Rear diff question

What difference is there between the sedan rear diff and the wagon rear diff? I know the wagon is wider, but by how much? Has anyone swapped in a sedan diff into their wagon? If so, what problems did you encounter, if any? By putting the narrower sedan diff in the wagon what would be the biggest wheel I can fit in the wheel well w/o any other modifications? Wheel offset?

Wagon axle is 3" wider and all mounting points are 1.5" off.

Some will say it WILL NOT FIT, but others have done it without issues.....

Also, would using the sedan control arms make any difference? Or are they of the same dimensions? Looking at a rear diff for real cheap, low miles, posi-trac and it comes with the factory mounted sway bar.

Control arms are the same...its the perch mounts that are off..

Nogonzo did it I think?

Bewb did it, there is a wagon down here that 94 SSled on ISSF owns with one (bought Klez's old two tone wagon), I have pics and email from another who did it.

I got a 96 9C1 rear on the side of the house I'm gonna stuff up under my 94 Caprice.
From the two I looked at in person, it's not that big of a deal unless you are going to take the car to the track. Yes the mounts are off a bit, aand I may re-weld the perches as I have access to a welder.

to semi-quote the guy who showed up at WF a few years ago, "I didn't know it couldn't be done until I did it and showed up here"

One caveat - remember that sedans are not rated to support the cargo weight (NOT towing weight, cargo weight) that the wagons are. Part of the wagon axle's uniqueness is that the rear axle bearings are larger. As we all know, GM does not select a unique part unless they really need to, so if you put a sedan rear axle in, don't go filling the cargo area with bricks or tile afterward.

Then again, if you're just doing it so you can fit big wheels/tires under, I trust you won't be stylin' at Home Depot anytime soon.

sherlock9c1 wrote:

One caveat - remember that sedans are not rated to support the cargo weight (NOT towing weight, cargo weight) that the wagons are. Part of the wagon axle's uniqueness is that the rear axle bearings are larger. As we all know, GM does not select a unique part unless they really need to, so if you put a sedan rear axle in, don't go filling the cargo area with bricks or tile afterward.

Then again, if you're just doing it so you can fit big wheels/tires under, I trust you won't be stylin' at Home Depot anytime soon.

Echoes of bill harper,.

Funny how nobody ever bats an eyelid about a half ton carrying twice its rated capacity,. or me and my 3/4 ton with 4400lbs of gravel in the box pulling a tandem trailer with 22x 100lb bags of cement,.

you really think the sedan rear would fail hauling a heavy load?
personally i doubt it,.and i,ve never heard of a case,.
but it makes good internets drama,.

There's a good reason for the heavier bearings. What IS it, Nick?

jimbeau wrote:

There's a good reason for the heavier bearings. What IS it, Nick?

I dunno,. you tell me,.

I'll make a wild guess that testing at GM found they were needed for the axle to hold up under frequent full-cargo weight use.

Just a guess, you understand.

jimbeau wrote:

I'll make a wild guess that testing at GM found they were needed for the axle to hold up under frequent full-cargo weight use.

Just a guess, you understand.

Reasonable guess, i,d guess,.

wonder if the bigger diameter axle has anything to do with it?

wonder if we took the two bearings and subtracted inner dia from outer dia etc,. wonder where we'd end up ? what conclusion might we come too?? width plays a part too,.

Then we need to put into the mix the availability of parts already being used,. uniquely to specific is one thing,

The GM 10 bolt rear is used in a whole lot of vehicles,.not just wagons and sedans,.
different axles fit more than one vehicle, different spline counts,. yet the side gears can be changed to use a different but similar axle,. blah blah blah,...

oh and if you study parts interchange books you'll find certain specific, or "unique" bearings are used by different manufacturers for their rear ends, not oem brand specific,.
I.E the timken 1559 bearing used in a gm 10 bolt is also used in a chrysler 7.5 diff etc,. etc,.

So as i said,.i personally wouldn't worry,.

having said that, if the sedan rear in a wagon was used 12hrs a day to haul full capacity loads at 70mph while towing at full capacity,.and to satisfy the type "A" personalities that are always looking for that 1 possible scenario and frantically using google to find it,.....

then i might switch the axle for a full floating 14 bolt corporate,.,.

but thats just me,..

ever wonder why some folks spend so much money on 1 super duty million mile part, only to drive it occasionally??

It makes 'em feel good,.

Nick

I wouldn't worry either, but I also wouldn't chide Joel for adding factual information.

phantom 309 wrote:

width plays a part too,.

Some would say that's what it's all about.

Nick, well put. It's all an engineering judgment, just laying it out there. Good counterpoint.

jimbeau wrote:

I wouldn't worry either, but I also wouldn't chide Joel for adding factual information.

factual?,. somewhat,. dramatic?,. definitely, with no shred of scientific proof or even hearsay evidence,.,.

Had it just been left at "the wagon has a bigger rear outer axle bearing to better deal with heavy loads under extreme conditions",. but the inference to driving to home depot and adding a load, and that imminent catastrophic failure will ensue,........Pfffft,.

No,... i'll chide a little,.

Nick
2 bolt vs 4 bolt mains? 9/16ths ball joints vs 5/8ths? orange vs green coolant,.mechanical fan vs twin electrics,.
yada yada yada,.

TBI vs. LT1

Olds Weighty Eight wrote:

TBI vs. LT1

I see what you did there.

Is the differantial the same in all 8.5 10 bolt rears. I have a 9C1 limmited slip diff. to use if they are the same.

Thanks
Randy

yakko wrote:

Is the differantial the same in all 8.5 10 bolt rears. I have a 9C1 limmited slip diff. to use if they are the same.

Thanks
Randy

make sure the cones are still good before you do,.
if your car has 2.56 gears? it won't fit,.(just the carrier we're talking here)
2.93 gears? it will fit,.

what year 9c1 diff?
if its the 3;42 setup use the gears and diff,.

yes it will physically fit,.

Nick

It is a 1994 9C1 with 3.42 gears. I was thinking of swaping all the guts over.

Randy

yakko wrote:

It is a 1994 9C1 with 3.42 gears. I was thinking of swaping all the guts over.

Randy

94's came factory with 3.08's,.
93's were 3:42's

Nick

gmtech wrote:

Also, would using the sedan control arms make any difference? Or are they of the same dimensions? Looking at a rear diff for real cheap, low miles, posi-trac and it comes with the factory mounted sway bar.

Not sure the sway bar would work without some adaptation on the sedan rear in a wagon. There might be enough wiggle in the slotted holes in the bar.

But of course the Ford sedan bar would work.

Nick,
The 94 9C1 I have was rebuilt with 3.42:1 gears. I was thinking of changing out my wagons 2.56:1 carrier and gears with the posi carrier and gears. I think the 30 spline wagon axles fit the 30 spline sedan diff. I just need to move the carrier and gears from the sedan axle into the wagon. Right? Of course I would have to go through a set up with pinion depth and back lash. But the carriers have the same perch. or are they different?

Randy