24 replies to this topic

[RobWill116]

I believe my brake master cylinder has gone on my 1983 City E, the pedal all of a sudden hit the floor with no pressure at all. Strange this was that there was slight smoke coming from the brake fluid resevoir - odd. Anyways is this the correct master cylinder for my age car? It doesn't have a servo.

Minispares - http://www.minispare...id=36659&title=

Minisport - http://www.minisport...nfo_GMC227.html

Thanks

[tiger99]

There are some contradictions here. Why do you suspect the master cylinder? How much fluid is left in the reservoir?

"Smoke" from the reservoir generally means that the fluid is boiling somewhere in the system. I assume that you had used the brakes quite a bit, so they were hot, just before they failed? Vapour is compressible, hence the pedal goes to the floor. When was the fluid last changed? It really does need to be done every 18 months or so, as it absorbs water, and the boiling point falls.

The only other possible cause of smoke is an electrical fault in the fluid level warning light switch, but as the current is limited by a very small bulb, I can't see that as being very likely.

Oh, and you have had a double failure if the pedal went all the way to the floor. It is unlikely that the fluid in the rear brakes boiled as they don't do much work. Are you sure that your rear brakes were working before the failure? Obviously the front brakes were, or you would notice. Was there an abnormal amount of pedal travel? Were the brakes properly adjusted?

The other thing which can happen is that if the front circuit fails, the PRV then allows full pressure through to the rear brakes, which can immediately fail too if the hydraulic system is in bad condition. Are you using copper brake pipes?

Total failure of a dual circuit system is a very serious matter, and the design is such that it should be impossible.

[RobWill116]

The resevoir is full, and the fluid was only change about 4 months ago before the car went back on the road.
Regarding the smoke, I wasn't driving hard at all to make the brake fluid boil. I was just driving to work! aha

The rear brake were working fine, all the brakes have been overhauled so are brand new. Pedal travel was normal too.

Yes the system is all copper piped.

Is my brake system dual circuit though? Didn't dual systems come in around 85? Mines an 83

The only thing I haven't mentioned is that I've converted the front drums to 7.5 cooper s discs. Would they be putting extra pressure onto the master cylinder?

Edited by RobWill116, 25 May 2012 - 07:16 AM.

[RobWill116]

Just done a bit of research and dual circuits came in about 1975 so mine will be dual circuit

[Ethel]

Correct, they got dual circuits when they got big subframe tower bolts and hazard switches. Suppose it's possible and electrical short is using the brake pipes as a conductor and heating the fluid, might be worth looking at the battery cable, or more likely, earths.

You can test the master by blocking off its outlets*, the pedal ought to go solid with minimal bleeding.

* crimp over a short length of pipe in a union - a ball bearing in place of the pipe would also work.

[RobWill116]

Correct, they got dual circuits when they got big subframe tower bolts and hazard switches. Suppose it's possible and electrical short is using the brake pipes as a conductor and heating the fluid, might be worth looking at the battery cable, or more likely, earths.

You can test the master by blocking off its outlets*, the pedal ought to go solid with minimal bleeding.

* crimp over a short length of pipe in a union - a ball bearing in place of the pipe would also work.

I will check this out when I get chance to look at it properly. I've looked for loose connections and shorts, isn't many cables that go to near my master cylinder for pipework.

I've wanted to take my engine out for a while now to paint it up and re-spray the engine bay. So I might just re-plumb all the pipe work whilst I'm at it.

Edited by RobWill116, 25 May 2012 - 11:32 AM.

[Ethel]

Also, that would be the right replacement, I think Jonspeed were flogging them a bit cheaper on Fleabay. That "yellow band" cylinder has a stepped bore and hasa larger union (M12x1) on the bottom: so you can tell if it'd be a direct replacement, if it isn't you'll need some new pipes to connect it to the brake regulator. There's info on Minispares site, with the conversion pipes.

