Are 2.45 gears bad?

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Mick Semantel

Mick Semantel

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I don't have a clue on gear ratios. My engine is a 360 with eddy performer manifold, eddy performer cam, 600 cfm eddy carb, stock 904 trans with stock torq. converter. I'll be throwing in a 8 1/4 rear that has 2.45 gears. Is this gear ratio o.k. or should I go a different route? I like a little performance but I'm more into cruising and going to shows. The car is a 75 Dart Swinger.
 
It will be very sluggish out of the hole. It'll top out at more than you could ever want on the highway, definately not a choice for a decent mix. 3.23/3.55 is a good mix
 
Depends on they type of driving you do, 2:45's are very much a highway gear not a performance ratio. You can cruise at high speeds with low rpm's and get good mileage. If you want to race you want to go much taller like 4:11. A really nice compromise is 3:55's, that's what I'm looking for.
 
Like they said:

Cruising - good (mileage!)

Racing - bad (slow!)
 
Cool, I do want a respectable cruiser. I'll go with the 3.55's then. Is that a hard swap to do, or should I have a professional do it?
 
I think you will have to get a new carrier...Go ahead and get the sure grip....BTW I have one for $125.00 + shipping...
 
It's not that it is difficult than it is more that you will need an assortment of shims and some tools that most people don't usually have. As far as the tools you would need an inch pound dial torque wrench for the pinion bearing per-load and a dial indicator for checking backlash on the ring to pinion gears. On the shims, you have to put a certain amount of them between the pinion gear and the inner bearing to get the pinon depth right, this is probably the most important thing on setting up a ring and pinion. This process usually involves removing and re-installing the inner bearing a few times to get it were it needs to be.

Since you removing 2.45's you will have to find a different carrier for the other ratios. 2.45 gears use a carrier that is specific to 2.45's. The carrier you need will fit all ratios from 2.73 to 4.56, basically anything but 2.45's.


Chuck
 
if it were me instead of putting alot of money in an 81/4, you could find an 83/4 for what it would cost to do the gear swap on the 81/4. and have a beffier rearend plus the advantage of gear interchange that is easy.
 
yeah i think u should try to get ur hands on and 8 3/4 much stronger and it is a brease to change the 3rd member. for instance u could have a good highway gear like 2.76 and if u wanted to swap to a 4.10 it would take 45 mins to an hour and u cud have way more umph...u shud deff try to get an 8 3/4
 
Mike, 8 3/4" A-Body rears with 3.23's were pretty common, plus new gears and Sure Grip units are as close as the dealer (Dakota). If you have a 7 1/4" now, you should keep your eyes peeled for something else, it's not worth spending money on.

Add big bolt axles and B-Body brakes to the cost of an 8 3/4 swap. Driveshaft cut and rebalance with either choice.
 
I have that gear set in my daily driver, works great for highway driving on the gas mileage, not so good in town. The bad on that gear set is that the differential is not upgradable. If you have a 2.45 gear set you can not change it you will have to buy a whole new diff.
 
Thanks for all of the advice. I'll shop around for an 8 3/4. It just seem's that the people who have the 8 3/4 rears want a small fortune for them. I paid about 200.00 for the 8 1/4.
 
OK there are a few over zelous folks giving costly advice....if you are a casual cruiser and just want some pep go find an 8 3/4 with a 355 sure grip ( posi) for an A body...there are gobs of them out there and I think they repop them....a standard rebuild/gear swap is around $600 and they bolt right in if you have the 4 inch pattern on the fronts keep it...unless you are planning to run 600 hp and do 5800 neutral slams it will work like new money....unless you plan to racce...keep all 4 wheels the same BP you do not need larger than stock brakes or disc brakes unless you are planning to race it regularly...if you are just doing the ocassional burnout and a few stop light to stoplight runs the stock brakes are MORE than adequate......most classics see maybe 500 miles per season, you do not NEED enlarged brakes OR disc brake conversions for that level of driving.....remember drum brakes stopped cars for almost 50 years before the disc brake was invented and back in thsoe days the avg car weighed in at over 5000 lbs. Everyday driving or racing invest the money in high end brakes.... crusing from show to show and buring out here & there STOCK stuff will hold ya fine and dandy and for one helluva lot less money. Mancini racing has the different sized u joints to bolt right in and your stock shaft should be fine......
C'mmon guys not everyone is building a 600+++ HP street rod, fun true, but things can be done for a few less bucks and still give a neck snapping smokeout when the pedal hits that firewall......355's are a decent all round gear set and wont take you broke to install or to drive with them.....391 is hotter but gas is more and top cruising speed is around 60, 410's are hoter yet but gas is stupid expensive and you cant hear yourself think you rev so hi on the e way......but 391 & 410 will throw you back in your seat and keep you there!!! depends on how much you wanna spend & what you wanna do....decide that the rest falls into place...
good luck
 
