Bleeding Brakes

[mct_cars]

HI All,

Wondering if anyone has come across this problem before.

I've replaced the master cylinder and am trying to bleed the brakes.

I've started at the rear as I should, however there is air coming out, but no sign of any fluid - probably pressed the brake around 20-30 times. Also, the pedal is not going all the way to the floor when trying this (like there is too much pressure to push it all the way).

As a test, I've bled the front brakes and there was no issue - pedal went right to the floor and lovely clean fluid came out after half a dozen presses.

Am I right in thinking it is airlocked somewhere? I've tried both rears and getting the same issue. Could it be airlocked in the ABS unit? somewhere else? I've opened up the nut on the master cylinder for the rear brakes and there is definitely fluid to this point.

 

[John Jones Jr]

I recall having a similar problem like that but on a BMW. From what I remember, it was the rear brake proportioning valve that was causing the issue. We set the car level on the ground, added some weight in the boot and then bleed the rears. Can't be more specific, it's a good while back but it solved the problem.

 

[flango]

As above car has to be level ie not jacked at any point. Best done on a ramp working from underneath if still no fluid load up the rear we used to have one in drivers seat on the pedal the other person in the middle of the rear seat

 

[Druk]

Two other points. It's good practice to start the bleed with the brake furthest from the pedal. Logic would say that was the NSR...however, because of the route the pipes take it is actually the OSR which is the furthest and that should be done first followed by the NSR. Also. NB that the portion of the reservoir on 107's dedicated to the rear brakes is small in comparison to the front and is filled by fluid spilling over the cill divider in the tank from the front half. When bleeding the rear close attention has to be paid to the fluid level as it is easy to re-introduce air to the circuit by dint of the fluid quickly running low.

 

[mct_cars]

I'll try the above thanks. I think it might be air locked from the reservoir though as there is no fluid getting into the chamber when the reservoir is in place. Take it off and pour into the chamber and it goes in no problem. As soon as the reservoir is in place it empties. As mentioned, fronts are fine.

I'm going to try a pressure bleeder next to try and force some fluid through..... we've been using the two person method so far which is a lot slower, but also the pedal won't go to the bottom as the front cylinder is working well, so guess the rear piston isn't getting a full stroke at each press!

Thanks for the tip DRuk, I had started at the OSR as figured this was the furthest away, although as they both use the same pipe to the rear would think there's very little in it.

 

[Druk]

Thanks for the tip DRuk, I had started at the OSR as figured this was the furthest away, although as they both use the same pipe to the rear would think there's very little in it.

Correct, although the union that splits the pipe left and right is across to the NS which makes the OS further there's not much in it. Might as well do it right though

 

[mct_cars]

Just to finish this off. Lowered the car, no luck. Basically not enough pressure to move the fluid through the lines with the pedal.

Lent a pressure bleeder and turned into a two second job. Or at least it did when I worked out you must have fluid in the pressure bleeder or it bypasses the fluid reservoir and pushes air through the pipes. #dumbass

Have bled them once tonight, intend to leave it a couple of days and do it again so any trapped air has a chance to accumulate. Nice clean fluid!

 

[Westbarn1]

I use a Mityvac, which basically sucks the fluid through.

 

[nb_racing]

Glad you got it sorted.

There's always the motorbike technique:
Due to the calipers being so much lower than the master cyls, when dry you can back-fill with a syringe through the bleed nipple up to the reservoir.