Slant Six Forum
https://mail.slantsix.org/forum/

School me on rebuilding a complete 8.75" rear axle.
https://mail.slantsix.org/forum/viewtopic.php?t=63841		 Page 1 of 2
Author:  SpaceFrank [ Fri Jul 19, 2019 6:38 am ]
Post subject:  School me on rebuilding a complete 8.75" rear axle.
Does anyone have a good write-up (or video) for rebuild of an 8.75" axle assembly? I have a complete A-body housing with a couple of center sections (I think a 742 and a 489) and a sure-grip unit, and I want to replace all the bearings and rebuild the SG before installing it in the Race Dart. I also need to install a new set of 3.55 gears, which I have not yet purchased.

I've never screwed with rear axles before (aside from unitized wheel bearings on my Jeep), and I'm not really sure where to start. But I am about to have a few days recovering from sinus surgery where I can't do anything but lay around and read, so now's a good time to do research.

It won't have to deal with a whole lot of power; even if we get around to adding forced induction to the Slant it'll still be well south of 300 hp. I just want to make sure this thing is ready for being thrashed around a road course.
Author:  GregCon [ Fri Jul 19, 2019 7:39 am ]
Post subject:  Re: School me on rebuilding a complete 8.75" rear axle.
I've done a million of them...doing one now. See attached lol.

I wouldn't go into the SG unless you have reason to think it's bad. The 489 case cone type aren't rebuildable if you go by the book...and the guys who do rebuild them are doing some shaky stuff in order to rebuild them. The clutch type (which is what usually came in 742's) are rebuildable but they are not easy to do.

The axle bearings....probably do not need replacing but if the outer seal is leaking (and it probably is if it's 50 years old) then there is no way to replace it without removing the bearing. And there is no way to remove the bearing without ruining it. I have a special puller for making the removal as easy as possible but the bearing still gets ruined.

The carrier bearings are easy enough to replace but if the rear end had oil in it they are probably OK...especially for a limited use race car. It's not like you're gonna demand 100,00 miles out of it.

If it were me...I'd go into it as a ring and pinion swap rather than a full rebuild. I'd clean up the guts of the third member with Varsol or mineral spirits, pull the carrier, swap the gears, then put it back together using the same bearings and all new seals. I actually prefer a set of used bearings provided they are not worn out. They're already seated and 'proven'.

On the axles....I'd plan to replace the bearings with stock type tapered roller bearings and new seals. You could go with the 'Green' bearings but for a track car that sees cornering...the stock bearings are waaaay stronger.

I'd also add a 1/8" NPT female thread to the bottom of the housing while it's apart. This makes it a hundred times less messy to drain the oil. You can tap the housing itself with good results or...as I do...weld on a small fitting so you have a little extra meat for the threads to ride in.

I'd be glad to help you with the axle bearings and drain plug if you like. I'm not so hot on cleaning parts though lol...

Attachments:
8.75.JPG
8.75.JPG [ 129.59 KiB | Viewed 8912 times ]
Author:  Charrlie_S [ Fri Jul 19, 2019 7:52 am ]
Post subject:  Re: School me on rebuilding a complete 8.75" rear axle.
Frank, the factory service manual is probably as good as it gets. Manuals are available here to read or download.
http://www.mymopar.com/index.php?pid=31
Author:  Joshie225 [ Fri Jul 19, 2019 8:28 am ]
Post subject:  Re: School me on rebuilding a complete 8.75" rear axle.
Before you buy 3.55 gear know that they were common in vans and pickups. I've almost always been able to buy a whole 3rd member for less than a new ring and pinion.
Author:  Greg Ondayko [ Fri Jul 19, 2019 2:33 pm ]
Post subject:  Re: School me on rebuilding a complete 8.75" rear axle.
Just finished one now.. The 3rd member is not in nor did I drive it yet but this is the first time I had replaced outer seal between the bearing plate and axle flange. - It's not hard. Follow what others have said.

A Shop press is helpful for Studs and Bearings: (sorry no pics of the bearings going on).
Image


Image

Image



Image




Sometimes removing the old bearings from the differential and axles are just a grind cut and replace with new.

A lathe with 200, 323, 400,600, grit(s) emory cloth is nice for cleaning up the Axle seal surface(s)


A parts washer is nice to clean everything up!
Image

Image


Image







Find an old oven or if your wife or roommates' let you.... put the ring gear in your kitchen oven and the diff in the freezer when you put them together. It will make them slide right on before both come back to room temp.



Greg
Author:  SpaceFrank [ Sun Jul 21, 2019 8:03 am ]
Post subject:  Re: School me on rebuilding a complete 8.75" rear axle.
Thanks for all the info, guys. I went out to the garage to refamiliarize myself with what I've got. I got all this stuff dirt cheap from a guy at work who'd probably been sitting on it for years after he swapped over to a Dana 60 in his drag car.

I have a bare 489 housing with just a pinion installed, a 742 housing installed in the axle, and another 742 installed in a homemade workstand. The seller said one of them had a SG installed, so I assume it's in one of the 742s. (I'm recovering quicker than expected, but I'll still need to wait a few days before I start turning wrenches.) He also said the only gears he had were in the 4.xx range and worn out. So I think I'll start keeping my eyes open for 3.55 gears for the 742, or a complete center section I can swap my SG into. Maybe take this 489 case to a swap meet and see if I can make a trade.

