Now for the 8 3/4 diff

[74chAARger]

Just to recap, I am trying to rebuild the 74 Charger in stages and keep it driving more often than not.

So far - complete small block six-pack carb, intake and air cleaner sytem
- 360 engine stroked to 408, gives the carb something to work with
- rebuilt 727 trans

Now I am building a 8 3/4 diff to replace the 8 1/4 that origanally came with the car, and is still in there.

First I saw an ad 8 3/4 for sale, so I went and bought it. The unit was too narrow for the 74 spring perches, but I was able to sell it for use in a Dart.

Then I went to the pick and pull and found a 72 B-body with a 8 3/4 diff. Yanked it out and brought it home. It has 2.76 gears, but the 408 stroker should handle that. Having some time available during the holiday, I started work on it. First came a new Power-lock clutch type posi. Made in China, I know, but they are available on E-bay. The oil looked fairly clean in the used diff, when I yanked the pumpkin, and sent it to a gear shop for install.

The 8 3/4 diff has 11 inch brakes, so it will be a brake upgrade as well. I started the Charger, when we had some warmer ( -2 here in Canada) weather, didn't even need a boost, and the electric choke was working. I drove it around the block and parked beside the garage, ready for the diff install.

 

[74chAARger]

The gear shop ( they are also racers) called and said they can't install the posi without some grinding on the case. He says all the Chinese posi's are too wide and he has to clearance them. It takes longer, you have to remove the pinion and clean any grit out of the unit.

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The grinding was done just above the red mark, in a curve, and about 3/4 inch into the case. Not a lot, but still a PITA. The fluid in the diff was fairly clean, must have been changed. I am using synthetic fluid and posi additive.

I cleaned out the old fluid


and added 2 litres (about 2 quarts) of 75-120 synthetic, and the posi additive. Then it went back together.

 

[mosquito13]

you just sold me on a eaton true trac.

 

[747mopar]

That doesn't surprise me at all, I swear they have a completely different method of mearsuring over there called "looks close enough". USA is the only way when available which is getting to be the issue.

 

[Ron 73]

That doesn't surprise me at all, I swear they have a completely different method of mearsuring over there called "looks close enough". USA is the only way when available which is getting to be the issue.

X 2 A rolling project and does seem to be working out good for you.. good luck it sounds like a good set up!

 

[74chAARger]

I am going to rebuild the brakes as well. The drums and pads were available locally. I had to order the spring and hardware kit on ebay from rehrenberg, a seller with a lot of NOS and USA made parts for these cars.

While waiting for the kit, I will get some new rear wheel brake cylinders as well. Not sure what size to use, rehrenberg recommends smaller than stock, to prevent rear wheel lockup.

 

[Ron 73]

Im putting on new shoes and wheel cylinders on the back of my car, Did they say why stock ones would do this, or am i missing it, mines only has them in the back (73 Satellite) and there 11", thought i might ask before i put these new cylinders on mine.. If this is the case. Ive never heard of this before...

"rehrenberg recommends smaller than stock, to prevent rear wheel lockup."

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I know what there trying to say but i don't understand why stock would do it if there the same, Im missing something here ill wager lol..

 

[74chAARger]

The larger 11 x 2 1/2 brakes will lock up before the front discs do, resulting in loss of control. Putting in smaller wheel cylinders will slow down the lock up. There are 4 sizes of rear brake wheel cylinders, and the 8 3/4 diff has the largest ones, being 15/16 inside diameter. There are 7/8, 13/16, and 3/4 inch I D, sizes available, so selecting a size of wheel cylinder, will select the amount of lock up. I think I will try the 13/16 units, NAPA part no 37696.

 

[Ron 73]

Thanks i appreciate you explaining it, mine is a 9.25 and never gave it any thought until i seen this because i never had problems with them before, id like to upgrade to disk in back to but just don't have the money to put into it right now, kind of to many irons in the fire.. Thanks again, ill have to learn a bit more, im not working on the car right now anyway but want everything ready when i can.