Hi all, new to Discoverys but I’ve been a series rover person for 35 years. Just got a 94 D1 that’s been in a super hot climate.

I’d love some help diagnosing a potential bad brake Booster. They’re pretty expensive so I don’t want to buy it just to see if it fixes the issue.

There is a very loud constant hissing (like a very bad vac leak) suddenly coming back of the engine right side. If I unplug the vac line that goes to the brake booster (and cap it on the manifold) the sound stops. The sound is not when I press the pedal it’s all the time.

I just redid the whole hydraulic brake system including the master cylinder and everything seemed ok. Then the sound started. I was guessing I cracked the booster diaphragm while bleeding the system and then diaphragm it failed shortly after?

BUT! I found an older thread discussing an o-ring while installing the master cylinder ??? I did not install any o-ring between the master and booster. Is one needed? Could that be the leak?

The older thread also mentioned a yellow plastic tube on the master cylinder. The new one came with one that I removed. I thought it was a shipping protection part and not on the old cylinder. Was that required?

Thanks for any advice. Not sure if failing boosters are common on discos— Don’t want to buy a new boaster if I just needed an o ring.

 

The plastic cone and o-ring that goes around the base are needed, If you threw it away it can be purchased again as kit.