8 1/4 upgrades

[SouthBay]

Just picked up a 8 1/4 out of a Aspen wagon for my Fifth Ave. It's an open diff, 2.94's in it. I plan on adding a locker and either 3.2x or 3.55's.

I know stock is 27 splines? I see Detroit Locker makes a carrier for 29 splines. But I'm not sure where to find 29 spline axle shafts. Anyone know the length of the shafts I would need if I have custom ones made?

I want to end up with 400-450hp. Don't know if I want a 408 stroker or 5.9 magnum. I'd keep it on street tires.

Any other upgrades to beef up an 8 1/4?

 

[BudW]

I have a couple of questions:
What year wagon did the 8¼” come out of. I have in this thread FMJ Differentials (mid-way down) a bit more on measurements (except for axle length), and the change between the '76 to mid-year '80 and mid-year '80 to '89 8¼'s (the older ones are 1 inch narrower than the newer ones are).
Both will interchange with each other – but if you have purchased custom (ie: wide) wheels – then you might have a clearance issue with leaf springs and/or quarter lips if you get the “other” width differential.

The '68 to '96 8¼” use 27 splines.'97 and up 8¼”use 29 splines. There are no 29 spline stock axles that will fit into FMJ's so a person will need custom axles – if you are not able to find a 27 spline limited slip carrier. There were plenty of new and used carriers for these cars a decade ago, but today they are getting harder to find (not produced any longer – I'm guessing).

On an open differential, all a person has to do is change the spider gears to the appropriate spline – for the carrier case is the same between the years. A person “could” do that with either version of limited slip (clutch or cone) – but no one has the spider gears available separately for either version limited slip carrier.

Jeep has an air locking limited slip system as well as an electric actuated limited slip (both in 29 spline) – but either is not worth the effort to change to (both systems (air and electric) were troublesome from the factory).

If you are not able to find a '68-96 limited slip carrier, then getting custom axles made might be the next step. I would remove either axle and use it for measurements.

A few limited slip carriers (27 spline) I found on eBay:
POSI CARRIER DANA SPICER 27 SPLINE TRAC LOC DODGE CHRYSLER 8.25 INCH 10 BOLT | eBay
76-96 Dodge Chrysler 8.25" 3.55 Ring and Pinion 27 Spl Traclok Posi USA Gear Pkg | eBay
Dodge Plymouth Mopar 8.25 8 1/4 Sure Grip Trac Lok Posi 3.55 Gears 27 spline | eBay

Note: I am not afraid to use a used limited slip carrier. If it holds according to factory specifications (ie: you can't rotate a rear tire if vehicle is in park (or in gear) with rear brake(s) off/disengaged and vehicle is in the rear – then I'd use it.
If tire does rotate with car in park and in the air and you can see the other tire spinning the opposite direction, then the limited slip might be rebuilt – depending on which version was installed in car. The clutch type carrier is not too hard to rebuild. The cone type carrier, if not holding in above test, is now a boat anchor or a door stop (for they can't be rebuilt).

Going back to the topic of axles. The rear wheel bearing/axle bearing's inner race rides on the axle shaft itself. When the axles are out and removed, see if the area where the bearing rides at can (or will) catch a fingernail. If so, the axle bearing(s) will need to be replaced with offset bearings (something that is fairly new to the market). The offset bearing uses a different part of axle so axle itself can be reused.
BudW

 

[SouthBay]

It's from a '77 Aspen wagon. It's got 10" drums. I see in the aftermarket that there is not a huge price gap between 27 and 29 spline carriers. Rock Auto has a 29 spline Dana carrier for $450 if I remember correct. I would like to upgrade to 29 spline with a new aftermarket carrier.

I plan on going through it with new parts, so I have no problem with getting custom axles made.

I also plan on a 5 leafs setup for now, and 275 or 255's on a 8 inch wide wheel. I don't think I'll have clearance issues with that.

 

[LSM360]

Are the 8.25's in Police cars any different? Awhile back I ordered parts for mine and the mechanic sent back some parts stating they didn't fit. I recall bearings were included, and maybe races. It's been awhile, so I don't remember if there was anything else, but it was smaller parts, not ring and pinion, which were also being changed. I had not specified "Police" when ordering, just Chrysler 8.25.

Anyway, FWIW, I have 8.25 AHB with 3.2 and sure grip and engine dyno'd at 469 hp and 528 torque and it's held up very well. No slicks or track time. My previous AHB had a crate engine MP Magnum 360 pushing 300 hp and 400 lb/ft torque and it also held up very well for 60k miles before I sold it working perfectly.

