Brake master cylinder gone?

[tom7035]

BE SURE TO LET US ALL KNOW THE OUTCOME!
Good luck, Tom.

 

[turnipsock]

I got some new pads from the dealers today and they gave me 30% off! They are overstocked in these pads.

I have also got some new bleed screws, mine are corroded beyond recognition.

 

[E200 Simon]

Fixed.

I bled the brakes and they were a little better, so I flushed and changed the fluid and they're perfect now. 8)

While I was bleeding them the first time, I had a look at the O/S front which has been knocking slightly. I found some movement in the wheel, caused by play in the bearing, and tightened the bearing. (About 3/4 of a turn.)

I'm now wondering if the slight movement in the wheel had been 'knocking' the caliper piston back, which would also have led to increased initial pedal travel. Any thoughts?

My front anti roll bar drop links are boned again too, they only seem to last about a year/50K miles. Is this a known issue?

 

[nicky]

Fixed.

I bled the brakes and they were a little better, so I flushed and changed the fluid and they're perfect now. 8)

While I was bleeding them the first time, I had a look at the O/S front which has been knocking slightly. I found some movement in the wheel, caused by play in the bearing, and tightened the bearing. (About 3/4 of a turn.)

I'm now wondering if the slight movement in the wheel had been 'knocking' the caliper piston back, which would also have led to increased initial pedal travel. Any thoughts?

My front anti roll bar drop links are boned again too, they only seem to last about a year/50K miles. Is this a known issue?

Yes if the disc moved it would push the piston back,then you would have more travel on the pedal to get a brake...it would feel as if you had air in the system.................

 

[paulcallender]

Yes if the disc moved it would push the piston back,then you would have more travel on the pedal to get a brake...it would feel as if you had air in the system.................

I make it that these things would affect braking effect per given amount of pedal travel, assuming good brake fluid:

Master cylinder diameter
Disc diameter, ie how far from the axis the pad is.
Area of pads
Weight of the car
Friction coefficient of the pads.

And only the friction coefficient would possibly change, once you fit new pads. Merely pushing pistons back would not normally (but just might) affect the caliper pistons, but would not affect the master cylinder in any way.

 

[E200 Simon]

Yes if the disc moved it would push the piston back,then you would have more travel on the pedal to get a brake...it would feel as if you had air in the system.................

But it didn't feel like air in the system, that's why I suspected the MC.

It was firm when it happened, but took too long before it got there.

That's why I'm suspicous about caliper piston knock back. I wish now that I'd tried only one fix at the first attempt.

Anyway, they're sorted. 8)

I make it that these things would affect braking effect per given amount of pedal travel, assuming good brake fluid:

Master cylinder diameter
Disc diameter, ie how far from the axis the pad is.
Area of pads
Weight of the car
Friction coefficient of the pads.

And only the friction coefficient would possibly change, once you fit new pads. Merely pushing pistons back would not normally (but just might) affect the caliper pistons, but would not affect the master cylinder in any way.

What about the black bits in the fluid resevoir? This is still concerning me.

I've got an ongoing, involved multi-pot brake issue with a BMW M3 going on HERE, any thoughts Paul?

 

[paulcallender]

But it didn't feel like air in the system, that's why I suspected the MC.

It was firm when it happened, but took too long far before it got there.

That's why I'm suspicous about caliper piston knock back. I wish now that I'd tried only one fix at the first attempt.

Anyway, they're sorted. 8)
What about the black bits in the fluid resevoir? This is still concerning me.

I've got an ongoing, involved multi-pot brake issue with a BMW M3 going on HERE, any thoughts Paul?

I'd assumed good fluid. After all, its a prerequisite of all the other braking components working properly. If I had black bits in the fluid, I'd do my best to scoop them out, change the fluid, then use the car for a couple of weeks and re-check the fluid to observe if its still clear and free of black bits.

I'll have a brief look at that BMW M3 issue and see what I can make of it....not yet read it through!

 

[E200 Simon]

I'd assumed good fluid.

Rather embarrassingly not.

The Merc is my workhorse and has done 100K since I've had it, without a fluid change.

After all, its a prerequisite of all the other braking components working properly. If I had black bits in the fluid, I'd do my best to scoop them out, change the fluid, then use the car for a couple of weeks and re-check the fluid to observe if its still clear and free of black bits.

That's exactly what is happening now.

I'll have a brief look at that BMW M3 issue and see what I can make of it....not yet read it through!

In a nutshell...I've got a huge Brembo kit that'll fit with 16" gravel tyres or 17" tarmac tyres. It won't fit without wheel spacers and I won't use wheel spacers.

So I'm trying to wring the best from single pot sliding calipers.

Any input welcome. 8)

 

[paulcallender]

Rather embarrassingly not.

The Merc is my workhorse and has done 100K since I've had it, without a fluid change.

That's exactly what is happening now.

In a nutshell...I've got a huge Brembo kit that'll fit with 16" gravel tyres or 17" tarmac tyres. It won't fit without wheel spacers and I won't use wheel spacers.

So I'm trying to wring the best from single pot sliding calipers.

Any input welcome. 8)

Keep it standard. End of.

 

[Bolide]

Pad knock-back

A loose front wheel bearing could cause pad knock back but I'd think it'd have to be pretty loose (or a disc pretty warped) for it to be noticeable

My Triumph TR4 had pad knock-back so bad you get into the habit of pumping the brakes before very time you use them. When I was racing it I had pump it up after each corner because the harder you cornered, the more the uprights / wheel bearings / everything else flexed. Aaargh!

It played havoc with my Merc driving - into roundabouts with an unconcious stab on the brakes to pump them up and your teeth ended up wrapped round the steering wheel!


Nick Froome
www.w124.co.uk