[RobertSpain]

Hi and sorry for mistake posting on Rear End.

Involved in a 1992 Astro LT restoration with non funcional front traction. After taking out diff, we find the reason. Missing ring. RPO codes say that rear is GU6 and G80, so i assume that ratio is 3.42, 7.5" ring diameter and positraction in rear axel, and of course, 3.42 ratio and 7.2 in the front diff.

My question is... A ring from a 1998 Chevy Blazer who has GU6 in his RPO´s will fit to my orphan diff ? I was reading about and entire diff will not fit as Blazer´s shaft is slip but i´m only interested on ring. I think i should change pinion too, but not sure if it will fit because slip in.

A rebuild diff cost me about 1800E from rockauto. Customs and shipment cost as much as spare. I saw this in Rockauto and GU6 equivalences.

Any idea or suggestion ?

This is what in spanish we say "una putada".

Thanks everybody.

 

[markmitch]

Same front differential, the only thing different is the S-10 diff has a set-up to lock it in or out with a vacuum switch. You can just swap out the axle housing, I believe. On the driver's side with yours.

 

[Rod's Trucks]

I would not recommend trying to replace just the ring gear. The ring and pinion have run together so long that trying to mate used ring gear may result in a very noisey combination ( lots of whine) no matter how well one tries to set it up. I would definitely try to find a used complete unit to install, or at least salvage the ring and pinion as a set.
Rod J
Issaquah, WA

 

[tungtide]

I would go Marks direction first. Or do just thr ring gear. The ring from both front diffs are the same. Either way it all has to come out.

 

[RobertSpain]

Same front differential, the only thing different is the S-10 diff has a set-up to lock it in or out with a vacuum switch. You can just swap out the axle housing, I believe. On the driver's side with yours.

Are you sure-sure ? ´92 Astros has four srews for coupling front shaft to diff. It´s not slip-in as i think it´s on 1998 Blazers. Hope you were right !!

I would not recommend trying to replace just the ring gear. The ring and pinion have run together so long that trying to mate used ring gear may result in a very noisey combination ( lots of whine) no matter how well one tries to set it up. I would definitely try to find a used complete unit to install, or at least salvage the ring and pinion as a set.
Rod J
Issaquah, WA

I think so. A voice inside me says the same.

There is one thing rounding my head. The reason. Why should somebody take out the ring ? Pinion seems to be ok. Perhaps a transfer viscose problem, rear diff of different ratio,... I can see some writings on front diff as if it has been swapped. Could it be done with a different ratio one ?, but...pinion has 12 teeth which corresponds to 3.42 (41 teeth ring) and rear GU6 . I´m confused. Perhaps it only responds to gas economy reasons. Who knows !!

Thanks everybody.

 

[augidog]

removing the ring seems like a bit of work if disabling front drive was the goal. but it doesn't seem like an incorrect way.

like you, i want to know "why" and since you don't mention the cv-shafts misbehaving, it has to be something before the differential.

so, yeah, it could mean they've changed the rear specs, but it also could mean the TC is toast. have you picked it up while running and checked for TC output?

 

[RobertSpain]

removing the ring seems like a bit of work if disabling front drive was the goal. but it doesn't seem like an incorrect way.

like you, i want to know "why" and since you don't mention the cv-shafts misbehaving, it has to be something before the differential.

so, yeah, it could mean they've changed the rear specs, but it also could mean the TC is toast. have you picked it up while running and checked for TC output?

Hi.

TC front output works fine. Shaft rotates in the correct way. One reason for taking out the ring could be a toasted viscouse coupler inside TC which could make strange things when in load.

Rear specs has not been changed. This afternoon we opened rear diff and i could see 4112 engraved over the edge of the ring. It means 3.42 ratio. So, that´s not the reason.....

What a mistery!!!

Thanks

 

[augidog]

TC front output works fine. Shaft rotates in the correct way. One reason for taking out the ring could be a toasted viscouse coupler inside TC which could make strange things where in load.

that's true, it could spin under no load but crap the bed when loaded.

oh hey, have you checked the TC fluid for any signs of contamination, glitter, etc?

in other words, you could get a clue, and it could be something other than the coupler itself.

this IS still weird, tho, when taking off the output shaft would be easiest.

that's all i got. best of luck with this, i'll be watching.

 

[RobertSpain]

that's true, it could spin under no load but crap the bed when loaded.

oh hey, have you checked the TC fluid for any signs of contamination, glitter, etc?

in other words, you could get a clue, and it could be something other than the coupler itself.

this IS still weird, tho, when taking off the output shaft would be easiest.

that's all i got. best of luck with this, i'll be watching.

No. TC is still unchecked inside. It´s waiting to test transmission train when installing front diff. Perhaps, missing ring responds only to economy. Gas in Spain is more expensive than in USA. It costs about 1.60-1.70 euros per liter. Mileage difference between awd and rear only could be significant and if previous owners didn´t drive offroad at all, it has no sense.

