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Brake problems

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Cuno

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Hi all!

My R4 ('74) has a 2-circuit brake system. Yesterday i found that there where no breaks as i went to work. Checked the fluid level, and one container was empty... So i filled up, and startet getting the air out of the system. Left front went ok. The problems started when i tried to bleed right front brake -- i could not get any oil (or air) out at all, despite very many presses in the pedal. So i pressed harder and harder on the brake pedal, until suddenly the pedal 'fell through'. Don't know what happened. Suddenly i can not get any (brake-)oil pressure at all, and there's a squeeky sound from the main brake cylinder when i press the pedal. Squeek, squeek, squeek....

Any ideas? I guess i'll have to disassemble the main brake cylinder huh?
 
sounds like ypu have pushed the seals off the piston inside the master cylinder. don't know if you can repair or not though.
 
Any signs of where the fluid leaked to? I'd say SussexR4 is correct though. The seals would have been on the verge of dying, the fluid leaks out, you top it up and try to bleed it. The pedal gets pushed into the corroded, dirty, rarely used end of the master cylinder (with pedal going to the floor), the seals would have been nicely torn and now no longer seal. The squeak is R4ese translating as, money, money, money :-)

It certainly will be a pull apart job, a re-sleeved or replacement master cylinder and at least a new seal kit if the pistons can still be used.
 
Thanks for your replies!

I guess you're right. I just removed the master cylinder, and will "borrow" the one from my other R4 to see if that corrects it.

Edit: I didn't find any leaking problems, my hope is that it evaporated :) I recently bought the car, and have never checked the levels. Probably hasn't been checked for some years.
 
Cuno, try to check if the right front brake hose is clogged or the rigid pipe is pinched, restricting fluid flow, after you fit the new master cylinder. It sounds strange to have pressure on the left wheel and not on the right, since both wheels are being fed from the same circuit.
 
It is quite common for old flexible brake hoses to collapse inside and restrict the flow of fluid. I just loosen the nut on the other end and pump the pedal to see if fluid comes out. If it does then replace the hose and bleed as normal.

Steve
 
Thanks guys, you're right -- the hose is clogged. I just bought a new one.

I didn't change the master cylinder. I turns out there's a brake specialist right next to work, so i just went over and showed him the pistons and gaskets. He said they looked ok, just a nearly invisible dent in the inner one (i.e. the one to the rear brakes), but nothing to speak of. The cylinder looked ok inside too.

So i've re-assembled the master cylinder, and i'm of to change the hose now. Hopefully i'm down to 'just' getting the air out of the system.
 
Nope, that was not it. Still no pressure :( I must have broke something when i pressed too hard on the brake. Still the funny noise in the master cylinder.

I'll swap master cylinder this weekend, i guess. Hopefully that will be the end of it.
 
One more note, Cuno. If your R4 has a tandem master cylinder it should be fitted with a pressure drop indicator ("Nivocode") and this has also a bleed screw. You should bleed it after all four wheels have been bled. It sounds strange to me to be able to break something in the master cylinder since these components have a high safety margin. The classic failure point is where the master cylinder pushrod is connected to the pedal by a pin. On high mileage cars this pin wears away (it has never happened to me to break this pin, even after its diameter had ben reduced to half). Try also to see if you have pressure on the rear brakes, sometimes you should bleed them first, in order to build pressure in the master cylinder.
 
I would first address the issue of where the fluid has gone ? sounds like to me that you have leak somewhere and knowing a R4 its one of the awkward main brake pipes along the chassis .Forget the master cylinder !you have no pressure due to a leak .My money is you find the leak and rectify the fault and bleed the brake pipes coming out of the master cylinder THEN bleed all 4 wheels cylinders the last of all the master cylinder bleed nipple and Voila a good brake pedal .
 
I found a leaking rear brake cylinder now, that should explain why the front container went dry. I've bled the front brakes according to the original workshop manual, i.e. using compressed air on top of the hydraulic fluid containers, and still no pressure at all when i push the pedal. Shouldn't at least the front circuit build up pressure??

