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[Mikew]

Hi Folks
Changed the brake master cyl on my series 2 and I have no air from wheel cyls but don't have a hard pedal have to pump it to get some sort of brake. I understand air can get trapped in the M Cyl. How can I bleed this?

Any help appreciated.

Mike

Please email me on my email [email protected]

[w3526602]

Hi,

Our RAF instuctions were to always bleed the master cylinder first..

OK ... OK ... I'll get my coat.

But if push really came to shove, I'd disconnect the outlet pipe from the master, replace it with a bleed nipple (bought especially for the occasion) and bleed that.

Once I know the master is not the problem, return to the original set up, wash the spilt fluid off the bulkhead, then bleed as normal. Usually (but not always) I build in a bleed nipple close to the master cylinder.

602

[Robin]

It's usually enough to loosen the outlet pipe on the master cylinder, plenty of rags under, and pump the pedal a couple of times.

I find that seems to clear any air trapped in the master cylinder.

[milesr3]

If it's a CB cylinder then it's very easy to trap air and you need to lift the front end up very high to get the ports on the cylinder horizontal to get the air out. It's easier to fill the cylinder on the bench before fitting, encouraging the bubbles out with a light jiggle or by suction. It's not easy because you have to remove and refit the whole brake assembly without depressing the pedal and squirting the brake fluid out. It helps if you can secure the bungs with some tape to block the ports.

I made the mistake of fitting my very first CB cylinder dry and the pedal would travel to the floor. When I replaced it I did the above and the difference was quite remarkable with the pedal firm over the first third of it's travel.

[Larry S.]

If it's a CB cylinder then it's very easy to trap air and you need to lift the front end up very high to get the ports on the cylinder horizontal to get the air out. It's easier to fill the cylinder on the bench before fitting, encouraging the bubbles out with a light jiggle or by suction. It's not easy because you have to remove and refit the whole brake assembly without depressing the pedal and squirting the brake fluid out. It helps if you can secure the bungs with some tape to block the ports.

I made the mistake of fitting my very first CB cylinder dry and the pedal would travel to the floor. When I replaced it I did the above and the difference was quite remarkable with the pedal firm over the first third of it's travel.

I'm too paranoid to bench bleed, so we are prepping to lift.

Following is a pic showing what one guy does.

[w3526602]

It's not easy because you have to remove and refit the whole brake assembly without depressing the pedal and squirting the brake fluid out.

Hi,

When re-placing hydraulic pipes, I usually (but not always) put a three-way union close to the master. Three way means one in, one out, and a bleed nipple. I have been known to put a bleeding point in each of the four pipes.

Four pipes? All of my new chassis rebuilds have had the rear brakes piped/hosed individually - flexible hose to each, similar to the front brakes. Tying pipes along the rear axle only encourages the use of binder twine (farmers and horsey readers will know what I mean), but even if done to factory spec, those two pipes are a PITA, and look untidy.

Difficulty in "charging" a new master cylinder? Bleed the master before connecting the "out" pipe. Use a short screw, bleed nipple, or even you finger to stop air getting back in when you lift the pedal. Memory says all our RAF trucks (Austin Loadster/Lodestar and Bedford SL/RL, etc) had a bleed nipples, especially for the occasion, ON the master cylinder. Our instructions were to always bleed the master cylinder first, and then the longest pipe, with shortest pipe last. (I'm not sure that complies with recent thinking.)

I hate bleeding tandem master cylinder systems ... my arms aren't long enough.

602

[w3526602]

Hi Michael,

"Changed master cylinder ..... "  New or second hand?

Whichever, remove bean can filler cap, and eyeball the fluid while the lady in your life presses the pedal. A surge of fluid, bubbles, or mud indicates that the recuperation valve is kna faulty. CB master? Oh dear .....

602

[geoff]

 Master Cylinder change : have you adjusted the free play on the operating rod    It has to be the first thing to do.

 

[Avalon]

I just changed my CB mc but I can't tell how to determine the 1/16 clearance on the push rod. Is there a simple way to tell the proper clearance?

John

[milesr3]

Unless you have a genuine LR or Girling CB cylinder the 1/16 clearance doesn't exist. The clearance is just a little gap between the pushrod and retaining washer with the piston in its fully retracted/resting position. Nothing more than a little rattle.

The significance of the comment in the Green Bible is (I believe) due to the risk of not allowing the piston to return to its fully retract/resting position. Not allowing the inlet port to be exposed by the recuperating seal and therefore not recharging the cylinder with brake fluid. The 1/16 clearance, aka "rattle" is evidence that the pushrod is not under pressure at rest.