My kind of guy. I'm going to stick with the 8 1/4, and put the 3.55's in. Car wont see more then 500 mi. in one season. The car wont exceed 300-350 horse (at it's peak), and it won't be "officially" a racer on the track. It is a street car, and won't be abused.
 
OK its your call....I dont know anything about 8.25's pos or neg, I know 7.25's are essentially junk and 8.75's came std in 340' 360' 383 & some 440's the rest of the 440's and the hemi got the 9.25 Dana.......I was talking about the 8.75 not the 8.25...I have no idea how that rear end will handle even moderate abuse........
 
The only other mopar I had was a 72 Scamp with a 318. granted it wasn't a power house car, but after I had a shift kit put in, it would take some punishment. From brake stands to high r.p.m. shifts, it would hold up. I was impressed with it. I don't know what type of gears where in it.
 
I think the 8 1/4 will hold up just fine..I think it is kind of like the 904 auto.. Its terribly under rated... If you try to tear up the rear end yeah you can do it. But for a pretty good street small block it will do just fine.... Is this not the same rear put in R/T Durango's, 5.9 Dakota's, and half ton trucks??? How many have you ever seen give out??? Just my $0.02....
 
The 8 1/4 has an 1 5/8 pinion diameter which is larger than the 741 case 8 3/4 and only 1/8" smaller than the 742. It is much stronger than most people think. The weakest link in the 8 1/4 is the 27 spline axles. As long as you are not using slicks with any kind of torque not much chance you are going to break one. My '77 Corboba came with an 8 1/4 and a 400 from the factory. The car runs mid 14's and haven't had a bit of trouble with it.

For comparison of pinion diameters from the "other" guys;

8.8 ford 1.625
9" ford 1.313
12 bolt chevy 1.625


Chuck
 
Mick Semantel said:
My kind of guy. I'm going to stick with the 8 1/4, and put the 3.55's in. Car wont see more then 500 mi. in one season. The car wont exceed 300-350 horse (at it's peak), and it won't be "officially" a racer on the track. It is a street car, and won't be abused.
Click to expand...

Best bang for the buck
 
SleeperScamp said:
Is this not the same rear put in R/T Durango's, 5.9 Dakota's, and half ton trucks??? How many have you ever seen give out??? Just my $0.02....
Click to expand...

It is the same ring and pinion but the later 8 1/4's had 29 spline axles because Mopar knew this was the weak spot.


Chuck
 
SleeperScamp said:
Is this not the same rear put in R/T Durango's, 5.9 Dakota's, and half ton trucks??? How many have you ever seen give out??? Just my $0.02....
Click to expand...

FWIW, I broke the ring gear on my '97 Dakota 5.2 five speed 4WD. Not long after that, I broke my transfer case chain. Different application and I was wheeling it pretty hard here in Colorado. I tend to be kinda tough on my trucks. Not long after that, I traded it in on a 2001 5.9 Ram1500 OffRoadster which came with a corporate 9 1/4. Couldn't break that rear end or T-case.

As far as I know, all post '70 (and most likely earlier, but I have no personal experience with them) half-ton dodge trucks had the corporate 9 1/4. Please correct me if I'm wrong on this.
 
A lot of good feed back. Thanks guys, and keep the comments coming. It's good to hear both sides.
 
8 1/4 with 3.55 gears are your best choice for the horsepower and usage you speak of Mick, no need to go overboard.

Terry
 
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