04 Sierra Broke Down

manminder · October 16, 2009

Problem started couple of days ago, I would occasionaly here a thump or a clunk from the rear. So i got under the truck and checked the shocks for looseness, but they were fine. the rear end has no leaks, rest of the driveline is dry no leaks. So today i pull out of my driveway about a mile later, the truck started making loud thumping noises. Now when i put it into drive, its not moving and is making grinding noise. I had the truck towed to my house, when the towtruck driver unhooked the truck it was in park, but the truck rolled back when it was in park? Please help

cbsaf · October 16, 2009

It is the transmission. It sounds like the parking tab has ground off. It may have created metal shavings that ruined the rest of the transmission.

asilverblazer · October 16, 2009

The driveshaft is still connected?

KMGZ400 · October 16, 2009

how many miles are on it? your trannys probably done. luckily when mine went in my burban, 1st gear still worked

manminder · October 16, 2009

how many miles are on it? your trannys probably done. luckily when mine went in my burban, 1st gear still worked

Now the truck sits in my driveway, I put it in 4wd and pulled forward about 30 feet and it makes a thumping sound as it rolls forward, it does the same in reverse. Now the truck is stuck in 4wd. Could this 4wd switch be causing all this problems?? I crawled under the truck, and from front diff to the rear diff all the components show no leaks including the tranny. I bought the truck 6months ago it has 100K miles on it. I dont know if its the original tranny.

asilverblazer · October 16, 2009

Sounds like the transfer case, driveshaft or rear diff to me, transmission is getting power to the tranfer case, otherwise 4wd would have no affect on the situation either the transfer case is not sending power to the rear out put, or it is and the driveshaft is sending it, or the rear differential isn't. You could have somebody put it in drive and look to see if the rear driveshaft is turning. If it is, the rear diff is the culprit.

MXZ800rider · October 16, 2009

You have just grenaded the GM "cuckoo-cluster" design limited slip differential in the rear axle. There is no longer a physical

connection between the transmission and rear tires. I know this because I am there.

The idenitical issue happened to me four days ago. Clunking noise over time, replaced u-joint, turned right and accelerated through turn and heard a 'bang!'

The truck wouldn't go anymore, just made an uncomfortable grinding noise.

Engaged 4WD and limped to side of road and called the auto club because even limping to the side of the road the driveline

would 'wind-up' and release very uncomfortably.

My differential failed spectacularly - spider gear multiple pieces, 'cuckoo' pin and cluster in pieces as well.

Installed an Auburn TRUE limited slip - a real 'posi' unit with actual clutch packs. Has excellent reviews on other sites.

I will report on how it works after this weekend when I get some miles on it. And fortunately I was picking up replacement

tires when the diff failed so I'm taking the old ones down to the cords!

pm26 · October 16, 2009

You have just grenaded the GM "cuckoo-cluster" design limited slip differential in the rear axle. There is no longer a physical
connection between the transmission and rear tires. I know this because I am there.

The idenitical issue happened to me four days ago. Clunking noise over time, replaced u-joint, turned right and accelerated through turn and heard a 'bang!'

The truck wouldn't go anymore, just made an uncomfortable grinding noise.

Engaged 4WD and limped to side of road and called the auto club because even limping to the side of the road the driveline

would 'wind-up' and release very uncomfortably.

My differential failed spectacularly - spider gear multiple pieces, 'cuckoo' pin and cluster in pieces as well.

Installed an Auburn TRUE limited slip - a real 'posi' unit with actual clutch packs. Has excellent reviews on other sites.

I will report on how it works after this weekend when I get some miles on it. And fortunately I was picking up replacement

tires when the diff failed so I'm taking the old ones down to the cords!

How many miles on the truck? I am wondering if these failed "locking differentials" have been abused and therefore failed prematurely, or do they have a very limited lifespan? Now I know why they call it a locking differential - eventually it will lock up permanently.

