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Discussion Starter · #1 ·
I just installed a ford 8.8 rear end on my 94 YJ and I’m having some issues with the brakes. The new axle has disc brakes and my stock brake master cylinder seems like it can’t quite handle it. I did a ton of brake bleeding after the swap and I’m pretty positive I have all the air out, but when I go to hit my brakes the first pump is pretty soft and causes my brake dash warning light to come on. Then the second pump is nice and firm and makes the dash light go out and the brakes work fine. I think the problem is the stock cylinder doesn’t pump enough fluid with one pump to fully pressurize the rear brakes.

So I’m wondering, is there a master cylinder off a different model jeep or dodge or something that has all disk brakes that would bolt on to my YJ?


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I don’t know much about yjs, but my stock tj master cylinder and prop valve work fine with my 8.8 disc brakes
 

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I replaced my master cylinder and brake booster with new ones for my 93 YJ when I did my 8.8 swap and my brakes are extremely tight now. I didn't upgrade anything, just went with news ones that were from NAPA.
 

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My guess is that OP still has air in the system somewhere.
I suggest getting a cheap harbor freight brake bleeding pump with a plastic reservoir.
Starting at the passenger side rear (right rear) bleed that brake line until you get clean brake fluid in the bleeder reservoir. Make sure you don't run the master cylinder reservoir dry. Then go to the drivers side rear and do the same thing. Then passenger side front and then drivers side front, all the time continually checking to not allow the master reservoir to run dry.

When you're done, you'll have all new brake fluid and should have a good pedal.
Use DOT3 or DOT4 brake fluid. They're compatible to mix. The DOT 4 is better for disc brakes. Usually you'll find the can marked DOT3-DOT4. What that means is there's DOT4 in the container, but it can be used in systems that have DOT3 fluid.

Good Luck, L.M.
 
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Is the brake light is coming on he still has air in the system, specifically the proportioning valve that has the sensor in it.
 

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Discussion Starter · #7 ·
Huh I bled the brakes a LOT after the swap and I didn’t see any more bubbles so I thought it was good. Maybe I got air in the master cylinder or something, I’ll try bleeding that too I guess


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I'm not sure if this is the way to do it, but I understand that if you stomp hard on the brake pedal, that will reset the proportioning valve as long as what tripped it was repaired.

I've heard that old brake fluid can absorb moisture and become less effective through the years. That's why I suggested bleeding the brakes at each wheel until the fluid runs clear. Once done, you should have all new brake fluid throughout the system.

Are you sure your booster is functioning and set properly?

Good Luck, L.M.
 

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Do not fall into that BS that you need a bigger bore master cylinder to “Push More Fluid” because of the rear calipers. I’d did. I was naive and listened to all the Internet forum BS. Stock 1” bore master will give you better feel.

Sounds like you just need to bleed it better or your master is bad which I would replace with stock. Also check all your brake lines for weepage that might be letting air into the system.
 

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You don't have the calipers upside down do ya?

Bleeders need to be at the top
 

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You don't have the calipers upside down do ya?

Bleeders need to be at the top
Not gonna lie, this happened to us. :censored: We got the 8.8 from a fellow Jeeper and didn't really pay attention to that and I guess they had put them on backwards after they cleaned up the axle to sell. It was quite frustrating for a little while until we figured that out and now my Jeep stops super quick with very little peddle pressure.
 
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