Check out my rear end

[89Suburban]

I always thought that every truck in the 80's got either a Gov Loc or an open diff, but @89Suburban had a rig with a factory installed limited slip.

With Andy's info, then in 1980 GM did still have their posi units in some trucks.


The RPO code, would that be different than G80?

Hey Paw Paw, @89Suburban any info you can share on your Suburban?

I don't recall about the RPO code, but I do know that the G80 cade was also used in 80's cars that had a limited slip.

PawPaw's Burbs were '89 and '90, but I don't remember which one had the limited slip and not a gov-loc.

@89Suburban

I don't remember brosephs. I did some searching and found this thread with pics and RPO sheet. It was from the '89 for sure, I see the coil over shocks in the one pic. I swore the '90 was LS too. I don't ever recall running a gov-bomb rear.

10 Bolt Rear Axle Oil Change w/ Factory Limited Slip

10 Bolt Rear Axle Oil Change w/Limited Slip Break the bolts loose on the cover. 1/2" socket needed.....

www.gmsquarebody.com

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[bucket]

I don't remember brosephs. I did some searching and found this thread with pics and RPO sheet. It was from the '89 for sure, I see the coil over shocks in the one pic. I swore the '90 was LS too. I don't ever recall running a gov-bomb rear.

10 Bolt Rear Axle Oil Change w/ Factory Limited Slip

10 Bolt Rear Axle Oil Change w/Limited Slip Break the bolts loose on the cover. 1/2" socket needed.....

www.gmsquarebody.com

You must be registered for see images attach

Hmm, going through that, it seems we never determined if that was factory installed or not. Maybe it was Silvy? Did you get that one from the original owner?

I swear at some point it was determined you had a factory installed limited slip. But maybe it's just been too long and my memory is going.

 

[Turbo4whl]

I don't remember brosephs. I did some searching and found this thread with pics and RPO sheet. It was from the '89 for sure, I see the coil over shocks in the one pic. I swore the '90 was LS too. I don't ever recall running a gov-bomb rear.

10 Bolt Rear Axle Oil Change w/ Factory Limited Slip

10 Bolt Rear Axle Oil Change w/Limited Slip Break the bolts loose on the cover. 1/2" socket needed.....

www.gmsquarebody.com

You must be registered for see images attach

Thanks for the link. Interesting read.

 

[82sbshortbed]

I have a 3.73 gm Trutrac 8.5 10 bolt posi rear end in my 82. New 700r4 and driveshaft. When I pull out on the street slow turn it always kinda chatters like was mentioned by the op. I have always thought it was the inside tire doing that because the outside tire has to travel faster than the inside tire but, with posi they spin the same speed. Am I missing something? I don't think it's the clutches since it's brand new.

 

[TotalyHucked]

I have a 3.73 gm Trutrac 8.5 10 bolt posi rear end in my 82. New 700r4 and driveshaft. When I pull out on the street slow turn it always kinda chatters like was mentioned by the op. I have always thought it was the inside tire doing that because the outside tire has to travel faster than the inside tire but, with posi they spin the same speed. Am I missing something? I don't think it's the clutches since it's brand new.

No, you're thinking of a locker where the axles *always* spin the same. A locker keeps the two wheels locked together at all times and chirps the inside tire on tight turns. A posi should lock and unlock as needed, so it should typically operate like an open diff around turns.

A posi works by using a combination of wheel speed differences and torque being applied by the engine/driveshaft/pinion to lock up. Your TruTrac is a gear-type posi, not a clutch-type. I have no experience with them, but I have heard for years how smooth and seamless their operation is.

I have a clutch type posi unit (Yukon Duragrip) in my C10, with the automatic, it was almost seamless in operation. It would only lock if I really romped on the gas and usually that would induce a slide because I was on the gas pretty hard. Now that I have a stick, it's locking more often/chirping the inside tire because there's more torque being applied to it during acceleration than with the auto (torque converter "softens" the blow), so I'm constantly chirping/chattering the inside tire.

If yours is chattering all the time, regardless of speed/amount of throttle, first go to a parking lot and do several slow speed u-turns in both directions to try to unlock the posi. If it continues to do it, I'd take it somewhere to be checked out just to make sure. You don't wanna grenade that thing if something is wrong.

 

[82sbshortbed]

No, you're thinking of a locker where the axles *always* spin the same. A locker keeps the two wheels locked together at all times and chirps the inside tire on tight turns. A posi should lock and unlock as needed, so it should typically operate like an open diff around turns.

A posi works by using a combination of wheel speed differences and torque being applied by the engine/driveshaft/pinion to lock up. Your TruTrac is a gear-type posi, not a clutch-type. I have no experience with them, but I have heard for years how smooth and seamless their operation is.

I have a clutch type posi unit (Yukon Duragrip) in my C10, with the automatic, it was almost seamless in operation. It would only lock if I really romped on the gas and usually that would induce a slide because I was on the gas pretty hard. Now that I have a stick, it's locking more often/chirping the inside tire because there's more torque being applied to it during acceleration than with the auto (torque converter "softens" the blow), so I'm constantly chirping/chattering the inside tire.

If yours is chattering all the time, regardless of speed/amount of throttle, first go to a parking lot and do several slow speed u-turns in both directions to try to unlock the posi. If it continues to do it, I'd take it somewhere to be checked out just to make sure. You don't wanna grenade that thing if something is wrong.

Thanks for the information on this. I'll look into it. It's not really chirping but I feel it a little in a slow turn pulling on to the road from a stop. If I romp on it or accelerate pretty good it does get sideways because both wheels are spinning. Should I put in some additive in it? I may have my mechanic look at it. He's the one who put it in my truck.

 

[Bloodhound1981]

So I pulled the driveshaft and brought it to the driveshaft shop. It was a little out of balance, but they said due to the long length of this shaft, and the small diameter of the tube, it's probably oscillating when I get to higher speeds. They were surprised I didn't have a 2 piece driveshaft, which I know some long beds came with. So I decided to just have a whole new one done up in aluminum. Threw it in today and hit the highway. Things are definitely smoother, but there is still some vibration happening in 4th at low rpm over 60mph. But if I get on it, it goes away. So I'm still thinking rear end, I don't know. I got up to 80 and all was good. At this point I'll probably deal with that in the spring since this shop is already booking into mid-December.

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[77Dmax]

Look at your driveline mounts for wear/play. These engines move all over the under load.

Your chattering might be due to the springs in the carrier. There are three different rates available for those springs. Back in the day rebuilders typically put the strongest spring set in to maximize preload against the clutches. This practice made these units beasts, they were almost like lockers. Both tires would spin under nearly any circumstance. The down side is they drive like dump trucks with spools. The excessive preload would also burn the clutches out faster.

The springs were identified by color and I'm sure with a Google search you can figure out the spring rates and see if this is your issue. You can probably go down to the normal rate and it'll slip around corners again.

Edit- I did some googling to refresh my memory. Those springs look a little red to me, which would make them the 800 lbs springs. That is your issue.. swap them for the 200 or 400 lbs set and you'll be happy. You can order the springs from summit..

 

[BRetty]

I don't know how I found this thread but lots of good info here.

I have a vibration in my driveline, and looking at driveshafts for a longbed 2WD C10, they are absurdly long. ~73" is off the charts of custom driveshaft shops, actually. Reminds me I have to get down and measure right now before it gets too dark.