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Discussion Starter · #1 ·
Hello, I haven't posted in a few years but here goes.

I have been reading other posts regarding S10 rear end noise and I just wanted to confirm before I have it serviced again.

About 3-years ago I was having this whining noise from the rear end that was most noticeable around 52-60 mph when on the throttle. It progressively got worse and even whined slightly when coasting. I changed the rear end oil and didn't find any unusual wear or metal fragments. I took it for a free estimate at the Chevy dealer who put it up on a wheel rotating machine and quoted a price of $1,800. I then went to a local speed shop guy who mainly works on muscle cars and explained the situation. We took it for a test drive and he said it sounded like rear end bearing. I asked him if he had ever worked on an S10 rear end and he said yes. I had him service it for if I recall under $450, but when leaving the shop the noise came back and he had to service it again. This time he did something else as the issue was mostly gone. I could still slightly hear something but it was livable until just before I put it away for the season last fall.

The truck is not an Xtreme model, but it is that optional lowered sport package (GU6) with 16" wheels. Having owned it since 2009, and getting another car for daily driving in 2013, I rarely drive it over 1,000 miles a year. It is in great shape otherwise with only 135,000 miles on it. The rear end is supposed to be a posi but always spins one tire.

Specifications:
2002 Extended cab WBLS
GU6, G80 58U
4.3 L35
3.42 rear end stock (not positive if original one on vehicle)
4L60 transmission

Observations:
10-bolt rear end (unable to find any tags for further identification) There is an unused welded bracket on top of the rear end tube on the passenger side that may be for an exhaust hanger?
8 3/4" circumference around tube with tape ruler is what it looks like
Wheels spin opposite directions when turned manually on jack stands

Per other posts does this sound like the bearing is shot again and did the previous service fail because of pinion depth, bearing preload/backlash, or shim clearances were done incorrectly?

Thanks for hearing me out!
 

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You need to have it rebuilt...completely. That bracket on the housing is for the 3rd shock. Check the frame and see if there is another bracket there. Two things come to mind. Either the previous owner removed the shock/frame bracket, or they replaced the rear end and it had the bracket on it. I'd check ebay for the bracket and shock...they are desirable pieces.
 
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To be honest, I would look to get a replacement rear axle assembly from a pull-a-part yard at this point before spending more money on a troubled unit. LKQ has them for $125 including core charge in my area. This is the whole assembly, drum to drum or disc to disc. Just make sure to get the same ratio and brake setup, unless you want to try and upgrade to Blazer disc brakes while you're working on it. Also, research what size rear assembly you have. Someone correct me if I'm wrong, but I believe you can interchange between 7-5/8" and the 8-1/2" or 8-5/8" (the full assemblies, not the internals).

FYI, I also have the G80 posi in my truck. Mine won't lock the axles until you spin the tire to fast enough, and it can be surprisingly violent.
 

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To be honest, I would look to get a replacement rear axle assembly from a pull-a-part yard at this point before spending more money on a troubled unit. LKQ has them for $125 including core charge in my area. This is the whole assembly, drum to drum or disc to disc. Just make sure to get the same ratio and brake setup, unless you want to try and upgrade to Blazer disc brakes while you're working on it. Also, research what size rear assembly you have. Someone correct me if I'm wrong, but I believe you can interchange between 7-5/8" and the 8-1/2" or 8-5/8" (the full assemblies, not the internals).

FYI, I also have the G80 posi in my truck. Mine won't lock the axles until you spin the tire to fast enough, and it can be surprisingly violent.
The problem with that is you don't know what you're getting on the reliability scale. A plus to his current rear is the hop shock bracket. He could change to an 8.5,. but the d/s will most likely have to be shortened. He's mentioned nothing about V8 power, so his rebuilt 7.5 should work fine.
 

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Discussion Starter · #5 ·
You need to have it rebuilt...completely. That bracket on the housing is for the 3rd shock. Check the frame and see if there is another bracket there. Two things come to mind. Either the previous owner removed the shock/frame bracket, or they replaced the rear end and it had the bracket on it. I'd check ebay for the bracket and shock...they are desirable pieces.
Alright, I had a chance to roll under the truck to take another look now that you explained what that bracket is for. I do not see where that would attach a shock onto the frame so yes, something is missing. Looking back at my glove box sticker I do have the ZQ8 chassis option which includes that feature. I went onto ebay and tried looking up the bracket/shock combination but came up empty. I probably had the wording incorrect as I pulled up other parts along with complete rear ends.

