1965 7-1/4 Refurb - Sure Grip Upgrade

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PocketAces

PocketAces

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Against all the advice on this forum, I decided to retain the original 7 1/4 rear axle in my 65 Dart. I want to keep the stock small bolt pattern for use with the Cragar wheels I've already purchased and to match the Kelsey Hayes front disk brakes that I've also already purchased. That rules out the 8 1/4 option. And I'm not wild about the expense and additional unsprung weight of an 8 3/4.

It's going behind a 273/904 combo with factory four barrel, Egge domed pistons and an Isky E4 cam. Compression ratio should be less than 9.5:1 and I'm not one to abuse a vehicle.

I have read that the sure grip versions hold up better due to less wheel spin and also due to the presence of 4 spider gears instead of 2.

Based on all of this, I purchased a 7 1/4 sure grip differential from FABO member Freezerman. He removed it from the housing for me to cut down on shipping weight and it arrived quickly.

I gave it a bath in gasoline and took it apart to see what I had. Turns out it's a cone style sure grip so only 2 spider gears.

Does anybody know if a later cone style sure grip will fit in my 65 axle housing? I guess there is one way to find out.

Here's some pics of the sure grip. Cute, isn't it?
 

Attachments

I never knew there was a clutch type made for it. Why caint you refurbish that one?
 
RustyRatRod said:
I never knew there was a clutch type made for it. Why caint you refurbish that one?
Click to expand...

The clutch style units have replaceable clutch discs which wear out. But they can be rebuilt over and over. Provided you can still get the clutches. The mopar part number seems to be unavailable, but there is a rumor that Dana 30 Power Lock clutches will fit.

In the cone style units like this one, there are no clutches to replace. It's just metal on metal. The cones wear and eventually bottom out. At that point I guess you can machine a little material off the bottom of the cone and add a shim to the top to compensate. But there is a limit to how much of this can be done.

This unit is not bottomed out and there are no wear marks at the bottom of the cones. I placed a couple dabs of Permatex on both sides and fit the cones together. Once the Permatex dries, hopefully I can separate them and measure the thickness of the Permatex. If that doesn't work, I'll need to get some modeling clay.

If the cones are good I'll use it. I would have preferred to have the 4 spider gears in the clutch type, but as long as I have this one I might as well use it.
 
Honestly if the side bearings are the same # dont see why it wouldnt fit. as long as theres no weird gear raito split for carriers. If i recall the 65 7 1/4s use them stupid shims for backlash & carrier bearing preload like c&%#y's do. Man shoulda waited a little longer,cuz im rounding up parts for a 8 3/4 for my 65 dart & will be selling the o.e. 3.23 clutch style sure grip 7 1/4 diff.
 
I think it's a worthwhile project. I replaced my 7.25 only because it kept leaking out the seals and wrecking my brakes. Now I know I could have fixed that with Speedi-Sleeves. I used it as an excuse to get an 8.75 SG, but that's an easy bolt-in on my 67 (I got a 72 A-body version with SBP). More hassle for you, of course, with a 1st gen car.
 
I'm ready to start assembling this rear axle. I have all the parts and the housing has been cleaned, blasted and painted. I just need to choose the gear ratio and I'm ready to go.

My choices are the 2.93 that came in the car and the 2.76 that came with the sure grip diff.

The engine is a fresh 273 with 9.5:1 compression (measured) Isky E-4 cam and stock 4 bbl intake and carb.

The transmission is a 1984 TF904 with lockup converter and the lower 1st and 2nd gear ratios.

Tires will most likely be 215/60/15 which are somewhat larger than the stock 6.50-13 used when new.

I did all the math and here's what I come up with. It's hard to know the rpm's at lower speeds because of torque converter slip so I computed them assuming no slip to compare them relative to one another. The other thing I haven't factored into the numbers is the lockup torque converter. Without the lockup converter I should have more rpm's at highway speed, but not sure how much.

View attachment ratios.jpg

So with the 2.93 gears I'll be pretty close to the factory 3.23 setup in first gear and slightly better than the factory 2.93 setup at highway speeds (bigger tires and lockup).

With the 2.76 gears I'll be somewhere between the factory 2.93 and 3.23 setups in first gear and significantly better at highway speed.

So opinions please. What's a good cruising RPM for a 273 4 BBL? Will I notice a big difference between these two setups off the line? As long as it's not a dog, I'll be happy. Not planning to do too many burnouts.
 
I've read that the torque converter locks up at part throttle around 45 mpg. I did one more calculation and found that at 45 mph with the 2.76 gears, the engine will be turning only 1660 rpm. The Isky catalog lists the E4's rpm range at 2000-5500. Is there any danger that I won't be making enough torque to cruise at 45 mph with the torque converter locked? With the 2.93 gears the engine would be turning 1762 rpm.
 
