I want to replace my mono trac rear for a sure grip. I am not that knowledgable on recognizing the different types. To what year did they put 8 3/4 rears in mopar vehicles that will work in my 66 Fury? I ask due to a co worker who does demo derby and he has a 75 or 79 cordoba he is about to chop up into a derby car. He beleives it has a sure grip 83/4 and will sell it cheap if I can use it. Also what are some good sources of vehicles in junk yards to look for a donor?
Joined: Sat Dec 10 2005, 04:28PM
Location: United States
Posts: 4954
Ahhhh
They varied. 8 3/4 was used, to my knowledge, in all the C's up to 69 or 70. Then they went to 8 1/4 for the small blocks and 8 3/4 for the big blocks (Excpet wagons). So if it had a 400 or larger, it was 8 3/4.
However, if the spline count is correct, you can change the carrier and use your axles without changing the housing. You should have an open 8 3/4 in the 66 already.
If you want to maintain the same ratio, you'll have to check the carrier numbers and see if the ring gears and pinions will swap over. Someone must have a book for that somewhere. I'll bet they are pretty close though
The last 8.75 was used in the 74 model year, it was gone after that. There were versions of that same axle that date back to around 1957 or so, plenty of them out there.
If you swap in the whole differential assembly (hogs head, pig, chunk, whatever), they'll ALL interchange. Spline count was the same from start to finish, regardless of what engine was driving it. The only hangup MIGHT be with the type of Sure Grip (limited slip), as most used one type of thrust block, but a few used one that was slightly different. I can't remember what the difference was. It's almost not worth worrying about.
Expect to pay $3-400 for a good used SG in a common ratio (like 2.76-3.23), $4-500 for 3.55 and up, and $8-900 for a completely rebuilt unit with your choice of gears.
I've lucked out in the past finding them in the salvage yard. For some reason, I've heard vans came with them more often than trucks, so you might check those as they don'y get as much attention in the yard...
Joined: Mon Oct 10 2005, 01:49PM
Location: Grand Rapids, MI
Posts: 421
I have the best luck looking under vans, trucks and even Jeeps for SG 8.75's.
Quick way to check is get both rear wheels off the ground, give em a spin, and if they both turn in the same direction, you have yourself a SG pig. !thumb
Your Fury should have one already. If your buddy has one, it will fit your housing. <span class='smallblacktext'>[ Edited Sat Oct 07 2006, 05:45AM ]</span>
Great info , eveyone needs to save that one to Favorites .Keep in mind for your swap , stay away from the 57-64 models , as they are junk . The drums usually warp when removeing with a puller , and then the pulley doesn t work and the torch comes out . NC
But the differentials from the 57-64's work just fine in the later assemblies. I had to pass on one a long time ago because I couldn't get the dang axle apart in the salvage yard... dang tapered axles!
THe 8 1/4 actually started under B bodies in '69. Yes, B bodies and probably C's as well. THe B body I am referring to was a '69 CHarger with a Turnpike package and a 383 2 bbl.
My '70 parts car (318 Fury) has a 8 1/4 with a 2.71 rear end. However, my convertible was a manual trans. car and that had an 8 3/4 with a 3.23 open rear (was 318 3 speed.) My '70 FSM confirms both.
I think you'll find a lot of C's in the heap with an 8 3/4, but the liklihood that smallblock cars had the smaller rear is a strong possibiilty.