Going from a 7.25 to an 8.75

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Sublime69

Sublime69

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OK guys i need a little help and some advice. I currently have a 1974 7.25 rear dif in my 69 dart. I have an A-body 8.75 that i need to put in it. I have a few questions.

First, I need to use the same wheels that I have on the car currently and there is not much wiggle room side to side. (mayyyyybe 1/4") Judging by this chart attached, the two rear ends should be exactly the same width from flange to flange. Now I want to put disc brakes on the 8.75.

What are my brakes options? Will the disc brakes change the width from wheel mounting surface to wheel mounting surface?? I obviously rather not have the housing narrowed or lengthened. Plus then i can use stock length axles.

That leads to my next question, the 8.75 I have now has a 3.23 sure grip in it. Not sure the condition of it. Is there anything better I should up grade to? (locker, new sure grip, etc...)
And what axles should I go with?

Thanks guys!
 

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Go to Dr.Diff (.com) and get what you need.

The disc brakes do not add width. (I don't know how you can think it might.)

The gear ratio and the differential, if working fine, are fine. Upgrading what ever is in there now to a stouter piece would be needed if your power plant calls for it. This YOU would know. Otherwise, the OEM units, even the small U joints are fine for drivers and upgraded engines that ether get driven a lot and/or get used with a spirited driver.

AutoX &/or Drag racing should be upgraded.
 
-Is your 7.25 a later large bolt one? (I'm guessing due to the wheels that it is)
-Do you already have aftermarket large bolt axles for the 8.75?

I think the best overall kits available are the Doctor Diff cobra ones (either type, but if you have stock front brakes, the smaller ones are a better match). They are known to add about 1/8" to the track width per side as the rotors are thicker than the drums on the wheel mounting flange.
 
Yeah the 7.25 is a large bolt pattern and I don't have axles yet for the 8.75. I saw those brake kits, they look nice. I'm actually thinking about going with the wilwood kit. I'll eventually upgrade the front then too if I go that route.
 
rumblefish360 said:
Go to Dr.Diff (.com) and get what you need.

The disc brakes do not add width. (I don't know how you can think it might.)
Click to expand...

How can you think it wouldn't?Even a neon rotor "hat" is .250" thick,
the only ones that ever came close to being as thin as an old OE drum were the GM
1st gen W-body abortions composite frt. rotors.Any normal slip-over style rotor will
likely add .125" or more to ea. side.
 
rumblefish360 said:
Go to Dr.Diff (.com) and get what you need.

The disc brakes do not add width. (I don't know how you can think it might.)
Click to expand...

I'm pretty sure that discs add a decent amount of width to a mopar rear axle. The rotor thickness alone as previously stated is quite a bit more than a drum. And then you have the caliper mounting brackets. Several of the disc conversion kits I've seen have the bracket go between the housing flange and the axle/bearing retainer just like the drum backing plates do, but the caliper brackets are thicker than drum backing plates...
 
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