 

[SouthBay]

Anyway, FWIW, I have 8.25 AHB with 3.2 and sure grip and engine dyno'd at 469 hp and 528 torque and it's held up very well. No slicks or track time. My previous AHB had a crate engine MP Magnum 360 pushing 300 hp and 400 lb/ft torque and it also held up very well for 60k miles before I sold it working perfectly.

That's good to hear. I want around 400hp when I'm done with everything. Slow work in progress. So much back and forth I see between 8.25 and the b body 8 3/4.

 

[LSM360]

I really don't think you'll have any issues. I don't drive like a madman, but I have had two AHB's now with built 360's and plenty of occasional rompings, and no issues whatsoever. I think it's a somewhat underestimated rearend. Change the fluid, and use the antifriction additive if you use a sure grip.

 

[BudW]

The wagons had an unique 10” rear drum (finned, and only came on wagons) – but a normal 10” brake drum will fit and work fine.

The '77 differential will be 1 inch more narrow (½” per side) than your existing Fifth Ave differential is.

One limited slip I would recommend using is the Eaton TrueTrac. It doesn't use clutches or other wearable parts and also doesn't require limited slip additive or other special fluids. It is more expensive than a clutch or cone type limited slip but it is what I recommend when building differentials.
The down side is there is not one that fits the 27-spline 8¼”.

I am interested in who you use, and the costs involved for your custom axles, for this project.

Custom axles will almost always be stronger than the factory parts are. A plus is the wheel/axle surface and seal surface is brand new – so neither will be a concern like when working with used axles.


One thing you might want to consider doing is converting to 11” drum brakes, converting to Liberty rear disk brakes or possibly converting to aftermarket rear disk brakes. There are pros and cons to each but either will work better than 10” drum brakes. I'm only tossing the idea out there.
BudW

 

[SouthBay]

The current brakes I got on the car are less than a year old, maybe 3,000 miles on them. So I'm going to transfer the brake parts from the 7.25 that I have for now. Eventually yes I want disc more than likely from the Liberty.

Any issues I'll have putting a 29 spline carriers in the 8.25? Aside from custom axles. The yoke has 2 broken bolts in it from the yard I got the axle from. But looking at replacement ones it doesn't seem too expensive.

 

[BudW]

Are the 8.25's in Police cars any different? Awhile back I ordered parts for mine and the mechanic sent back some parts stating they didn't fit. I recall bearings were included, and maybe races. It's been awhile, so I don't remember if there was anything else, but it was smaller parts, not ring and pinion, which were also being changed. I had not specified "Police" when ordering, just Chrysler 8.25.

The police aspect is a non-issue for Chrysler differentials.
The problem is the similarity of size names. 7¼”, 8¼” and 9¼” look so close when you look at part numbers.
In this case, one brand of rebuild kit part numbers are (respectively) R7.25RMK, R8.25RMKB or R9.25RMK. When your grabbing a box from the shelf – all three part numbers look the same – which I think happened in your case.
BudW

 

[BudW]

Any issues I'll have putting a 29 spline carriers in the 8.25? Aside from custom axles.

Nope.

The yoke has 2 broken bolts in it from the yard I got the axle from. But looking at replacement ones it doesn't seem too expensive.

One can get a drill and try to “easy-out” the broken bolts. The bolts are small and shouldn't be hard to do. The yoke is exactly the same between the two differentials as well so if needed, you could rob the existing one.

Personally, I prefer the larger U-joint (7290) over the small ones used for your car (7260). You are either going to need a shorter propeller shaft or take existing one to shorten it, anyway – so getting larger U-joints is not that much harder – with exception of the front A904/A999 slip yoke. Almost all slip yokes Chrysler made/used for that transmission uses the smaller U-joint.
BudW

 

[Duke5A]

That's good to hear. I want around 400hp when I'm done with everything. Slow work in progress. So much back and forth I see between 8.25 and the b body 8 3/4.

Traction, weight and manual transmissions are what kills axles. If you're running an auto and don't plan on any track time I wouldn't worry about an 8.25". If you're mounting slicks on the back and going racing go 8.75".

 

[SouthBay]

If I ever do take it to the track it'll remain on street tires. But I don't plan on ever tracking it enough to make paying for slicks worth it. I plan on keeping it a fun street car. But I drive all my cars hard.