S2 brakes - solid pedal
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Neil
S2 brakes - solid pedal
Does anyone have any experiences and remedies of a S2 coupe with brake problems, where the pedal has limited travel most of the time, a very short stroke and usually very firm, sometimes after a short distance it appears all calipers have siezed on. After letting them cool for 30 minutes or more, they are then free and the brakes work correctly until they lock up on another day. The brake calipers look in good working order and the pistons have been checked that they move freely. Would this be a master cylinder problem or a servo problem - or even both?
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Peter Cripps
Re: S2 brakes - solid pedal
Making the (perhaps dangerous) assumption that experience on one breed of Italian car can be transferred to another ...
... these symptoms can be caused by defective flexible brake hoses. They may look OK from the outside, but internally they are almost fully collapsed. When the brakes get warm, the collapsed section acts as a non-return valve, and the calipers stay pressurized, with the brakes locked on. After a cool-off period, the pressure is released, and the brakes disengage.
Peter
... these symptoms can be caused by defective flexible brake hoses. They may look OK from the outside, but internally they are almost fully collapsed. When the brakes get warm, the collapsed section acts as a non-return valve, and the calipers stay pressurized, with the brakes locked on. After a cool-off period, the pressure is released, and the brakes disengage.
Peter
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P. de R. Leclercq
Re: S2 brakes - solid pedal
Peter,
You've reminded me of an experience I had about 25 years ago when working on a Mercedes-Benz 280SL. This had exactly the problem you describe.
Mind you, ATE brakes have never done much for me!
Paul
You've reminded me of an experience I had about 25 years ago when working on a Mercedes-Benz 280SL. This had exactly the problem you describe.
Mind you, ATE brakes have never done much for me!
Paul
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Huib
Re: S2 brakes - solid pedal
Interesting
There were other postings on the Italian, German and Dutch forums on this subject. I don't remember if a clear cause was found. Let's hope we can establish the cause in this case
As Peter says the flexible brake hoses may give problems if old. Like brake pads, these hose come in a variety of qualities (and prices). The standard rubber hoses have a shelf live of 5 years and a usefull life of also 5 years. If older, they should be replaced.
Another cause may be not enough free play on the pedal. If so, the plungers may not fully return and the compensation hole remains closed.
In another case the brakes seized after exactly 70 kms. After cooling down the car would do another 70 kms and the brakes would seize again. This was solved by swapping the servo as I found out the owner had opened the servo and closed it again. Not recommended.
I have never understood the compensation circuit for the chamber serving the large cilinders on the front callipers. There is no compensation hole in front of the seal if the plunger is in rest position. If the fluid is heated it cannot expand back into the container.
The plunger consist of two parts which does provide a compensation if the pads have worn and retraction is less than the action but as I said, I have never figured how the fluid can expand back into the container if the fluid expands.
There were other postings on the Italian, German and Dutch forums on this subject. I don't remember if a clear cause was found. Let's hope we can establish the cause in this case
As Peter says the flexible brake hoses may give problems if old. Like brake pads, these hose come in a variety of qualities (and prices). The standard rubber hoses have a shelf live of 5 years and a usefull life of also 5 years. If older, they should be replaced.
Another cause may be not enough free play on the pedal. If so, the plungers may not fully return and the compensation hole remains closed.
In another case the brakes seized after exactly 70 kms. After cooling down the car would do another 70 kms and the brakes would seize again. This was solved by swapping the servo as I found out the owner had opened the servo and closed it again. Not recommended.
I have never understood the compensation circuit for the chamber serving the large cilinders on the front callipers. There is no compensation hole in front of the seal if the plunger is in rest position. If the fluid is heated it cannot expand back into the container.
The plunger consist of two parts which does provide a compensation if the pads have worn and retraction is less than the action but as I said, I have never figured how the fluid can expand back into the container if the fluid expands.
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Neil
Re: S2 brakes - solid pedal
Thank you for your suggestions, we will certainly look at the hoses, quite a short life expectancy at 5 years, I suspect few do get changed at that interval. Would disconnecting the servo prove anything, apart from the brakes would be more difficult to operate?
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Huib
Re: S2 brakes - solid pedal
Disconnecting the servo is a good test to see of the servo is not the cause. If you pull the vacuum hose, plug it to avoid an air leak into the intake manifold
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Neil
Re: S2 brakes - solid pedal
The servo problem has now been discounted, the brakes and pedal still locked with it disconnected. The master cylinder has been dismantled and cleaned, there was some contamination inside, which was removed, refitted and with new brake fluid, and bled all round. After a thorough test at varying speeds the car was transformed the pedal felt much better, 200% more movement. However after one week the problem has returned, now looking at new set of seals on the master cylinder. The flexible hoses are fairly new and look in good condition.
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Huib
Re: S2 brakes - solid pedal
When you do the master cilinder, check if the two parts of the 2nd (counting from the pedal) plunger slide easily. Sometimes they get stuck transforming the plunger in a one piece plunger. If you don't know you will never think the plunger really consists of two parts.
And check the free play of the pedal. There should be a few mm's of play before the pin hits the 1st plunger to ensure the plungers always come back to the rest position.
Also check with the master cilinder on the bench if the plungers come back easily when you push them forward
And check the free play of the pedal. There should be a few mm's of play before the pin hits the 1st plunger to ensure the plungers always come back to the rest position.
Also check with the master cilinder on the bench if the plungers come back easily when you push them forward
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Neil
Re: S2 brakes - solid pedal
The brake problem saga appears to have a happy ending, another used master cylinder was obtained, it was stripped down and carefully cleaned, and compared to the original. Overall the original was in much better condition. However the 2nd plunger, furthest from the pedal, was the same build as the one on the car without the tiny port on the front chamber and with an O ring as the rear seal on the front piston. Decided to use the inner section of the front piston with it's O ring which is slightly thicker section and a better fit on the bottom of it's bore than in the original cylinder. Release the two parts, clean up the piston and O ring and reassemble the whole lot into the original cylinder. Refit to the car, bolt cylinder in place and bleed the brakes, now it's all back together and the pedal feels good, testing so far has been succesful, runs now further and faster have not been a problem. Hopefully problem solved now, thanks for your useful suggestions along the way.