Brake master cylinder

[alaric]

Hi all,

I've just been chasing a fault with my clutch master cylinder - it didn't work at all. There's a small seal at the reservoir end of the bore that stops fluid flowing into the reservoir when you press the pedal. If this fails, no fluid goes into the pipe going to the clutch slave cylinder and there's no pressure at all in the system - pumping does not help. After stripping and cleaning my clutch master cylinder now works fine.

The brake master cylinder appears to be exactly the same design but bigger bore. I'll be stripping that tonight to check it out. Problem is, that if that seal fails in the brake master cylinder, I'm history - can't even pump the brakes to stop!

So has this been a problem for others on the forum? I remember a thread recently where the brake pedal was going slowly to the floor - was that this seal failing... Is the bore of the hole in the end of the brake master cylinder, relative to the piston bore, small enough to allow me to at least stop if the seal fails?

As this is a single point of failure that'll potentially kill me, I'm interested to know if there's a replacement that I could use instead. Any suggestions?

Sean.

[Elanintheforest]

I think that this is probably one of the most important posts I?ve seen on this forum. What makes the situation worse is that our cars are now well over 30 years old, some approaching 50, which is way past the designed usage.

I wonder how many folks on here have taken it on trust that their master cylinder is in perfect shape internally? Certainly the temptation is to rebuild it with a kit for a few pounds, but that doesn?t really guarantee it working properly for the next few years. Not many cars get their brake fluid changed every two years, and the build up of water in the system ensures that some corrosion has occurred in the bore, potentially leading to premature seal failure.

If you?re keeping the original master cylinder, I guess that the least-risk way of maintaining it is to have it professionally overhauled, and maybe re-sleeved, by a professional. The alternative is to get a new cylinder. They are not expensive.

You could always look at installing a tandem cylinder which gives you a second chance!

If anyone out there has a car and they don?t know when the master cylinder was last checked over then they must surely be taking a very real risk of failure.

Mark

[alaric]

Ah. Ok. So I'm not completely barking then. I was expecting to be told no no it's not a problem don't worry about it. My master cylinders are both actually new in that they've never been used. They were bought at least 10 years ago though, and have spent a lot of that time in my loft. They obviously need to be checked out.

Thanks.

Sean.

[ppnelan]

If you do have master cylinder failure there's always the handbrake...

Matthew

[alan71]

I?ve had that happen several times, the pedal goes straight to the floor with no resistance, it?s quite scary. The first time was in a Spitfire as I approached a roundabout, fortunately there was no one in the way and it was a big roundabout so I got round without slowing up.
When it happened in the Elan I pressed the pedal again and everything came back, the seal must have re-seated.

When I stripped the master cylinder, which was only a couple of years old, the rubber seal to the reservoir was completely knackered, and when I bled the brakes the fluid was full of little black particles. I blame this on the silicon brake fluid, others may disagree but I have never used it since.

Alan.

[mikealdren]

Mark,
Do you know of a twin circuit cylinder that fits?
Mike

[steveww]

I always change the brake and clutch fluid every 2 years with out fail. The master cylinder is relatively new so it has some years left in it yet.

As has already been pointed out brakes is one area where taking short cuts is not a good idea

[Elanintheforest]

Mike
The later US spec Elans used twin circuit, and I'm sure that the racer boys must have something...may be worth trying TTR?
Mark

[RotoFlexible]

Mark,
Do you know of a twin circuit cylinder that fits?
Mike

I have a dual M/C on the shelf that will bolt in, but I've never fitted it. It is designed to be used with a booster and I don't want a booster. I believe that if fitted it w/o a booster, pedal effort would be unacceptably high.

Despite Alan's experience noted above (which he attributes to incorrect brake fluid), I don't believe the M/C is a likely point of sudden failure. I think it's more likely to give plenty of warning before it quits.

I've had three total brake failures in the car. All were my fault. Once, a pad retaining pin came loose and the pad popped out. Twice, a flexible line that had been nicked by a wheel failed. One of those cost me the nose of the car, fortunately nothing else!

Sean: do you have any idea why the clutch M/C failed as it did? Was the check valve seal damaged or was there something that prevented it from closing? Whatever you may have found, make sure the same condition isn't present in the brake M/C, and you should be fine.

