Brake Servo 'too'efficient!

Hi,

Trying to track a problem with my brakes on 92 mk2 gti. Started late last week - jumped in the car and drove down the road - immeadiatly noticed the brake pedal was travelling further down and felt 'soft'.

i`ve replaced the rear calipers (as they were knackered anyway and new pads there too. New master cylinder aswell - bled them - pedal is now hard with no engine running. As soon as you start the engine though and drive it, the pedal is nearly going to the floor. Hold your foot on the brake as you drive (servo loses vacuum) and next time you press it, brake feels harder and higher - more normal.

Have i missed something!?

Thanks, MIke

 

When you fitted the rears did you wind the pistons out when fitting the pads and bleed them with the load compensating valve open?

 

Load compensating valve?

I didn't do that as I didn't know there was one!

Where is that?

Thanks

 

Near side rear, mark the spring adjuster on the bracket then loosen it off to release the spring. Pulling the spring closes it so you need to move the lever on top of the valve the other way. At this age you need to make sure the lever pivots freely too.

 

Cool thanks - well I've bleed then loads now making sure the compensate lever is the right way! Even used an easibleed aswell.
There is pure clean fluid with no bubbles and pedal is nice and hard - but it still feels spongy when driving!
Could it just be the new pads bedding in?

 

Is the sponge consistent or does it come on as the chassis is in a more neutral position (at the end of a braking phase or in traffic)?

 

Hi, it's consistent sponginess.

The brake booster pipe - do you mean the vacuum pipe going to the servo? If so, it and the seal both look good. If there was a crack or bad seal, wouldn't that cause the brakes to be hard all the time?

 

did the pedal go hard when you lost them or go soft to the floor?

 

Did you try the handbrake test at all? Don't take you hand off of it or the button just raise temporarily to put a bit of light tension on the rears when you feel the pedal sinking. If it firms up the pedal the sponge is rear piston travel.

 

needs bleeding more , ive had the same with an easy bleed and a bit more tyre pressure fixed it

could also try removing the calipers to try and encourage the air to leave