Degraded brake performance

[murphster]

I have noticed over the past 3/4 times I have taken the chim out the brake performance has slowly got worse to the point now that it is dangourous. Break fluid levels are normal and I have just checked the pads and disks all are good and have even wear.

Am I correct in thinking that the brake servo needs replacing or do I need to check something else first? Any way of confirming the servo is the problem?

[Graham]

What's the problem, if the servos not working the force you need to press on the pedal would be much harder.

If the pedals spongy it will be something else.

If it is servo it could just be a leaking vaccum hose.

[murphster]

I am pressing the brake pedal to the floor (hitting the floor - mechanical stop) but the pads are only being applied lightly. Hope that makes sense?

[haircutmike]

The vacuum hose runs from the offside of the plenum, (actually trumpet base) across to the inner wing on the offside to the servo. Worth a check.

I'm in Surrey if you want an opinion.

[Dr Mike Oxgreen]

On most cars (and I assume the Chimaera is the same although I can't remember if I've tried it), you can test the brake servo as follows:

• With the engine off, pump the brake pedal. It should go rock hard after a few pumps.
• Press the brake pedal, and while you're still maintaining pressure on the pedal - start the engine.
• As soon as the engine starts, you should feel the brake pedal soften under your foot.

If the above happens, your brake servo is working.

The symptoms you describe, however, do not sound like a failed servo.

Edited by Dr Mike Oxgreen on Sunday 27th May 20:58

[murphster]

Dr Mike Oxgreen said:

On most cars (and I assume the Chimaera is the same although I can't remember if I've tried it), you can test the brake servo as follows:

• With the engine off, pump the brake pedal. It should go rock hard after a few pumps.
• Press the brake pedal, and while you're still maintaining pressure on the pedal - start the engine.
• As soon as the engine starts, you should feel the brake pedal soften under your foot.

If the above happens, your brake servo is working.

The symptoms you describe, however, do not sound like a failed servo.

Edited by Dr Mike Oxgreen on Sunday 27th May 20:58

Cheers I'll try it out - at least I can rule it out

[murphster]

haircutmike said:

The vacuum hose runs from the offside of the plenum, (actually trumpet base) across to the inner wing on the offside to the servo. Worth a check.

I'm in Surrey if you want an opinion.

Hi Peter, Thanks for the offer might take you up on it. I'll check the vacuum hose and see if I can see anything wrong with it.

Simon

[Bassfiend]

murphster said:

I am pressing the brake pedal to the floor (hitting the floor - mechanical stop) but the pads are only being applied lightly. Hope that makes sense?

That sounds more like master cylinder seals to me ... If you press the brake pedal with the engine running but the car stationary does your foot simply sink to the floor with a bit of resistance?

Phil

[simonej]

Have the pads seized in the carrier? When I first got mine the inboard pads on all four wheels were rusted in place and weren't making full contact with the disc.

[Bassfiend]

simonej said:

Have the pads seized in the carrier? When I first got mine the inboard pads on all four wheels were rusted in place and weren't making full contact with the disc.

That would stop the brakes working though - not allow the pedal to hit the floor, no?

Phil

[Graham]

Pedal going to the floor as said sounds like master cylinder. With a servo problem you still have brakes just need to push really hard.

I wouldn't drive the car, as it sounds like master cylinder and that can mean no brake!

[redgriff500]

Master cylinder OR air in brake fluid.

But if you haven't been messing with them then M cylinder is most likely.

[Barreti]

If your brake master has gone it could have leaked all the fluid down into the drivers footwell and the carpets have soaked it up so you won't have noticed.

Pull out the drivers side footwell mat and see if its soaked in brake fluid and the far end.
And put your hand under the pedals and feel the carpet on the inside of the wheel arch.

[Alexdaredevilz]

Sounds like you got a leak some where, check fluid level to see if that has gone down or just a simply air in the system and needs a rebleed

Id advise not driving it at this stage if your pedal is hitting the floor

[Simon says]

redgriff500 said:

Master cylinder OR air in brake fluid.

But if you haven't been messing with them then M cylinder is most likely.

< This

[haircutmike]

I had the master cylinder leak on a car with no external signs of a leak, it was leaking and collecting in the brake servo!

[Simon says]

haircutmike said:

I had the master cylinder leak on a car with no external signs of a leak, it was leaking and collecting in the brake servo!

To true Peter, that is quite a common way for a master to fail in my game I have seen many a servo filled with brakefluid that needed to be vac'd out only for some to fail not to long after where the diaphragm as failed/perished it can go 50/50 sometimes

[simonej]

Bassfiend said:

That would stop the brakes working though - not allow the pedal to hit the floor, no?

Phil

It allowed near full pressure on the outboard side of the disc combined with very light pressure on the inboard side (pad contact of maybe 20% of the disc area) and max braking wouldn't even lock the wheels in the wet. The pedal could be pushed all the way to the metal, although as you say it shouldn't in theory allow it to do so - maybe it was a combination of many other factors.

[murphster]

Dr Mike Oxgreen said:

On most cars (and I assume the Chimaera is the same although I can't remember if I've tried it), you can test the brake servo as follows:

• With the engine off, pump the brake pedal. It should go rock hard after a few pumps.
• Press the brake pedal, and while you're still maintaining pressure on the pedal - start the engine.
• As soon as the engine starts, you should feel the brake pedal soften under your foot.

If the above happens, your brake servo is working.

The symptoms you describe, however, do not sound like a failed servo.

Edited by Dr Mike Oxgreen on Sunday 27th May 20:58

Managed to try this out this evening and everything happens as you have described so it is not the servo (as you suspected!) Thanks

[murphster]

haircutmike said:

The vacuum hose runs from the offside of the plenum, (actually trumpet base) across to the inner wing on the offside to the servo. Worth a check.

I'm in Surrey if you want an opinion.

I think I have checked the vacuum pipes and there are no obvious splits/leaks (the pipes in the centre of the pic cable tied together?)