So GM has determined that my rear leaf springs are sagging 3"-6" and are defective. The truck is riding on the overload (helper) springs constantly. According to the dealer my truck weighed in at 10,200 lbs. Max GVWR on my truck is 12,000lbs, as listed on the door jamb. My rear axle rating is 8600lbs. The front axle rating is 4800lbs. It's never been overloaded. I've never towed even close to the max rating. The sagging suspension has altered my driveline anlge, driveshaft vibrates at all speeds, ruined my carrier bearing, and my rear G80 axle makes a ton of weird clunking noises. They are trying to blame me saying that you have to add wind drag when factoring in the weight of the truck and driving down the highway.

It all started around 10,000 miles. I brought it in because the axle was engaging both sides and chirping around corners. Every now and then I would hear clunking noises. I told them the suspension looked like it was sitting a little low. They ignored my comments, what would I know. They drained the fluid and determined it was low on fluid, no leaks though. On the fourth trip to the dealer, before 15K miles and one year, they shimmed my carrier bearing, installed new pinion gears, and clutch packs in the axle. It was better, not fixed, but made less noises. The axle was still engaging both sides on some corners. At about 20,000 miles it started making very loud clunking noises when driving up a dirt hill and turning to the left.

Now here I am at 38,000 miles and a total of 10 trips to the dealer. They are still coming up with excuses not to fix it. So far they haven't found any but they keep searching for reasons not to fix it. I've sent GM's lawer my lemon law notice hoping this would encourage them to fix it. I've also filed a complaint with the BBB. A GM customer service rep called me but is taking her time. Correct me if I'm wrong but I think once they are notified they are suppose to have 7 days to fix it. I'm going on 4 days and its sitting in my driveway. They are "consulting their engineers".

Has this happened to anyone else?

Considering my axle is shot will this ruin my transmission too? So far the trans seems to be ok.

Is there anything else I can do to get this fixed? I'm desperately trying to avoid lemon lawing this truck. Seems a little silly to do so all over faulty suspension and an axle. I wish they'd just take responsability and fix it.

I assume the box and weight of the truck has been relatively close from the first trip to the dealer??


At 10,200 (~7200 on rear) you should be close to engaging the overloads, I dont have a way to measure that, specific weight, however at ~8100 lbs on my rear axle (this is with my trailer connected) I am very much on the overloads.

In my opinion if they have seen the truck in the same configuration from day one and are now admitting to a defective spring, then they need to fix it. It is my opinion however.

One point to avoid this in the future, when putting a constant change to the truck, i.e. the toolbox bed, it would be wise to reset the pinion angle to middle of the spec for "normal" operation. It could save you a lot of time and trouble for something as simple as shims.

Springs settle over time. Does you truck appear lower in the rear than the front? Maybe you can get the General to replace them under warranty?

As for the axle noise, you've got a rear with a G-80 in it, with a couple of teeth out or a bad flyweight etc. It is a locking differential and will have different characteristics than a Posi. But yours sounds as if damage has occurred within.

Read up on a G-80.

The weight has remained about the same. Plus or minus 200lbs.

I ordered the truck from the dealer. It took 5 months for delivery. I think if the shim should have been added they should have done it for me before giving me the truck. I realize GM does not have anything to do with the body but they built this truck knowing what was goin on it and I ordered it like this so it was no surprise to them.

Interestingly 4800 lb front axle plus 8600 lb rear axle= 13,400 lbs. It's weird that the axles are rated more than the truck. I'm guessing the suspension is the weak link here.

I'm trying to get them to replace the rear leaf springs. It does sit real low. They are consulting their engineer.

I'm not a mechanic but I agree my axle has some problems internally. When they rebuilt it last time. They said the pinion gear(s) had track marks on it and replaced it. They also replaced the clutch's. I'm thinking I must have some bearing damage in there and it's only going to get worse.

Shimming the center carrier down is not the solution for driveline vibration.

The tranny to center bearing shaft runs nearly level and should be left that way.

If you suspect U-joint angles being off for your vibration, know that the angle of drop at the middle U-joint should cancel the angle of the shaft rise at the rear axle.

If you have a 3 deg down at the center joint and a 3 deg up at the pinion, that's perfect and Ideal.

Sagging rear springs tend to make the pinion point down more meaning the shaft angles don't cancel.
Since a pickup does have a range of heights dependent upon load, the pinion angle math will vary, but should still be set for perfect cancellation at the position that is most normal.

Did any one every measure the drive shaft angle?

They did measure the angles. I don't know what it was at or was suppose to be at. Their engineer had them shim it. I don't know if it was shimmed up or down. When they shimmed the carrier bearing it was better for a while. The vibration went away for a few thousand miles. Then it slowly came back. They had replaced one or 2 pinions gears and the clutch packs at the same time they did the shim. This helped the axle but it was still engageing both sides when turning occasionally. The axle became worse over time again and began making more noises. Now my center console shakes pretty bad while driving at any speed.

Just read through my records. I was wrong. They did not shim carrier bearing. They did shim the trans. This is what it reads:

"Found 3 percent angle on front joint. Should be 0.5 to 1.5. Shimmed trans up 3/8. Got angle to 0.5. Measured rear shaft working angle. Working angle ok. Advised to add 2 percent shim to rear axle to bring diff down to compensate for heavy loads. Added shims and tested ok."

You just need to keep fighting or find a new dealer.

And, remember, you have two distinct problems.

Inadvertent engaagement of the locking rear differential.
Inexcusable vibration levels.


If the G80 has a given set of problems, technically it can contribute to the vibration.

Specifically, the diff needs addressed first. http://www.dieselplace.com/forum/showthread.php?t=298905&highlight=g80

Well it took a little over two weeks but I picked the truck up from the dealer on Thursday, it when back in on Friday, and I picked it up again today, Sunday. I met with the engineers a week ago. They seemed like nice guys. Here's what they did:

They weighed my truck again and it came in about the same weight. So I'm about 1800 lbs under my max of 12,000lbs.

I was getting axle wrap causing a vibration at take off. They put a metal shim between my lowest leaf spring and the top of the axle tube to twist the front of the axle down. The first time I picked up the truck, on Thursday, the lowest leaf on one of the leaf springs had shifted to the side. They reset it and gave the truck back to me. It seems to be moving again though. I'd like some opinions as to whether or not this is acceptable or should they have added some leaf springs to bring the truck up to it's intended ride height instead of shimming it to get the angle correct?

Then they discovered the two rear most u-joints were binding so they replaced them.

The carrier bearing was out of line. They cut the bracket out and shifted it to the side to make the driveshafts line up in a straight line. Re-used the carrier bearing.

Now the confusing part. They think the clunking noise in the axle was my pinion gear skipping a tooth. They said the clutches are designed to slip under enough torque and mine must not be slipping. They put limited slip axle fluid in my G80 so it will slip easier. The one thing I don't understand is how does a gear skip a tooth without breaking something? They did take the rear cover off and showed me everything was in good shape inside. I did not see them drain the oil but they said is was very clean and there were no metal peices in it.

I'd like opinions as to wether or not this work is acceptable? I haven't had time to drive it on the highway. On the way home from the dealer I had no vibrations though. My biggest concerns now are if I should be worried about the axle still and if the leaf springs are going to be a problem?