Will take some photos and post them. I´m falling in love with this van..Step by step learning how things work in this vehicle.

Thanks for your interest and help.

 

[MechBob]

Ring and pinion are matched sets.
I suspect a transfer case problem, and this was done to cover that up.
The only thing that would make sense is the viscous coupling is seized up, so locked in all the time.
Otherwise, if parked on a slight grade/hill, no parking brake, the van would have been drifting/slowly rolling away. They will do this also with no front driveshaft.

 

[augidog]

Otherwise, if parked on a slight grade/hill, no parking brake, the van would have been drifting/slowly rolling away. They will do this also with no front driveshaft.

I'm trying to wrap my mind around this. i picture a hard connection at the tranny and transfer case, so i figured "parking" the tranny "parked" the rear driveshaft/differential. i don't understand how disconnecting front drive allows for creep when in park.

please explain or link to a mechanical diagram.

 

[Mmusicman]

Perhaps, missing ring responds only to economy..

Maybe (from a misunderstood point of view)... but the difference would likely be very minimal. The previous owner may or may not have known this.

It's "my guess" that this was more than likely done due to some issue with the AWD system. But again, previous owner may have simply thought he'd pick up some mileage.

Good luck

 

[MechBob]

I'm trying to wrap my mind around this. i picture a hard connection at the tranny and transfer case, so i figured "parking" the tranny "parked" the rear driveshaft/differential. i don't understand how disconnecting front drive allows for creep when in park.

please explain or link to a mechanical diagram.

Trans in park. So output to t/case is locked. So no drive power to spin the viscous coupling(V/C),right? Now, think of your V/C as a rear differential. Ring gear "locked", trans in park, that would be the V/C case. BUT, you have 2 axles, floating in gears, connected by only smaller spyder gears. That would be equivalent to the front and rear drive shafts in a Astro. Then add in some clutch plates, not touching, but with holes, that connect only by the friction of the oil passing between the front and rear set, that is a V/C. Take that "open rear diff", pull one wheel off,jacked up, make it a "limited slip",aka a diff with clutches, can you turn the "free" axle?, not by hand, but put a long bar on it, and the clutches will slip. Same thing.
V/C's go bad 1 of 2 ways,generally, they seize up, or clutches burn up, offering no resistance, the oil leaking out is a prime example of this.
To explain perhaps a bit better, early AWD USA trucks had AWD in the way of the NP203 transfer case. Guess what connected the front and rear driveshafts? 2 "axle" gears and 4 spyder gears. They had a locking collar that locked in, when shifter was moved, to provide true 4x4. So now you also know why I and others do transfer case swaps, to have true 4x4.
On a side note, the predecessor of all these was the Jeep "Quadratrac, a differential between front and rear drive shafts, locking collar for true 4x4, but with the addition of limited slip clutches between the front and rear, the first true "torque bias" AWD. Quite ahead of their time,back then.

 

[augidog]

I get that the tranny-out drives a chain that drives the V/C (and I get how V/C works)...and I can see how the V/C will definitely allow creep of the front wheels, like a tranny in neutral.

what I still don't get is, if the tranny and rear diff are parked, meaning the chain to the V/C is parked, how can the vehicle creep just because the front wheels are disconnected from the V/C?

i swear i re-read your explanation a few times before i asked again.

 

[RobertSpain]

Hi again.

Some pictures about process..

This is which came with van. You can see the missing ring.

This is one for a ´98 Blazer from junkyguard. Seems better than mine, but it´s not swapable as is.

In this pic, we can see why. Upper is Astro´s shaft. Same problem with driver´s side. Also need to change input because coupling is different too. Case and other components are identical.

Upper is Astro´s.

You can see case is the same, ready but awd is not selectable in Astro.

´98 Blazer ´92 Astro

So, i have to change input coupling installing plate one from Astro. Swap boths shafts and also install new seals.


Thanks to everybody and have a very good Sunday.

 

[MechBob]

I get that the tranny-out drives a chain that drives the V/C (and I get how V/C works)...and I can see how the V/C will definitely allow creep of the front wheels, like a tranny in neutral.

what I still don't get is, if the tranny and rear diff are parked, meaning the chain to the V/C is parked, how can the vehicle creep just because the front wheels are disconnected from the V/C?

i swear i re-read your explanation a few times before i asked again.

OK, will try to make simpler. So, you do understand that a V/C is nothing more than a limited slip diff., good. But, for our example we will use a open/normal diff.
You take your 67 Camaro, open diff. park on a "slight grade"(hill).
Trans is in park. Rear ring and pinion cannot move because of this. The chain in the T/C is irrelevant, it is not "parked", it is not directly connected to the transmission.
OK, now back to the Camaro, In park, on a hill. Take a floor jack, with wheels, and jack up one side, by the leaf spring, lifting the tire/wheel off the ground.
What happens??
Yep.
The left and right axles are equivalent to the front and rear driveshafts.

 

[augidog]

The left and right axles are equivalent to the front and rear driveshafts.

o-tay! thank you.