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MG Midget and Sprite Technical - Replacing front brake caliper seals

I am renewing the piston seals on a set of front disc brake calipers.

The seal kits come with two rubber seals per piston. One is a simple square edged rubber ring The other has a V shaped groove in the face that contacts the piston so it forms a double lip. But which one goes into the cylinder first, and which goes nearer the exposed end of the piston?
GuyW

The square section seal is the fluid seal. The grooved seal is the dust seal.

It is often difficult to tell, as by the time you have removed the old ones, they don't bear much resemblence to the new ones.
Dave O'Neill 2

Thanks Dave,
That is as they were when removed, outer V shaped, inner square. But I wasn't fully confident that they had been put together correctly. I did wonder if the double lipped one might have ben the fluid seal. So its good to have confirmation

GuyW

Its years since I last did caliper seals and Dave has confirmed what I seem to remember !
There was also a retainer for the dust seal ISTR

Does this help

http://www.northwestautomotivehydraulics.co.uk/LOCKHEED%20CALIPER.SERVO%20APPS..pdf

think type 428 is similar.

I did mine without splitting the caliper - held on piston in with a clamp and used a footpump to blow the other out, replaced seals / piston and then reversed operation for the second side - special red grease came in the kit.

R.
richard b

The link didn't work for me so go to the site, select Lockheed catalogues and then select Lockheed caliper and servo illustrations.

R.
richard b

Agreed Richard. I am not splitting the calipers!

Airline and blocks of wood gets the pistons out without damage, first one, repair, then the second. Just unsure about which was which of the seals
GuyW

I did mine (for the disc conversion) a while back and have forgotten the detail but I remember the dust seal retainers being difficult to re-insert.
Bill Bretherton

Somewhere l have a special tool l made for getting them to go in square. Just need to find it, although it's probably just as quick to make another!
GuyW

Was it a wooden tool, Guy?
Nick and Cherry Scoop

I'm guessing a sharpened hook pick would do the job

Prop
1 Paper

Prop,
Tool for replacing the retainers not getting them out.

Its quite difficult as there is not much room if the calipers are not split.

R.
richard b

The tool was jigged up from two pieces of wide flat bar, connected by 3 threaded setscrews and nuts. One bar goes between the caliper halves and the other across the outside. As you tighten the nuts it squeezes the outer seal retainer gently into its seating. The three bolts, 2 one side of the calper and one on the other allow one to adjust the clamping action so the seal goes in straight. It worked ok last time - about 25 years ago - although I think one really needs more than two hands to get it to work properly.
GuyW

Guy,

Sounds a good tool. I remember the seal retainer being quite thin and easily distorted so you need a tool which covers the entire seal retainer to keep it flat and ease it into place.
David Billington

You can do this with a valve spring compressor and a suitable packer. I cut a disc out of 6mm aluminium with a tank cutter in the pillar drill but I can't remember where I put it.
Greybeard

Softwood solution here. A 12" long piece of 1/2" batten, shaped amidships to cover the retainer, held down by hand on one side, tapped on the other. Cost me 6 retainers in total, to get four in square.
Nick and Cherry Scoop

When I rebuilt my calipers I split them. I know you are not supposed to but I cleaned the surfaces very well and there were no leaks. When I installed the retainers, I used a bearing cup LM67010 to press the retainers in. I don't remember if there is enough room to do this w/o splitting them. The thickness of the cup is about 7/16 inch. Also I froze the retainer and the bearing cup to make it go in easier.
J Bubela

No one mentioned the obvious about those easily-damaged-hard-to-insert piston dust seal retainers.

Why remove them?

The V -notch rubber seal lifts out and a new one can be inserted without ever disturbing the thin metal retaining ring.
GuyW

Having now done this job, I have belatedly found a very good discussion on this on the MGExperience web forum with a few more good tips and advice. Including advice from Peter Cadwell - who suggests leaving those retaining rings in place!

Anyone else replacing brake caliper seals might be interested to read more ideas here:
http://tinyurl.com/y7q6ccgo
GuyW

Do the pistons pass the retainer? I guess lots of people want to have a look at the piston, while they're at it.
Nick and Cherry Scoop

Yes, Nick

Pistons come out - I used compressed air - leaving 2 seals and the outer seal retaining rings in place. The two seals then lift out with a spike, leaving the thin metal retaining ring in place. After cleaning the inside of the cylinder the new seals just push back into their respective grooves.
GuyW

As this is all about brake calipers - I fitted Stainless Steel pistons from mini spares, no more seals needed for a long long time.
Rob Armstrong

Yes - I daresay the pistons couldn't do much braking without passing the retainers. Duh.
Nick and Cherry Scoop

This thread was discussed between 22/11/2017 and 29/11/2017

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