Strange brake issue

Michael Kaye

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Long story short, new servos (boosters) and master cyclinder were installed today.

for the first time since having the car I realise how it an E9 should brake!!!

The problem is that after the servos activate (I hear that vacuum “shussing” sound), the brake pedal is forced back up, literally pushing my foot back up.

I’m convinced something is connected the wrong way as I expect the pedal to do the opposite after the servos activate.

Hopefully this make sense to someone out there and they have some idea of the cause/problem.
 
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Thomas76

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Just guessing here, no experience with the booster. If the vacuum check valve is installed backwards would it act like that?
 

Michael Kaye

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Just guessing here, no experience with the booster. If the vacuum check valve is installed backwards would it act like that?

thanks Thomas. We tried reversing the vacuum check valve and that basically just meant the booster just didn’t activate.

no push back on the pedal but no boosted braking sadly.

thanks for the suggestion. It really is an odd issue.
 

Drew20

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there shouldn't be any shussing of air, that sounds like a vac leak. What is the history of the remote servos? Are they both making that noise, or only one?

I don't think it'll be the inline check valve, if that was the wrong way round it would stop vac getting to the remote servos in the first place
 

gazzol

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Is this issue with the engine running? The reason that your foot is being pushed back is that the vacuum is either being depleted or leaking away.
 

Michael Kaye

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there shouldn't be any shussing of air, that sounds like a vac leak. What is the history of the remote servos? Are they both making that noise, or only one?

I don't think it'll be the inline check valve, if that was the wrong way round it would stop vac getting to the remote servos in the first place

yes tried with the valve the other way and as you say it stops the servos even activating.

will check for vacuum leakages.

thanks all.
 

gazzol

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An easy way to check for leaks is to use a piece of windscreen washer tubing or the like. Stick one end of the tube in your ear, then with the engine running go along the servo vacuum hose with the other end of the tube either touching or very close to it. Any air leak will be immediately audible. Good luck
 

Michael Kaye

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An easy way to check for leaks is to use a piece of windscreen washer tubing or the like. Stick one end of the tube in your ear, then with the engine running go along the servo vacuum hose with the other end of the tube either touching or very close to it. Any air leak will be immediately audible. Good luck

thank you. Will try now.
 

sfdon

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As a thought- the test for brake booster being good is to step on brake pedal multiple times with engine off and then start engine. Pedal should rise with addition of vacuum activating the diaphragm. Sounds like you are depleting your vacuum. Use a handheld vacuum pump to test depletion/storage/quantity of vacuum in the booster system. Should hold vacuum through several cycles of brake pedal application- if not you may not be holding enough vacuum in reserve. One reason is that you could have a leaking booster sys.Leaking booster system will have constant vacuum drain on the gauge with pedal applied and vacuum will go to zero. Vacuum should only go down in increments on each pedal application.
have fun and good luck!
 
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Michael Kaye

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Hey @sfdon

Thanks for the advice. the brake pedal does rise when the engine starts.

the problem is that it’s doing the same thing when applying the brakes. ie it depresses as you’d expect, but fights me as I’m doing so i.e. the pedal is trying to rise at the same time.

The servos do seem to be holding vacuum ok.

completely stumped by this at the moment.:(
 

Drew20

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Can you see if they still hold a vac when the brake pedal is pressed? You mentioned the shhhhh sound when you used the brakes. Put a vac on them with a hand held, and get your beautiful assistant to gently/ firmly press the pedal.

This link has good info on remote servos. I've never needed to pull one apart, but I think I leak in the air valve diaphragm might cause the symptoms you have, maybe...?


What's the history of the servos you fitted?
 

Michael Kaye

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It does seem to be holding vacuum.

in fact I’m the assistant (not beautiful) to my mechanic (bill).

these servos came from Jaymic a while ago but had been left sitting around. Bill rebuilt them with seal kits from John “Yoda” Hudson.

they seem good...but I do think it’s time to measure the vacuum.
 

Michael Kaye

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Still not fixed but rear brake compensator is leaking now.

Does anyone know if there a rebuild kit for it or are replacements easy to get hold of.

need to fix before we go back to the servos:(
 

Drew20

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Rebuild looks to be an option, in the US at least

Or very pricey, from Germany... ouch
 

Michael Kaye

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Thanks @Drew20 that is expensive. Hopefully we will be able to rebuild it ourselves.

I’m heading over to a friends later to check how his E9’s breaks work. Hopefully will give me a further clue as to how they should be working!
 
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