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Old 13th June 2024, 15:38   #11
SD1too
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Originally Posted by Fred Byrne View Post
The piston will not move back any futher so it must be the seals that are blocking the ports and not allowing the wheel cylinders to re-charge.
Are there any suggestions please?
Hi Fred,

Once upon a time a repair kit comprising the items within the dotted line (2) was available:


Diagram provided by Motaclan.

This suggests that it's possible to detach the reservoir from the cylinder. If you do that, you may have access to the seals which you suspect are the cause. They may have just been "flipped" if excessive bleeding pressure was used in the past.

Simon
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Old 13th June 2024, 17:11   #12
Fred Byrne
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Hi Simon;
I have got the reservoir off. The onlyway I can access the interior is to remove the circlip at the end of the cylinder facing the servo. This looks difficult but I'll have a go at it tomorrow. I have nothing to lose.
When I blow into either of the outlet pipes there is total blockage and ditto when I bow into the reservoir. The piston is hardup agasinst the circlip so obviously it is as far back as it will go. I feel roughness at one point when I push the piston in by hand and that does not bode good methinks.

My ancient Rover '100' is so much easier and has taken over routine duties once more. If it could speak it would say " told you so; these youg 'uns have a lot to learn from us oldies"

Thank you as always for your interest.

Fred
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Old 13th June 2024, 19:19   #13
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My ancient Rover '100' is so much easier ...
It was my father's Rover 100 that started it all for me.

Simon
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Old 14th June 2024, 11:34   #14
Fred Byrne
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The Rover 100 is a magnificent car. I suppose your father's car is no longer on earthly roads. We were staying in the Fairmont hotel in Monte carlo a few years ago and the door man insisted on parking my car at the front door.. Doorman said someone might steal such a valuable car. Iit displaced a modern Bugatti which the door man told me were two a penny. Bugatti man was furious but the door man in Monte Carlo is king!
I have dismantled the master cylinder. The piston at the front end had jammed. This must have happened when the garage was bleeding the brakes after replacing the brake lines. When I reassembled it the front brake cylinder compartment recharged but the rear one didn't. I cannot see what is wrong. I attach pics.
Fred
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File Type: jpg Brake Master cylinder rear end.jpg (110.9 KB, 15 views)
File Type: jpg Brake master cylinder front end2.jpg (118.9 KB, 16 views)
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Old 14th June 2024, 13:28   #15
Fred Byrne
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I have decided the brake cylinder is beyond repair and have decided to replace it and also the servo unit. So into the scap it all goes. Many thanks everybody who took the time to reply but the brakes are too important. So that's that

Fred
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Old 23rd June 2024, 14:14   #16
Fred Byrne
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I dismantled the master cylinder this morning and I think I have an explanation for the fault. Picture 1 shows the components laid out on the table. I have called the piston to the front of the car the secondary piston. This piston has two seals . One seal has the wider end facing the front end of the cylinder and provides the braking. The other seal is to the back and prevents the fluid from the other piston from entering the secondary piston when the brakes are applied. All seals are in perfect condition.
The other two components are a bronze threaded bung and what I have called the insert pin. This pin and bung are inserted into the bottom of the master cylinder shown in picture no. 4. the pin engages with the slot on top of the piston shown in picture 3. Its function seems to be to limit the stroke of that piston. There is a mark on the slot where the pin has jumped out of the slot and so allowed to piston to move too far towards the car and also jammed the piston in this position. This meant that not only the secondary piston was out of position but the primary piston( nearest the bulkhead) was also out of position. The result was that neither piston could recharge and both pistons were forced to operate with a charge that could not be refreshed and that was degrading with each application of the brakes.I am not sure but it is possible that the brakes only operated on two wheels as I am only a very light user of brakes but I would have expected brake imbalance if that was the case.
I have purchased a new master cylinder and servo. i expect to fit them some time this week.

Fred
Attached Images
File Type: jpg Main components 2.jpg (116.4 KB, 21 views)
File Type: jpg Main components.jpg (113.9 KB, 19 views)
File Type: jpg secondary piston.jpg (112.2 KB, 19 views)
File Type: jpg Bung intercept pin with brake cylinder.jpg (112.4 KB, 19 views)
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Old 23rd June 2024, 21:15   #17
SD1too
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Thanks very much Fred for your explanation and photographs.
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There is a mark on the slot where the pin has jumped out of the slot and so allowed to piston to move too far towards the car and also jammed the piston in this position.
Have you any idea what might have caused this?

Simon
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Old 24th June 2024, 15:21   #18
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I think that the pin was close to the negative end of the allowed tolerance. There is a bright scratch mark on the forward end of the slot. I couldn't get this to show on the photographs. It is about one thou deep and only about two thous long. I think this could have happened when the brakes were being bled. If the bleeder let the pedal fly back during the bleeding process it is conceivable that the piston had sufficient momentum for the pin to slide over the edge of the slot.The piston was definitely jammed at that position when I dismantled it.

Everything else was perfect within the unit. If the pin had been longer this could not happen. I think that I have been unlucky.

Fred
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