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MG MG Y Type - Brake bleeding YB

I have overhauled my brakes and master cylinder..the reason being I was unable to bleed the rear brakes..no fluid or little fluid coming out of the bleed nipples. Brake nipples are free and have no blockage ....checked
the master cylinder and it's fine too. Front brakes bleed fine. Any ideas what the problem might be. Rear brake pipes and hose look ok. Handbrake works fine too.
D MULLEN

Is the brake line pipe along the chassis been damaged (squashed)? Have you removed the brake hoses from the brake cylinders to check if fluid is flowing from the pipes / hoses?
Stuart
Stuart Duncan

Hi, How old is flexible brake hose ,the hose can look OK on the outside but be breaking down on the inside with old age. BOB ( 40 odd years in the motor trade) PS... STAY SAFE....
R Wood

Dave

Check the free play on the brake pedal. If there is too much free play you will lose stroke on the pedal. If there is insufficient the brake pedal will be partially depressed and the brakes will be bound on slightly wearing out your shoes and heating up your brake fluid (DOT4 loses efficiency when heated and fails when boiled I understand).

Check the Workshop Manual as I believe this covers the pedal free play and how to compensate for it using the adjuster nuts on the master cylinder piston. I do not have access to my YB WS manual on CD as they are at home and I am at work, but I am pretty confident that should help you there.

Paul
Paul Barrow

Most likely you will find that the flex hose to the rear differential has degraded inside. This usually presents itself as swollen rubber that effecively swells the line closed.

These rubber flex lines only have a lifespan of 8-10 years before they degrade. With my experience on re-doing the brake system on my YT, I found the rear flex line required replacement. After replacement, all was good.

Undo the brake pipe fitting at the rear flex and pump some brake fluid through.

... CR
CR Tyrell

Dave,
I concur with CR. I have experienced swollew inner linings on brake flex hoses several times.
Please consider using DOT 5,i.e.,slicone, brake fluid and purchase stainless steel flex armored small bore teflon hoses.
I have done this to all my MG's and have not had ANY problems for many years.
Stay safe. Stay well. STAY HOME.
Rocky
Rodney C "Rocky" von Dullen

Yes try disconnecting the pipe at both ends and seeing if you can blow compressed air in and out?

Paul
Paul Barrow

Thanks everyone...it was indeed the rear brake hose....what a nightmare undoing it too... no amount of force would undo the locknut on the chassis bracket..had to resort to cutting the hose off and using a blow lamp to hear the nut up.. worked though. Yes these hoses look ok from outside but can be blocked internally.




D MULLEN

A variation on this theme.
Attempted first bleed today after entire braking system replaced (but 4 years ago, and sitting quietly since then). So new lines, flex hoses, wheel cylinders and master cylinder. New silicone dot 5 into m/cylinder. Clear tube over back of chair, then down into jar with fluid in it. Followed my usual preference of manual pumping of brake pedal ( body is off chassis), starting at rear nearside bleed nipple. Nothing. Collapsed with near exhaustion, no sign of fluid after 5 minutes. Tried other corners, still no luck.
Tried a shiny new suction device, attached to air compressor. Suction at the attachment is not actually very strong, but it did produce very aerated fluid if I stuck at it for minutes on end. Not really fluid, just bubbles.
I should add that my local mechanic mate disassembled the m/cylinder yesterday, made sure it pumped and sucked (returned), and I put it back in on the basis that it appears to be ok.
SO - back to the drawing board, but I've "walked away" from it for today. Very frustrating.
Any suggestions extremely welcome.
John.
J P Hall

Crack the fitting on the master cylinder & bleed slowly from there, working your way from the nearest to the furtherest (is that a word ?).

It is very easy to get bubbles in Silicone fluid, so don't expect a hard pedal without bleeding 2 or 3 times. You need to work very slowly with silicone - you don't want to trap a bubble in a high point of the lines/hoses.

Some people suggest that gravity is the safest way to bleed using silicone, but with the master cylinder under the floor it can be a slow process.

Silicone fluid can be a pain, but it does not eat paint, so worth the effort.

Safety Fast

Tony Slattery
The Classic Workshop
A L SLATTERY

Good comments thanks Tony.
It turns out the fault was with my shiny new air-operated suction device! A mate turned up with a similar device; it had a better sucking power, and after 2 cycles we had good fluid through all 4 bleeders, but still with a but of air. We switched to the good old 2-person manual operation, and after another 3 cycles we had full braking power and all adjusters adjusted, if you see what I mean.
I agree with Tony, the initial setup took longer than usual, but the end result is good, and although much fluid was spilt, no damage to paintwork.
It will be interesting to see how, with my wife's spirited driving, ("leadfoot"), the silicone fluid performs.
John.
J P Hall

I'm not siicone fluid fan --no real reason--i just don't like it
If you want a good high temp fluid there are plenty about without going silicone

Interested to know what influenced your choice to go that way---

willy
William Revit

Hi All,
If Silicone bake fluid is gods gift to cars
as we ae led to believe, why to the race men still use Dot4 brake fluid !!? I think there is a lot of myths about brake care possibly started by the manufactors, change the fluid etc etc I have had around 12 or so cars in my life and never once changed the fluid other than with brake bleeding.
master cyl rubbers change etc the old sierra now 32years old still has the factory filled system less a little when i rerubbered the rear wheel cyls it all ways sails through the mots
John YB0362
JC Jebb

Ha! - I was afraid someone would ask me that.
I am a 68-year-old traditionalist; my boarding school memories (East Africa, UK, Australia) are of the smells and sounds of British cars of the 60s - Spitfires, Alpines, earlier Alvii, and don't even mention the Jensens, Jags and even the Scimitar.
So I am truly a Reluctant Bride. Until the last minute I was still going to "go with what I know" and pour in the good old dot4. But then I do have room for sensible upgrades - the BGT has a Supra gearbox; the TD has ... well, indicators. The YA has been a labour of love on and off for 20-odd years, is basically stock standard, and is at the "put everything back on" stage. So I figured if I was going to try silicone fluid on any car, it might as well be when all rubbers etc are new.
Tony S and others have spoken of the virtues, including no damage to paintwork. Obviously that is more relevant when the bits are on the firewall, but still I listened and am prepared to give it a go. I believe it will be wise to flush (and so remove any condensation) after a year or two - something I have never done with dot 4; and there might be a slighly more spongy brake pedal, although at the moment, untested on the road, it feels very firm.
Willy and John, I hear you brothers - but "nothing ventured, nothing gained".
Thanks for your interest. If you like, I'll post any findings down the track.
Yours,
John.
J P Hall

This thread was discussed between 12/04/2020 and 16/02/2022

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