8.75 Rear End Confusion

[Jeradaktyl]

I have a 69 RR with a 8.75" rear and 742 case, 3.23 gears (have 3.91s ready to be installed) so my first problem is when cornering it makes a loud bang noise...I pulled the Diff to find chucks of my spider gears laying in the housing. So my confusion starts with the fact I thought Posi 8.75" rear ends were sure grips and I didn't see any springs just mauled spider gears.. so really I'm not even sure what I have! Do you? Any input is much appreciated, I'd love to find new spider gears and hit the road but if I have to get a different diff. Then so be it.

 

[Jeradaktyl]

This is what mine looks like, on summit they call it a sure-grip but for an 8.25 rear, are all spider gears for the 8.75 interchangeable?

 

[1969CoronetR/T]

I would guess that is not a Sure-Grip limited slip differential and has an open differential.

 

[Jeradaktyl]

But wouldn't an open differential be non posi? My car is most definitely posi? Forgive my stupidity

 

[dla4567]

Post pictures of yours and you will get your answer.

 

[Jeradaktyl]

Well I would love to but my garage isn't wide enough to pull the axles ( I live in an apt.) And the shop I get to work out of is full at the moment...all I know is I don't see springs like a sure grip, my spider gears and wrecked, it is posi, and the gentleman I bought it from said he bought a reman. Posi rear for it off eBay :-/ if spider gears are interchangeable I'll just order them and cross my fingers

 

[1969CoronetR/T]

Posi traction is a GM term for a limited slip differential. Sure-Grip is a Chrylser term for a limited slip differential. If you can jack the rear wheels off the ground and spin the wheels to determine open or LSD (Sure-Grip) differential. With the rear wheels off the ground, spin one wheel and see if the other follows. If not, it is an open differential.

 

[Jeradaktyl]

Both tires spin

 

[1969CoronetR/T]

Cool. Hopefully someone else can chime in on the interchangeability of the spider gears.

 

[Jeradaktyl]

I'm finding another term...Pwr-Lok? That resembles what I have, I'll probably just order it and hope for the best however I'm blown away that the gears are $306.00 lol can get a new sure grip for 400

 

[pturner]

Both tires spin

I would look for pieces of metal in the spider gears and the axle gears. this would lock the two axles together. sure grips have plates and springs, similar to the GM.
just my thinking
PT in Tennessee

 

[1969CoronetR/T]

I wonder if power lock is similar to a Detroit locker? I would stay away from a locker. Make sure the Sure-Grip is a clutch type and not the cone type. The cone type cannot be rebuilt.

 

[Jeradaktyl]

Thanks a lot guys! To me it only makes sense to just get a new sure grip for the price that way I'll know what I have exactly...I appreciate all your input

 

[Habib]

You could of had a Open Dif and someone Welded the Spider gears together. Get a Sure-Grip. Posi is Chevy talk, Stop that.

 

[66Satellite47]

There are two types of limited slip differential in 8 3/4 axles. One has the "clutch" style like Dana 60, the other has the spring style. If you don't see the springs and it does spin both wheels in the same direction seems like the "Dana" style diff. I always thought the Dana style, clutch type is preferable. Salvage yard parts to repair? Good luck.

 

[Jeradaktyl]

I check my local salvage yard yesterday and they didnt have anything unfortunately, I'll keep looking otherwise I might order a sure grip from Dr. Diff

 

[1969CoronetR/T]

I put a Eaton Trutrac in place of my Sure-Grip in my 8.75 and it works great. I think it was about $600.00 for the unit, but it has worm gears instead of clutches so it will never need rebuilt.

 

[Jeradaktyl]

Do you still have your sure grip laying around?

 

[1969CoronetR/T]

Sorry, I sold it with my 741 case to another member last spring. I changed my center section to an 849 (?) and changed my gears to 3.55. Mosier Enginnering supplied all the parts.

 

[Cranky]

This is what mine looks like, on summit they call it a sure-grip but for an 8.25 rear, are all spider gears for the 8.75 interchangeable?

View attachment 342688

There is a unit similar to this one that is called a Trac Lock. There are clutches outboard of the side gears (side gears that are splined). My 9 1/4 rear in my Durango has one and imo, it's crap. It's also hard to install new clutches in the one piece case without the proper tools. Also, the spiders in all 3 different diffs for the 8 3/4 are different. The cone unit (Borg Warner anti spin Sure Grip) spiders will not interchange with the Dana style clutch unit (Power Lock) spiders and the open diff non Sure Grip spiders are not either. Cone type rears can be machined to work well again so long as someone took it out of service when it quit making both tires spin. They will not last for very long if they keep using them as a one wheel peel rear end.