[alaric]

Hi all. Andrew, I got the clutch master cylinder to work simply by stripping it and cleaning it out. There appears to have been some rusting going on, which I think was mainly the spring but may also have been the 'bucket' that the spring seats onto. I think the spring was siezed, and therefore not pushing thre return valve home.

My plan, as you rightly suggest, is to strip the brake master cylinder and see if there are signs of rust. With that cylinder I may just replace if it looks at all unhealthy.

I think the likelyhood of the problem would be greatly reduced if there were no components in the master cylinder that were likely to rust. In an ideal world the fluid is changed regularly and the rusting does'nt happen. Also, in an ideal world, my car would have been on the road 4 years ago...

My interest in this thread is really to ascertain, from the experience of other elan owners, whether it's likely to leave me with no brakes.

Anyway, back to work - how many of you, like me, are taking a sneaky couple of minutes away from what you're supposed to be doing... my justification is that I don't smoke, so don't take regular 10 minute trips outside.

Sean.

[cabc26b]

Gent's

I like to keep things (sort of) original if I can, however, I will not be putting the original master cylinder on to the S1 - I will be useing a tandem - I will keep the origal in a bag for the next owner .

There are a couple options out there that do not require a booster - one is made by AP racing , the other is a ford/girling thing ( maybe, have to look at the numbers-there may be another as well) , I will be moving the tandem ( not re-installing) off the S2 onto the S1 and getting the AP racing tandem for the S2 and adding an in line proportioning valve for the circuit to the rear - my lack of skill and finess requires me to late brake.....

George

[mikealdren]

Sean,
Most problems with brakes are gradual, usually sticking cylinders in the callipers due to corrosion over the years. Disks corrode as well but that usually just wears your pads more quickly. If the disks are too thin, you may experience brake fade but it?s unlikely on a road car.

The master cylinder being aluminium, doesn't rust but it can corrode and wear. If it does, fluid will seep past the seal and you will get a leak as well as losing performance. You'll probably only get a complete and sudden failure is the seal splits but this is unlikely.

Other ways you might get a complete failure are through:
? Split hoses
? Pads sticking and wearing to the backplate ? the brake fluid will then boil

When I got my Elan, I drove a couple of hundred miles home and all seemed well. I then took a friend out for a ride and had to stop quickly as traffic lights changed on me. The car only just stopped. On the long journey, under light braking, I'd noticed nothing wrong. However, the brakes were very corroded and most of the pistons were sticking in the callipers. I would strongly echo Mark?s point about old parts, if you haven?t done so, get your system thoroughly serviced and then regular maintenance should keep it ok.

I?m sure other owners had a wry smile at the idea of the handbrake being the secondary braking. The sad thing is that it would have been exactly that when the car was subject to ?Type Approval? by the old Department of Transport. I can imagine some poor engineer at Lotus spending hours tweaking the system to get the required performance, just like we do for the MOT.

Mike

[bcmc33]

One thing that concerns me about this subject ? how do you know that the seal kits are genuine? I?m not sure what I mean by genuine, but how do you know they are not crap forgeries like the cheap brake pads?

I am interested in knowing if there is a good option kit available to go tandem M/C. I guess it would mean removing the booster, or fitting a second booster. Clearly something for the experts to clarify.

[alan71]

If the valve seal doesn?t seal the hole from the fluid reservoir when you press the brake pedal all the fluid in the master cylinder is pushed up into the reservoir and you get no braking effort whatsoever. In my experience this is not something which happens gradually it?s all or nothing and happened without warning. As I said it was quite scary, you would almost think you had missed the brake pedal, it just goes straight to the floor.

The last time I blamed the silicon brake fluid mainly because of all the tiny black particles which came out when I drained the old fluid out, which I assumed to be bits of rubber seal.
Maybe it was a faulty seal and the same thing would have happened with any type of brake fluid. I don?t know, but I?m not going to risk it.

Alan.

[alaric]

I totally agree with you Alan. It's the sudden failure and complete lack of pressure in the fluid that concerned me.

My old M100 elan had awful brakes - I shot right onto a roundabout once. The guy in the car that stopped to avoid me just waved me through - it was as if he knew! Actually he probably saw the terror on my face and the whites of my knuckles.

All the best.

Sean.