Very poor footbrake

[Thunderbox1000]

The brakes pedal just about works at the floor level and pumps up slightly. A full bleed is clearly necessary but are there any known problems with the servo that would also account for this?
Cheers
Al

[Martec]

From my own experience the servo usually works until an oil seal becomes worn then you will start to lose brake fluid, it may all go in one burst of white smoke from the exhaust (sucked into the engine and burnt) or as in my case steady leak which allowed me to get it home from France.

If the servo has been rebuilt then the position of the long internal rod is important, too close to the piston and when hot this can lock the brakes (on mine did) or is a little too far away then there is a little pedal travel before a firm pedal.

If you have had a replacement servo then the latter may be be your problem, but if the pedal comes up after pumping then this sounds more like air in the system. I've found that using a Gunson pressure bleeder solve the problem. Some times after initial bleeding a trip around the block will move the air so that the next bleeding session clears it.

Best of luck
Brian

PS Dot 4 brake fluid must be changed every 2 year as it absorbs moister, the fluid goes darker and dirty looking - a dead give away. don't forget the clutch fluid as well.

[Thunderbox1000]

Right...... servo OK, no loss of fluid anywhere. Have bled the rear brakes today and fluid is very milky, and huge problem getting any kind of decent footbrake all despite bleeding a 1 litre of fluid through. One moment the pedal is at the top, two pumps later on the floor again. The brake master cylinder makes a noise when the brake is applied.
Question: Could the brake m/c be admitting air ?? It looks easy to change so would that be the next step?
Also when the brake pedal is pumped there are a few bubble appearing in the fluid reservoir.

Any ideas??

very many thanks
Al

[JAGAZ]

When you say there`s no fluid loss ,do you mean that the level in the reservoir isn`t dropping or that you have no leaks showing any where as my servo was filling with fluid ,so no leaks apparent but the level in the reservoir had dropped.New seals fitted and it`s OK now.

[Thunderbox1000]

Hi Jagaz.
No fluid loss from the reservoir of pipes apart from from bleeding the rear brakes. I think the main thing is: is there a way for air to get into the system particularly via the master cylinder?
Cheers

[piman]

Hello Al,

is the car new to you?

If it is I would look carefully at the condition of the flexibles, and if in doubt renew them all.
Then do a full bleed until fresh brake fluid is seen at all four cylinders. If you do that and don't see any air coming out and you still have a variable pedal, then it may be a master cylinder problem. That is what I would look at. It is also worth looking to see if any of the brake cylinders are seized?

Alec

PS, If you modify your forum account page to give a location, you may find there is someone local to you who could advise further?

[Thunderbox1000]

Understood and I will persevere further

[Martec]

The master cylinder has 2 seals, one to seal off the oil return to the reservoir and the main one to pump oil to the calipers via the servo.

When I replaced the servo this year I also overhauled all the master cylinder and caliper pistons, but i made a mistake in fitting the M/C rubber and broke the very small belville washer below it. the result was that this seal sometime coggled over and allowed oil to return to the reservoir and so no brakes. So in a long winded way there could be a fault in your Master cylinder and you would not lose any oil.

You don't say if you have worked on your system/ replaced any parts, my new servo initially made some strange noises that have now almost gone.

Best of luck
Brian

[Thunderbox1000]

There's the important bit:
The brake fluid is foamy... It won't bleed clear.
Pressure on the foot brake doesn't reveal any obvious leaks though. Could that still be shot master cylinder seals? Does it exclude servo?
Cheers for your help
Al

[stuarthardy]

Hi

If your brake fluid is foamy then you're getting lots of air into the system, probably from the master cylinder. Try bleeding the master cylinder on its own by breaking a joint in the line from the master cylinder. If the hydraulic fluid is foamy coming out of the master cylinder then that's where your problem lies. If not, then its likely to be the servo that's introducing the air.

Work through the system methodically and you should find the source of the air leak. An Eezibleed is an excellent tool to help you here as you don't need to keep pumping the pedal.

Good luck

[Thunderbox1000]

Right - update - master cylinder seals replaced, system bled and now a good brake!!! BUT - system holds pressure so after a few braking episodes the brakes bind and bleed nipples need easing off/on to release and get the pressure back to normal. Any ideas as to why this would happen??
I will start a new thread too as I'm really keen to get his sorted. Thanks to all.