xj poor brakes w/ e350

[StudNuts]

I did the 86 e350 on an 88 xj. The pedal goes all the way to the floor.(the brakes were mush before the e350 swap) The mc was bench bled and bled when i bolted it up(ran lines from the output to the resevoir and pumped brakes madly until all air bubbles were gone). The brakes are still mush. When I pump the brakes up w/ engine off, they build up pressure and work fine. When I start the engine, pump the brakes, they just go to mush. There are no leaks in the lines that I can see. I bled the brakes starting from the pass rear.

The only thing i can think of is vaccuum. I pull the booster vaccuum hose, and the engine revs up to 1500 rpm.

Any suggestions.

[Myanarchy]

Sounds like booster problems. If your sure your getting good vacuum to the booster then its probably bad.

[Kilby]

A bad booster would be my guess too, just from what I've learned from my system. The single diaphragm booster's in the '88 are weak anyway. That's why I was talking about swapping in a '96 booster. That one's a more boosterific DOUBLE diaphragm model that supposedly has the same length/style pedal rod as an '88.

[StudNuts]

Originally Posted by Kilby

A bad booster would be my guess too, just from what I've learned from my system. The single diaphragm booster's in the '88 are weak anyway. That's why I was talking about swapping in a '96 booster. That one's a more boosterific DOUBLE diaphragm model that supposedly has the same length/style pedal rod as an '88.

joel, we may have to talk a bit more about this. The 88 and the 96 boosters are about the same price. If the rod is the same, may have to upgrade to a double diaphram. Just have to do some research to see if the 86 e350 mc will bolt to the 96 booster.

[Kilby]

I don't see why it wouldn't... the '96 is s'posed to be a direct swap for the '88. You would probably still have to drill out the flange holes on the master cylinder, though. Gimme a shout whenever.

[71cj5]

my xj does the same thing. i have a e350 m/c , d44/14b. drums in back. when the engine off the pedal gets stiff. when u start it they get mushy.

[StudNuts]

Originally Posted by 71cj5

my xj does the same thing. i have a e350 m/c , d44/14b. drums in back. when the engine off the pedal gets stiff. when u start it they get mushy.

just got a zj booster, will report back after its installed....

[AZFJ]

Ditto on my buddys 88 XJ..D60's front and rear with disk brakes....Wilwood Prop valve for the rear..mushy as hell....I've been researching this too..Havnt figured it out yet...This is some help..maybe we will try this route too!

[71cj5]

anyone come up with anything?

[StudNuts]

well, we attempted the 96 xj booster swap. It is deffinitely not bolt in. The pedal rod would have needed to be cut/welded, and new lines run from the prop valve to the mc. Unfortunately, we didnt have time to do all of these mods(the xj is the guys dd) so we just got a new stock booster, put the e350 mc back on and the brakes work fine. They dont lock up 35"s though. Maybe one day with more time, actually do the booster swap.

[ashmanjeepXJ]

Originally Posted by 71cj5

my xj does the same thing. i have a e350 m/c , d44/14b. drums in back. when the engine off the pedal gets stiff. when u start it they get mushy.

That is how the booster works, you have no boost with the engine off... when the engine is on the booster engauges so the pedal feals softer. if your pedal feals the same with the engine on or off, then you have a booster issue.

I Havent removed the proportioning valve in my e350 MC yet, Ive heard that is the problem. My pedal is stiff, with a new 88 booster and e350MC, with d60 front disks and d70 drums it couldent lock up 37s... I currently modifying to have 1ton calipers at each corner, and will try removing the valve.