With an aftermarket CB cylinder there is no rattle, so you have to be careful in setting the locknut on the pushrod so that the cylinder is not prevented from reaching its fully retracted/resting position. After some searching of the old site I found the advice (from Mark Ramsey) to tighten the first locknut (nearest the cylinder) up to take up the play and then back it off two flats. After setting the correct pedal height of course. Then tightening the second locknut will actually pull the pedal down a tiny bit, but you then know that the adjuster on the pedal box isn't then preventing the cylinder from fully retracting at rest.

With a little trial and error you can set the pedal height a little too high and then lower it down to where it should be with the locknuts. It could be argued that it's much simpler just to set the pedal height with the locknuts on the pushrod rather than the adjuster on the pedal box. This was how I found mine had been setup and I originally left it like this until I thought there must be something wrong with it because there wasn't the 1/16 clearance...

There is also a little slack in the pedal bush, but the advice was to leave this alone and not to try to adjust it out because the various parts expand when they get hot.

Hope that helps!

[Larry S.]

Unless you have a genuine LR or Girling CB cylinder the 1/16 clearance doesn't exist. The clearance is just a little gap between the pushrod and retaining washer with the piston in its fully retracted/resting position. Nothing more than a little rattle.

The significance of the comment in the Green Bible is (I believe) due to the risk of not allowing the piston to return to its fully retract/resting position. Not allowing the inlet port to be exposed by the recuperating seal and therefore not recharging the cylinder with brake fluid. The 1/16 clearance, aka "rattle" is evidence that the pushrod is not under pressure at rest.

With an aftermarket CB cylinder there is no rattle, so you have to be careful in setting the locknut on the pushrod so that the cylinder is not prevented from reaching its fully retracted/resting position. After some searching of the old site I found the advice (from Mark Ramsey) to tighten the first locknut (nearest the cylinder) up to take up the play and then back it off two flats. After setting the correct pedal height of course. Then tightening the second locknut will actually pull the pedal down a tiny bit, but you then know that the adjuster on the pedal box isn't then preventing the cylinder from fully retracting at rest.

With a little trial and error you can set the pedal height a little too high and then lower it down to where it should be with the locknuts. It could be argued that it's much simpler just to set the pedal height with the locknuts on the pushrod rather than the adjuster on the pedal box. This was how I found mine had been setup and I originally left it like this until I thought there must be something wrong with it because there wasn't the 1/16 clearance...

There is also a little slack in the pedal bush, but the advice was to leave this alone and not to try to adjust it out because the various parts expand when they get hot.

Hope that helps!

I'm getting ready to make the adjustments on the brakes and clutch - this will come in handy.  Thanks!!   

[w3526602]

Hi,

I don't know what I'm talking about ... but it might be worth running with it, just a little ...

Could it be that the "washer" that stops the push-rod falling out is different between the old cylinder and the new? There is something in my mind that the original is sort of recessed. And maybe the pattern washer isn't. . I don't know, but it might be worth a few seconds of thought.

If YES, just fit the old "washer" into the new cylinder.. If NO, compare the shape of the "ball end" on the end of the pushrods.

602

[Steve_C]

I also had the non-existent free play with my CB cylinder.
Discussion on old forum here:
https://www.series2club.co.uk/forum/forum/index.php?topic=93444.0

I agree with the adjustment process given by milesr3 as it ensures that the pedal stop screw does not prevent the cylinder from reaching its fully retracted position.

Steve

[milesr3]

I'm too paranoid to bench bleed, so we are prepping to lift.

Following is a pic showing what one guy does.

I don't think you need to lift the front quite as high as this. 

If you have a little spirit level, then just get the machined surfaces of the inlet and outlet ports level. You will find it easier to bleed without  the pipes attached, or at least you'll be able to see the last of the bubbles coming out. You do need to make sure that you don't re-introduce air when you reconnect the reservoir though. I'm sure you'll figure it out.

I tried to bleed mine by lifting the front and it fell off the dodgy jack arrangement that I had contrived, so be careful! It is worth persisting with this though - my brakes were night and day different from bleeding (filling) the cylinder on the bench.

[milesr3]

Discussion on old forum here

Here's another old thread, although less useful than yours because it was mostly about me being confused...
https://www.series2club.co.uk/forum/forum/index.php?topic=99459.0