I've ordered a new rear brake cylinder. There's no way of getting a new master cylinder though, or even parts to it. I've just called all the scap yards in my area, and no one has got any parts for the R4. So i hope you are right, Liam4R4SPARES. I miss my R4....

BTW: Does anyone have a good condition master brake cylinder for sale? It should be for a 2 circuit system, with 2 containers, and a check valve block mounted. My car is a -75.
 
Yes i have one i removed from a car about 5 months ago but i would personally first fit the wheel cylinder, then bleed the master cylinder pipes[at the master cylinder] and make sure this is primed before you consider going to the wheel cylinders and start bleeding things .Best to drop me a line and i will explain how to do it ! tel 01491 411564 evenings [if engaged i am online]
 
Thanks Liam4R4SPARES. But i would probably miss half of what you'd say, since i don't know all the technical terms in english. But i think i know what you're talking about. I haven't thought of bleeding the short pipes at the master cylinder. But still, i think that the way i did it should bleed those to -- I have drilled a small hole in the lid of the hydraulic fluid container, to connect an air compressor to push the hydraulic fluid all the way out to the brakes. So i bled the brakes without using the brake pedal. Surely that must take care of all the air in the system?

I may have found a master cylinder, the owner should look in his garage and i will get back to him in a day or two to find out. I still hope the one i have is as it should though.
 
Have you tried bleeding the brakes by the conventional two-person method???
 
Yes, my brother assisted me on that.

I've found a guy who had the exact same problem, and that was fixed by fixing the rear brakes. Apparently the emergency brake system (that redirects all brake power to the rear in case of brake failure) is the cause to that.

I actually have found a new master cylinder too! :) But the problem will hopefully go away when the leaking rear cylinder is fixed.

Thanks for your input guys! I'll let you know the progress. The new rear cylinder will be in by tuesday.
 
easy way to see if the master cyl is duff is to clamp the rubber hoses, the pedal should now be solid, if not the master is duff or you have a leaking metal pipe.

If its solid and stays solid (thats important) take the clamps off 1 by 1 and when the pedal falls to the floor you have found the problem.
 
Thanks Chris! I've tried a few other things.

I changed the leaking rear cylinder, and bled the brakes. Still no pressure. So i switched the master cylinder with a used one. Have no idea if it's working as it should - i tried to press manually and could not hold the pressure with my thumb, so there should be some pressure once on. So after the master cylinder switch i just bled the left front and the emergency circuit, just enough to bleed both circuits at the master cylinder. The result -- now i can actually pump up a pressure! I have to pump every time i want to break though. Is this normal for a system with air in it, i.e. do you think i will get a working brake once i've bled the system properly?

I'm beginning to think my R4 is haunted :(
 
Pull on the handbrake and if there is then less travel on the footbrake it is a adjustment issue with your rear brake shoes .Sounds like you have cleared most of the air but your need to go around once more and bleed all 4 corners then the master cylinder bleeder .If then once all the air is out and you still have a poor pedal its adjustment.
 
Bleeding brakes is a pain.

I use the manual method (which requires 2 people). One person opens the bleed nipple, then shouts to the other person (inside the car) to press the brake pedal down. Then close the bleed nipple and shout to lift off the brake pedal. Repeat until the fluid from the bleed nipple is free from air.

Start with the rear bleed nipple furthest away from the driver (in UK cars this is the RH rear), then go to the opposite rear side, then the front that's furthest from the driver, then the opposite front side. Then the master cylinder.

After that sequence has been completed, get the bloke in the driver's seat to press up and down on the brake pedal very quickly lots of times. This makes the air bubbes in the system into very small air bubbles which will bleed out.

Do the bleeding again.

Then your brake system should be free from air. :D
 
I do it similarly, but I didn't know the trick for making the small bubbles. I'll keep it in mind.
A translucent flexible hose that fits the nipple, can help you put the old liquid cleanly into a bottle or can and you can see if there are bubbles in the hose to know if you're ready with that tyre. Another extra bonus of the hose is that if anybody gets distracted or communication fails, you won't get that much air back into the cylinder when it resets.
 
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