My original intention for the truck was to be a show truck but in a show stock class as I don't like to modify like I did when I was a Pontiac guy including a 1967 GTO convertible. I also had a first generation 1992 S10 5-speed 2.8L that I bought new lasting until 2009 when it was too far gone from spending its life outside in Midwest weather environment. Every body panel including the roof was rusted through at some point.

I am just maintaining the truck for now and had some bodyshop work done including the passenger rear cab corner patched and painted, as you know that is a common rust place. I am currently running KYB Gas-a-Just shocks that were installed 10-years ago. That and replacing the BF Goodrich 235 series tires with new ones makes the truck ride and handle like a dream. I even ran Brembo rotors with some high end pads in the front for a couple years until I wore those out. Ultimately, I have thought of doing a frame off rotisserie restoration but it does not make sense to me economically at this time. So, I want to keep everything as stock as possible but that new generation GMC 4.3L sure would be nice!

When you say the rear end needs a complete rebuild what does that include? I would likely have someone do it for me as I don't wrench much anymore.
 

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Here's a link to what you need..

I'd search for a reputable shop that actually rebuilds rear ends and have them strip it bare. There are other LSD's that are better than the G80 that came with it. I believe Eaton & Tru trac are a couple of them.

As far as that new 4.3...completely different animal.
 

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Discussion Starter · #7 ·
To be honest, I would look to get a replacement rear axle assembly from a pull-a-part yard at this point before spending more money on a troubled unit. LKQ has them for $125 including core charge in my area. This is the whole assembly, drum to drum or disc to disc. Just make sure to get the same ratio and brake setup, unless you want to try and upgrade to Blazer disc brakes while you're working on it. Also, research what size rear assembly you have. Someone correct me if I'm wrong, but I believe you can interchange between 7-5/8" and the 8-1/2" or 8-5/8" (the full assemblies, not the internals).

FYI, I also have the G80 posi in my truck. Mine won't lock the axles until you spin the tire to fast enough, and it can be surprisingly violent.
I want to keep it stock and maintain what I have. I went on eBay and saw some rear ends but all said without ZQ8 bracket. As mentioned I measured my rear end around the tube at 8.75", likely 8.5" though when I see some ads saying 7.65 (7.5) ring gear I am not sure what I actually have inside or even if I have the original 3.42 rear end for that matter. I saw an Xtreme rear end from a 2WD Blazer mentioned that may work but then by the time I get it with shipping I am spending $500. I guess I may better off having mine rebuilt but unsure of the cost. As I mentioned I am going for stock but did see a nice Summit Racing disc setup a few years ago for $500.
 

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A quick visual will tell you if it's an 8.5. About 3" out from the center section, the tube will narrow.
 

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8.5" would be the diameter of the ring gear. Truthfully, I'm not sure where it's measured though. Here is my 8.5". You can see the necked down tube @Rhotpursuit mentioned. You can also see the factory G80 posi unit. One of the visual differences between the larger and smaller rear ends is the 8.5" has a round bolt pattern/cover, whereas the 7.5" is more squarish.

As far as compatibility, I have no idea if the driveshaft is different between the two sizes, though I guess that could make sense. That's why I recommended he do some research to determine first what he has and then see what his options are going forward. Another reason I recommend trying a different rear axle is this one has clearly had issues. It seems way too early to need it rebuilt already. Might be worth getting a different rearend. But you're right, he already has invested money into this one, and I was thinking with the perspective of switching the assembly myself, so that is a factor too.


Auto part Differential Transmission part Brake
 

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Seems it's the luck of the draw. The rear in mine started howling at about 20K. Bearings were toast.
 

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Discussion Starter · #11 ·
8.5" would be the diameter of the ring gear. Truthfully, I'm not sure where it's measured though. Here is my 8.5". You can see the necked down tube @Rhotpursuit mentioned. You can also see the factory G80 posi unit. One of the visual differences between the larger and smaller rear ends is the 8.5" has a round bolt pattern/cover, whereas the 7.5" is more squarish.

As far as compatibility, I have no idea if the driveshaft is different between the two sizes, though I guess that could make sense. That's why I recommended he do some research to determine first what he has and then see what his options are going forward. Another reason I recommend trying a different rear axle is this one has clearly had issues. It seems way too early to need it rebuilt already. Might be worth getting a different rearend. But you're right, he already has invested money into this one, and I was thinking with the perspective of switching the assembly myself, so that is a factor too.


