Installing a (used) replacement differential

Installing a (used) replacement differential
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Rust Bucket

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Location
Alpharetta, Georgia
Vehicle(s)
'75 CJ5 304 3 speed, '12 GMC Terrain, '07 F-150
My stock front end diff needs some serious work before the 4wd is operational. So, I am considering replacing the diff with a "used" one from another CJ5 . The replacement has disc brakes and my original had drums. So, here's the question. Do I need to convert the brakes to power in order to get the proper amount of braking from the rear drums?

I am concerned the back brakes will not even function if I install discs in the front. :confused:

I know some of you have dealt with this issue, so what should I do?



I'm
 
That is a function of the proportioning valve. It's the thing that has all the brake lines fed into it bolted to the inside of the frame on the drivers side. there are different valves for different combinations.
correct me if wrong, you are replacing the front axle not just the differential.:cool:
 
IOPort51 said:
That is a function of the proportioning valve. It's the thing that has all the brake lines fed into it bolted to the inside of the frame on the drivers side. there are different valves for different combinations.
correct me if wrong, you are replacing the front axle not just the differential.:cool:
Click to expand...

You are correct. I'm replacing the entire axle. So, I need a new proportioning valve? No other parts, well, brake components?
 
I would say yes and I don't think so.:cool:

Rust Bucket said:
You are correct. I'm replacing the entire axle. So, I need a new proportioning valve? No other parts, well, brake components?
Click to expand...
 
you did double-check that the new axle has the same gearing as the old one, correct?
 
3.73 is fairly common, count the teeth on the ring and then count the teeth on the pinion of your old axle and divide those numbers. The ratio should be stamped on the ring gear as well.

I never changed my proportioning valve when I went to discs. There is a residual pressure valve on your master cylinder that sits inside the port where your brake line connects. It is there to keep pressure on the lines so the wheel cylinder keeps pressure on the shoes in the drum. It is a little rubber reed looking deal that is behind the brass flare fitting. There are a few write-ups online about how to go about it.
 
Jokenring said:
3.73 is fairly common, count the teeth on the ring and then count the teeth on the pinion of your old axle and divide those numbers. The ratio should be stamped on the ring gear as well.

I never changed my proportioning valve when I went to discs. There is a residual pressure valve on your master cylinder that sits inside the port where your brake line connects. It is there to keep pressure on the lines so the wheel cylinder keeps pressure on the shoes in the drum. It is a little rubber reed looking deal that is behind the brass flare fitting. There are a few write-ups online about how to go about it.
Click to expand...

Thanks! It sounds like I just need to make some minor mods to adjust the pressure to my back drums.
 
None needed. Mine works just fine with no other adjustments.
 
Jokenring said:
None needed. Mine works just fine with no other adjustments.
Click to expand...

Got it. So, you're 100% sure the back brakes are actually functioning properly?

Several people have told me the front brakes will actually completely lock up before the back will even begin to engage. My main concern is the ability to stop, mostly off road, in loose dirt, mud, or gravel. If the front has Limited traction, I want to ensure the back will actually slow the vehicle. Obviously, I know nothing about this and rely on people like yourself as a source. :notworthy:
 
Yup, back brakes function at about 40% with 60% on the front. It stops real quick on the street, and dirt too. On a fast stop all four will lock up on the street, same for the dirt.

(Irok's make big rubber marks) :D
 
Jokenring said:
Yup, back brakes function at about 40% with 60% on the front. It stops real quick on the street, and dirt too. On a fast stop all four will lock up on the street, same for the dirt.

(Irok's make big rubber marks) :D
Click to expand...

LOL. Sold, I will pick up the new axle this weekend. Then, I have to save money for springs, shocks, and all the other goodies!
 
I put disks from a 78 Dana 30 on my 73. No rear brakes. So I put a 78 master cylinder on. Worked great. Then I put disks on the rear and added an adjustable proportioning valve from Summit. Works great!

Good luck.
 
73CJ said:
I put disks from a 78 Dana 30 on my 73. No rear brakes. So I put a 78 master cylinder on. Worked great. Then I put disks on the rear and added an adjustable proportioning valve from Summit. Works great!

Good luck.
Click to expand...

The master cylinder is a good point. I guess I can change the master cylinder if I'm not getting proper stopping in the rear. Thanks for the input!
 
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