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MG Midget and Sprite Technical - Replacing the seals on a combination brake/clutch

Hello Gentlemen

I have a '66 midget MkII with a combination brake/clutch master cylynder. It it leaking, and I'm hoping to get away with just replacing the seals. I really don't want to remove the body from the car, so is it possilbe to replace the seals with the body in situ? Also, any hint and tips would be greatly appreciated. for example, getting the push rods out, flushing the body, etc.

Thanks, Richard
R George


You probably could change everything without removing it but...

It will be easier and better to pull the whole thing out. That way you can check the bores for any pitting and clean them up as necessary.

Getting the push rods out is easy. Pull the cotter pin out of the pin that attaches the rod to the pedal, slide the pin out, remove the rod. Don't change anything on the rods since you'll be putting it all back together just as you took it all out. Remember/mark/photograph everything so that you put the correct push rods, pistons and seals into their original holes since they are of different lengths.

Cleaning the master cylinder is straight forward. Use your favorite cleaner, make sure all of the internal holes aren't blocked and assembly everything using clean brake fluid as a lubricant. Pre-fill the master and install. This will make bleeding a bit easier though I'm sure you're aware of the problems that may arise with this operation.

While you're at it, check the holes in the pedals where the rods attach for roundness, the push rods also and the pins for any wear. Replace/repair and grease as necessary. Good luck and let us know how it went.

Martin Washington

You sure can, Richard. Here's the rough guide for rough mechanics.

Jack the front up. That lets gravity work in your favour, as well as being kinder to your back.

Bleed out the fluid until the upper chamber's empty, and then a bit.

Arrange rags around the body and keep a roll of loo paper handy to catch that corrosive fluid, and pull your pistons.

Have a look at the bottoms of the cylinders, around where the back cup sits at rest (I mean the one nearest the front of the car), and decide whether they need any attention. Bear in mind that pitting tends to fill up with glaze, and if it feels reasonably smooth, it'll last quite a time on new seals.

Make sure the pistons are absolutely clean and rust-free before you put the new cups on, or they might not take up the right profile.

The only thing I have to add to Martin's advice is that, with the body in-situ, you might have to fiddle with the rods to get them out - probably shortening them by using all the adjustment - but they will find their way out somehow. Same with the cotters, which won't want to pass the next-door fork - but you'll get there.

Told you I was rough!


I have the cotter pins out, and one of the connecting rods had been shortened in the past, so the fork fell off it. The other rod is still threaded through its fork, so I guess I will need wind it back in.

If I do remove the body, can I take it out without disturbing the pedal box? The bolt inside the car at the back will need to have a flange modified to allow it to be removed, but is there any other "gotcha" that will stop the body from being removed?

Regards, Richard
R George

There are only 8 or 10 bolts holding the pedal box in (don't remember for sure). For me, it would be easier to remove the whole box than to stand on my head for 20 minutes while turning a nut 1/8 of a turn at a time and have stuff fall into my eyes. Plus it gives you a chance to check if the pedal pivots are OK and you can grease them up a bit while you're at it.

But that's just me.
Martin Washington

I'm with Martin. I have a '65 Sprite (same M/cyls)and it doesn't take all that long to get the pedal box out and once you get it on the bench it will be much easier to see the condition and do any work needed.

b higginson

There are some very cheap new master cylinders on ebay (item 390081803297). I have seen it for as little as 65.
It is a TRW Lucas. Does anyone have any experience of these please?

Graham M V

Graham - it's the 7/8" dia that makes it relatively cheap. And it's the 3/4" ones that are as rare as hens' teeth. I think Richard's car needs a 3/4", and Moss is looking for about 175 (less than it used to be!)

I got an old 3/4" from Alan Anstead, and had it sleeved. Cheaper than a new one, and perhaps better.


Its just that I was speaking to a supplier and the subject of the mc came up. I mentioned I was buying a new one as it was not considerably more than just the rubbers and he told me it would be the Lucas TRW and I should avoid it. So interested to get another opinion.
Graham M V

This thread was discussed between 21/02/2010 and 26/02/2010

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