Wj brake booster swap in an 88 hissing

[90xj06]

I just swapped in a brand new WJ brake booster and master cylinder into my 88. The original single diaphragm had a hissing noise and I wanted to upgrade to something better than the suggestion of stopping.

Swap went well. I didn't use a spacer but peddle hight was fine. Used weather stripping to make sure no water would come in. Started up the jeep and the hissing noise is still present. With the original booster if I took the vacuum line off and plugged it the hissing went away. I can't imagine it's supposed to hiss at all. Sounds like it's coming from between the booster and master it changes sounds slightly when you wiggle the master.

Is there supposed to be a seal between the master and booster?

 

[cruiser54]

It should not hiss. New parts from china?

 

[90xj06]

probably...
i got them off of rock auto.

I pulled the master cylinder off and its missing the o-ring.

 

[old_man]

Is there supposed to be a seal between the master and booster?

Absolutely, and it is a common problem when swapping boosters that it does not mate up well. Make sure there is a good seal.

 

[90xj06]

i grabbed an oring from work today that was surprisingly The correct size.

and low and behold i have BRAKES!! I have never had a jeep with actual brakes! just a slowdown device.

also the brake booster i purchased had a flat spot on the end of the shaft that lined up perfectly for the brake switch. i still think the brake light switch a mystery on the early jeeps.