Im confused; 1st post says Oct/2013. Is that right?
Anyway, it should be fine with the 2.76s. Your car is light,the motor is strong, its A/T so the convertor will help and the trans has a nice low gear. Im guessing from the 2000 to 5500 spec its a fairly mild cam( something like 210*@.050 or less) so it will cruise fine down there in the basement.I had a 73-318 A-body with a stock cam and it cruised at 1500 @85mph with a double O/D A-833.
Do you actually intend to cruise at 45 mph? Not that it matters but yes..plenty of torque. Usually you are just passing through 45mph to get somewhere else.
The tranny doesnt usually jump into lock-up immediately at a set mph. It usually varies with throttle position and sometimes time. So if you are accelerating to get to 65mph loc-up might not occur til you get there and lift off the throttle to cruise.
Also I think the 1984s were electric shift so you could splice in a toggle switch and command loc-up from the drivers seat. Id still go with the 2.76s cause you say that you are not into burn-outs or abuse.Also theres only about 6% difference in the rear ratios and nearly 12% in the tranny. Yeah, 2.76 for quiet economical cruising.The heavy 73Dart 318-2bbl A/T I had with 2.76s was not a dog.
That extra 12%lowgear will make your 273 feel 12% bigger, ie. 273 x 1.12 = 306, at least until the shift.
 
Yes it's really been that long. I'm doing a full restoration so a lot of things are being done in parallel.

The Isky E4 cam is 216*@.050 with .425 lift. Not a monster by any means. I've read it's the closest off-the-shelf cam to the factory 4 bbl setup.

Here are some torque curves I found for the 1965 273 with 2 BBL and 4 BBL setups.
http://www.automobile-catalog.com/c..._dart_gt_convertible_273_v-8_torqueflite.html

http://www.automobile-catalog.com/c...nvertible_273_v-8_power_pack_torqueflite.html

If these are accurate, the 2 BBL setup makes its peak torque between 1500 and 2000 RPM, while the 4 BBL setup has a pretty steep curve and doesn't peak until just over 4000 RPM.

Based on that, I'm leaning toward the 2.93 gears.
 
I've figured out that early 7.25 rears did not use crush sleeves. The 65 FSM describes using shims to adjust pinion preload. The shims came in .001" increments. The 72 FSM describes using the crush sleeve for the same purpose. The kit I bought with all the bearings included the crush sleeve and not the pinion preload shims.

The FSM also describes a pinion depth gauge tool that eliminates the trial error on pinion depth. Without that tool, I have to go by contact pattern to get the right pinion depth, which means I have to assemble the whole thing to test each pinion depth shim.

I've collected all the shims from three axles but I don't think that's enough.

I installed the pinion with the medium sized preload shim and checked the preload and found it was too tight. So I installed the larger preload shim and now it's too loose. Unless I find that the pinion depth is wrong, I'm going to need a shim somewhere between the ones I have. But if the pinion depth is wrong then changing the pinion the depth shim will also change the preload. What a puzzle.

I'm guessing I can ignore pinion preload until I get the pinion depth where it needs to be. That should save a little time.

What I really need is the dealer's pinion depth gauge and larger assortment of shims.

Another possibility is to hunt down a ring and pinion set from a newer car that uses the crush sleeve.
 
Here's the contact pattern for the first setup.
View attachment 20140907_115818.jpg
Pinion Depth Shim: .091"
Carrier Shim - Ring Gear Side: .269"
Carrier Shim - Differential Side: .262"
Backlash: .003"

I have the carrier shimmed with zero end play but I haven't used the spreader to add any preload. Backlash is a little too tight, spec is .004-.007

Looks like the pinion is too deep. I'm centered pretty good on the coast side, but the drive side is definitely to the toe.
 
I think the next step is to install a thinner pinion depth shim to reduce the pinion depth. But since I don't have access to a bearing press until Monday, I decided to play with the backlash instead.
View attachment 20140907_124015.jpg
Pinion Depth Shim: .091"
Carrier Shim - Ring Gear Side: .262"
Carrier Shim - Differential Side: .269"
Backlash: .008"

To maintain the same zero end play on the carrier, I simply swapped the carrier shims to the opposite sides. This increased the backlash to .008, which is a bit too much.

This moved the drive side contact pattern away from the toe and more to the center. That was a good result, but I know that when I move pinion, I'll probably have to swap them back to compensate for the increase in backlash.

I really don't know how much I should change the pinion depth but since I only have one other smaller pinion shim, I guess I'll try that one. I think it's about .004" smaller, but I won't know for sure until I can pull the first one out and measure it.
 