View attachment 339423
As mentioned mine came with the ZQ8 suspension and the limited slip though I think it may have been changed out? I do have the 3rd shock mounting bracket on top of the rear axle but no shock or visual place on the frame to where it would go. I have the round cover but as stated earlier when turning the tires manually they both go opposite directions which is an indication that the current rear end is not a posi. I saw this on a Napa site - " All 8.5” 10-bolt rears have two squared-off ears at the 4 and 6-o’clock on the bottom of the pumpkin, that is the #1 tell-tale sign, if you don’t have those, you don’t have an 8.5” 10-bolt." I do have those notches showing, but as Rhotpursuit mentioned about the tapering tube from center I cannot not visually tell if changes size as there is a sway bar connection at 3" out from center, but the notches mentioned above should confirm 8.5 10-bolt though not posi for some reason?

Not that I am going to buy all of the stuff now as I will likely take it to a shop that does this regularly, but I speculate I would need both rebuild kits - bearing spline kit and carrier rebuild kit?

I have seen some limited slip lockers advertised with the economy ones under $400, and some Eaton Detroit Tru-Trac at $537. I would like to put it back to stock limited slip but want to keep the whole thing under $1,000 including labor. Would a limited slip such as the Spartan or Yukon take care of those rebuild kits mentioned above all in one shot?


Thanks
 

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I have the round cover but as stated earlier when turning the tires manually they both go opposite directions which is an indication that the current rear end is not a posi.
The G80 differential only locks when one wheel is spinning faster than a certain number of RPM (I don't know the specific number). Under normal conditions, it operated like an open diff.
 

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At this point I think you may be best off to take it to a shop that rebuilds rear axles and have them give you a quote on the specific rearend that is in your truck. Let them verify axle size, ratio and posi so they can order the correct parts. The shock mount you are looking for will be forward of the rear axle up by the bed crossmember which makes the shock absorber almost horizontal.
 

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As mentioned mine came with the ZQ8 suspension and the limited slip though I think it may have been changed out? I do have the 3rd shock mounting bracket on top of the rear axle but no shock or visual place on the frame to where it would go. I have the round cover but as stated earlier when turning the tires manually they both go opposite directions which is an indication that the current rear end is not a posi. I saw this on a Napa site - " All 8.5” 10-bolt rears have two squared-off ears at the 4 and 6-o’clock on the bottom of the pumpkin, that is the #1 tell-tale sign, if you don’t have those, you don’t have an 8.5” 10-bolt." I do have those notches showing, but as Rhotpursuit mentioned about the tapering tube from center I cannot not visually tell if changes size as there is a sway bar connection at 3" out from center, but the notches mentioned above should confirm 8.5 10-bolt though not posi for some reason?

Not that I am going to buy all of the stuff now as I will likely take it to a shop that does this regularly, but I speculate I would need both rebuild kits - bearing spline kit and carrier rebuild kit?

I have seen some limited slip lockers advertised with the economy ones under $400, and some Eaton Detroit Tru-Trac at $537. I would like to put it back to stock limited slip but want to keep the whole thing under $1,000 including labor. Would a limited slip such as the Spartan or Yukon take care of those rebuild kits mentioned above all in one shot?


Thanks
Sounds like you have a similar (8.5") rear axle to mine. My truck is also a ZQ8 with 4.3L and G80 positraction, but because of it being a 5-speed manual, I have the GU4 3.08 ratio. I also have the hop shock from the factory. In the previous picture you can see where the sway bar is attached to the axle. I had to remove it to take the cover off.

Like TomA said, the positraction from GM acts like an open diff until a certain rpm of spin differential (not sure the actual number), at which point the posi unit "catches", or locks. With my truck on jack stands I can cause mine to lock by spinning one tire by hand. Maybe the difference in gear ratio makes it harder to activate by hand in your truck? But like I said, it acts like an open differential until it suddenly locks, which is pretty violent.

The G80 positraction is nothing like the factory limited slip in my 6th Gen Camaro SS. That one works wonderfully, in that it is smooth and progressive, and effective. So if you want a better locker or limited slip, they are out there. Unfortunately I have only experienced my two factory ones, so I have no aftermarket experience.
 

