Brake troubleshooting

Hello all,

Trying to chase down some braking issues ahead of the MOT.

When desires the pedal, I get a slight initial braking force (no pedal resistance) that dissipates, with the pedal going to the floor.

If I push hard once it is on the floor it will brake properly, but with little movement of the actual pedal.

I’ve bled the brakes & adjusted the rear drum brakes (1988 110), and installed a new master cylinder.

The weird thing is, even after a full bleed, the pedal still goes to the floor on the first go (albeit with slightly sharper braking force once on the floor). I can ‘pump’ the pedal quickly which gives a nice firm pedal and shortens the travel.

Does anyone have any ideas? Thanks!

My first thought was that you were losing fluid past the master cylinder seals, but you have changed that.
My next thought is that your brake pedal isn't actually pushing the master cylinder in, somehow the pushrod is too short or something is not adjusted correctly.

Post a picture of the vacuum and master cylinder.

Still air in system I recon. I would try gravity bleed.

tom.brandford said:

Hello all,

Trying to chase down some braking issues ahead of the MOT.

When desires the pedal, I get a slight initial braking force (no pedal resistance) that dissipates, with the pedal going to the floor.

If I push hard once it is on the floor it will brake properly, but with little movement of the actual pedal.

I’ve bled the brakes & adjusted the rear drum brakes (1988 110), and installed a new master cylinder.

The weird thing is, even after a full bleed, the pedal still goes to the floor on the first go (albeit with slightly sharper braking force once on the floor). I can ‘pump’ the pedal quickly which gives a nice firm pedal and shortens the travel.

Does anyone have any ideas? Thanks!

Click to expand...

Is the fluid dropping ?

Is the servo holding pressure ?

2-ways to check the servo -

Press the brake pedal quite hard and then start the engine - the pedal should sink about an inch and then go solid once again

After the engine has been switched off for a few hours - pull the pipe out of the servo (including the one-way valve). There should be stored vacuum in the servo and you will hear a hiss as it's lost

A short hiss is quite normal when the pedal is pressed, but should not be continual

Wind the brake adjusters all the way in when you bleed, then adjust properly once done. This gives you less chance of air trapped in the wheel cylinder.
Are you bleeding in the right order?

You might have some air trapped in the master cylinder, or the new master cylinder is dodgy, did you get a good brand?