The axles have tapered bearings installed that seem to be in alright condition, but I'll plan to replace them along with the seals. They're 5x4" bolt pattern, but the 5x4.5" wheels I plan to run will require a thick billet spacer anyway, so I'll just get a pair of adapters.
Author:  GregCon [ Sun Jul 21, 2019 8:14 am ]
Post subject:  Re: School me on rebuilding a complete 8.75" rear axle.
If you take a photo of the carriers, the SG can easily be identified.

If you wanna end with up the big bolt pattern, I have a pair of Moser axles you can have...they're for a stock width A body housing. They have two issues. One is they use Green bearings and might or might not work with stock bearings (never checked). The other issue is Moser screwed up the lug holes and they will need a new set drilled or the old holes need some attention.

Or, I have a set of stock C Body 4.5 BP axles you could get shortened and resplined. I think Moser will do this and I know Dutchman will.

I don't have any 10" big bolt pattern brake parts I can spare but I have tons of 11" parts.
Author:  SpaceFrank [ Tue Sep 24, 2019 8:00 pm ]
Post subject:  Re: School me on rebuilding a complete 8.75" rear axle.
Well, here's the carrier:

Image

Unfortunately, it appears to have some issues. The spider gears are all broken. (Apologies for the bad lighting)

Image

I haven't torn it down any further yet, but at this point I'm wondering if it's even possible to rebuild. Unfortunately this is the only carrier I have.
Author:  Dart270 [ Wed Sep 25, 2019 4:49 am ]
Post subject:  Re: School me on rebuilding a complete 8.75" rear axle.
That is a clutch type rebuildable sure grip. Not sure if the spiders are busted like that. Teardown necessary... Doctordiff (.com) should have parts for you.

Lou
Author:  GTS225 [ Wed Sep 25, 2019 5:11 am ]
Post subject:  Re: School me on rebuilding a complete 8.75" rear axle.
DAMN! That carrier looks in a bad way. You have broken ring gear teeth, probably broken pinion teeth to match. There's a piece of a spider wedged between the carrier and the ring, on the outside of the carrier, and a couple of the edges of the casting are questionable, (IMO). I think, if I didn't find anything obvious on teardown, I'd have that carrier Magna-fluxed for cracks. Might even have the hogs-head checked, too. It looks to me like that is the cause for the previous owner to have swapped to a Dana 60.
You might just have a handful of scrap metal right there.

Roger
Author:  SpaceFrank [ Wed Sep 25, 2019 7:59 am ]
Post subject:  Re: School me on rebuilding a complete 8.75" rear axle.
The previous owner said the installed gears were trashed, but I don't know if he ever opened it up to see the full extent of the damage. Either way, I can't complain for the price I paid.

I priced out parts from Dr. Diff for a full rebuild including all bearings, because with all this damage I'm not sure I can trust anything in there. It looks like a brand new clutch-type carrier is only about $160 more than all the parts I'd need to rebuild the one I have (assuming the housing itself isn't garbooned). I'm definitely leaning toward a new one, but I'll give him a call later today to make sure I'm looking at all the right parts.

Since I'm looking at a full rebuild now, I'm also leaning toward using my 489 case. If nothing else, it'll allow me to use a crush sleeve eliminator from Dr. Diff at no additional cost.
Author:  GregCon [ Thu Sep 26, 2019 6:09 am ]
Post subject:  Re: School me on rebuilding a complete 8.75" rear axle.
In case you haven't seen them, there are a number of sellers on ebay, including Dr Diff, who sell carriers for about $415 and other parts needed. It's a good source for parts.
Author:  Danarchy [ Thu Sep 26, 2019 8:12 pm ]
Post subject:  Re: School me on rebuilding a complete 8.75" rear axle.
Quote:
You might just have a handful of scrap metal right there.
:shock:
Author:  GregCon [ Fri Sep 27, 2019 9:04 am ]
Post subject:  Re: School me on rebuilding a complete 8.75" rear axle.
It also looks like the ring gear is missing some teeth-pieces.

I am not sure how the spider gears could be broken up like that but I guess both the spider gears and ring gear could have digested some metal chunks. Sometimes...the center pin breaks (they often break into two pieces). That's OK because the two pieces stay in place until you pull the axles. But if someone did that and left one or both halves swimming around in there....

The worst thing you can do, generally, is run two different sized tires in back. Or, tire that are inflated differently. That way, your clutches are constantly slipping as you drive down the road.
Author:  GTS225 [ Fri Sep 27, 2019 1:51 pm ]
Post subject:  Re: School me on rebuilding a complete 8.75" rear axle.
Quote:
I got all this stuff dirt cheap from a guy at work who'd probably been sitting on it for years after he swapped over to a Dana 60 in his drag car.
********************************************************************************

Here's the key statement from SpaceFrank's post. This explains all the damage in that carrier. A hard launch, on slicks, in a heavy car, and he shattered the spiders. Some of the smaller pieces got out of the guts, and tangled up with the R&P, causing the chips out of the ring before the car finished rolling to a stop.

Now, you may be able to salvage the carrier and "hog", but it's going to need spiders and sides, and possibly a clutch pack. For sure will need a R&P, of the ratio of your choice.

That being said, A-body 8.75's, especially with a SG unit, bring a premium, so it might be well worth your while to attempt to save it.

Roger
Page 1 of 2 All times are UTC-08:00
Powered by phpBB® Forum Software © phpBB Limited
https://www.phpbb.com/