SWB brakes - master cylinder?

Hi,

can I just get confirmation that I’m likely right that the master cylinder is to blame for struggling to get them bled?

‘72 SWB 10” all round, so one slave per wheel. Single line, no servo.

ive done the following

- new slave cylinders all round.
- new flexis
- no visible leaks from any joints
- after struggling, put on axle stands and clamped all slaves fully in.
- bled all until no bubbles
- sort of got a pedal, yet holding down, pedal finds itself touching the floor.
- so, clamped all flexi hoses, but same as the pedal still gets to the floor. I’d hoped it was firm at this point and then remove all me clamp at a time

No signs of leaks anywhere. So I’m thinking fluid is passing the seals in the master... so even without air, it moves to the floor?

is there any other way of proving it’s the master, I considered fitting a spare line to the master with a bleed valve connected, and see if it can be bled literally on it’s own.

if that’s likely the case that it’s fooked, is there a recommended master cylinder make?

should I consider upgrading at this point?

If there any advice at this stage I’d appreciate. Ta

It is quite common for master cylinder seals to fail after bleeding as the seal moves further whilst bleeding as opposed to just braking.
Is there any sign of fluid in footwell usually drips on the pedal.

Hi, no, no leaking around the master or the pedal or floor. Can the fluid pass a seal without peeing out?

Have you adjusted the brake shoes and are the springs fitted correctly, ie one spring between lower shoes and one spring from post on backplate to leading shoe.

Yes they were all correctly fitted and adjusted. However, today I clamped all the slaves in fully. So eliminating all the movement and minimising the space for air in the slaves.

It does sound that fluid is passing inside the master. [ there are some rubbish parts out there these days ]

Hint for all. When fitting a new master before it goes on the vehicle put a few drops of fluid in the pipe attachment holes and work by hand.
Have known new ones to stick at the bottom of the stroke at first press and even damage the seals.

If its the master leaking internally (and they can, I've had this) then the pedal goes slowly to the floor or is soft, but its not springy like it is with air.

Dare I ask which brand you've bought?

Yes, goes slowly to the floor.

The master cylinder is the one that came with it. Previous owner has said he couldn’t get a pedal, so he bought a new master, which I think is what’s on it but can’t be sure. I have a receipt from last year in the file of papers, but don’t know if he actually fitted it. I think it’s a TRW one as it seems to have the markings of one on the side. So, it’s a little unknown.

The new slaves are Britpart. Bit worried about them to be honest as I’ve learned pretty quickly some their stuff is a bit poop. The shoes I bought just don’t fit properly on the front. They are now a better brand!

costing a fortune chasing this all through to be honest!

DeviousLandyGod said:

Yes, goes slowly to the floor.

The master cylinder is the one that came with it. Previous owner has said he couldn’t get a pedal, so he bought a new master, which I think is what’s on it but can’t be sure. I have a receipt from last year in the file of papers, but don’t know if he actually fitted it. I think it’s a TRW one as it seems to have the markings of one on the side. So, it’s a little unknown.

The new slaves are Britpart. Bit worried about them to be honest as I’ve learned pretty quickly some their stuff is a bit poop. The shoes I bought just don’t fit properly on the front. They are now a better brand!

costing a fortune chasing this all through to be honest!

Click to expand...

Within 6 months I'd replaced the britpart shoes with borg and beck then replaced the slaves and master cylinders with delphi ones and it transformed the brakes

CB or CV master cylinder?

My whole s2 braking system is britpart, and have to say and it does pain me to say it! they are okay.
I go through a master every few years, as they seize up due to lack of use

At one time the mintex shoes were the dogs danglies, but they quickly fell apart, well the brake spring pin fell out! and then everyone started to use britpart.

