8.25 with trac-lok backlash issue

[squareone97]

Hello!

I decided to upgrade my XJ to ZJ rear disks. What a great improvement!

My issue is that while helping me reinstall the axles my nephew rotated the diff and spun the spider gear thrust washers out. Because of how tight everything was due to the trac-loc I had to pull the carrier to reinstall the thrust washers

I have no experience with differentials so this was a large learning experience, even made a tool to reach in the axle tubes to adjust the backlash

I reset the carrier to .005 backlash and torqued the betting preload to 75ft/lbs

After driving home from my sisters I noticed that the diff rumbles pretty good at 65+ but is silent slower then that. It’s a lot like a rear u joint vibration.

There is also a serious clunk from the diff when shifting into drive.

I’m pretty sure the backlash was set wrong and is too loose. I patterned the gears today and have a dial indicator coming tomorrow to verify as the one I used was borrowed.

I’ll include the gear pattern pics so maybe a more practiced eye can chip in some feelings on it


Drive side
https://ibb.co/8zb59TF


Coast side
https://ibb.co/pwKxHDK

 

[squareone97]

Trying to imbed pics

Coast side

Drive side

 

[squareone97]

Drive side

Coast side

Sent from my iPhone using Tapatalk

 

[RCP Phx]

No trac-loc in your pics!

 

[squareone97]

It’s definitely factory LSD. Even has the glove box still still

I could see the clutch plates while it was out. I mostly put that it was Trac-loc to give full info on the diff


Sent from my iPhone using Tapatalk

 

[RCP Phx]

Did you measure the backlash before you dis-assembled it? Did you mark the ring gear location (index) to the carrier before dis-assembly?

 

[squareone97]

I didn’t think to check the back lash before pulling the carrier out. I didn’t remove the ring gear from the carrier, so it’s position didn’t change.

The reason I’m concerned is because both the loud clunk when shifting into drive and the high speed vibration are new.

When I match the pattern in the photos to an example of proper mesh it seems to confirm that the backlash is too large. I was just hoping some with more experience reading the pattern would chime in if they saw something else I’m missing


Sent from my iPhone using Tapatalk

 

[RCP Phx]

On new gears .005" is on the super tight side, but when re-setting a good working set of used gears you want to go back to what it was set at before dis-assembly. The clunk is either something not re-installed correctly or it's not related. As for any howling/growling it could be from the backlash or the bearing pre-load.

 

[grantb]

On the 8.25, backlash must be measured after the preload torque is set. What I saw, when setting up new gears, is a 0.004 to 0.006 increase in backlash between setting the left (driver) side and the right (passenger) side / preload. So it becomes an iterative process of
1. set the backlash using the left adjuster to ~0.005 less than spec
2. torque the right adjuster to 75 ft-lbs
3. measure backlash again and adjust if incorrect

 

[xcm]

Experienced gear guys can’t read the drive side of a used gear set… it’s too worn in! Your wasting your time and chasing your tail.
If I was doing what you just finished doing, I would first thing take an existing backlash measurement… then make sure you set it back it was broken in…

Also, .005 of backlash is way too tight for used gears. Spec should be 6-10ish

I’d take it back apart, set it at like 8-10 of backlash, and hope for the best.

 

[squareone97]

Damn, Well I just checked the backlash and it’s at 13 thousandths. I guess I’ll try and reset it at 8-10 and see if it helps.

So if I keep having an issue my choices are hope it wears back in a bit or replace the ring and pinion gears?

At that point I’ll just throw a locker in and replace all the bearings.


Sent from my iPhone using Tapatalk

 

[squareone97]

Ok, so I adjusted the backlash to .009 and the new pattern seems to now match the wear marks from where the gear ran before. I’m gonna fill the diff and run it tomorrow and see what happens. Hopefully I g eat lucky


Sent from my iPhone using Tapatalk

 

[squareone97]

So after testing with the backlash at .009 it seems a bit better. No noise at any speed.

Im convinced the vibration is more likely a tire imbalance or something related. I noticed that with the disks being thicker than the drums the rear wheels don’t sit nearly as deep in the hub.

I wonder if this is throwing them off a little.

Sent from my iPhone using Tapatalk

 

[RCP Phx]

Most OEM wheels, specially steel rims are "Hub-centric" while most aftermarket wheels are "Lug-centric" but it shouldn't matter either way. My TJ Rubicon rims are "lug-centric", look at the large chamfer........

 

[xcm]

There’s no doubt running a gear at 13, after being setup and broken in at like 7-10 will cause a noise…

I’d be more concerned about lug nut thread engagement. Most disc swaps call for longer wheel studs, luckily your running steel wheels, but you should still get longer ones.

 

[squareone97]

Everything still still seems good after a few highway trips. I longer wheel studs when I did the swap.


Sent from my iPhone using Tapatalk