Master cylinder or brake servo?

[chris s]

Hello,

I've been doing some brake work on the wife's Torslanda and I'm still struggling to get a firm brake pedal.
The brakes worked well before any work but the MOT was due so I gave it a visual checkover.
I installed new front pads and discs and decided as I had a NOS master cylinder in the loft I may as well fit it too.
After repeated bleeding (manual and with an Eezibleed) the pedal is hard until the engine is started then the pedal sinks but slowly continues to sink. I bled the distribution block and lightly tapped the calipers with a hammer to free up any air bubbles, so I'm sure there's no trapped air in the lines. The brakes are working but there's far too much travel for my liking.
The servo check valve works and tomorrow when my local motor factors is open I'm sourcing a new servo hose although it looks fine.
I'm now wondering if the NOS master cylinder may have been faulty. I filled it with fluid before installation but maybe the seals were dried.
Does anyone have any ideas on anything I may have missed? I'm running out of ideas and I want the old 240 back on the road!
Thanks in advance,

Chris

[Stephen Edwin]

This is reminiscent of Nick Lewin's brake troubles ... an earlier thread.

As I recall ... [part of] the problem was an adjustment to be made between the servo and the master cylinder. His thread will doubtless explain it.

Good luck.

[AlexO]

Chris,

Are you bleeding in the right order? Otherwise the next stop is bleeding from the distribution block. I see you've already done this but in my experience it can take a surpringly long time to get the last bits on air out of those pipes.

Hope that helps,

Alex

[chris s]

Thanks chaps for your suggestions.
It was indeed the servo push rod which was out of adjustment. Half an hour and a handful of tools and it's so much better!

Cheers,
Chris

[Stephen Edwin]

Originally Posted by AlexO

Chris,

Are you bleeding in the right order? Otherwise the next stop is bleeding from the distribution block. I see you've already done this but in my experience it can take a surpringly long time to get the last bits on air out of those pipes.

Hope that helps,

Alex

Wot he said...."it's the bleedin brakes init"....

Sorry ALex.

Yes as I have heard often in the forum. Brake nipples must be bled in the right order, including that junction thingy. And perhaps with the rear of the car slightly raised?? Is that right?

Stephen

[Clifford Pope]

I've said this umpteen times before, but in view of the known difficulties often reported with bleeding the brakes after an overhaul, I make it a rule never to remove more than one brake component at a time, and to get any air out of that one before moving on to the next.

There is no need to do any bleeding when replacing a master cylinder if you refill the cylinder on the bench and plug the holes, plug the disconnected brakepipes, top them up with a syringe before reconnecting quickly, and leaving the unions slightly loose and gently pushing the pedal just in case you have let any air in, before retightening.

You can similarly replace calipers too.
Frequently it is enthusiastic pumping of the brake pedal during bleeding that causes a new internal leak inside the master cylinder.
I have never comprehensively bled a 240 in 20 years of ownership. Everyone rushes to drain out all the fluid during overhauls, and then discovers the problems.

[AlexO]

Originally Posted by Clifford Pope

There is no need to do any bleeding when replacing a master cylinder if you refill the cylinder on the bench and plug the holes, plug the disconnected brakepipes, top them up with a syringe before reconnecting quickly, and leaving the unions slightly loose and gently pushing the pedal just in case you have let any air in, before retightening.

Clifford, I'm unhappy to have to disagree with you but on this occasion I think it's required. Whilst you can go through all of the above and technically ensure that no air has entered the system, you're almost certainly going to trap some air when you reattach those brake lines to the cylinder. Even with the best will in the world it's always going to happen. It's not the end of the world if it happens as this air can be bled out at the distribution block in about 5 minutes but I find it's always good practice to assume you've trapped some air at the brake-line-to-cylinder junction and work from there. Whilst you could potentially lose 100ml of fluid unnecessarily that's much preferable to finding a mushy peddle when you're trying to brake.

Just my two cents but having done this job last week it's especially fresh in my mind, otherwise I totally agree with you.

Alex

[classicswede]

You want to avoid letting air in. But only open 1 point at a time and bleed that before doing the next.

The mistake so often made is fitting a new set of calipers then bleeding them. Best to fit one caliper, bleed then fit the next.

[Clifford Pope]

Originally Posted by AlexO

Whilst you can go through all of the above and technically ensure that no air has entered the system, you're almost certainly going to trap some air when you reattach those brake lines to the cylinder.x

Well, it's always worked for me. It was a trick taught me decades ago by a garage owner - he claimed never to have bled brakes after replacing a master cylinder.

If you fumble things a bit and do wonder whether a bit of air got in, don't press the pedal hard and send it round the system, leave the union half a turn slack and very very gently give a short stroke on the pedal to bleed it out again at the joint. It's just like bleeding a domestic radiator - you might get a short hiss as the air bubbles out, then you close the valve when it's pure fluid.

[Nicholas Lewin]

Chris

Enlighten me if you would... the servo push rod. Do you mean the pin that comes out of the front of the servo that pushes the M/C?

If so, do you know what that should be set at or did you set it by trial and error?

I ask as I have very noisy brakes which also bind when hot. My belief is that the servo is applying slight pressure on the M/C all the time - this is exacerbated by heat and only needs slight adjustment to get the pads off the discs and shut the brakes up

(And if it's not that, then I reckon it must be faulty refurbished calipers which are not returning properly after the brakes have been applied...)

Be interested to know, cheers, Nick