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MG MGB Technical - Front Calliper sticking on

I have a late rubber bumper GT with dual circuit brakes.

When driving the front nearside (passenger side in Britain) brake calliper gets progresssively tighter, each time I apply the brakes.

If I stop the car and release the pressure in the brake lines by releasing fluid at the master cylinder unions, works fine until I apply the brakes a few more times again.

Can't make up my mind if it's the calliper that's sticking, or the master cylinder that's causing the problem.

Needless to say she's off the road until weekend at the earliest, until I can get a betterlook.

Any opinions will be greatfully received

Steve.
Steven Williams

Funnily enough, I came on to the BBS today with the intention of raising a similar story.

Only difference is I've not looked into it at all. My car is a '66 Roadster with std brakes. My front-offside caliper is sticking (and heating the axle up). I'm going to change the pads and fluid at the weekend, but was wondering what else to look at.

Chris
Chris Byham

It has been known that a bit of rubber brake hose (internal) can break free and get caught somewhere
in the system (at the m/c feed port, caliper hose port, or one of the hose-tubing joints) and act as a
one-way valve. Try a complete flush-out and re-bleed of the front hydraulics.
Daniel Wong

Chris. For your problem, Daniel's suggestion of a bad flex hose is the first place to look. The second is a caliper rebuild due to a sticking piston. You should have the single reservoir master cylinder and, thus, a master cylinder related problem should be seen at both front calipers.

Steven. Your problem is more complex. I believe the UK spec cars used the same integral servo and master cylinders that the US spec cars did. Normally, the fact that the right caliper is working properly and the left one is bad would point to a problem in the left caliper, the rubber flex hose or the hard line going from the MC to the flex hose. However, since you state you can loosen the line going to the left hand caliper and cause it to release, this looks like the bit of rubber or grit that Daniel mentions, this time at the line to master cylinder junction area. This assumes that the right caliper is actually functioning properly. If it is not, this could indicate the piston in the MC is not retracting fully enough to allow pressure to be released in the entire front system, but you do not notice a problem in the non-functioning right hand caliper. I think I would put the front end up on jack stands, then verify that both front calipers are working correctly. If so, the common area is the master cylinder since there is a seperate line to both wheels. Normally, when the flex line fails internally, the check is to loosen the bleed nipple which releases the pressure. When you can release the pressure by loosening the line going to the MC, the MC is the most likely suspect. Les
Les Bengtson

Chris

I thought the problem was in the Master Cylinder, so last weekend I re-sealed a spare Cylinder I had. but it still gives the same problem. It's not that it just sticks it just keeps applyiing more and more pressure to that particular wheel, as if there's a none return valve in the line.

Daniel

I can see your point regarding there being some obstruction in the line but I've pumped out the fluid on that side (direct from the line). The only other reason I could think of was the wall of the flexible pipe had collapsed and causing an obstruction, but they are Googridge S/Steel and have only been on the car about 2 years.

Thanks for prompt response.


Steve

Steven Williams

Les

You must have posted just as I was.

Thanks for your comments. It does appear that it's only the passenger calliper that sticks. Had the car on stands at the weekend and noticed that the right caliper retracts when pressure is removed from the pedal.

May have a look tonight and try draining all the fluid from the right side and check the caliper as well

Steve
Steven Williams

Sorry that should have been left side

Steve
Steven Williams

The stainless steel on the goodridge hoses is only a braid around a rubber hose. This gives you better feel in braking due to the rubber hose not being able to expand and also protects the outside of the rubber hose from nicks and tears etc.

It is entirely possible that the rubber has failed inside the hose, *flapping* into the pipe on braking pressures and not being able to retract upon release.

There lies the problem with stainless steel braided hoses, you cannot tell the condition of the rubber underneath! You would normally change the rubber hoses on a car roughly every 2 years or so, therefore it stands to reason that you should still do this to stainless hoses for piece of mind.

My goodridge hoses came with a lifetime warranty card, so i would think yours did too. If you take off the pipe and on inspection find the rubber pipe is faulty, they should replace it. If you kept the old rubber pipes when fitted (mine were relatively new when i changed so i did), you could always fit one and check the problem this way....

Regards ~PHIL
Phil

I see I've managed to make this thread really confusing to read!!

Les / Daniel: Yesterday was the first time I've had her out for six weeks due to me not finding time to replace the front dampers until last Saturday. I had new calipers put on about two years ago, so would be surprised if they were duff. I'm going to try new pads and fluid this weekend, and hopefully this will cure things.

Chris
Chris Byham

Chris

I had a new caliper fail in 6 months..!

~PHIL
Phil

To test for a collapsed brake hose.... apply brakes, if the cylinder/caliper is locked, open the bleed screw. If the caliper releases, then the problem is not mechanical ie. pads, pistons, but hydraulic. If it happens to only one circuit, then 99% of the time it is the hose having collapsed. Sorry for the brevity. Peter C
Peter Caldwell

OK, if you do not suspect the hose(s), then I'd look at the caliper itself.

I've only had a caliper lock-up on me once - just days after a total system rebuild.

The cure was found in the BBS archives:

Install an old set of pads (the thinner, the better) - then pump the system to drive pistons out
as far as they'll go (without expelling them) - and then manually push them all the way back in.
Be sure to wipe the piston walls clean before pushing them back into the caliper. Do this several
times. This helps to seat the seals squarely. Install the working pads and road test.

It worked, and I haven't had another lock-up in over 3 years.
Daniel Wong

Well

I looked at the system last night and passed fluid through the flexible hose in both directions without any problem, so turned my attention to the caliper.

The caliper, Disc, suspension etc. was all replaced about 2 years ago. I found the seals on left hand side completely had it. Plating on first 4mm of each piston was badly pitted. So, as I had a spare seal kit and pistons I decided to overhaul the caliper. Finished it last night about 10:00pm, didn't have chance to bleed and test though, leave that for tonight. Report back tomorrow.

Steve
Steven Williams

Steven from your first post"releasing fluid at the master cylinder"tells me and, if my reading of his post is correct, also tells Les that the problem is "above" where you break it to release pressure.
Ask yourself:If the flex hose/caliper is cloged,keeping the caliper pressurized, how would"releasing fluid at the master cylinder" unclog it?-Ric
Ric

Didn't have much spare time last night so not done anymore on the brakes.


Yes Ric, I still think the problem is in the master cylinder, but when I saw the state of the piston and seals on the caliper I decided that should be done anyway. I also checked the flexible hose at the same time and found no blockage.

Steve
Steven Williams

While I don't think this would affect only one caliper, it may amplify another problem. If the brake light switch is "screwed" in too far, it can prevent the master cylinder from releasing its pressure. From your first post, it seems that the MC is holding (at least some) pressure which may seem like one caliper is sticking.

Wayne
Wayne Pearson

Wayne

Think you may have hit the nail on the head, though I can't see why either. When I stripped the MC down at the weekend the shuttle valve was released.

Now checked the right caliper and the piston on that is pitted at the end, not as bad as LH but decided to replace that as well.

Also found one rear cylinder with slight leak. So, decided to do complete overhaul of brakes and use Silicone fluid, as I will have, by then, have replaced every seal in the system.

Also found slight leak on Clutch MS, which has damaged my nice new paitwork.

Let you now when everythings working.

Steve
Steven Williams

Due to illness, I never even looked at my MG this weekend. Maybe next week!!
Chris Byham

This thread was discussed between 23/04/2003 and 28/04/2003

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