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The Gentleman's Express: Tech-Tips from the JIOC

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Brake Master Cylinders and Boosters

Author: CFF

Jensens, in the U S, have three different master cylinders: 7/8" bore, 1 “ bore and 15/16” bore; and two different power assisted servos. If the wrong combination of master cylinder and power servo is used, this can cause a situation for poor braking. The English have perfected pedal action on the Jensen and Jaguar. Once accustomed to the pedal `feel’ on a Jensen you will wish all your other cars behaved in the same way.

The brakes will not grab all of a sudden as other cars do, nor will you have to increasingly apply extra pedal effort the further it goes down to stop the carfaster during panic stops. The pedal action is smoother and sure throughout its range. It is perfectly all right if the pedal goes halfway down before significant braking takes place. all four wheels have self-adjusting disc brakes; therefore, the pedal should always feel the same regardless of whether the pads are new or completely worn out. This, of course, is the danger of self adjusting brakes on all cars; you do not know when the brake pads need replacement. If you wait `till the brakes start to squeal it is already too late and metal to metal contact has been made (very expensive to correct).

If servo and master cylinder units are mismatched, pedal pressures required might be too high or the pedal might have to travel pretty far down to the floor before anything starts to happen. This is not bad in itself as long as you are aware of it. The situation cannot get worse unless you run out of brake fluid, which happens with properly matched but badly maintained systems. So make sure that your float sensors are hooked up and operating

So be sure that your mechanic rebuilds your system with the proper replacement parts and that he appreciates the fact that there are different units available which can be the wrong ones!

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Contents copyright 2008, 2009 - Jody F. Kerr

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