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I recently finished doing an 8.8 SOA swap in my 1991 Jeep comanche Pioneer 4.0 manual. I need to do something about the brakes because they are seriously lacking in stopping power. Currently all I have done is eliminated the rear proportioning valve.


I am going to swap in a 95/96 XJ brake booster, master cylinder and proportioning valve.

My question is seeing that the 8.8 has disc brakes do I need to find a brake booster, master cylinder and prop valve from a donor vehicle that also has disk brakes or will a donor with drums work?

What would be the best set up to keep the rears from locking up before the fronts under extreme braking conditions?

Thanks in advance.

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Some guys have swapped in the double booster and everything was fine.  others have paired it with an XJ prop valve to pare down the rear power.  still others have gone with an adjustible inline prop valve for the rear to dial it to perfection. 

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'98 XJ, technically yes, but rod length is longer so either your pedal will sit way high or you'll need to space it off of the firewall more.  '99 WJ, yes.


To answer your original question, here's what I did:

- '95/'96 XJ dual diaphragm booster

- XJ prop valve (disassemble and clean out really good)

- ZJ prop valve innards (spring and inside valve from ZJ with rear discs, some had drums, so check first)

- Remove load-sensing valve under bed


Brakes are gold.

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Thanks for the reply.

How much longer is the rod length? Will using the 1/4" plate space it off the firewall enough?

Why did you use the ZJ innards? Can you not just use a ZJ prop valve?


I'm not sure how much longer the rod is, but it's not complicated to overcome.  Washer, extra aluminum plate spacer, etc.


As for my reasoning behind the prop valve innards... I didn't want to have to mess with undoing the brake line compression fittings (again) that are prone to rounding.  I did the brake booster swap and the 8.8 swap two years apart.  It was easier for me in a relatively tight space to just undo that front nut and replace the innards.  With that said, you can use the whole ZJ prop valve.

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