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MG MGA - Clutch Seals

My clutch master cylinder seals have given up the ghost for the second time in 20 years. The cylinder is still like new, but the seals have worn out.

Last time I did the job (about ten years ago) I had trouble finding seals that fit the original lockheed MC without causing the piston to bind solid in the bore.

Who is supplying seals that fit?

Hoping to be back on the road asap, so would appreciate all answers asap.

dominic clancy

Been there, lots of times. Stuck when new, yes. "Stuck Solid" may be a bit misleading. When repacking in situ this can be a problem; on the work bench much easier to deal with. See here:

I guess you're not complaining about ten year life of the seals. That may be about par when using DOT 3 or DOT 4 fluid. With DOT 5 fluid the seals might last forever (but you still have to bleed/flush the system occasionally). On a couple of occasions I have had the opportunity to remove 10 to 12 year old seals from a system using exclusively DOT 5 fluid, and in each case the seals looked virtually as new, clean and smooth, flexible, and the raised molding numbers still perfectly legible. Silicone oil seems to be a natural preservative for all sorts of elastomer materials.
Barney Gaylord

I've got my last two sets from SF. They were fine. The only time I've encountered binding is when the seals were not properly seated on the pistons. I've seen (have) two styles of pistons. One on the seals go over a flange to hold them in place on the other the seals fit between two flanges. The first type is much tougher to get the seals to sit properly.
G T Foster

Well I bit the bullet and bought from my local supplier, and 15 hours later received a kit that not only fit perfectly, but also contained everything (not like the last Moss kit which was missing the rubber seal to fit under the spring on the clutch master).

I have taken the MC out of the car to do the seals this time (I remembered it was a real pain doing it in the car last time). The old seals were still in good structural shape, just worn out. They were not swollen or rotten or soft. The cylinders and pistons are in great shape too (after cleaning out the gunge of two generations of seals), and after rinsing the cylinder through in my cleaner, rinsing with acetone and then blowing through with an air line, it is also very clear that there is no rust on the MC or pistons at all. This MC has 20 years of constant use, including 10 years of daily driver status, and apart from needing new seals is like new. That's DOT 5 / Silicon fluid for you.

Barney is right, I am not complaining about the clutch seals - I think that 10 years and 60k miles is very acceptable.
dominic clancy

My entire hydraulic system made it 12 years and 129,000 miles on DOT 5 fluid the first time around after first restoration (flushing fluid every 2 years). I was changing all seals and hoses as a matter of preventive maintenance, not because anything leaked. All seals looked like new except for a little edge wear. If I knew in advance it was in that good condition I wouldn't have been rebuilding it.

After the rebuild I ran DOT 4 fluid for a few years, expecting another long term test with not much problems. Alas, I was finding brackish color and bits of rubber in the fluid every 6 months until the master cylinder started to leak. I wouldn't blame it on the DOT 4 fluid, more likely bad rubber seals in the master cylinder kit from the late 90's. Then I redid the entire system again (all seals and hoses), switching back to DOT 5 fluid in 2001. If there was any possibility of bad rubber bits in the rebuild kits, I figure they had better chance of survival in DOT 5 fluid.

It has been 7 years and 57,000 miles since then, always clean fluid, and I don't expect any hydraulic problems for at least another 5 years (or maybe a lot longer). If it doesn't leak I'm not touching it again. Can't wait to see how long it might last this time.
Barney Gaylord

> Can't wait to see how long it might last this time.

That last line made me smile Barney, since waiting is exactly what you do have to do if you want to see how long it lasts.
Andy Bounsall

OK, I have to add my additonal TCW to this thread. I do not believe that the fluid type has anything to do with seal failure under normal conditions. Seals are not lubricated by the fluid. By their very definition, seals prevent fluid from leaking past. The seals slide against the cylinder bores. The cylinder surface finish (condition) and usage is what determines seal wear. As long as the fluid does not attack the seal, causing it to swell or soften it, the fluid type should have no effect upon seal life. As far as I know, most brake parts are designed to be used with DOT3 not DOT5. Most OEMs use DOT3. Very few systems are designed to be used with silicon. Race cars don't use DOT5 because you can't get the same pedal "feel". I've used DOT3 in my cars (all of them) since 1964 and never had problems.


Hey, the editing feature does work!
G T Foster

I have had to flush back into the master cylinder to remove air from the firewall side of the lines after connecting the rebuilt cylinder, especially the clutch. Is this common or is there something I'm missing?
Russ Carnes

Yes, the clutch is especially hard to bleed. The clutch side doesn't have a valve in it like the brake side does, so if you try to bleed using just the pedal it has to be a slow two person operation. I like using the Eezi Bleed which pressurizes the master, and some people like the vacuum bleeders.
Jeff Schultz

The vacuum bleeder (MityVac) I have is only any use for emptying the master cylinder before doing work on it. Easily the worst value for money of any tool I have ever bought (is that a cue for a thread??) as a cheap syringe from the local pharmacy does the job just as well.

To bleed the clutch this time I just connected the Eezibleed and undid the bleed nipple on the slave. The air shot straight through in seconds. No helper needed.

What really stood out was that the clutch adjustment on the pushrod is critical. The clutch was still not working right until I adjusted the pushrod again so that there is a minimal slop at the pedal, then it works fine - and that's only a matter of a half turn on the pushrod.
dominic clancy

It looks like it may be time for DOT 5 for my A.
Good point about the pushrods, I haven't adjusted them in years! I'll check it out. Thanks!
Russ Carnes

This thread was discussed between 30/08/2009 and 06/09/2009

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