Front Differential troubles

Jminter6001 · December 19, 2018

I drive a 2008 GMC Sierra 2500HD 6.6 LMM. Everytime I put the truck in 4x4, (floor shift), my actuator starts leaking diff fluid. So I guess something in my diff is malfunctioning and breaking my actuator. Done broke 3 already. I'm looking for a front differential and want to make sure I get the right one. I know I need a 3.73. But what years will work with my truck. I cant find a used 2008 front diff anywhere. I did find one that I thought might work. It was a 2014 with the GT4 code. But the description says it only fits models 2011-2017

davester · December 19, 2018

Have you considered fixing it? It's not unusual the locking gear and/or the passenger side axle to fail.

Also, I know for my '04, I can remove the diff, front cv's, and front driveshaft, tape up the actuator connector so it stays clean, and it's fine to drive around while working on the front diff, and your '08 should have the same setup.

Formulabruce · December 19, 2018

/\ /\ /\ This is what I would do too. /\ /\ /\

Jminter6001 · December 19, 2018

My mechanic skills are pretty low, so I would have to get someone else to fix it for me. But this is the first I've heard of the locking gear or passenger side axle failing. Not sure exactly what your talking about, but I'm learning as I go right now. I'll look into it. I really appreciate the advise! Thanks!

davester · December 20, 2018

The actuator you've been replacing has a rod that comes out, when 4wd is engaged. That rod pushes against the edge of a tube with a bunch of splines on it. When that tube is pushed over by that rod, the tube connects the axle shafts on that side of the diff together.

That sliding tube in particular is a weak point, and the two stub axle shafts it connects also have a tendency to fail.

And by 'tendency to fail', it's not common with the regular use of 4wd, when you use it to gain more traction on snow/ice/gravel, but more if you go off-roading in 4wd with the go pedal on the floor.

And if you aren't interested in wrenching, that's fine, but if you want to learn how to do it, and want to save money on getting your truck repaired, and know what's happening with it, I would suggest getting a online subscription to the full-service manual for your truck. It details what's involved with removing and reinstalling the diff, how to split it (right where the actuator screws in) and how the above bits work together.

Jminter6001 · December 21, 2018

That helps tremendously! I have a friend of mine that's going to help me check out what your talking about. He pulled up a diagram of the diff and totally agrees with your diagnosis. This online subscription you speak of...is it a certain website? Thanks for your help!

davester · December 21, 2018

alldatadiy.com, helminc.com, maybe others. Personally, I shelled out for the paper manuals (5 volumes, about 2000 pages/volume), as I don't like using a computer while I'm working on the truck, but the online subscriptions are a lot cheaper. And don't get sucked into getting the chilton/haynes manuals, they are pretty basic (as in, don't cover the whole truck), and large portions of them are pretty generic. They are generally only a couple hundred pages (vs the 10000 pages of the f.s.m.)...

Note, it's also possible the diff itself has failed, but that's less likely to be the problem. If you want, you might be able to see something with an inspection camera (or just looking into with a flashlight) through the opening the front actuator screws into.

Edited December 21, 2018 by davester

Jminter6001 · January 3, 2019

So I found the (many) problems!! The actuator wasn't leaking diff fluid after all. Just had a strategic oil leak that happened to be falling onto my actuator. Also the connector to my actuator was broke and was not making a complete connection to the actuator. THEN....we found out that a shop that had installed a transfer case for me last year installed the wrong transfer case. They put in a 2 speed transfer case, only allowing for 2 wheel and 4 Low. They modified the wiring from my truck to fit this 2 speed transfer case. (I needed the 4 speed). Which their rewiring efforts also killed my 4x4 indicator light on my instrument cluster. ?? So, I have a legal battle on my hands now.