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MG Midget and Sprite Technical - Hard brake pedal

What I actually mean is that when I haven't used the braked for while (for example after a long motorway run), the brake pedal feels hard and also won't return as usual. I can still lock the wheels if needs be and it will revert to its usual brake pedal feel if I'm braking regularly.
Is this likely to be a problem with the master cylinder? I have a later plastic reservoir type MC.
No loss of fluid either.
frogeye Gary

What brake hoses do you have fitted. An ageing problem perhaps? (hoses, not you)
Guy W

Braided hoses about 6 years old
frogeye Gary

Id say your hoses are okay... the SS braided never wear out, because its a plastic core

It could be the master is sticking inside

But my 1st look would be the brake caliper, if its setting for awhile between runs, it could be the pistons is rusting/sticking into the caliper

The pistons on these calipers or made from simple plain ol mild steel... the stuff. That loves to rust

I had this same issue several years back after washing down the front suspension and letting it sit for a period of time...eventually it rusted closed and wouldnt return to release the disk, without a hammer and rebuilt calipers solved it...

They do make a SS piston... I think peter may carries them

ANOTHER POSSIABLITY....The O-rings in the portioning valve have worn out and are tripping the safty limp mode mechinisme of the portioning valve

But im leaning towards partially rusted piston

Thats my 2 cents
Prop and the Blackhole Midget

The peddle assembly isnt binding up some wear like around the clevis pin is it ?

Prop and the Blackhole Midget

Just an excuse, Gary, to mention that you're ageing!
Guy W

Gary, If it were the calipers then unless they have both deteriorated equally then the car will brake unevenly. I have known braided flexible pipes to play up but it is unusual. is it worth bleeding the system and see if the fluid is expelled promptly when the pedal is pressed. If not then try the master next. When was it last overhauled.?
Bob Beaumont

Mine were like that before I overhauled after the 10 years off the road. The problem was rubber that had deteriorated (I presume the lining of the flexis) which had got into the calipers / in the banjos. Hard to break, brakes worked fine and slow to return.
I removed calipers and cleaned out. Replaced flexis, banjos and unions. Ensured calipers moving OK. General clean up. Reassembled. Blew out all old contaminated fluid.
Brakes now work really well; much better than I ever hoped after becoming used to modern assisted brakes.
Dave Squire

BTW on a 1500 there is a small vent hole in the master cylinder cap that needs to be clear for the brakes to work properly. Is there one that needs checking on yours?
Dave Squire

Prop, the car rarely sits for long between runs as it's used very regularly.
The fluid hasn't been changed for who knows how long, a long time and may brake pads and disks also haven't been changed for ages. having said that' the brakes stop the car very well when needed.
I imagined that it might be rubbers deteriating, but I think that it would be a good time to overhaul the MC and replace disks and pads and fluids while I'm at it.
I sgal report back once it's done but I'll also look out for a vent hole and check that it's not blocked.
Many thanks for the feedback and suggestions.
frogeye Gary

Sounds like a plan gary....I look forward to hearing what the issue is

Prop and the Blackhole Midget

the cap of my replacement plastic see-through MC doesn't have the circular hole in the top, I've always meant to ask about this but keep forgetting

if the fluid hasn't been changed since you can't remember when then give the whole system a bit of a flush out on your existing system and on the new system just in case - brake fluid is cheap so you can afford to be very liberal with its use (crashed cars and people are much more expensive)
Nigel Atkins


Brake fluid is hygroscopic and if it hasn't been changed for a long time, the water it has absorbed can cause rusting of pistons that causes them to stick. That happened to me and cost me new calipers and rear slaves. I'm now much more stringent about changing brake (and clutch) fluid regularly.
Peter B

This thread was discussed between 28/10/2013 and 29/10/2013

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