8 3/4 question

[marksmopars]

Hello fellow mopar fans! I am still working on my 70 dart project and finally have extracted a potential doaner rear end from a c body I had in my spare parts pile. problem is I don't know much about rear ends, but I do know FABO. Can anyone out there take a look at this picture and tell me if this rear end can be/should be modified for my dart? Also, my information is that this is supposed to be a 4:10 posi, how do I positively ID this, tell if it is a posi and determine the gear ratio? Any assistance is greatly appreciated. Like I indicated I don't really know anything about these but am ready to learn with your help!

 

[Powerflite]

A 742 case is a good strong unit that uses a rebuildable clutch style sure grip if it has one. I like them better than the slightly stronger 489 because they don't use a crush sleeve for the pinion setting. To tell if it is a sure grip, turn one axle. If the other axle turns in the same direction, it is a sure grip. If the other axle turns the opposite direction or if it stops it is open.

To tell the gear ratio, look for a tag affixed to one of the bolts. If it is absent, and it is a sure grip, just count 20 turns on the pinion and see how many times the axle turns. Divide the pinion turns by the axle turns to get the ratio. If it is an open gear set, stop one axle to prevent it from moving. Then do the same thing only this time multiply the resulting ratio by 2.

 

[marksmopars]

OK - it seems like it is sure grip but I still have the drums on it and they are hangin up , so will have to remove to find the ratio. But they both want to turn the same direction so if I understand you correctly, that means sure grip so thank you very mush Now, can anyone tell me if this can be shortened to make it work on an A body? It is off a 1965 C body?

 

[Powerflite]

It can be shortened to use in an A-body but make sure the axles are 4.5" bolt pattern so that the brakes will match when you are done. Otherwise you will need to purchase brake backing plates & drums too. It will cost around $150 to shorten + $100 for new ends + $50 for pad mounts & welding + $350 to purchase new axles. But you will have big bolt pattern when you are done so that isn't too bad.

By the way, it isn't really worth it to cut and respline the old axles. the new splines won't be nearly as strong as fully heat treated and hardened new splines and the cost difference isn't enough to even make it tempting to do.

 

[marksmopars]

Thank you, great information.

 

[marksmopars]

well guys I have been trying to learn about rear ends here, specifically 8 3/4 units. I was told this car i got for parts had a dana posi with 4:10 gears. I learned pretty early that it was not a dana and was an 8 3/4. I thought that's OK, 4:10 8 3/4 unit would work just fine! Well I have finally taken the unit out of the donor car and disassembled it for ID. I am pretty certain that it is a 3:23 open unit - surprise, surprise! Anyway I am posting some pictures to ask if one of you can verify this conclusion for me.

I have learned a bit about these units along the way and learned (once again) that if you haven't seen it don't believe it ](*,)

I also have posted a picture of the inside end of one of the axles since during my investigation someone mentioned tapered units and I was not certain of this was tapered or not. Please someone who knows if you could look and help me learn some more it would be appreciated.

Also, thanks to all who have been so much help in my most recent education.]

 

[grumpuscreature]

Yep, 3.23 open. Those are the axles you want. The taper that you don't want runs almost halfway down the axle. I'd feel comfortable sending those axles to Moser and having them cut and resplined for an A body. After all, they will be as strong as a stock C body axle and those held up to a 440.....

 

[66fs]

Actually, It looks like you have the perfect rear for a Dart. 3.23 Gears are good for all around performance. It looks like the axles are thick enough, measure the thick part of the axle, it should be bigger than the OD of the splines. And long enough, 28 inches from the wheel flange, to be shortened and resplined by someone like Mosers. Tell them what you are doing and they will fix you up. They can even keep your track, wheel flange to wheel flange, the same. Then just add a sure grip, adjust your backlash and good to go. Resplining axles is fine unless you are going to put some serious torque to them racing. You might be surprised how cheap your total will be. If 3.23 are too high for you, it only takes an hour to change to 4.10, if you are slow.

 

[marksmopars]

Thanks for the very helpful input, I am planning on putting a big block (413) in my 70 swinger project and trying hard to keep it low buck as a father son effort. Started off with $200 dollar car and a free 65 300 rust bucket donor. Trying to use as much of the pieces as I can and think we will have the housing and axles shortened. I appreciate the assistance and will be back when I get to the next stage.

 

[daredevil]

If you really want to do it on the cheap use a early b rear.1.25 wider each side so you only have to move the perches in a half inch each side and run it. They can be found for 150 to 250 complete. You can even get away without moving the perches but bushings may fail prematurely.

 

[fishy68]

With the torque of a big block you don't need low gears. You might very well like those 3.23 gears. Only thing is you really need a sure grip unit or you'll just be spinning the right tire and going no where. It's easy to remove the open carrier and replace it with a sure grip. Only adjustment is to measure the backlash and set it back to where it was.

 

[marksmopars]

Thanks, I will look into placing a sure grip into this unit, if you have guidance I will take it. I did connect with Moser and they will cut and respline the axles for $125 which seems real reasonable.