Soft brakes - Am I bleeding them correctly?

[TRTerry]

Our 1963 Moggie Traveller had the servo conversion to improve braking performance. I have just replaced the rear shoes, cylinders and drums and have bled the entire system. But still find excessive travel on the brake pedal, and a soft feeling. I suspect that air is in the master cylinder, but don't know how or if it should need bleeding. Is there a bleed nipple as I cannot see one? The brakes are operating, the rears lock on handbrake, the fronts will stop, but only with excessive pedal travel.

Any other thoughts?

[mogbob]

Is the master cylinder set up original ? i.e. no remote reservoir in the engine bay.
If you have a remote reservoir ,is your Servo higher or lower than the reservoir.It coud be that there is air in the
higher pipework to / from the Servo.
Assuming normal brake fluid being used, put plenty of rag around the Servo union ( outlet leading to the rest of the braking system ),assistant to operate the brakes and just open the joint enough to let air, say half a turn or so with the brake spanner.Re-tighten and check fluid levels and the feel of the pedal again.Worth a go, if only to eliminate.
Bob

[MarkyB]

Try gentle pressure on the pedal, if it will sink all the way to the floor it may be the MC.
Are you getting any air out when you bleed them?
If you are from all of them, the MC is shot.

[Alex'n'Ane]

I agree with 'bleeding' the servo outlet, as if no remote reservoir then this will probably be the high point of the system. Also try bleeding the servo inlet, worked for me when having servo issues.

[Jefftav]

Not trying to tell you how to suck eggs here but I have just a similar issue with my brakes. It is about being systematic and checking your work to make sure new cylinders and shoes are installed correctly and don't leak and that all the joints/bleed nipples are nipped up tight.

Then start bleeding at the rear n/s nipple then rear os and front ns and front oside and as some others have said at the servo if the pedal still isn't firm. There is no nipple to bleed the mcyl. A willing assistant is good to sit in the car and help bleed the brakes so you can concentrate of the brakes. The pedal should come up firm and not sink when holding your foot against the pedal.

I had bother with a barely detectable leak at the BL switch and air that only came out after bleeding uptime times - the joys

[bmcecosse]

Cars with servo should be 'bled' with the engine running.....

[TRTerry]

Hi Chaps,

Thanks for your suggestions. It looks like a combination of new shoes and a little air in the system. Bled and bled again, including at the top of the servo, now much better, better still once shoes bedded in.

Another problem? The engine falters, then stalls on braking. It's not the lights draining on the battery. I can hear a hiss from the servo when the brake pedal is depressed. The hiss is slight on a partially depressed pedal and louder on a fully depressed pedal like a 'sshh' and you can hear the engine note change to lower revs then die. I have never noticed a hiss before, but I don't normally have the bonnet up while pressing the brake pedal, so don't know if this is normal.

Any ideas?

I have also posted this fault separately as well.

[bmcecosse]

Hiss like that does suggest an excessive leak. You do realise the servo doesn't 'increase braking performance' - that can only come from overhauling the existing brakes, or upgrading to larger ones. I see you have done the rears - you may need to do the fronts too.

[TRTerry]

The servo was also at fault. It had a 5cm gash in the diaphragm. Replaced and now the brakes are back to their normal standard.

Thanks to everyone that posted replies.


Terry