Brakes: 140: Bleeding problem!

[Audrey Old]

After fitting a new master cylinder, overhauled rear brake valves and calipers, new flexibles and new copper brake pipes plus fittings to our '68 car, I still can't get any resistance on the brake pedal after repeated bleeding.

Although we get plenty of fluid out of the nipples when using a pressure bleeding device in the specified order, still nothing at the pedal. The actuating rod from the pedal through the servo works fine, the cylinder ditto and there is no obvious leakage, so I am wondering if the pipes should be double-flared (if you follow) rather than the single flare we got when using the first tool. Could air be getting in this way, without fluid leakage? No book seems to say.

Also, Haynes says take the nylon spindle brake-fail thing out of the 6-way block near the master cylinder, but should this be replaced before testing after bleeding (although no fluid leaks out)? Should we use higher pressure than the spare tyre, to force maybe an obstinate air bubble out?

I remember years ago that the Amazon needed different pipe fittings to those normally supplied by a factors, which didn't give enough thread to stop leakage: could the same reasons apply to the 140 range?

Any help will be gratefully received for continued work tomorrow.

[Snowman]

I've done this loads of times to my 140 and it does seem to take an age but I get there in the end. If the pipes are all tight, air shouldn't be getting in and assume the fluid level is always kept up in the cylinder when doing it. Leave the brake light switch out until all done.

There is a specific order listed in the book to do it and I do it manually rather than with pressure and always allow over a litre of fluid to do it properly. Even if a seal had gone, you should see excess leaking somewhere.

Good luck

[cassell]

Just one observation, the nylon/brass plunger in the terminal block is not just a switch, it centralises the balance shuttle valve between the dual-circuit systems and I've always had it in place (centred) when bleeding the brakes on my ES which has the same layout.

I'm not an expert, but with it removed during bleeding will one circuit not get full fluid or pressure?

Regards,

Paul

[Snowman]

Paul, assuming the ES system is the same as the 140, the nylon rod is a sensor designed to pick up a problem in the circuit. If one circuit goes, the rod moves and activates the warning light. If you bleed with it in place, it will be pulled around hence why the book says leave it out until all done.

I've left it in by accident once and having done the job, the brake warning light stayed on....doh!

[B20F]

I've left it in by accident once and having done the job, the brake warning light stayed on....doh!

That also means only one braking circuit will be working. The other circuit doesn't get any pressure as it is blocked by the valve. The sensor pin prevents the valve to come back in the center position as it should be to get pressure on both circuits. That is why you MUST remove the sensor before bleeding and put back after the bleeding is done. When removed while bleeding the valve can move freely to bleed both circuits.
Sometimes it is impossible to get an airbubble out of the rearbrake pressure regulator. In that case put the back of the car a little bit higher than the front, say about 10". Than bleed, if that doesn't do the trick bleed with engine running to get the servo working.
And my ES has double flaring on the brakepipes, not sure about the 140 though.

[Audrey Old]

Thanks for all your help so far, especially B20F for confirming our thoughts re that nylon plunger. It won't go back until bleeding is complete.

Today we decided to redo all the copper brake pipe ends using the flaring tool that makes double-flares, and I must say they look very similar to those on the old pipes, so assume this to be the proper way. If time available will refit tomorrow or Friday, cross all our fingers and toes and try to bleed them again. I note you advising possible air bubbles in those valves underneath, so will be especially thorough on the rear brakes AND will bleed in the order in the books!

Will send progress report when/if successful.

[jrobkirby]

I am having the same problem. I have replace the master cylender, the calipers and pads. The system will not bleed, even with a power bleeder.
I pump it up with the brake pedal, step out of the car then try it again and straight to the floor.
I took out the warning valve in the 6 branch union before bleeding and it seems to be leaking fluid. Should it be wet ?
Any advice would be great.
Rob