Master cylinder pushrod adjustment/servo?

[HWKWallis]

Thoughts on the scenario below (Amazon)?

- new brakes and lines throughout
- new servo (girling changed to Lockheed)
- original near new but aged master

Bled out as normal and expected job done but..... If brakes are used with engine running then they stay on including brake light.
Eventually they clear. Without the engine running they seem to work and release.
Seems then the servo must be the cause putting pressure into the system without depressing the pedal...... But can this be due to adjustment?....

If the applied pressure does bleed away when engine off and the pedal at normal level then that's fine and I have to assume the servo is introducing the pressure in error?

Jim

[norustplease]

Brakes jamming on in these circumstances often implies that the recuperating or compensating valve that allows the system to top up from the reservoir is not able to work properly and hence is not allowing the pressure from the pedal to release.
You don't say what exact model or age of Amazon this is, so it isn't clear exactly what kind of master cylinder you have, but if your pushrod is not correctly adjusted with some free play, this may well mean that the master cylinder piston cannot withdraw enough when released, to expose the drilling for the feed from the reservoir, and hence, pressure cannot release. This will no doubt be amplified by the servo.
Try adjusting the brake pedal pushrod free play in the first instant.

[HWKWallis]

Thanks... Will try tomorrow.
Playing around a bit more earlier indicates that the brakes lock as soon as the engine starts without touching the pedal. A previously depressed pedal rises when the engine is started.
I was amazed that the brakes worked at all when it had the original girling unit on which was flooded with fluid!
Maybe the rod has been adjusted to compensate.

[Derek UK]

Maybe the non return valve in the manifold to servo hose is the wrong way round. It has an arrow on it and that should point towards the servo.

[HWKWallis]

I had assumed the new servo had an integral valve so don't have one in line.
That the brakes lock even once the engine is off and I can release vacuum and the brakes by removing what I presume is the relief valve serves to confirm that?

[Burdekin]

Originally Posted by HWKWallis

I had assumed the new servo had an integral valve so don't have one in line.
That the brakes lock even once the engine is off and I can release vacuum and the brakes by removing what I presume is the relief valve serves to confirm that?

Is it a B18? I have heard the NRV on the flame trap can fail also so you might be losing vacuum there. Try without the flame trap line connected to the servo line; a direct line from the manifold to servo.

[HWKWallis]

1967 B18 which was single carb but now twin SU. Vacuum line is direct from manifold to servo as with the original set up so no change there as I can see.

[Burdekin]

Originally Posted by HWKWallis

1967 B18 which was single carb but now twin SU. Vacuum line is direct from manifold to servo as with the original set up so no change there as I can see.

No worries. I thought they just tee’d off that line when a servo was fitted. I don’t think it will be your problem thinking about it but have you got a hose going from the flame trap to the manifold also? If the NRV isn’t working above the flame trap you could be losing vacuum there.

[Derek UK]

https://www.mmoc.org.uk/Messageboard...ic.php?t=52244

[HWKWallis]

OK.. So 2 informative bits there; I need to create a fuel traps but seems also to use an inline valve in addition to the one already on the servo.
As the cheapest option will try that next {FAG cylinder has no adjustment I can see)

Thanks Derek