The brake actuation linkage assembly? Looks like a giant rat trap to me - Rolls-Royce and Bentley Forums
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post #1 of 51 (permalink) Old 03-04-2019, 10:09 PM Thread Starter
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The brake actuation linkage assembly? Looks like a giant rat trap to me

All, I was finally able to move my 79 Silver Shadow onto the lift where I could put it up in the air and see what's going on. Here's the story so far:
  1. Car did not run when i got it but I have it running pretty well now
  2. Trans did not shift but I figured out that it was just low on fluid
  3. Brake lights are always on and the pedal does not return by itself
  4. When the car runs, the brakes lock up to the extent that the engine cannot overpower the brakes
  5. I put the car up in the air and saw a bunch of wet brake fluid under the drivers side floor
  6. Pedal appears to be connected to the brake actuation assembly
  7. When I run the engine and pump the brake the brake actuation assembly leaks

I suspect that there's a blockage that it not allowing brake fluid to return and hence locking up the braking system as pressure builds up. Has anyone experienced these symptoms? I'd be interested in feedback.

Thanks
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post #2 of 51 (permalink) Old 03-05-2019, 06:59 AM
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Locking is usually associated with trapped brake fluid. Every flexible hose should be replaced. The internals are breaking down and clogging the circuits. You will notice upon draining the old fluid it will be grey/dark grey in color with small black particles. Start with a turkey baster at the reservoir and work thru the system. A flush will not be the answer. There are hydraulic components that are so finely machined, such as the brake distribution valves (in the trap) that have no seals at all around the actuator rod. They are usually wet.
Your brake light switch is not returning either due to corrosion or switch adjustment or failure. Every brake caliper has to be overhauled. The plating on the pistons will corrode and will easily stick. Kelly has SS pistons. (BritishToolWorks)Be prepared for alot of labor and cost. There is no way to cut corners with the system overhaul. Shops charge close to $10 k for this and its one of the reasons they end up sitting around or sold at auction. It happens all the time.

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post #3 of 51 (permalink) Old 03-05-2019, 03:31 PM
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If the OP has got the car in the air and was able to identify and remove the rat trap cover, then I think he is capable of replacing all the hoses himself, reducing a 10k bill down to under 1k. Obviously there is a learning curve, but that's the purpose of internet forums like this one. Good luck Al, keep us posted on the progress!
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post #4 of 51 (permalink) Old 03-05-2019, 07:49 PM Thread Starter
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Thanks all, the rat trap cover was already removed but pulling the rest of it apart and cleaning it should not be too hard provided that I can continue to ask stupid questions. I need to get this off the lift ASAP.
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post #5 of 51 (permalink) Old 03-05-2019, 08:03 PM
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I would not pull anything apart in the trap area since there really isn't anything in there to service. Your focus is hoses, hoses, hoses, calipers and so on. All of which require the lift and patience.

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post #6 of 51 (permalink) Old 05-31-2019, 08:23 AM Thread Starter
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Quick follow up on this. I removed the calipers and was able to compress the pistons with them off the car. The steel lines going to the calipers were rusted and the brake hoses were in really bad shape. I thought that this might be what caused the blockage which may result in the rear calipers clamping shut so I re-made the hoses and bent some new lines up.

I installed them and bolted everything up tight but as soon as I ran the engine. the rear brakes locked up.

I'm now looking at the rat trap and the valve block behind it.

Can anyone look at these pictures and tell me if everything is piped correctly? From the look of it, the lines that I circled might be reversed (from the look of the pipe routing).

Thanks
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post #7 of 51 (permalink) Old 05-31-2019, 01:41 PM
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Unlikely pipes are reversed. You have no clearance at distribution valve pushrod, this will apply brakes whenever engine is running. See circled area on pic. Linkage is corroded and tight not allowing pedal to return. Free up pedal and linkage in rat trap until you have clearance at both upper and lower distribution valve pushrods. Pushrods may be seized in distribution valves too which will keep brakes applied. Make sure they are moving in and out when linkage is freed up.There are two springs in the rat trap to pull linkage and pedal back, make sure they are not missing.
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post #8 of 51 (permalink) Old 06-01-2019, 12:21 AM Thread Starter
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Thanks, tell me about the springs? my pedal does not return so this could be the problem.
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post #9 of 51 (permalink) Old 06-01-2019, 01:58 AM
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You can just see one below the white circle I drew on your pic. The other one may be be hidden or missing. If the springs are both there they may not be strong enough to overcome the seized linkages. If your pedal is not completely up the linkage will be pushing on the distribution valve plungers which will activate the brakes. From the looks of the rust at the plunger they may be stuck in applied mode. Free up the linkage/pedal and check that there is free play at the plungers with pedal up, and that the plungers move in and back out.

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post #10 of 51 (permalink) Old 06-01-2019, 06:10 AM
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Al The brake distribution valves have critical tolerances and if the shafts have any corrosion they should be replaced on an exchange basis. The shaft to body tolerance is extremely close and there is no seal used., however it is designed to weep around the shaft to provide lubrictian. These are expensive components.
As Jim noted there seems to be an issue of springs (missing or weak) overall freeing of levers and moving parts and checking the brake distribution valves as indicated when the car is started, something is causing the sytem to be stuck in the applied mode.

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