Brake bleeding advice

[RotorChris]

Just had the calipers rebuilt, and fitted braided lines / new pads & discs. All good except we can't get the brake pedal to stay firm. We've been bleeding the system for about 2 hours and have put almost 2 litres of fluid through it. We're not seeing any more air come out or any leaks from the joints we can see.

The pedal is soft on the initial push, then firm and solid on the next push. If you leave it a few seconds it goes back to being soft again.

The fluid was pretty much empty once we'd got everything off, and the manual says the reservoir is a combined clutch / brake fluid reservoir. Am I missing something - are there any bleed points other than on the calipers, or somewhere that's known to airlock?

Chris.

 

[jack.am]

Clutch line? Clutch and brake all share the same fluid.

Are you using speed bleeders and a vac pump?

 

[Paulm]

I used a sealey pressure bleeder. Had to pump the pedal a fee times to get it started, but braked bled fine.

 

[RotorChris]

Sadly manual bleeding, the speed bleeder caps didn't fit the reservoir.

Is there a valve between the brake and clutch systems to prevent air in one getting into the other?

 

[Mid Night FD]

I have just manually bled my system from dry and had no issues. Open nipple, down on pedal, close nipple, up on pedal and repeat as usual. I then pump the pedal until as firm as it will get and open the nipple until pedal down and close off. With a friend's help of course. I have always wondered about getting airlock in the ABS module but havent had such issue (mine is an early '93 car if it matters). Im guessing you have no slight weeps or leaks from any of the lines and if new the brake nipples are seated well?

Have you checked the master cylinder itself hasnt stated leaking in the footwell or internally? Working on old cars that sit around and such, when you bleed the brakes the seal in the cylinder will go further than its normal operating distance and can sometimes stick, get debris caught on the seal or even flip the seal if it picks up crap/sludge that may sit in there when bleeding brakes, just a thought

I would try a pressure bleeder as others have mentioned and try from there.

 

[Rhino]

No valve, just a take off from the reservoir to clutch master cylinder, it’s not linked on the pressure side.

It does sound like a leak or weep somewhere as it’ll hold pressure for a bit. Otherwise, as previously suggested, it would be worth looking at the master cylinder, the seals could be degraded or there’s some crud inside there.

Some cars have the brake master cylinder angled slightly upwards and that can sometimes trap air at the very end, hence when installing a new master cylinder it recommended to bleed them before installing on the car. Although I think the FD m/c is reasonably level, also it doesn’t sound like that as it holds pressure for a bit.