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MG TD TF 1500 - Master cylinder damage

Don't know if you can see from the attached image but the bore of my master cylinder is pitted. The far end of the damaged area is about an inch from the inner edge of the bevel. This is the only area of damage the rest of the bore is good. My questions are: -

1 The brakes seemed to work fine before I took it apart! Is there any reason to worry about this. Half of the damaged area is covered by the piston and rubber seal.

2 Can I repair it by honing the cylinder. I've never done this before. How many times can you hone the cylinder before it gets too big?

3 The rear adapter at the other end seems to be seized. I'll need to get it off to hone the cylinder but I'm concerned that it'll leak when I put it back together. Moss Europe don't sell the original copper washer any more, they recommend using 2 Triumph TR2 washers. Does anyone know why they'd call for two washers? Is this a potential problem area?

Thanks

AJ


A R Jones

I would not trust the corrosion; it can cause damage the seal, or to leak by. Brakes are obviously not something to repair half way only...

My experience is that a clean-up with a knobby hone is best, but don't expect it to clean up any really deep corrosion - it really just polishes. If it doesn't clean up with a half dozen passes with a knobby hone on a drill (lubricate with brake fluid), have it sleeved in stainless or brass, then rebuild as usual and don't worry about it again. I don't happen to know anyone who does sleeving in the UK; there are two or three in the US. The alternative is to replace with a new M/C - but most of the new ones sold today have internals that are not interchangeable with the older style, which I prefer.

I don't believe you need to remove the adapter to hone; you will be concentrating mostly on the outer end where the piston and seal ride.

Hope this helps.

Tom
t lange

Hi AJ

I have just had a similar problem wih my master cylinder. My car had sat for 2 years before I bought it, the brakes worked, but the hand brake in particular was not good, so I decided to do a complete rebuild. I found that the master cylinder was a Lockheed unit, probably new in the early 1990s. It had a pit in much the same place as yours. I do not think it a good idea to leave such a pit, as it will probably damage the seals. I spent hours trying to hone out the pit using a two arm cylinder hone. I gave up when I had reached 12 thou oversize - by this time the area of the pit had halved, but I figured by the time it had gone completely the cylinder would be too large for the piston to seal! It was not necessary to remove the adaptor from the end for the honing operation.

I have now purchased a replacement master cylinder, an aftermarket one rather than a Lockheed one to keep the cost down.

Have you checked your wheel cylinders? Mine exhibted pitting, but in this case I have managed to remove the pits with light honing and am proposing to reuse them.

Matt
Matt Davis

I have tried rejuvenating pitted master cylinders numerous times, because they dripped out of the pedal box. Honing doesn't restore them, and they still dripped with new seals. They worked fine, but as soon as they got too low on fluid, no brakes. I've installed a remote glass reservoir to keep an eye on the level easier. The best remedy is sleeve it or replace it.

My latest approach was to install a New Old Stock Chevette dual circuit master cylinder and proportioning valve. The mc was $25 including shipping and the valve about $45. It took approx 15 to 20 hours total rework. But it drips, too! My new puppies chewed the seals when the were out though. Last night, I ordered another new Chevette master cylinder off ebay for about $16; that's cheaper than a rebuild kit. Sure hope the seals are the same!
Jim Northrup

After rebuilding mine a few months ago with all new Moss parts I put it on the chasis to test the brakes. I had ignored the advice to "bench bleed" the thing. Guess what? The piston wouldn't budge! Back to the bench for honing and bleeding. Just used a cheap honer for electric drill with some oil. Worked great after that. Was not hard and I'm not an expert. Just hone it until the parts move as you would expect.

Moral - honing is NOT an option when installing new MC parts, at least for me. Nor is bench bleeding. By the way, not sure what "rear adapter" you mean, but my fitting where the rear pipe goes in was not removed and the honing went fine. But you must remove that tiny rubber washer inside at the rear end! The honer will destroy it! It's not easy, but you can get it out.

Here's a picture of what's in that thing should you not have one. I found it "handy".
Ed



efh Haskell

Thanks guys, especially for the picture Ed. As usual I found I didn't take enough pictures when I was taking it apart! I've found someone in the UK who will sleeve it in stainless for 40. Better safe than sorry!

AJ
A R Jones

What I meant was "...honing is not an optional step - it is required...". Just wanted to clarify my English.
Sounds like a good choice AJ. Make sure he (or you) still fills it with fluid and bench bleeds it when sleeving is done...imho.
efh Haskell

Aj - great solution. Be sure the sleeve does not have a sharp edge at the beginning of the bore (some stainless guys chamfer it a bit) because it can tear the seal going in.

Tom.
t lange

Internal corrosion of brake components means water in the brake fluid. Since brake fluid is hygroscopic (absorbs moisture), it should be changed annually in humid climate otherwise every second year. If you don't (apart from corrosion) you can experience rude awakening when your brake fails after a long hill descend with continuous breaking. That happens because the water in the fluid begins boiling locally from the friction heat. Water boils at MUCH lower temperature than brake fluid. The vapor bubbles act like air bubbles in the system. Kiss your rectum good bye in a critical situation...

I don't fool around with reconditioning the master cylinder. It ain't worth it. There is a fork lift brake cylinder from EIS (have written the part number down, but can't find my note book right now)that is a bolt-on replacement for the TD. The only modification required is extending the rod of your brake pedal by about 1/2 inch. To determin the exact length difference, you have to measure it when comparing the new EIS with the original. If anyone wants details, please contact me by e-mail.
I had the EIS cylinder in my TD for the past 15 years without problem. It is much cheaper than the original and very good.

I. M. Fodor

I would suggest you send it out to be sleeved with a Stainless Steel sleeve. I had my MC and all 6 wheel cylinders bored and sleeved with SS. Works outstanding and it will never pit again. Much better solution than a replacement that will just pit again. Surprised no one else has mentioned this?

Also a great time to switch over to Dot 5 fluid.
l rutt

I did suggest stainless sleeving in my original reply to AJ's question, and he notes later on that he has found someone in the UK to do it.

Tom
t lange

This thread was discussed between 24/02/2011 and 27/02/2011

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