brakes - very frustrating day!

[Grumpy21]

all stared by investigating a poor handbrake. cables fully wound up but levers on rear cylinder still free.

Opened up rear drums to find all well but very little dust - drums came off easily, no movement on either rear cylinder, either both rear cylinders are seized or there's a brake fluid blockage. easy check -crack a bleed nipple and see if I can get fluid flowing. Yes I can so its seized cylinders.

Put everything back and order some new rear cylinders. The brakes worked ok even with seized rear cylinders so I thought Id take the car back to the lockup at the bottom of the street while I wait for the parts to arrive. About to leave home - no pedal, straight to the floor, almost zero pressure. Remember all I've done is to bleed maybe 20ml out of one rear cylinder.

Now it goes from bad to worse

I must have bled nearly a litre through the four brakes in correct sequence with the help of a trustee trainee who knows what to do.. I cannot get the air our of the FRONT nearside cylinders. All the other 3 are perfectly fine, nice clean and bubble free. The front nearside is just. bubbles and bubbles and no good pedal. This is using a variety of pedal pushing methods, usual crack the nipple, down, tighten the nipple, up; pump the pedal to get pressure then crack the nipple; hold the pedal firm then crack the nipple. Still just bubbles and bubbles. Absolutely no sign of and leaks even under as much pressure as my assistant can manage for 5 mins, assumption being if there air getting in the there should be signs of fluid getting out. None.

Tea time and I get some new Borg and Beck front cylinders, fitted them in an hour and bled the system - exactly the same, no pedal and loads of bubbles.

whits end now...........

ps MC dry and not leaking, pushes fluid out of all other brakes fine, get the little fountain on releasing the pedal. All unions tight and NO leaks anywhere

[svenedin]

When you bled the fluid out of the nipple at the rear cylinder, was an assistant pushing down on the brake pedal? With a nipple open to bleed fluid the pedal goes to the floor. No air should have got in to the system but the piston in the master cylinder will have traveled much further than it usually does. Sometimes there is a wear lip in the bore of the master cylinder. When the pedal goes to the floor, the piston goes past the wear lip and seals can be torn. I suspect this is what happened. The valiant bleeding efforts were unfortunately a complete waste of time. The solution is a new brake master cylinder.

Stephen

[Grumpy21]

thanks for the reply - that was my thought but then why can I successfully bleed all three other other corners without a trace of air?

[Bill_qaz]

You can be drawing air but not enough pressure in bad side to see leak. Flex hose, link, pipe across cylinders.
If you pushing air out completely on other wheels its unlikely to be master.
Clamp flex to rear and to good front and see can you build pressure to bad one.

[svenedin]

Have you checked the 4-way junction near the radiator? 3 brake line junction and brake switch.

Stephen

[Grumpy21]

No sign of leaks anywhere.

However small update. Clamped all 3 flexis and I’m back with a good pedal so I’m assuming for now the MC is OK?

Waiting for an assistant to make further progress.

[Bill_qaz]

So its definitely that wheel , did you refit original bleed nipple or new with replacement cylinder? If original is it definitely seating on taper. Are you on drums if so have you adjusted the brake before bleeding?
Have you got a syringe so you can push fluid from bleed nipple backwards to either displace trapped air or show a leak.

[Grumpy21]

potentially solved.

assistant pumping the pedal with results as follows;-

all clamped - hard pedal minimal travel

drivers front released - good pedal longer travel

rear released - good pedal minimal travel (rears still seized remember)

passenger front released - pedal to floor doesn't lock brake.

so with just the front passenger unclamped (this was key I think) we slowly and carefully pumped another half litre of DOT 4 until no more bubbles.

now all clamps released and we have a good pedal with decent travel. Ill leave it overnight before I called it solved but I'm quite hopeful now.

The mystery remains, why did bleeding maybe 20ml from the rear cause a problem at the front that required two new cylinders and 1 1/2 litre of fluid to solve?

When I change the rear cylinders I'll clamp the Flexi for sure.