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Brake Bias
pbs - 18/6/05 at 04:55 PM

Had my car running for a couple of weeks now and today I bled the brakes and took the car up and down the drive a couple of times just to test the brakes.

The brakes are very heavy and not very effective so I suspect the the master cylinder sizes are wrong. The pedel travel is ok though.

The car has Seirra disks and calipers on the back and Serria disks and Mondeo calipers on the front with a twin master cylinder brake bias set up.Both master cylnders are Girling 0.75. Anyone body have any susgestions on how I could calculate which size of master i should use or have any other susgestions as to what the problem could be.

Hellfire - 18/6/05 at 05:03 PM

We have a single tandem system (22mm - 7/8" from a Sierra. Pedal feel is hard but very responsive, nothing like a modern braking system though... just like it should be.

britishtrident - 18/6/05 at 07:39 PM

quote:
Originally posted by pbs
Had my car running for a couple of weeks now and today I bled the brakes and took the car up and down the drive a couple of times just to test the brakes.

The brakes are very heavy and not very effective so I suspect the the master cylinder sizes are wrong. The pedel travel is ok though.

The car has Seirra disks and calipers on the back and Serria disks and Mondeo calipers on the front with a twin master cylinder brake bias set up.Both master cylnders are Girling 0.75. Anyone body have any susgestions on how I could calculate which size of master i should use or have any other susgestions as to what the problem could be.



3/4" is to big for balance bar set up the norm is 5/8" or 0.7" -- In the locost world when using disc on the rear this translates to 0.7" rear 5/8" on the front to enable the balance bar to be set in a near the central position.

This should give a 22% reduction in pedal effort. Don't forget also the brakes will need a handful miles to start to bed in.

[Edited on 18/6/05 by britishtrident]

pbs - 19/6/05 at 12:22 PM

Thanks BT,

Does the fact that Iam using Mondeo calipers on the front, which i believe have larger pistons then Serria front calipers , make any differance with regards to the size of the m/c I will be using. IE if I switch to 0.625 front and 0.7 rear will the 0.625 be ok for the larger pistons or will the brake pedal have to be pushed harder to stop the car due to the larger pistons at the front?

JAG - 20/6/05 at 12:45 PM

Bear in mind the fluid displacement capacity of any m/cyl' and the calipers that it is used with.

If you have a small diameter m/cyl' piston then you have less potential fluid volume.

In the event of pad fade* you may end up with the m/cyl' pistons bottoming out in the machined bore. Therefore no more brakes

Brakes with big pistons (you are right about Mondeo calipers having bigger pistons) will mean that if this happens the m/cyl' will bottom out quicker.

Do some calc's and let's be careful out there.



* pad fade; reduction of friction coefficient due to heat/pressure/speed. Recovery action is to press the pedal harder.

pbs - 20/6/05 at 09:50 PM

quote:
Originally posted by JAG
Bear in mind the fluid displacement capacity of any m/cyl' and the calipers that it is used with.

If you have a small diameter m/cyl' piston then you have less potential fluid volume.

In the event of pad fade* you may end up with the m/cyl' pistons bottoming out in the machined bore. Therefore no more brakes

Brakes with big pistons (you are right about Mondeo calipers having bigger pistons) will mean that if this happens the m/cyl' will bottom out quicker.



Yes, thats what I suspected. Has anyone any idea how to work this out as I dont know where to start.