Morris Minor Owners Club

I have had endless brake trouble, nearly everything sprang a leak back in October.. replaced all and bled... but the system wouldn't bleed completely.... after the advice of a mechanic I used it occasionally and gingerly to try and work loose the air lock... and it went to what anyone would say is ok, not perfect but useable for the little use... however, this weekend having been spent bleeding throughly has made things worse.... everything was fine until we bled the drivers side front (having followed the correct sequence).
Is there anything that could cause air to get in? (If you can refrain from insulting my intelligence by saying "a leak" or anything similar please) just something that might not come easily to one when thinking about brakes?

cheers folks

Hi,
I take it when bleeding you have been getting your assistant to press the pedal before opening the bleed screw and keeping the pedal down at the floor then closing the screw?
If you have replaced all the cylinders and the M/C and everything is tight then all it can be is air in the system.
Are you getting clean fluid when bleeding?

When I replaced my m/c I bled the system in reverse order first (driver side front,pass side front,pass side rear and drivers rear) then followed the sequence in the manual.

Richard

Some times minor can be hard to bleed. I have had sucess a couple of times with leaving the master cylinder cap off and leaving gentle pressure on the pedal overnight with a block of wood or something similar. Then take for a drive with some hard braking and re bleed if necessary.

yes, bled just as you said... I did worry that there's just some air trapped... the overnight trick might do it... cheers

what are the brakes like,long pedal,spongy? Why do you believe you have air in system,a description of the fault may help.

A trick i was told was not to release the foot brake gently when bleeding the system but to slide your foot off so that it "bangs" back, the idea being that this sucks brake fluid back as quickly possible to the master cylinder and it can "Pull" any air bubles with it.

where about are you? if you are local to me I more than happy to pop over and give a hand.

It really shouldn't be this hard. There must be a leak somewhere. I would suspect the master cylinder.

Check the condition of the seals on the master cylinder.

from a memory long ago of battered fingers and twisted back ,there are two seals in the master cylinder one might be dodgy,bit of a pig to change

Does the rubber bleed tube have a non-return valve in it?
Holding the pedal down is ok but a check valve helps in my experience.

Once we had a Minor in the BMC garage and it was a pig to bleed, the air would not come out whatever we tried. Eventually by using the garage high lift jack and raising the front and rear (not at the same time though) as high as possible we disloged the air and restored the brake pedal. Minors are usually easy to bleed and at the same time give very little trouble when doing so. Yes a good hard push down when the bleed nipple is undone does help (try not to get splashed). Put some brake fluid in a see through container (so you can see any bubbles coming out) and at all times keep the bleed pipe below the surface of the brake fluid in the container so as not to allow air back into the system. The bleed pipe must also be a tight fit over the bleed nipple and do not have the bleed nipple too loose as air can be sucked back into the system past the bleed nipple threads. Tighten the bleed nipple screw before releasing the brake pedal. Regarding damaged seals allowing air into the system - a scored master cylinder bore can allow air to be sucked into the master cylinder past the piston seal when the pedal is released as there is very little line pressure to keep the seal against the cylinder bore. Of course when the pedal is pressed the line pressure builds up which makes the seal do its job. Unless you are very sure of the condition of the master cylinder I would be tempted to remove/examine both bore and seals. Fit new seals (if bore OK) even if they look serviceable. One last thing of which I am sure that you are doing is to keeping the master cylinder topped up when bleeding. It is surprising how quickly the level falls.

I might be worth running the car up ramps ,leaving overnight ,to let the air rise to the top then bleed the higher wheels ?????

master cylinder is alright.. nothing appears to come from it... (checked that as one of the first things). I seem to notice the advice is similar to that of the mechanic who said to leave them - raise the end you're bleeding... I think it is just some trapped air because the pedal is spongy, then closer to the end of the stroke it gets hard (same if you pump) - just as one would expect from there being air... I guess it's just a case of bleeding it out, wherever it is...

Cheers folks!

charlie_morris_minor wrote:A trick i was told was not to release the foot brake gently when bleeding the system but to slide your foot off so that it "bangs" back, the idea being that this sucks brake fluid back as quickly possible to the master cylinder and it can "Pull" any air bubles with it.

where about are you? if you are local to me I more than happy to pop over and give a hand.

thanks for the offer, but aside from being miles away in Shropshire, my hours that I'm free are far from sociable...

If the pedal becomes hard after a few pumps try pumping up the pedal to make it stiff before opening the bleed nipple, that way you will have some pressure behind the air and fluid to force it along and out of the bleed nipple.

that sounds genius... genuinely wouldn't have thought of that... good call!
thanks

if the seals are duff you will not see a leak ,you get a spongy feeling due to the non compression of the fluid

Is there a servo fitted?

A simple check to see if the M/C is leaking is for brake fluid in the chassis leg, under the M/C.

Reading through the thread -it seems to me that the brakes are not adjusted up sufficiently. And be sure to slacken off the hand brake cables before adjusting up the rear brakes - then tighten the cables again to bring the handle to where you like it. I've never had the slightest trouble bleeding Minor brakes - letting gravity do the work while I enjoy a cup of coffee...