Faulty Booster?

**flagg** · 13th November 2013, 09:23 PM

Hi All,

I've just done a rear disk conversion of my 110 using one of Ridjidij's kits, and replaced the county booster with a new D1 booster.

It is all bled up, and the pedal is solid until I start it.. then the pedal get softer and softer in a linear way until it just hits the floor. Re-bleeding it with 2 litres of fluid has shown no air bubbles at all.

When I turn off the engine the pedal quickly goes hard again and there is a hissing sound coming from the pedal box. I've checked all the vacuum lines and they all seem sealed. (the hissing sound may be there when the engine is running too, but may be too soft to hear)

The only thing I can think of is the booster isn't right, and is leaking some how... but I don't know how they work enough to tell if that would cause the pedal problems.

If there was a leak in a line there would be bubbles in the air lines... and fluid leaks. From what I can tell, there are neither..

**Vern** · 13th November 2013, 09:27 PM

Masters not leaking back into the booster?

**d2dave** · 13th November 2013, 09:36 PM

Stick your head down near the brake pedal and push it with engine running. As the rear of the booster where it bolts to your firewall is exposed to your cabin, if it is leaking on that side of the booster it should be easily heard.

This however should not cause the pedal to go all the way to the floor, it should still work ok, just with a leak.

Have you got brake line clamps? Clamp each flexible hose and if this still happens I would reckon that your master cyl is faulty.

**460cixy** · 14th November 2013, 07:16 AM

It won't be the booster are you northside?

**flagg** · 14th November 2013, 07:11 PM

Originally Posted by Vern

Masters not leaking back into the booster?

No signs of fluid leaking anywhere, I haven't taken it off but I loosened it enough that any fluid between them would seep out.

Originally Posted by Mr Whippy

Stick your head down near the brake pedal and push it with engine running. As the rear of the booster where it bolts to your firewall is exposed to your cabin, if it is leaking on that side of the booster it should be easily heard.

This however should not cause the pedal to go all the way to the floor, it should still work ok, just with a leak.

Have you got brake line clamps? Clamp each flexible hose and if this still happens I would reckon that your master cyl is faulty.

Yeah, when i put my head in the foot bay I can hear it with the engine running. It stops when I press the brake, but when I stop pressing it it starts again (reguardless of the pedal position..) so there is something wrong with the booster.. but I think I may have two problems.

I've also just fitted fancy stainless lines... will a clamp damage them?

Originally Posted by 460cixy

It won't be the booster are you northside?

Yeah I am.. PM Sent

Double checked all the fittings and bleed nipples after holding my foot on the brake firmly for a while.. again no signs of fluid. Starting to think it may be an air bubble that wont bleed out properly - it has happened before but the pedal was never firm like it is now. When I pump it it doesn't seem to get harder like it does with a bubble.

I mean, the fluid has to either compress or be leaking right? So if there isn't a leak it must be air?

**d2dave** · 14th November 2013, 07:28 PM

I have never had any experience with fancy stainless lines, but I am guessing that clamps would not be good for them.

As for your problem. Master cyl can give problems with no air in system. Fluid can bypass seals internally causing spongy pedals.

I have spent a few years working as a brake specialist. (30 odd years ago) It is very hard trying to diagnose over the net. If I had the vehicle in my shed I could probably pin point the problem easily, although the stainless lines do eliminate a diagnostic option.

**flagg** · 14th November 2013, 07:48 PM

Thanks Dave. Always the way. I spent a fortune on new parts because I didn't want any problems.

**d2dave** · 14th November 2013, 07:55 PM

It does annoy me a bit when people here have problems that I could probably diagnose if I had the vehicle, as I like to help people.

No one seem to live or break down near me.

**Bushie** · 14th November 2013, 08:01 PM

Originally Posted by Mr Whippy

I have spent a few years working as a brake specialist. (30 odd years ago) It is very hard trying to diagnose over the net.

Not as hard as it would have been 30 years ago

Martyn

**steveG** · 14th November 2013, 10:46 PM

Have you fitted the O-ring that goes between the master and the booster?
Its a quite a thin one and would be easy to miss if you got the parts separately, but you'll get a vacuum leak there if its not fitted.

I know you said the sound seems to be coming from the pedal box, but sound is a strange animal....

Doesn't seem to fit with your pedal problem though.

Don't clamp those stainless lines. Fab up something in the way of blanks for the master to test with if you've still got issues after sorting out that booster leak.

Steve

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