4wd troubleshooting help needed ASAP

[Philberto]

Hey everybody. Just got back from a trip to the snow, no 4wd engagement was needed or tried, however when I was driving to get food, I heard some noises from the front end that didn't sound so good. The sounds were clunks, and a thud, then just some squealing in turns. I figured it was either a bearing or my spacers, however it appears to be much worse.

I took off the tires, have the car on jack stands, and engaged 4wd HI to move the front shafts... I hear this HORRIBLE loud ratchet-like noise, coming from the area that I believe to be the front differential area. I also noticed that somewhere, I lost my plastic cover for the oil pan skidplate, but I had no impacts on the undercarriage this past trip.

Worth noting: upon engagement of 4wd, I get that horribly loud sound, but no/little movement from the front hubs, as though 4wd is not engaged. There is no service 4wd light on the dash, and the lights on the selector switch illuminate as normal.

ETA: last 4wd engagement was approx 1 week to 2 weeks ago, it was definitely engaged, and was making no noise until I got back from my trip today.4wd h i was only engaged offroad, and 2wd was re-engaged before touching pavement. I never, ever use Auto 4wd.


ummm.... help please? I have work Monday, and would like to get this repaired before then.

[Zero]

If you are able to engage the front wheels, but there is a ratchet like sound, I would suggest pulling out your cv shafts and checking the spline. Odd though that no idiot light has come up on the dash to tell ya something is not right. Have you checked all the fluid levels?

dif x2
tranny
transfer case

Do you have access to a scan guage or scan tool to see if a code was thrown?

This is def a question for JD or TheRoadie

[Philberto]

I also wanted to add that both front hubs can be turned by hand when the vehicle is in 2wd and when it is in 4wd... in 4wd, however, there is a clunking noise that would be the ratchet-like noise

If you are able to engage the front wheels, but there is a ratchet like sound, I would suggest pulling out your cv shafts and checking the spline. Odd though that no idiot light has come up on the dash to tell ya something is not right. Have you checked all the fluid levels?

dif x2
tranny
transfer case

Do you have access to a scan guage or scan tool to see if a code was thrown?

This is def a question for JD or TheRoadie

I am going to check the fluids now before it rains, the transfer case is fine, the shaft is rotating properly, tranny is fine, as it makes no funky noises or anything when the front wheels aren't moving, and I'm banking on the front diff, but exactly what is wrong is yet to be determined.

I have access to a Tech2 Scantool at work, but not until Monday. Waiting for JD or Bill to chime in in the meantime.

[Trail X]

Here's a good flow-chart of what to do in order to narrow down your issue:



Just from what you've stated, I'm guessing it's the differential... but you need to run through the entire self-test sequence.

[Philberto]

Damn... it looks like a problem with the differential then... I've drained the fluid out of the case, but outside of metal chunks, is there any other signs of failure I should be looking for with the fluid? I know gear oil smells like shit anyways, but is there a particular smell if it's "burnt?"


Prop shaft doesn't turn, when one wheel is spun, the other turns backwards, wheel is free to spin when other one is on ground (I think), though I can't do the wheel on ground test as the tires are off and the whole car is in the air...

Now the big questions are:
a) What can I do to drive the car while the front diff is down?
and
b) Should I think about upgrading gears while I'm working on the front diff anyways?

[Trail X]

If you followed the flow-chart exactly, and you arrived at a blown front differential, then the issue is most-likely the sun-gear to pinion-gear mating. Either the pinion or sun gear is ground down. If that is the case, you should see metal in the diff fluid. However, there may be a magnet in there that will attract a lot of them.

You may want to check one more thing. Engage 2HI and try to turn the front prop-shaft by hand. Does it feel crunchy when you turn it? Or can you turn it at all? That's the teeth having intermittent and misaligned engagement with the sun-gear.

If you absolutely need to drive it while the front differential is out of commission, take out your driver-side CV shaft and stay in 2HI.

[Zero]

Man i wish my printer was working so I could print out that flow chart, laminate it, and put it in my truck.

