Hola Gurus de Jaguar,

It has been a strange week. 4 days ago, my brake booster/servo stopped working on my morning drive to work. While I am used to manual brakes in my '66 Volvo 122S, this was a whole other dimension of scary. Not to mention tiring for my leg!

I'd been having problems with vacuum leaks from the heater tubes, so I just assumed it was related to that. However, after checking the brake fluid level after a 15 minute drive-it was empty! My trusty cork-in-the-tube warning light switch had failed me and I was stupid for not checking the reservoir every time I checked my oil level.

I filled up the brake fluid and still no booster effect for another day. Then this morning---brake booster works perfectly again.

My question is....what happened? Does brake fluid actually go inside the booster? And is it possible to still buy the felt filters that my shop manual talks about (and can apparently get clogged)?

 

When you push on the brake pedal, the actuating rod to the master cylinder passes through the booster chamber. The booster piston acts on this rod to boost your effort. So there is an hydraulic seal at the back of the master cylinder that you don't see because the cylinder is bolted onto the front of the booster. Therefore leakage may not be obvious. Once fluid gets into the booster chamber it can be sucked into the engine via the vacuum pipe that provides vacuum to work the booster.

 

Thanks Fraser. I had optimistically hoped that the problem was over. However, I have a slow brake fluid leak between the servo and the master cylinder. I'll be unbolting it this weekend--is there a chance it might be just a leaky gasket?

 

I had this problem previously in my S2 and replaced the seals/gasket between the master cylinder and brake booster. It resolved the problem for about 6 months, and then the master cylinder started leaking from a completely unrelated problem and got replaced altogether.

Moral of the story, yes you can fix it, or replace it. Either will work as long as the seals and gaskets are all installed properly.