driving conditions, particularly under hard braking or acceleration in corners and any time the vehicle is driven on wet or slippery roads. Like any locker or limited slip, hammering the throttle in a corner will lock the differential, and the rear will want to come around.

Since it fits in the stock “open” differential case, installing the Powertrax requires only stripping the components out of the differential and installing the Powertrax parts in their place. Because the original case is used, the Powertrax can be installed without fully disassembling the rearend and resetting the gears. It seemed like the ideal upgrade for our street Dart. The installation proved to be as simple and quick as we expected, requiring no special tools, and we were back on the road in a couple of hours. Though we could hear it and feel it while driving, the added straight-line performance made it a worthwhile upgrade.

Powertrax1001 W. Exchange Ave.Chicago, IL 60609 864-843-9275 http://www.powertrax.com
 
The Powertrax Is A Component Kit, Which Replaces The Gears In A Stock Differential Case With A Locking Differential. An Inner Coupler Replaces The Side Gear And Splines Onto The Axleshaft. The Coupler's Straight Cut Drive Teeth On Its Face Side Match The Teeth On The Driver, Which Is Pinned To The Case With A Heavy Shaft. An Active Spacer Between The Two Works Through A Syncro System To Allow The Differential To Lock And Unlock.

The Powertrax Unit Is Simple Enough To Install At Home With Basic Tools. We Set The Dart On Jackstands Under The Framerails To Let The Rear Axle Hang. The Wheels And Tires Come Off To Get To The Axleshafts.

Our Rear Is An 8 1/4 Inch Which Like The 9 1/4 Inch Has A Rear Cover Plate For Access To The Differential. Getting In To Install The Powertrax Is Just A Matter Of Pulling The Cover. For 8 3/4 Inch Rears, Pull The Center Carrier From The Housing.

To Take Apart The Stock Open Differential, You Need Only One Wrench To Back Out The Differential Pinion Shaft Lock Screw.

Once Loosened, The Stock Pinion Shaft Should Slide Out Easily.

Turn The Differential Gears, And The Spider Gears Rotate Out Of Engagement. Then Remove The Spider Gears And Their Thrust Washer.

The 8 1/4 Inch, Like The 9 1/4 Inch, Uses C Clips To Retain The Axleshafts. To Remove Them, Just Push In The Shafts Slightly So They Clear The Recess In The Gears, And Slide The Clips Off. The Axleshafts Can Now Be Pulled Out Of Engagement With The Differential Side Gears. However, To Remove The Old Gears And Install The Powertrax Pieces, Only The Right Shaft Needs To Be Pulled Out A Few Inches For Clearance.

The Side Gears And Their Thrust Washers Are The Last Things Out Of The Stock Differential. With The Differential Now Stripped, The Powertrax Can Go In Its Place.

For The Syncros To Line Up, The Powertrax Components Fit Together In Just One Orientation. We Marked The Couplers And Driver Halves With A Marker In The Correct Orientation So We Could Visually Confirm That The Pieces Are Correctly Installed. The Couplers Slide In Place Of The Side Gears And Use No Thrust Washers In This Application. The C Clip On The Left Side Axle Is Now Installed. The Driver Half Is Fitted With Springs And The Spacer, And Is Then Slipped In To Engage The Coupler. If The All Parts Are Oriented As Specified In The Instructions, The Teeth Of The Driver And Coupler Will Seat

Next, The Four Spring Assemblies That Fit Between The Halves Of The Powertrax Are Put Into Position.

To Make Sure The Clearance Between The Halves Of The Differential Is Within Specs, The Powertrax Comes With A Simple Gauge. This Will Confirm The Assembly Is Correct; However, The Unit Is Not Adjustable.

With Everything Checking Out OK, The Right Axleshaft Is Pushed Back In, And The C Clip Is Installed Through The Window In The Powertrax. Pull The Axle Back Outward To Make Sure The C Clip Is Properly Seated.

The Last Step Is To Reinstall The Pinion Shaft, Which Has To Wiggle In To Get Past The Four Springs In The Pin Bore. Use The Lock Bolt As A Handle To Work The Shaft In, And Then Lock It Down.

Button It Back Up With The Cover, Fill It With Lube, And It's A Done Deal. We Prefer Quality Silicone To A Gasket Here. The Powertrax Requires No Special Lube Or Additive. Get The Tires Back On It, And It's Huntin' Season On Main Street.
 
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