[kez_19]

i have one for sale that dosent have the resevoir if you have the resevoir from your old one then mine will fit your car

michael

[tiger99]

Right, I now understand why the pedal went all the way to the floor. If discs are fitted at the front to what was a drum system, it is absolutely vital that the master cylinder is changed for one intended for disc brakes. The reason is that the volume of fluid displaced in a disc system is greater. The pedal MUST have some reserve travel when one circuit fails, otherwise it totally negates having a dual circuit. If the master cylinder does not have sufficient fluid displacement capacity, it will run out of travel, and a single point failure will lose ALL brakes.

Swapping brake components without understanding all the consequences is downright dangerous, although I expect that many hundreds of people here have done it, probably following instructions from others on this forum, the monthly comics, or from spares suppliers. It also almost certainly voids the insurance, being an improper modification, and infringes Construction and Use Regulations. It completely negates regular maintenance, fluid changes etc, and although all will seem to be well until there is a single failure, the system is actually lethal.

Basically, you can not fit discs instead of drums without increasing the master cylinder volume, which means increasing the diameter, which unfortunalely gives you a heavier pedal, but for legal and safety reasons that is how it must be.

The failure could have been in the master cylinder, or anywhere else in the system, with the same result.

There seems to be some confusion about why I asked about copper pipes.It has nothing to do with my suggestion of an electrical problem. The conductivity of copper pipes is high, and a short is not going to boil the fluid in them. The reason that I mentioned copper pipe is that there is no such thing as copper pipe specified and approved for use in vehicle brake systems. There is cunifer and bundy, both with proper international specs. Copper is not manufactured as brake pipe, it is fraudulently sold as such and has absolutely lethal fatigue properties. It will burst after a depressingly small number of heavy brake applications. If any supplier dares to argue, let them produce something like a BS spec to back up their claim that it is suitable as brake pipe. I have checked, and they can't.

The smoke must indeed have been caused by a hot spot in the fluid level switch, quite rare but the only way that even a tiny amount of boiling would happen in a system with fresh fluid.

Now to answer the question, the replacement master cylinder MUST be the one appropriate to a front disc, rear drum setup.

[RobWill116]

Tiger all I can say is thank you very much! You cleared that up for me big time, at the time I converted my drums to discs, I did plenty of research and follow all instructions I found on the forum and magazines. But I've never been told to uprate the master cylinder, obviously the reason it has failed. With regards to the wiring, and piping I am going to completely replace all the old piping with cupranickel (however you spell it) as I've been told its better reccomended if that's a good idea? And seen as my master cylinder already fitted is now obsolete I will need to change the wiring for the new master cylinder switch anyways.

Thanks a lot for your help!

[bmcecosse]

I had to smile (sorry!) at the proud owner advising he did indeed have 'copper' brake pipes. As above - they are not safe - I had one fall apart in my hand on a car I bought...... BUT - some pipes sold as 'copper' are in fact 'kunifer' - so check before changing them needlessly! Copper pipes look 'coppery' and kunifer pipes look dull greenish coppery grey.......

[tiger99]

Excellent! You will have a much safer car as a result. Cupronickel, trade names Cunifer or Kunifer is the very best brake pipe material. I used it on several cars, for very high mileages. I also used silicone fluid, but I am not going to suggest that you do so, because the forum is regularly reporting bleeding problems in Minis, and silicone would make bleeding even more difficult. It works well in cars which bleed easily, I did well over 120k miles in one car with silicone fluid, cunifer pipes, braided hoses, and what finished the car off was rust. The brakes only ever needed pad replacement.

[tiger99]

bmcecosse, yes I agree with all of that, and it is sad that those who supply the proper material don't advertise their product as well as they could. I would have thought that it was a good selling point.

[RobWill116]

P.s tiger I presume the replacement master cylinder that I gave links for in my original post is designed for disc brakes as it is the only master cylinder available now for minis up to 88, and after 84/85 discs were standard if I am correct?

[RobWill116]

I had to smile (sorry!) at the proud owner advising he did indeed have 'copper' brake pipes. As above - they are not safe - I had one fall apart in my hand on a car I bought...... BUT - some pipes sold as 'copper' are in fact 'kunifer' - so check before changing them needlessly! Copper pipes look 'coppery' and kunifer pipes look dull greenish coppery grey.......

I didn't realise copper piping was so bad, all the piping is the original from date of production. which i presume is copper. I now realise how dangerous it is, live and learn.