Brake booster vibrating

Guy · Post by **Guy** » Mon Jul 10, 2023 5:20 pm

I have a problem with the bellows vibrating. It doesn't appear to be given any assistance to the braking. The unit was rebuilt some years ago by a professional brake specialist, it was bench tested and appeared to work fine. The vacuum is holding up well with no apparent leaks. The brakes have been set up per the workshop manual so really struggling to understand what is going on. Any thoughts ?

Guy · Post by **Guy** » Tue Jul 11, 2023 8:12 am

Further update. I've been to the garage this morning to take a look at what's happening. If I depress the pedal slowly it doesn't vibrate but offers no assistance. With the vacuum flattened, brake pedal pressed and then start the engine, the bellows compress and starts to vibrate once it's reached the position of engagement. A light touch to the end of the unit stops the vibration. There is no brake assistance as the pedal does not move any further when the engines starts. Gauge shows good vacuum so I'm starting to wonder if it is the newly refurbished bellows unit. Is there an easy way to test the bellows off the car?

Matthew Keij · Post by **Matthew Keij** » Wed Jul 12, 2023 4:16 pm

Which booster do you have?

I’m pretty sure it’s booster itself. How does the engine run when you press the brake pedal?

If you have one with the rubber bellows.
The rubber can crack and when you press the brake pedal it can show. We had it happen on the bottom of the booster.

Guy · Post by **Guy** » Sat Jul 15, 2023 5:30 pm

It is the rubber bellows type. They were new when the unit was rebuilt a few years ago and the car has had little use since, the old bellows had several cracks in it. I didn't notice any appreciable difference in how the motor ran with the brake pedal depressed. We're going to detach the linkage to the master cylinder and try to operate the bellows in situ to check for full movement of the unit.

Guy · Post by **Guy** » Thu Aug 03, 2023 6:39 pm

Update on my brake booster problem. We got a couple of clamps on the bellows and compressed them. Started the engine, exercised the pedal a few times and released the clamps. To our surprise the brakes now work correctly. Not sure what happened but with the brakes working as they should be I'm happy.

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