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Discussion Starter · #15 ·
Sounds like you have a similar (8.5") rear axle to mine. My truck is also a ZQ8 with 4.3L and G80 positraction, but because of it being a 5-speed manual, I have the GU4 3.08 ratio. I also have the hop shock from the factory. In the previous picture you can see where the sway bar is attached to the axle. I had to remove it to take the cover off.

Like TomA said, the positraction from GM acts like an open diff until a certain rpm of spin differential (not sure the actual number), at which point the posi unit "catches", or locks. With my truck on jack stands I can cause mine to lock by spinning one tire by hand. Maybe the difference in gear ratio makes it harder to activate by hand in your truck? But like I said, it acts like an open differential until it suddenly locks, which is pretty violent.

The G80 positraction is nothing like the factory limited slip in my 6th Gen Camaro SS. That one works wonderfully, in that it is smooth and progressive, and effective. So if you want a better locker or limited slip, they are out there. Unfortunately I have only experienced my two factory ones, so I have no aftermarket experience.
When I bought my truck used in 2009 advertised at a Chrysler dealership, I went and saw it and ended up negotiating a real good price. Using a grass incline on their property I loaded my motorcycle in the back and secured it with the straps that I brought with. My only disappointment with it was that it wasn't a 5-speed though it turned out to be a good thing as I have towed with it a few times and is rated at 5,800 lbs. when equipped correctly. It was really hard to get used to the automatic and I found my left foot searching for the clutch on more than one occasion!?
 

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When I bought my truck used in 2009 advertised at a Chrysler dealership, I went and saw it and ended up negotiating a real good price. Using a grass incline on their property I loaded my motorcycle in the back and secured it with the straps that I brought with. My only disappointment with it was that it wasn't a 5-speed though it turned out to be a good thing as I have towed with it a few times and is rated at 5,800 lbs. when equipped correctly. It was really hard to get used to the automatic and I found my left foot searching for the clutch on more than one occasion!?
Most likely you have a 7.5 and the gov-maybe-it-will-lock. Judging from what I just spent to get a TruTrac, new different ratio ring and pinion and all new bearings in my 8.5 I think a reputable shop will charge $1000 to $1200 to do a similar rebuild on yours. Cost of living is high here so it might be less where you are.
 

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Way...way too much trouble and expense. Rear ends usually last the life of the vehicle. I’ve personally owned about 25 cars. Mostly rear drive and have had one rear end failure in 32 years of driving. That was on my S-10 and it had about 250k. It didn’t fail either. It was just noisy. Find someone on Marketplace parting a truck out and buy the whole axle. Make sure it’s the right ratio (I swapped from 3.08 to 3.42 which was amazing). Swap it in a couple hours and keep rolling. Save your money. It’s been my experience that most shops don’t know what they’re doing and you’ll be doing this again. FYI, Most 2wd Blazers I’ve seen have the 3rd shock. Unless your in a major rust belt area, these are still pretty common in yards and people’s backyards.
 

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Since you only drive it about 1000 miles a year and have been doing fine w/o limited slip or the hop shock, don't waste the money adding them now. Doesn't sound like you need or use either of them. If this was a performance build that would be a different story. I agree repairing your existing axle sounds like a waste of money since it's whined for a long time. Probably not set up correctly from the factory.
If it were mine I get a GU6 3.42 ratio out of a junkyard 2wd 4.3 98 up S10 and swap it in. Couple hours work and a couple hundred bucks. It'll likely out live the rest of the truck. I've only had one failure in 37 years of driving S10's and it was just the cheap azz G80 posi not working. Spent over $500 putting in a Zexel.
If it's not a loud whine just drive it. Since you use it so little it'll be years before anything actually breaks.
Maybe drain the rearend to check for any metal and put some Royal Purple synthetic gear lube in. That might quiet it.
BTW the fill plug on the side is not 3/8" and you can round corner it using one trying to remove it. Get a cheap 10mm drain plug socket off ebay and avoid a major hassle.
 
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Discussion Starter · #20 ·
Most likely you have a 7.5 and the gov-maybe-it-will-lock. Judging from what I just spent to get a TruTrac, new different ratio ring and pinion and all new bearings in my 8.5 I think a reputable shop will charge $1000 to $1200 to do a similar rebuild on yours. Cost of living is high here so it might be less where you are.
Per the Napa site " All 8.5” 10-bolt rears have two squared-off ears at the 4 and 6-o’clock on the bottom of the pumpkin, that is the #1 tell-tale sign, if you don’t have those, you don’t have an 8.5” 10-bolt." I do have those notches showing.
 
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