Restoring a beaty 1973 Silver Shadow 1 - Page 11 - Rolls-Royce and Bentley Forums
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post #101 of 124 (permalink) Old 11-09-2019, 02:20 PM
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Daniel, post pics of the blanked off height control system. We are both curious. The height control solenoid and the Lo & Hi restrictors are not involved with the M/C. The MC is totally separate.

My prediction is: The M/C is not returning to rest due to a problem with the unit itself, or thereafter, ie. rods, bushings, springs.

Let us know the results of physically disconnecting the M/C from the trap. It may speak volumes and like we said earlier, isolate things.
Problem solving involves throwing everything on the board, exploring possibilities, and crossing them off going forward.

The M/C circuit, in terms of the big hydraulic picture, is simple and straight forward.

You may want to PM Jim Walters who contributes regularly. He is in BC and has decades of experience. Suggest to him to have look at the thread and perhaps he can assist.

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post #102 of 124 (permalink) Old 11-09-2019, 02:20 PM Thread Starter
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Hi Steve well i was thinking that the low pressure was kind of connected with the HP system but i traced the lines and there not . ill look in to the link you send me, thank you Sir
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post #103 of 124 (permalink) Old 11-09-2019, 03:08 PM Thread Starter
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the Mbaster cyl is just building up pressure till the pedal is all the way up
so i losen up the line going to the rear lower breaks pistons will free them, up

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post #104 of 124 (permalink) Old 11-09-2019, 03:16 PM Thread Starter
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where would it cause it to build up and not returning ???
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post #105 of 124 (permalink) Old 11-09-2019, 03:28 PM Thread Starter
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i think thats it
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post #106 of 124 (permalink) Old 11-10-2019, 01:41 AM
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Your problem is one of two things.

One, referring to post 82 you must have free play at 1, where the pushrod contacts the master cylinder piston. If the piston does not come back far enough after application it keeps the end seal against the inlet port at the end of the cylinder and prevents fluid return from the rear caliper. The piston must come back enough so the end seal lifts off the machined end face of the housing where the inlet port is and allow fluid return to the reservoir. The piston only has to move down .050 inches to block the port. If the fluid cannot return it keeps the rear brake pads applied and further driving heats up the fluid, causing an increase in volume and pressure until the brakes lock up.

Or two, you have lines crossed between the high and low pressure systems, possibly at the jumper lines on the rear calipers.

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post #107 of 124 (permalink) Old 11-10-2019, 01:48 AM
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Hi Daniel,


I agree everything points to M/C, but then wonder why it seems to only happen when driving is what is confusing us all I think.


So many difficulties when not doing it oneself.


I even wonder if it is all piped up correctly at times. Again from memory the very very early cars I think actually had the upper pistons on the LP side and has someone mixed yours up and actually you are bleeding the HP line...........your taxing old grey cells here but just throwing out any possibility at the moment to be considered.


As you have traced the lines though I think we can dismiss this wild thought so again back to the M/C


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post #108 of 124 (permalink) Old 11-10-2019, 01:53 AM
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Jim,


I was typing before reading your post so maybe my wild thoughts were not that wild.


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post #109 of 124 (permalink) Old 11-10-2019, 02:13 AM
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And Steve you are right, on early cars the low pressure pistons were the top, and later the bottom. I can't recall off the top of my head at what VIN but it was very early on. Certainly a 73 model should be the lower pistons. I'm also assuming though that Daniel has traced the pipes.

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post #110 of 124 (permalink) Old 11-10-2019, 05:39 AM
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OK Daniel Jims observations are keeping us focussed into the right areas.


I think what you need to do now is start from the beginning (back to basics) and have a step by step work plan.


I know you are going to think 'I have done that' but do need to get simple step by step answers.


My first test now would be to depressurise the HP line by pressing the brake pedal 100 times or so and make sure the warning lights are on. Do not start the engine at anytime.


Now take one lower rear brake nipple and loosen, pipe into a container jar. Have someone then inside the car push down the brake pedal as if you were bleeding the system and make sure fluid comes out the bleed nipple (keep an eye on the resevoir level). Then do exactly the same on the other side rear lower nipple.


This idea hopefully may at least confirm the plumbing to each lower piston calliper is correct.



It is bad enough tracing these pipe lines with the car on a ramp in air so when doing on your back on the garage floor it is even harder.


Can't go any further with advice until you confirm each stage now and please also confirm you ARE getting your brake warning lights coming on.


All the best


Steve
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