ColoradoSkiCountry · October 16, 2009

I lost my Eaton G-80 Locking Diff on my 99 at 90,000 miles. Made all kinds of horible noises when I turned but was ok going straight, but mine had not blown up all the way. Differential place that rebuilt mine (using an older but better design of the locking diff for the pre-GMT-800s) says he was seeing these trucks come in (meaning the GMT-800s) at least 4 or 5 a week with the same issue. They don't hold up as well as people think and Mine sure as hell was not abused and had the proper fluid changed at the proper intervals. The guy said it doesn't matter. The design from Eaton isn't very good. So far no problems on my 07 with the G80 but it only has 23,000 on her

manminder · October 21, 2009

I lost my Eaton G-80 Locking Diff on my 99 at 90,000 miles. Made all kinds of horible noises when I turned but was ok going straight, but mine had not blown up all the way. Differential place that rebuilt mine (using an older but better design of the locking diff for the pre-GMT-800s) says he was seeing these trucks come in (meaning the GMT-800s) at least 4 or 5 a week with the same issue. They don't hold up as well as people think and Mine sure as hell was not abused and had the proper fluid changed at the proper intervals. The guy said it doesn't matter. The design from Eaton isn't very good. So far no problems on my 07 with the G80 but it only has 23,000 on her

Finally today i got the wife to put it into drive and roll forward 10 feet, while i lay on the ground waching the drive train, i heard a thump from the rear end and saw the rear wheels jerk. So it must be the rear end. Today i am going to open the rear end cover and see. I am a DIY type a guy but i never fixed a rear end before. Is this a DIY type of a job? Please help!

dlstewart01 · October 21, 2009

That is why I change the diff fluid in my G80 once a year. And with the Mag-Hytec cover it holds 4 quarts. Over kill, maybe but the g80 takes a licking and keeps on ticking.

pm26 · October 21, 2009

I lost my Eaton G-80 Locking Diff on my 99 at 90,000 miles. Made all kinds of horible noises when I turned but was ok going straight, but mine had not blown up all the way. Differential place that rebuilt mine (using an older but better design of the locking diff for the pre-GMT-800s) says he was seeing these trucks come in (meaning the GMT-800s) at least 4 or 5 a week with the same issue. They don't hold up as well as people think and Mine sure as hell was not abused and had the proper fluid changed at the proper intervals. The guy said it doesn't matter. The design from Eaton isn't very good. So far no problems on my 07 with the G80 but it only has 23,000 on her

Finally today i got the wife to put it into drive and roll forward 10 feet, while i lay on the ground watching the drive train, i heard a thump from the rear end and saw the rear wheels jerk. So it must be the rear end. Today i am going to open the rear end cover and see. I am a DIY type a guy but i never fixed a rear end before. Is this a DIY type of a job? Please help!

Depends on how extensive the damage is and what needs to be replaced. You need to properly shim replacement gears and adjust the gear backlash correctly. Technical knowledge and experience is is required here and If you never worked on differentials before, I suggest you let a professional tackle this job.

Seems to me that the entire differential will need to be replaced.

ColoradoSkiCountry · October 22, 2009

I strongly suggest you don't try to fix the diff yourself.. they are a major PITA...

manminder · October 28, 2009

Thanks for all the helping replys. MY diff is blown, I am thinking of buying this diff from the wreckers. I am a diy type guy, i crawled under my truck and saw i need to remove 4 bolts from each spring sides and 2 brake cables and 2 brake lines and shocks. Looks like a simple bolt on, Please help, Is this a simple job?????????]

punmax · October 28, 2009

Thanks for all the helping replys. MY diff is blown, I am thinking of buying this diff from the wreckers. I am a diy type guy, i crawled under my truck and saw i need to remove 4 bolts from each spring sides and 2 brake cables and 2 brake lines and shocks. Looks like a simple bolt on, Please help, Is this a simple job?????????]

No. Get it done by a professional.