Craig D (184.108.40.206)
|Posted on Sunday, 22 September, 2002 - 20:20: |
My name is Craig & I am in the process of overhauling Brakes on an S1 Bentley. I am a bit stuck & am in need of some advice. I have had the entire braking system overhauled new seals & sleeves in both the master & wheel cyclinders etc. I have managed to bleed it up ok but am having to apply the brake peddle twice to get it to stop quickly. It seems to me that the front brake shoes are slipping back when you remove your foot from the brake peddle. I am wondering if the shake back stops are working, but can't really tell. Could it be something else that I have not considered. Thanx
Bill Coburn (220.127.116.11)
|Posted on Saturday, 28 September, 2002 - 10:57: |
Craig, We assume you have the workshop manual. You have bled the brakes and tested the system for air. You have an oil free servo and dry drive plate. The 'ramps' in the servo are not brinelled.The various rod and actuator adjustments are correct and the back brakes are properly adjusted. If the answer to all those are yes try putting the car on stands (front and rear)take off the front wheels, start the engine engage drive (4) and firmly apply the brakes. Switch off engine release brakes and try to turn the front drums. There should be a significant drag. If not the shake back stops are slipping. Try cleaning them and reassemble them dry - lubricant or oily residue nullifies their purpose and effect. Consult the workshop manual and get the spring balance to check the drag. They may need replacing. These are not unique to RR and normally give little trouble. The more likely problem is being too efficient and causing binding brakes!
Bill Vatter (18.104.22.168)
|Posted on Sunday, 29 September, 2002 - 03:30: |
On a normal car we can feel the condition of the hydraulics in the brake pedal, i.e., spongy pedal means air in the system, slowly sinking pedal means leak (internal or external) and a firm steady pedal means hydraulics are OK.
On an early post war car (through Cloud III) the condition of the hydraulics cannot be assessed in this manner. Since you may have a hydraulic problem, I suggest you go under the car with a long screwdriver and press the master cylinder linkage forward to test for a firm steady master cylinder that does not move very much. A master cylinder linkage that moves a significant amount will cause excessive servo lag and in the worst case the trouble as you describe. However you could also have air in the system indicated by a spongy feel to the master cylinders, which could also allow the master cylinder pistons to stroke an excessive distance before communicating sufficient pressure to the wheel cylinders to cause the car to stop.
If the master cylinders move a very long distance, bottoming or almost bottoming, but become firm and steady after a pump or two, then you have a mechanical problem which may well be shake back stops not holding the shoes in place as you already suspect. However, if the shake back stops are correctly installed they should provide sufficient drag to the shoes and hold them in place.
It is quite possible the shake back stops are not correctly installed. As I recall, when correct, it is rather difficult to get the nut on the steady post because of spring pressure in the shake back stop mechanism. The test Bill describes will tell you if the shake back stops are doing their job.
craig d (22.214.171.124)
|Posted on Monday, 07 October, 2002 - 22:14: |
Thanx for the advice guys, haven't had time to check it out as yet but I'll keep you posted.