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Discussion Starter · #1 ·
Hello everyone,
I’ve had the hydraulic system on my RR overhauled recently and am trying to manage my expectations. I know its breaking system is different than a typical car. Is the brake pedal feel on an early shadow different than a later one? I know the basic functionality is the same with one exception being that the early shadows had a master cylinder instead of a block. Since the pedal on the shadow really just opens a valve to apply pressure to the system instead of pushing the fluid through a MC, what are the symptoms of air in the system? I would expect a low pedal but would you get sponginess?
Thx,
Jim
 

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Air in the system is characterized by the brakes seeming not to apply promptly when the brake pedal is depressed, followed by a really "grabby" feeling when they do. This is because air is compressible and until it is compressed enough that it's effective in pushing the fluid along to the calipers, you get no brakes.

Brake pedal feel is not dependent on whether or not there is air in the system (unless the master cylinder were to have air in it).
 

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Go back for a second bleed. From my experience, air is pushed further down the line and close to bleeders that are all over the system to exit. The sponginess is from the air trapped in the system, it acts like a spring, unlike fluid which doesn't compress. Your '67 has a master cylinder, known as the low pressure (relative) circuit.
 

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The pedal feel should be pretty well the same. Was the master cylinder replaced or rebuilt when the brake system was overhauled? If you have a spongy pedal, you have a master problem which is likely air in the master cylinder circuit, they can be difficult to bleed. If you have delayed braking, you have air in the power system.
 

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1971 Bentley T
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In my opinion it is worthwhile doing the modification to remove the master cylinder. I suffered from "difficult-to-bleed-the-master-cylinder". Then one day, near the bottom of a hill, the brake pedal went almost to the floor. It "pumped" to stop the car OK, but....

When it happened again, after I had fitted a new MC, enough was enough and I did it.

Never looked back.

Alan D.
 

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Discussion Starter · #10 ·
I’d prefer to keep the car as original as possible so I’ll give it another bleeding. It’s a very low mileage “survivor” car. If it becomes a safety issue I’ll consider the modification.
 

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1966 Bentley T1 SBH1460
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Hi Jim, When i bled my my master cylinder after removing and tidying up the reservoir I jacked the back end up as high as I could and left the front on the floor and fortunately had no problems getting the air out. Another approach is an old motor cycle trick and that is to reverse bled the brakes using a large plastic syringe say 100cc fill it and with a bit of tubing push brake fluid into the bleed nipple as you open it and back to the reservoir or you could try using the syringe to pull a vacuum at the bleed nipple but it may just pull air past the threads.
Best Regards Chris.
 

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1966 Bentley T1 SBH1460
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Having a think about your problem if all else fails
Automotive lighting Bumper Gas Automotive exterior Motor vehicle

you could lift the lid from the reservoir and remove the filter for the master cylinder circuit it's the raised one and possibly try the syringe/tubing directly to the filter post as I seem to remember the early bolt on filters post may be hollow. It's been a while since I was last in mine but this reminds me mine is overdue for a check and clean.
Best Regards Chris
 

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Discussion Starter · #14 ·
Thx Chris.
Pedal feel is ok now but pedal travel is too much which, according to Jim, is the high pressure circuit. I think the rear height control rams still need to be bled, hopefully that will help. I did a “panic stop” with it yesterday and it reacted well but I think the pedal should be higher.when depressed. I’ll keep you updated.
Jim
 

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Jim, pedal travel is controlled by the lower pressure master cylinder circuit. If you have too much pedal travel you still have air in the master cylinder circuit, or too much free play on the master cylinder pushrod, or incorrect adjustment of the rat trap linkage. The most likely reason is that you still have air in that circuit. Bleeding the height control rams will have no effect on pedal travel.
 

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Discussion Starter · #16 · (Edited)
Thx Jim, I’ll check the rat trap linkage. Is there an adjustment for pedal height? I know of some other cars that have that. I’ll also bleed it again.
I thought responsiveness would improve by bleeding the power circuit, of which the rams are a part? They haven’t been bled yet despite being rebuilt.
 

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It is extremely difficult to judge brake pedal "feel" on early master cylinder cars without driving. I live on small island with 40mph max speed. We always had loads issues with brake pedal feel. Any cars that came from mainland UK would have great feel compared with local cars. I put that down to clean/bedded in pads/discs, It is worth clamping flex pipes to rear calipers. Need to make sure which two flex pipes because as i remember master cylinder worked upper pistons on rear caliper and later cars lower- or other way around. Gives indication of whether problem in master cylinder, Don't forget some cars had bleeder on " G" valve as well
 

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The factory installed colored sleeves on the ends of hydraulic lines and a chart indicating what the line was for, much like a subway. It's in the WM. Clamping flex pipes/hoses is not a great idea since it prematurely shortens the life of the hose at that point causing major issues. Just plug the line at the source or use caps to dead end the male fitting.
 
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