-Yeah the pinion looks a bit deep. A 4thou thinner pinion shim might just do it.
-Also going back to the torque curves; dont forget those are WOT, full load curves indicating the maximums available.
-If I recall correctly our typical A-bodies require less than 40 hp to cruise at 60mph. And since hp = tq x rpm/5250; that would be 131 ft# at 1600rpm. Totally do-able with either gearset.
-And since a small 4bbl typically has smaller primaries than a 2bbl, atomization might be better on the smaller gear at the slightly larger throttle opening that may be required.
-I have heard of 318 As with 2.45 gears.
-I knew 273-2bbls had small cams but that torque curve really drives it home.
 
I swapped in my smaller pinion depth shim which turned out to be .003" thinner.
View attachment 20140908_223027.jpg
Pinion Depth Shim: .088"
Carrier Shim - Ring Gear Side: .269"
Carrier Shim - Differential Side: .262"
Backlash: .005"

So now my backlash is right in the middle of the range, my pattern is less deep, but my pattern is too close to the toe on the driver's side like the first pattern. The difference is that the first pattern had too little backlash so I had some room to increase the backlash and move the pattern away from the toe. This time, I have the same problem, but the backlash is perfect so if I increase it to move the pattern away from the toe, it will be too much backlash.

I'm starting to wonder if I'm interpreting the pattern correctly. In the first two patterns I had a very sharp line on the bottom of the pattern and a diffuse gradient on the top of the pattern. The sharp line was not all the way down at the root of the tooth. With the thinner shim in the third pattern, there's still a sharp line, although it has moved up the tooth a bit. Maybe this sharp line is normal and not indicative of the pinion being too deep?

At this point I'm inclined to go back to the larger pinion depth shim to get something closer to the second pattern, but with a different combination of carrier shims to get the backlash down to within the spec. Having the pattern a bit too deep on the tooth has to be better than having the pattern hanging off the toe end of the gear on the drive side, and it has to be better than running too much backlash to compensate.

Opinions welcome.
 
RustyRatRod said:
Take some more pinion shim out. It's still deep.
Click to expand...

Based on your advice I went back and did some more reading. Reducing pinion depth can indeed move the drive contact area away from the toe. It's called for when the drive side is toward the toe while the coast side is toward the heel. Not sure my coast side is toward the heel, but it's clearly not as close to the toe as the drive side. So it's worth a try. I ordered some shims and I should be able to try again on Thursday.

Thanks!
 
I ordered some pinion depth shims, Yukon SK 31402. When they arrived, I could tell they weren't right. They were much bigger diameter and the same as what came in the USA Standard Gear Master Overhaul Kit ZK C7.25 and the Yukon Minor install kit for Chrysler 7.25" differential (MK C7.25).

I'm guessing these shims are designed to install between the bearing race and the housing instead of between the bearing and the pinion gear. Since the shim I have between the bearing and the pinion gear is already too big, adding shims under the race would just make things worse, unless I eliminated the shim from between bearing and the pinion gear.

So I found a local differential shop that could sell me some shims.
 
I decided to remove a bit more from the pinion depth shim stack. That's when I ran into trouble. The new shims had a larger outside diameter than the originals. This prevented the bearing separator from getting hold of the inner race. We were able to get the bearing off by torqueing down the bearing separator bolts, but we jacked up the shims and the bearing.

Now I have to get another bearing and start over. This is very frustrating, although it wouldn't be so bad if I had a press in my garage and a collection of the correct shims.

On the bright side, perhaps the new bearing (Timken instead of Koyo) will call for a thicker pinion depth shim.
 
Was the shim kit for a early 7.25 or a Dakota. 7.25? They are not the same. I beat on my 7.25 SG differential with a 340 fo a years as a high school driver and it would probably still be running if i didnt do a neutral drop rollin backwards out of a driveway...
 

Hello all. I am new to the Forum. :) Doing a complete restore on a 71 Valiant. My 14 year old fell in love with it and so we are doing the restoration in time for his 16th birthday. I am looking for 7.25 Sure-Grip guts, anything out there?
 
On Friday, I spent the afternoon taking a different approach. I started with my thinnest original shim of .088" and I sanded it down on a granite block. After about 4 tries, I ended up with this pattern at .079"
View attachment 20140912_174248.jpg

Problem is, I didn't have the right preload on the pinion bearings. When I fixed the preload, it looked like this.
View attachment 20140915_132208.jpg

Lesson learned: don't bother making a contact pattern until you have the right bearing preload. When you put a load on the bearings, it pulls the pinion down into the housing and changes the pattern quite a bit.
 
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