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MG MGA - Front Disc Brake Calipers

Ok I have the caliper off the car.

Now to the rebuild.

1) is it necessary to halve the caliper to do a rebuild

2) how the hell do you get the pistons out

3) the piston end where it rides on the brake pad is not flat, it appears to have a section that is lower than the other. Does that mean I gotta replace the piston?

Thanks as always
Tysen

Tysen ,

You must separate the caliper in half to do proper rebuilt .It is hard to have the pistons off but not impossible . I had remove mine from caliper by putting some air througt one hole and blocking the other. Just be careful with putting air to avoid injuries when the piston come out. You can place a towel around the caliper to protect you and prevent piston going everywhere.

Remove rust , clean with alcool and install your first rubber in the lower groove in caliper . Lubricate with rubber grease to help with piston insertion .

If you have original piston on your caliper, you can easely replace them with MGB's piston. It will fit very nice inside the caliper but you have to remove the locating pins. The MGB pistons have to be installed with the concave section facing outside of theirs locations ( flat side down ).

Now then you can put the dust seal and the dust ring with the piston already in place .

This is what i do 2 times in 25 years . I use MGB pistons in MGA caliper since 1980 . The originals pistons are very expensive but you can have MGB ones for a fraction of that price . It work very fine with me .

Your's

Jules .
MGA MkII 62

Jules

Hy Tysen
Jules is right. If you did not disconect the brake line, you can use the brake pedal to force at least one out. Do not worry about brake fluid you will have to bleed the system anyway. See to all your bleeder nipples, since you are under so you can bleed the whole system.
Martin
Martin

No offense to Jules but it has always been my understanding that you want to avoid splitting the caliper at all cost as they are prone to leak afterward. I rebuilt mine as a unit with no problem. Be very careful if you use compressed air to remove stuck pistons. They can pop out with great force. Some find a way to pump grease into the caliper instead of air. The new pistons must be installed with the lower section you refer to oriented properly. This info is in the factory workshop manual and may come with the rebuild kit.
J.H. Hall

Splitting the caliper requires a new seal that may not come in the kit. The seal is a flat piece of rubber stamped like an "o" ring. I just rebuilt the calipers on my 58 (MGB brakes) and the O ring was not in the kits. Wrap the caliper in a rag and use air to blow it out. I definately would split the caliper, the seal between gets hard with age and should be replaced. The seal surface of the pistons is the only critical surface it must be perfect. If in doubt replace pistons.
R J Brown

I too rebuilt my calipers by splitting them. Also I fitted MGB pistons by removing the centre pin. Just a note about orientation. Both the MGA and MGB pistons have an area on the outer edge that is low, but the MGA workshop manual shows this in a different position to the MGB workshop manual? It would be interesting if someone could explain why this is.
Bob (robert) I get up real early somedays

I disagree with the people that say to split the caliper.

It is certainly not necessary to do so in order to rebuild the brakes, and I have NEVER seen a caliper that leaked from a bridge seal hardening from age.

OTOH, I have seen quite a few people come to grief when they split the calipers and had trouble getting it all sealed up again.

Go with the KISS principal!
Bill Spohn

Tysen,
You can split the caliper if you want, but it's not necessary. I've done it both ways. When I was young (and perhaps less knowing) I split them. If you do this, use new bolts and locking tabs from Todd Clark. He also sells a new seal I belive. However, I support Bill's contention that those seals will not leatk. Also, properly torqued, the bolts should not be reused because they stretch ever so slightly when tighened.
Now older, (and perhaps wiser) I rebuild calipers without splitting. My recommendation is to get a good master cylinder and use it to apply hydraulic pressure. Air pressure is hazardous. You can use a grease gun, but it makes a BIG mess and it's hard to get all the grease out of the calipers. Do one piston at a time. You may want to modify a 6 in. C clamp to use as a device to hold one piston in place and to press the new piston into the bore. Grinding some material off the C clamp body allows for the necessary clearance. There are a number of good information sources about how this is done without splitting the calipers. One is Mike Ash's "Tech Sessions from MGA!" book.
G T Foster

Bill and GT- In his other thread he has stated that he has broken off a bleeder in the caliper. Others have advised him use an easy out and or heat to remove it. Would any one of you want to take a chance of not spliting the caliper after doing this? I have split mine,and used Todd Clarke's hardware, but I suggest he send his to a pro
gary starr

Bob

You said... "Just a note about orientation. Both the MGA and MGB pistons have an area on the outer edge that is low.... It would be interesting if someone could explain why this is."

Not so long ago I had my calipers reconditioned by Moss, looked a good job. However the pads kept squeaking even after fitting shims. Remembering the drawing in the manual about this orientation, I checked my new pistons. Guess what upside down/180 deg out. Turned them round - squeaks gone!

Pete
Pete Tipping



Peter,

By strange coincidence the reason that cut out exists is to prevent brake noise.

Or that's what the family MG mechanic just told me.

TM
Tysen

Hi, Tysen - we had a big discussion about the cutout in the pistons over on the midget board. The cutout points toward the approaching surface of the disk rotor (or actually about 20 degrees askew of that).

Just as you have a leading edge on a drum brake shoe, you have a leading edge on a disk brake pad. The cutout shifts the pressure on the pad more towards the rear, helping to prevent chattering and squeal (as Pete mentioned), and causes the pad to wear more evenly.

Best of luck - - Alec
Alec Darnall

This thread was discussed between 04/11/2005 and 09/11/2005

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