I've been running a single diaphram brake booster on my XJ. I bought a dual diaphram from a 96 and installed it. Unlike the single, the dual looks different from the MC end, in other words no sealing diaphram right at the MC and you can see a big spring inside. The problem is that the booster is leaking vacuum and not working. Are you supposed to have to seal around the MC on a dual diaphram unit? Because it is sucking around the MC, or is this booster just shot?

Sorry if this seems a bit simple, but I have always run single diaphrams and never seen a dual apart.

To answer my own question.....As it turns out the master cylinder has to be sealed to the vacuum booster on a dual diaphram system, otherwise you get a horrible vacuum leak and no boost.

Hey, Old_Man!

You should have looked under the hood of my 94 XJ in Moab in October....... I did this a year and a half ago.

ChiXJeff

Did you have a leakage problem also?

None.

Pulled the original booster and m/c. Bolted the new booster up, connected the rod, and then mounted the new m/c. Added metric-SAE flare converters, bent up a set of lines to the prop valve, and away we go. Had to snug down a couple of flare fittings, but a well worthwhile modification.

Since then, I swapped an adjustable prop valve in for the factory, on the theory that I may eventually put in a set of rear disks.

ChiXJeff