Brake booster

[Nigbo]

I 've now got my dual booster fitted and an amazing transformation to the brakes. BUT........they start binding on if stuck in traffic/ low speed . Had to pull over open bonnet and cool off. I can feel the pedal "hardening up", so there's no slack in it before the brakes come on.

Its worse on hot summer days. Driving to work early in the morning i get no problems. Driving home on warm/hot summer days i can't even get home without having to pull over. So i undertook wrapping the whole manifold . No improvement. Put some heat shielding on the underside of the booster and the master cyl. No great improvement. Took the master cycl. off and shortened the pushrod from the booster to the MC about 3-4 mm, thinking the whole thing was expanding. No great improvement.

What is noticeable is the copper brake lines ( which are now much longer ) get very hot almost too hot to touch and the MC is also very hot. I've got some heat protection lagging for round the brake pipes from Demon Tweeks and going to extend the manifold wrap further down to include the collector pipe.

I've a M3 3.2 lump which clearly generates a lot of heat but this was never a problem before fitting the dual servo.

Before anybody mentions i have the Landcover return spring fitted and anyway its not that the pedal is sticking down , i can feel that , its as if somewhere is the whole system its expanding and taking up slack.

Am not hopeful that the pipe lagging will really stop the problem. Its like the brake fluid is expanding as it gets hot, which i would not have thought it would. There is a exhaust heat guard which normally fitted to the engine of an M3 which might help a bit although it could make things worse.

Getting exasperated ......any ideas

[Nigbo]

I've found a unrelated posting about problems with brakes binding when hot related to a faulty MC. It's not a big cost so maybe i will replace the MC.

[Mike]

Nigbo
These servos seem prone to "vacuuming themselves on" - you are not alone in experiencing this problem. As you have fitted the Landrover return spring, have you checked to see that there is small gap in the servo output adjuster to master cylinder? It is critical that the servo can close off the atmospheric pressure with the pedal at rest.
Try shortening your adjuster and see if the problem disappears. It leaves you with a slightly longer pedal, but helps prevent binding brakes.
Mike

Originally Posted by Nigbo

I 've now got my dual booster fitted and an amazing transformation to the brakes. BUT........they start binding on if stuck in traffic/ low speed . Had to pull over open bonnet and cool off. I can feel the pedal "hardening up", so there's no slack in it before the brakes come on.

Its worse on hot summer days. Driving to work early in the morning i get no problems. Driving home on warm/hot summer days i can't even get home without having to pull over. So i undertook wrapping the whole manifold . No improvement. Put some heat shielding on the underside of the booster and the master cyl. No great improvement. Took the master cycl. off and shortened the pushrod from the booster to the MC about 3-4 mm, thinking the whole thing was expanding. No great improvement.

What is noticeable is the copper brake lines ( which are now much longer ) get very hot almost too hot to touch and the MC is also very hot. I've got some heat protection lagging for round the brake pipes from Demon Tweeks and going to extend the manifold wrap further down to include the collector pipe.

I've a M3 3.2 lump which clearly generates a lot of heat but this was never a problem before fitting the dual servo.

Before anybody mentions i have the Landcover return spring fitted and anyway its not that the pedal is sticking down , i can feel that , its as if somewhere is the whole system its expanding and taking up slack.

Am not hopeful that the pipe lagging will really stop the problem. Its like the brake fluid is expanding as it gets hot, which i would not have thought it would. There is a exhaust heat guard which normally fitted to the engine of an M3 which might help a bit although it could make things worse.

Getting exasperated ......any ideas

[phil.coyle]

Have you checked the one way valve in the Hose to the servo.
Some are obvious in the Hose, and others are at the point of entry into the Servo.

[Mike]

Originally Posted by phil.coyle

Have you checked the one way valve in the Hose to the servo.
Some are obvious in the Hose, and others are at the point of entry into the Servo.

It is unlikely to be the non return valve in the vacuum hose.
If this is faulty you will lose vacuum, which is not your experience - quite the opposite!

The cause will be one of two issues:

The inlet valve on the servo not quite seating, allowing atmospheric pressure to exert a force on the servo's diaphragms, or

The mater cylinder is not returning fully, so retaining hydraulic pressure in the system.