[Philberto]

Another thing to consider: Hummer added available Locking Front Differentials to their H3 for 2009... I know AlekG used H3 gears in his front diff, is there any reason to think that a front locker is out of the realm of possibility?

Will run a magnet through the gear oil tomorrow, when sun's up... Also, when I have it in 2hi, I can turn it, but it does have an almost regular "skip" like a ratchet, as I said... Is this repairable? I know there is a whole bunch of stuff that must be done to align gears in a differential housing, but I hold some hope that I may be able to save money, repair my diff, and upgrade to a front locker at the same time! If I can swing it, may even switch to 3.73 or 4.10 gears and front/rear lockers.

[Trail X]

The H3 differential is a conventional front diff, unlike our side-mount diff. I doubt the differential housing is the same, but it's worth a look. However... I honestly wouldn't waste time on it - with a front locker you're just going to get a little further down the trail before getting even more stuck. That, or destroy something else on your front end.

For now, focus on figuring out exactly what's wrong. I certainly wouldn't recommend working on the diff internals by yourself either. They require very precise instrumentation and adjustments. Your best bet is to find a junkyard front diff with the same gears... unless you want to find a matching rear axle.

Good luck bud.

[Philberto]

Thanks. I have pretty much determined the same, however I am intrigued by the idea of swapping gears... Front diffs can be had from salvage yards (just the carrier I believe) for about $350, and rear axles are around $400 for something like a 3.73 with g80. May look into that, or just the front diff. Now the pain will be just getting out the parts... Disassembly will begin tomorrow, and I'll have pictures for everybody.

[The Roadie]

Sorry - had stuff to do today. Agreed - pull the driver's CV shaft to make it drivable. The diff is always spinning some internal parts, even in 2HI mode. You'll have to drain the diff at this point, or do what I did on the trail and plug the hole with a Gatorade lid.

There is no trail I ever was thwarted on that a front locker would have helped on, except to get me farther that the lack of ground clearance would have been a show-stopper within ten feet. Traction with aired-down MTs is way more than needed for all sorts of rock-crawling trails. And left foot braking helps if you have one front tire in the air. And the H3 Alpha that they put the front locker in ALSO upgraded the housing to iron. They were breaking front diff aluminum housings like crazy, even without the locker, due to torque issues. They were really wheeling those H3's though. We're pikers by comparison.

[Philberto]

Diff has been drained already... I hate the smell of gear oil. What about the passenger-side CV joint? Should I be pulling that as well? Or does it not engage with the diff?

[Zero]

Dont forget to take lots and lots of pics!

[Philberto]

And the plot thickens...

So I drained my differential yesterday, and went through the full diagnostic today, and apparently everything is now working properly?! No ratcheting sound when in 4hi anymore, and there were no strange chunks in the oil that I can find, so I'm at a loss. Should I thank the car gods for this apparent miracle? Or did something I did perhaps re-seat the splines or something? I am going to be filling up the diff and driving a bit to check, but everything appears to be okay at the moment.

[The Roadie]

Got any of those fiber optic borescope inspection gadgets at work? Getting one is back on my "cool tool" list.

[Zero]

Got one at my shop, even has a color screen.

[Philberto]

Got any of those fiber optic borescope inspection gadgets at work? Getting one is back on my "cool tool" list.

Haha I wish. Anything that gets that complicated in diagnostics usually means "R&R" or the customer isn't willing to have us work on it. I still have some funky noises coming from the front end, ranging from quiet clunks to a squealing, but there isn't any consistency to it, except it only occurs while moving.

[Zero]

Try fixing it the good ol' american way....


"Hit it till it works again, if you break it......you dignified the need for a new better part" hahahahaha

[Philberto]

I think I'm gonna drive it 'till something catastrophically fails. I've figured out that it's not brakes or steering, and I have AAA, so I'm not too worried. Broken parts = upgraded replacements.

[OregTrailBlazin]

The only think I could think of that would make a ratchet sound and not leave your diff full of metal would be the Axle disconnect. Not that its failing completely, but maybe not fully engaging, making the teeth jump in and out of engagement causing a ratchet sound!