Anyway back to the master,
Have you set the pedal height?
Have you set the pushrod free play?
Do both of these then try again.

just a couple of points,
regarding the m/cylinder,that is very likely to be the culprit,i might be tempted to fit a cheap,sub £10 replacement just to 'isolate' the fault ,rebuild kits cost almost as much and more.
i have fitted a 11" tls on mine and it is certainly the best upgrade out there,it will stop on a sixpence in a straight line,
the downside is that it took a lot of trial and error to get it right,servo,m/c etc, so my advice would be to accumulate the parts in advance and leave it as a winter project and use yours through the summer.
r

TRW parts are generally good quality they bought the Lucas brand and make lots of automotive parts Canadian company originally been bought out by a bigger company a couple of years ago.
Have TRW shoes on at the moment had some cylinders about eight years ago replaced a couple with Bearmach when the seal s failed and could not get the bleed nipple out.

lynall said:

CB or CV master cylinder?

My whole s2 braking system is britpart, and have to say and it does pain me to say it! they are okay.
I go through a master every few years, as they seize up due to lack of use

At one time the mintex shoes were the dogs danglies, but they quickly fell apart, well the brake spring pin fell out! and then everyone started to use britpart.

Anyway back to the master,
Have you set the pedal height?
Have you set the pushrod free play?
Do both of these then try again.

Click to expand...

CV master. I’ll check out the adjustments to pedal height. Just trying to straighten in my mind why the pedal travel would mean it doesn’t bleed up. The master cylinder piston will always start fully retracted so the only adjustment will be how far the pushrod travels moving it in. So, presumably it never starts out partially travelled, so it’s just the extent of travel. Could do with a sectional view of the cylinder to understand how it it works I think.
Thanks

I've had 2x 2a 88's and 2x S3 88's over the years and i fitted all of them with BP brake parts through out and even though the brakes were never 100% they was a lot better than on the 2a 88 i'm running now think the BP brake parts have worse since i had my last one with this one all brakes backed off all the way i could either have a good pedal but brakes binding, back the rod off on master cylinder and have useless brakes, adjust brakes so brakes worked but pedal was very close to floor, adjust brakes up to work better and have a better pedal and the brakes would bind, no matter what i did it would only be one or the other i could just not get it in between i even swapped the drums over left to right and that didn't do anything, i even bought better make drums and shoes and again same problems so in the end i decided to go disc brake all round and now it stops on a sixpence.

The master cylinder has a valve at rear to close off fluid resevoir if pushrod is not set right valve can stay closed so no extra fluid added on return.

DeviousLandyGod said:

CV master. I’ll check out the adjustments to pedal height. Just trying to straighten in my mind why the pedal travel would mean it doesn’t bleed up. The master cylinder piston will always start fully retracted so the only adjustment will be how far the pushrod travels moving it in. So, presumably it never starts out partially travelled, so it’s just the extent of travel. Could do with a sectional view of the cylinder to understand how it it works I think.
Thanks

Click to expand...

I think idea of pedal height and pushrod slack is to make sure you have a good known starting point.
Pedal height is adjusted by small bolt on top of pedal box, I think it is even mentioned in the green bible
Pushrod slack is a pita to get a spanner in there!

Mine is same as yours, and I have no troubles bleeding it with an assistants help or pressure bleeding.

Thanks, all good advice.

just had a little looksy over lunch. There’s deffo about 1 or 2mm movement on pushrod. I’ll check pedal height later.

There’s no leak at master cylinder visible.

if seal was leaking back into reservoir, would that have this effect? Presumably I’d see the level increase a little on pushing the pedal?

Until later, cheers

[QUOTE="DeviousLandyGod,

if seal was leaking back into reservoir, would that have this effect? Presumably I’d see the level increase a little on pushing the pedal?

Until later, cheers[/QUOTE]


No, fluid would just be swapping sides inside the master.

tottot said:

[QUOTE="DeviousLandyGod,

if seal was leaking back into reservoir, would that have this effect? Presumably I’d see the level increase a little on pushing the pedal?

Until later, cheers

Click to expand...

No, fluid would just be swapping sides inside the master.[/QUOTE]

mmm, again can’t figure that out. It’s a single line master, so only two seals, one to block the entry of fluid on pressing, the other compressing the fluid. If it doesn’t pass the main seal and doesn’t go back into the reservoir, then the cylinder should operate properly, you’d think.

I can understand a tandem cylinder and the fluid passing from one line to another maybe...