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I think my rear end went out? HELP

I think my rear end went out? HELP

Postby Noserave [OP] » Mar 28 2020, 1:16pm

2008 GMC Sierra 1500
3:73 gear ratio

The other day I was backing down a boat ramp to put a kayak in the water when I think my rear end went out. I backed down and put the truck in park at the waters edge. It was a steep ramp and I didn’t engage my emergency brake before putting the truck into park. When I got back in and put the truck in drive I heard a loud noise like a clunk come from under the truck, and I started rolling backwards into the water.

After getting a tow and looking at the truck on level ground I noticed that the driveshaft spins in D but truck won’t move. Also it makes a horrible grinding noise when I try to put it back into park from D. I have to shut the truck off before putting transmission in Park to prevent that from happening.

Any idea on what happened? Or what the grinding noise was when trying to go back in Park?
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Re: I think my rear end went out? HELP

Postby GBSierraSLE » Mar 28 2020, 4:11pm

Sure sounds like you sheared the rear-end gears or broke something. The grinding noise when you try to put it in park is the parking prawl trying to engage while the transmission is still spinning internally as if the truck was still moving.
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Re: I think my rear end went out? HELP

Postby Noserave [OP] » Mar 29 2020, 4:24am

GBSierraSLE wrote:Sure sounds like you sheared the rear-end gears or broke something. The grinding noise when you try to put it in park is the parking prawl trying to engage while the transmission is still spinning internally as if the truck was still moving.


I’ll take the rear diff cover off and take a look.. is it cheaper to just replace rear end with a used one instead of repairing rear gears in the diff?

How do I diagnose the parking prowl? I do believe it rolled while transmission is in park.. would that be a transmission issue?
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Re: I think my rear end went out? HELP

Postby 19trax95 » Mar 29 2020, 4:28am

If the driveshaft spins but the truck doesnt move the rear end is broke. Either the pinion snapped, or the axle shafts snapped.

Either way that is an issue.

And since the rear is broke, park wont matter since the trans relies on the gears being able to hold everything as well.

If you set the parking brake it won't move. But just the trans will no longer hold it unless you put it in 4wd and let the front diff hold the truck.
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Re: I think my rear end went out? HELP

Postby esox07 » Mar 29 2020, 5:54am

If your truck is 4wd, you could have engaged 4wd to move it up off the ramp.
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Re: I think my rear end went out? HELP

Postby ASTE25 » Mar 29 2020, 6:06am

My bet is going to be broken spider gears. Easy fix and relatively cheap (as far as other repair costs for a rear end).
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Re: I think my rear end went out? HELP

Postby ayalaman » Mar 29 2020, 8:03am

Looks like the diff is broken. We can guess all day what the problem is but until you remove the diff cover and inspect , you won't know for sure. The truck is going to move in park because something broke in the diff. So you don't have a tranny problem. Now If its just a broken axle , simple fix . If you broke the spider gears , again simple fix. If you broke the ring gear or pinion gear , then its a more complicated fix involving special tools to measure pinion depth and things like that. Labor calls for 4 hours the remove and replace the whole diff assembly if you go the used rear end route. If its a bad ring and pinion , the labor the rebuild with all new bearings and new ring and pinion is about 7 hours plus parts . I work at a shop in Los Gatos California and our labor rate is $160 an hour. So it might be better to replace with a good used one if you not able to rebuild it yourself.
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Re: I think my rear end went out? HELP

Postby Willfull04 » Mar 29 2020, 2:15pm

and not a single joke about hoarding toilet paper.

i'm dissapointed.
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Re: I think my rear end went out? HELP

Postby CT2500HD » Mar 29 2020, 4:24pm

ASTE25 wrote:My bet is going to be broken spider gears. Easy fix and relatively cheap (as far as other repair costs for a rear end).


This is the correct answer. The spider gears in an open differential are intentionally the weakest link. If they blow, hopefully its at low speed so the metal chunks don't get churned through your ring & pinion. In this is the case and the ring & pinion teeth look good, the spider gears are very inexpensive and the replacement job is an hour or two in the driveway without special tools. Note the the GM 10 bolt axle is a c-clip axle, meaning there are c-clips (huge ones) on the ends of the axle shafts that retain the axle shafts to the side spider gears and also keep the 4 spider gears in-place.
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Re: I think my rear end went out? HELP

Postby ASTE25 » Mar 30 2020, 4:15am

ayalaman wrote: We can guess all day what the problem is but until you remove the diff cover and inspect , you won't know for sure.

You don't say. Interesting....
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