8 replies to this topic

[rolf]

Hello all,
This is the brake master cylinder from my rover mini mpi 1996.
In the photo I have attached, I have put letters on the main points since I don’t know the terminology.

My rear brakes don’t work. By searching, I reached that the problem is on this part.
When I press the piston ( C ) brake fluid (air when the container is empty) will run from the hole A, which seems to send brake fluid at the front brakes, BUT, nothing comes out from the hole B.
So, to me is obvious that I have to change the guts inside of the cylinder.
If you have another opinion, its welcomed.

I have ordered the kit GRK1032 so I can put new guts into my cylinder.
My question is: How do I open the brake cylinder (C, D, E ) without damaging its parts, especially the white nylon seal (D)?

 Brake master cylinder.JPG   55.54K   34 downloads

[tiger99]

Sorry, but I am going to have to say that if you have to ask, you are not yet sufficiently experienced to be doing it. Never take a chance with brakes.

As far as I know, the procedure is documented in the Haynes manual.

[rolf]

Tiger, I took it to the brake mechanic and he gave me a wrong diagnosis, and I was on a goose chase for 2 months, so I don't think that we can easily find professionals that really know what they are doing. ...and it's not the first time that I find them wrong. Once I almost got killed because of a wrong repair.
So, dont tell me about professionals.
As for the Haynes manual,
It says nothing about the white nylon seal, which unfortunately is not included in the repair kit.
Anyway, thanks for your interest

Edited by rolf, 13 February 2013 - 08:39 AM.

[tiger99]

I did not actually mention "professionals", and I have passed comment about quite a few of them and their shoddy and sometimes unsafe work here. You don't need to be a professional to do this, just very careful, but you must have an absolutely clean working environment.

If you are really determined to do this yourself, and are very sure that you can, just extract the white seal using a thin screwdriver. You then remove the reservoir, take out the stop pin under the front reservoir port, release the circlip, and the springs will push most of the innards out. The white seal is not part of the hydraulic system, and does not appear to be a standard fitment. I believe it is a vacuum seal for the servo, and you will also have an O ring there to make a proper seal between the servo body and master cylinder. Try looking for a new seal, if needed, as part of a servo repair kit, but I am not convinced that it is needed.

Please be VERY sure that the master cylinder bore is PERFECT before fitting the repair kit. Any scoring, corrosion (even minor pitting) or wear and it is scrap. I have seen "professionals" overhaul master cylinders which were less than perfect, they invariably failed within a week.

If you have the slightest doubt about anything, please, for safety's sake, fit a complete new master cylinder. £97.55 from Somerford, which has to be a lot less than the value of a human life, as well as being a lot less fuss and bother than overhauling the old one.

http://www.somerford...page=page&id=58

[rolf]

"Any scoring, corrosion (even minor pitting) or wear and it is scrap. I have seen "professionals" overhaul master cylinders which were less than perfect, they invariably failed within a week."
Thats a good point tiger99.

The bad thing is that the front brakes are perfect, and the rear ones are dead. Now that you say corrosion, could it be because of corrosion?
If yes, how come the half part doesn't work and the other works perfectly?
If no, what the hell has happened inside the cylinder?

Edited by rolf, 13 February 2013 - 01:29 PM.

[tiger99]

I think it is more likely a swollen seal. Make sure that you flush the entire system with fresh fluid when bleeding, to remove any contamination.

Corrosion rips the very fine edge of the seal and causes leakage.

[rolf]

I think it is more likely a swollen seal. Make sure that you flush the entire system with fresh fluid when bleeding, to remove any contamination.

Corrosion rips the very fine edge of the seal and causes leakage.

But there is no leakage.
Infact, there is no flow from the one hole (of the rear brakes).

[MRA]

Could be blocked up with rust.....

When re-assembling use rubber grease, brake fluid has very little lubricity and as such can cause torn or damaged seals.

[rolf]

Thanks to both of you guys, problem solved.
Now I only need to go to check the effectiveness of the brakes.
Cheers!