Brakes: C70 - excessive brake pedal travel, little pressure

[DSK]

Several months ago, I ruined my brakes. At xxx mph I hit the brakes with all I had to stop at a roundabout (childish moment). When stopped, I knew something was wrong with the pedal but put it down to heat, completing the rest of my journey sensibly but the pedal now remained soft.

Fast forward;

New performance pads/discs/fluid - no difference
New Goodridge brake lines - no difference
New ATE master cylinder - no difference

The issue is when you brake, the brake pedal travels a long way down, there is a slight hiss when it does this and the brake force remains moderate at best, so no chance of doing an emergency stop. No one can see anything visually wrong so I though, lets chance the master cylinder in case but this has not cured the issue.

Does anyone have any ideas on what else could be causing the issue as I can't think what else could remain in the braking system to change that could have been impacted by the original incident.

[Bob Meadows]

Have you checked the Servo/Brake booster & associated parts:~
ie the valve and pipework- all worth checking.
Bob.

[DSK]

Originally Posted by Bob Meadows

Have you checked the Servo/Brake booster & associated parts:~
ie the valve and pipework- all worth checking.
Bob.

NO! no one mentioned this. I though that the master cylinder attached to it does the work so thought nothing more of it. I'll get the car booked in again and ask them to check/replace the servo as needed.

[Derek UK]

Don't just jump in and ask them to change the servo. It will be a big bill. Basic test, and the MOT should include this, is to remove all of the vacuum by pumping the pedal a few times until the pedal is rock hard i.e. there is no vacuum left. Keep you foot on the pedal pushing down quite hard. Start the engine. When the engine starts you should feel your foot go down a bit. Down to the position it normally does when braking. That should mean that the servo is OK. As said check the vacuum pipes and the one way valve.

[Clan]

Originally Posted by DSK

Several months ago, I ruined my brakes. At xxx mph I hit the brakes with all I had to stop at a roundabout (childish moment). When stopped, I knew something was wrong with the pedal but put it down to heat, completing the rest of my journey sensibly but the pedal now remained soft.

Fast forward;

New performance pads/discs/fluid - no difference
New Goodridge brake lines - no difference
New ATE master cylinder - no difference

The issue is when you brake, the brake pedal travels a long way down, there is a slight hiss when it does this and the brake force remains moderate at best, so no chance of doing an emergency stop. No one can see anything visually wrong so I though, lets chance the master cylinder in case but this has not cured the issue.

Does anyone have any ideas on what else could be causing the issue as I can't think what else could remain in the braking system to change that could have been impacted by the original incident.

when you do a REAL emergency stop the servo locks on ,

Your leg muscles rapidly loose their power after a second or so on max pressure . Volvo realise this so designed in this feature many years ago .. it keeps your initial MAX power on the pedal whilst your leg muscles fade away ...

I really don't know if this resets as it a rare event .. It only works when you have a life or death event ...

[klausc]

"the brake pedal travels a long way down, there is a slight hiss when it does this " I suspect that either the one way valve is leaking, the vacuum line has a leak, or the servo is kaput.

After checking that vacuum is present by pushing the brake pedal and then starting the engine, press the brake pedal several times and see if the pedal travel decreases or increases.

Did you check the flex brake lines at the rear? They may be expanding due to age. Probably not the problem if you hear hissing.

[Bob Meadows]

The valve & hose are relatively easy to check and shouldn't cost a kings ransom at the right garage- If the master cylinder has been replaced it could be as simple as the grommet holding the valve in place being disturbed so also make this part of the check list.
Good Luck
Bob.

[DSK]

Thanks for all the information and feedback.

The lines (all 5) were replaced with new Goodridge s/s lines so can't be those but, replaced just on the off chance there was any flex when in use.

I will check the vacuum and then try the pedal procedure tomorrow.