Brake System - Bleed

[Tripyrenees]

I have just changed out front and rear shoes, servos and flexibles so a lot of empty space and air is in the system.

The brakes did not work when I got this car although when I depressed the brake I did see the servos operate before I removed them.

I just filled up the master cylinder with new brake fluid and started with the rear to bleed them. But nothing - a million pumps of the pedal and not even a slight drop in fluid level.

I disconnected the pipes (one at a time) going into the master cylinder and fluid leaks out when pumped. But again no movement in the reservoir.

Do you think there could be a blockage from the reservoir into the master cylinder :?: What else could it be :?:

Very frustrating as this is the final job required before I go and get the tracking set and the MOT (Côntrole Technique) done.

 

[montenegro]

disconnect rear brake pipe at wheel, disconnect brake pipe at master cylinder and using an air line blow thru from the wheel end anything ? if ok then reconnect and try pumping fluid thru again. I made a brake bleeding tool from a garden pump up sprayer and master cylinder cap from a megane power steering reservoir cap [which is the same size cap with a plastic pipe attached] see similar equipment on you tube.

 

[Cornish4]

I'm not trying to be clever here but did you open the bleed nipple enough and did you have a length of hose from it into a jar of fluid, as when you keep pumping, air can be sucked back into the system. One small thing too, I think you mean wheel cylinder and not servo, something quite different. Oh yes, one other thing, always start with the cylinder furthest away from the master cylinder. Good luck, regards Brian.

 

[Tripyrenees]

Yes, I changed the wheel cylinders all round.

I am using a 1 way valve from the bleed nipple into a jar.

I did use a pressurised bleed kit but when I put pressure in the brake fluid just exploded out of the top of the reservoir. Even when I took the pipes out of the master cylinder (the 4 pipes on the side) and pressed the brake pedal, the fluid came out of each of the 4 holes but no movement in the reservoir.

Nothing from the bleed nipple of the master cylinder either. The master cylinder does LOOK quite clean and new but as with the rest of the car I have no history for it.

Should I remove the master cylinder

 

[Cornish4]

It does sound like there is a blockage somewhere so I'd go along with montenegros suggestion and use an air line to prove the pipes are clear. While you are about it I suppose it wouldn't be a bad idea to remove the master cylinder and strip it down just to check all is well, after all the car was standing unused for some time wasn't it. I'm told the quality of the new master cylinders available now is not good, so hope yours is ok.

 

[Tripyrenees]

I have taken it off and the 2nd pipe junction is totally dry with the other three full of the new green brake fluid I used.

Is it simple enough to strip down the master cylinder. Do I need the 6mm rod tool as suggested in the Haynes manual.


Untitled by Tripyrenees, on Flickr

 

[Tripyrenees]

I have traced the pipes and this is what it looks like


Brake System by Tripyrenees, on Flickr

The dry pipe looks to me to be the reserve line according to the haynes manual. I have checked the Franzose catalogue and the matching Master Cylinder to mine says it is for Discs. But mine are drums. Not sure if it would make any difference.

The Brake Limiter Valve at the rear has 2 inputs (coming directly from the Master cylinder) and 2 outputs going to the wheel cylinders. It also have a little spring lever - what does this do :?::?:

Also the bleed nipple and the pressure warning switch are totally dry too and nothing comes out when I push the piston in.

 

[Tripyrenees]

I have cleaned out the master cylinder and plenty of fluid is coming out now (except the larger bore output which I think is for the reserve circuit - this is totally dry). I have put it back on the car and bled the front brakes perfectly -

Nothing on the back - so next thing to do it disconnect the pipe into the limiter valve (but the bloody things are all seized, so prayed with WD40 and going to buy a proper brake line ring spanner so not to round off the nuts).

From the photo can anyone work out the spring lever thingie. And are these limiter valves prone to failure. :?:


Untitled by Tripyrenees, on Flickr

 

[Cornish4]

The brake compensator is to reduce the amount of braking on the back wheels when the car is on light load, so as not to lock up the back wheels under heavy braking. I imagine the spring is connected to a valve which opens as you increase the cargo. My car has disc brakes but the master cylinder has only three pipes no bleed nipple and the brake light switch is on the pedal, so it's quite a bit different and simpler.

 

[angel]

Why is your brake fluid green?! What brand/type did you use?

It may be the pressure limiting valve that is stuck/blocked restricting fluid flow to the rear brake lines Before replacing it try bleeding the rear brakes with the left hand rear suspension arm lifted up with a jack, to "fool" the valve that the rear axle is loaded.

On completely dry systems I have often found that pumping with one bleeder open will not draw any fluid. Using the technique "open bleeder-press pedal down-close bleeder-release pedal" has always worked for me.

 

[Tripyrenees]

All done - It was the Bl%^dy rear valve limiter. It was blocked full of gunky grease.

What a b$%^%d to get that unit off. Took a good two hours and then I went off in search of a new one. But nothing locally and all the ones I saw on thew internet were a different model for a lot of money.

So I decided to strip it and see what I could do. Pretty simple device and easily repaired.

Another 2 to 3 hours putting it back in - I am very sore

Brakes bled like a dream - handbrake adjusted and off for a spin.

See my project thread

 

[billythefish]

sounds like the seal in the master cylinder is leaking slightly hence no brakes

 

[Tripyrenees]

Master cylinder tests good. In the end it was a block in the valve limiter on the rear circuit. this also passes back to the master cylinder the reserve circuit so I could bleed the complete circuit from the master cylinder.

When it worked it worked perfectly so it was an ALL or NOTHING fault for me.

Passed its MOT perfectly yesterday so very happy.

 

[angel]

Did you find all the seals for the pressure limiting valve? Are they generally available? We had a similar discussion some time ago here.

 

[Tripyrenees]

The seals were in good order. It was just clogged with old grease. So just a good clean out and re grease and all was good.
In my workshop manual it states non repairable but they are (if the seals are good)

 

[Geoff in the Gully]

Keep a good eye on that limiting valve - check it regularly. They fail by leaking past that inside o-ring seal that the piston shaft goes through. Brake fluid leaks past the seal into the boot that is over the outside of the piston (where the lever presses), the fluid absorbs moisture, goes gummy and clags the piston.

They can look good when you put them together but a little while later . . .

So, a regular lift of the edge of the boot and you won't be caught unawares.

 

[pepper]

Just what I was looking for, I have exactly the same problem with my rear valve too..

 

[malcolm]

The thing that catches me out is the rear wheels need to be on the ground for bleeding. The rear valve is there to stop fluid going to the rear brakes when there is no weight on them.

 

[pepper]

Yeah I've jacked up the suspension arm, but I'm going to try it with all four wheels on the floor next. This is the earlier 4 pipe version and it's quite different to the later three pipe version I had before.

 

[Paul Narramore]

The thing that catches me out is the rear wheels need to be on the ground for bleeding. The rear valve is there to stop fluid going to the rear brakes when there is no weight on them.

That's very helpful as I am about to give the rear brakes a good clean before bleeding the system, and would not been aware of this. Mention was made earlier when using a pressure bleeding device (Gunson EasiBleed?) of the top of the master cylinder exploding with escaping fluid. I once did this using air from the spare wheel. Very little air pressure is required say 5psi, and certainly not the 25psi or so which would be in the spare.