Brake advice

[spoon.450]

When I originally purchased my 64 car ( 850 JWA ) it had been stood for around 10 years and the brake pedal went straight to the floor. It has standard S brake set up. I replaced the master cylinder with a new repro S tin one from Minisport and the servo with a new repro Lockheed Mk 3 S type, the rear cylinders and regulator valve with new Lockheed ones, bled them through many times in all sequences, including easybleed, but could not get a decent pedal, far too much travel. I have since changed the master cylinder to a genuine NOS item, replaced 90 percent of the pipework, new flexies, brake light switch, another regulator valve, a freshly recon Mk 1 servo and still cannot get a decent pedal. I have just fitted another Mk3 type servo and the pedal goes straight to the floor. I did once try it without a servo and got a good pedal but I do want to use a servo. Seems to me that all four servos that I have had fitted, including the new repro and the recon Mk1 are at fault. As the car was originally a 997 Cooper I started to question the pedal but I have compared this to my standard Mk2 S and the pedal assy seems the same, ie thicker ( approx. 5/16 inch ) brake lever material than clutch ( approx. 1/4 inch ) and brake sits approx. 3/4 inch higher than clutch. As the car is a bit of a "Triggers broom" I can only assume that this has also been changed sometime. Am I missing something ? I recently took the servo off my std. Mk 2 S ( to replace clutch thrust brng ) and when I replaced it, four or five pumps through the drivers side caliper and a brilliant pedal. Next move may be to take the servo off the Mk 2 to try on the troublesome Mk 1. Am I missing something ??? Any help will be much appreciated.
Many thanks
Dave

[Daz1968]

Only a minor thing but as you have new rear cylinders they are the correct smaller 0.625 bore ones and not later 0.750 bore ones, as they would consume more of the pedal travel. Also is the new rear valve the correct one, not much else I can think of unless the push rod in master cylinder is incorrect.

[Spider]

What are the front callipers like? Have you tried isolating them by pinching off the flex hoses?

[111Robin]

Stating the obvious but are the rear brakes adjusted correctly ?. Is there any significant wear in the drums or shoes ?. I guess if you get a good pedal without the servo then this is all OK,.

[spoon.450]

Thanks for your thoughts so far chaps. The rear cylinders are actually later ones, ( I fitted these because I already had them ) and I shortened the spring slightly in the regulator to get the bias ok. Perhaps this arrangement it part of my problem and I should fit small bore cylinders ( 1/2 inch ? ) and standard spring ?? The drums are new and well adjusted up and I forgot to mention that I also fitted new calipers part way through my process of elimination.

[dklawson]

I have heard that some people prefer to leave the servo loose during bleeding so they can orient it in a position to encourage any trapped air to get pumped through.

Since it sounds like you have gone through this multiple times, are you sure the calipers have the bleed nipples at the top.

As suggested by Robin, are you certain the rears have been adjusted properly. If the pedal has a lot of travel and is a bit "mushy" at the bottom, are you sure the shoes are on in the correct orientation?

[spoon.450]

If the pedal has a lot of travel and is a bit "mushy" at the bottom, are you sure the shoes are on in the correct orientation?

I will double check that, thank you.

[smithyrc30]

I did once try it without a servo and got a good pedal but I do want to use a servo.

Dave

Surely all the lines, hoses, brake cylinders calipers and shoes are irrelevant based on this statement?

If you can get a good pedal without the servo and then when you fit servo one thru four you have an issue with the servo, I would say that there is air in the servo. The information that is missing is whether the long pedal happens when you have the engine running or is when it is switched off.

I would get a vacuum bleeder and fit the servo slightly nose up, open the RHS caliper and attach the vacuum bleeder to that and suck away.

[ianh1968]

I have heard that some people prefer to leave the servo loose during bleeding
so they can orient it in a position to encourage any trapped air to get pumped through.

My Marcos when first built had the nose of the servo almost horizontal
and the brakes were very spongy.

Pointing the nose up by a few degrees to allow the air out does make
A LOT OF DIFFERENCE.

I am sure that I've seen pictures of some cars where the thing is dead
vertical, which would totally negate this problem. No a viable solution
in a Mini, sadly...

Ian

[spoon.450]

Thanks again for your thoughts chaps.
I managed to grab half an hour tonight and unbolted the ( used mk 3 ) servo and pointed the nose upwards. Removed the fluid outlet pipe from the servo and inserted a bleed nipple. Bled through ( so as to isolate servo and master cylinder ) and got a solid pedal, but still lots of travel, too much compared to my std. mk 2. This points to servo, master cylinder , or pedal problem in my eyes. Next move is to put bleed nipple straight in top of master cylinder and bleed from there. I would like to expect a solid pedal with minimal travel ???

[rich@minispares.com]

as mentioned above, a servo often needs the pipes cracking off and bleeding - the one on my er' hissed air out like a snake - and the pedal became perfect!

they are very intolerant of been mounted wrong and need to be angled in both directions to be a perfect 'bleed'


if there is ever any doubt about a servo, its pretty simple to make a temporary brake pipe and isolate it - once the brakes are perfect without it you will know where the fault is

[R&R]

Agree with Rich, but I've had an interesting scenario with some colour coded pads recently on an MG midget. The sponge in the pedal was driving me to distraction, but I could find no air in it despite bleeding everything over and over again. When I gave the brakes a pasting the brake pedal would hit the floor. Disc temperature was 240 degrees, so I thought it had perhaps boiled the fluid, when I bled it, the fluid was cold, but when i watched as my workmate pressed the pedal I could see the pads compressing like a sponge! Mintex pads, and we have a solid pedal.