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MG Midget and Sprite Technical - Brakes again

I have a problem with my brakes...

In order to get sufficient "pedal" I have to pump it.
The fluid hasn't gone down and I've inspected the whole system for leaks and it all seems fine.
The rear drums are adjusted correctly and I've had the drums off to check everything is sound.
This evening I tried bleeding them through ans they bled properly but still I need to pump them to get good braking in normal use.

Is it down to a dodgy master cylinder? Seals failing perhaps?
Bob T

I'd think you're right that the MC is leaking internally. I'm planning on rebuilding mine tonight. (for issues with the clutch, but I'll do the brake side too).
My Opel had similar symptoms, weak pedal for a while that got better with a pump or two then finally complete failure. Never a drop of brake fluid anywhere, after MC rebuild it was good as new.
J Van Dyke

Yeh I suppose my first thought is most likely the answer.

It wasn't that long ago I replaced the seals though.

Perhaps a new MC is on the cards although I really dont like the pattern of the new replacement units with plastic reservoir.
Bob T

It sounds to me like it's pulling/pushing a bit of air in/out. I'd try a new master cylinder as a matter of caution.
Rich Amos (1330cc Blaze Red '72)

I've got this too, Bob. Have had ever since my rebuild. Like you, I've checked right through the system, and bled it many times.

I've never touched the master cyl. because it was professionally re-sleeved, assembled and pressure tested.

Do you still get bubbles when you bleed it?
Nick

No bubbles in the reservoir or in the line. It bleeds as though all is sound and air free which is the infuriating thing about it.
I can only think that it is the seals in the MC letting by and retrieving the "lost" fluid as it retracts.
Oh well, a trip to see my buddies at Fishers later today then.
BTW would a failure of a MC have anything to do with the use of silicon fluid?
Bob T

If you get a new MC with plastic reservoir, be very careful when installing it that you don't twist the reservoir on the barrel. It's not really secured properly with only a couple of plastic nozzles intruding into the drum. A bit of twisting action can break the nozzles off.
Tarquin

I have word for word the same problem as you bob. a quick double pump and the brakes are great if not they seem to have a bit of travel before they really bite. I Also rebuilt my MC with new seals only 2000miles ago. I'm thinking uprated MC next.
Nick

testing!
Nick

ooh, i just discovered everyones pics!!! All these years and I didn't know they were there!!

ahehem, sorry, back on topic now!!
Nick

Can I add that before I replace my rear brake cylinders and shoes I had EXACTLY the same problem? My answer was to, uh, replace the rear cylinders and shoes and then bleed it 'the old way'.

Has been normal ever since. My vote is still on whichever component you haven't replace - the MC.
Rich Amos (1330cc Blaze Red '72)

Yep, I did new drums and shoes at the back first Rich - little difference in my case.
Nick

Bob, try pulling the hand brake on a couple of notches and try the brakes. If the pedal improves then you just have too much travel in the rear cylinders. Your check valve in the master cylinder may be bad and allowing the shoe return springs to collapse the cylinders more than necessary. I have about the same problem with my car after I changed the rear axle and got slightly larger bore rear cylinders. I have to keep the rear brakes adjusted real close to maintain a good pedal.
Bill Young

New drums fixed that same problem for me, too.
David "double-pumper" Lieb
David Lieb

This thread was discussed on 03/07/2008

MG Midget and Sprite Technical index

This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.