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Discussion Starter · #1 ·
Hello to all. Last week I bought myself a 50th birthday present...the car of my dreams, a Bentley Fixed-Head Corniche.

Due to the wet weather I have only been able to take the 'lorry' out a couple of times, and so am very unfamiliar with it. There are several quirks which I will address as I get to grips with it, However, in light of some research I was doing on this website one in particular is worrying me.

I drive slowly and always brake early and very gently to slow the car down in anticipation of traffic. The idea being to avoid stopping if at all possible. On a couple of occasions as I've barley tickled the brake pedal I've noticed that I seem to have taken the car out of drive, but the brakes haven't yet been depressed enough to come on. The car feels like it goes into a momentary freewheel until I depress the brake a bit further, at which point the brakes behave predictably. The overall sensation is quite subtle but noticeable.

I can only describe it by saying that it feels to me like there's a trip switch on the brake which turns off power to the wheels as you are braking. So I am wondering if by very slightly depressing the pedal I seem to be activating it before I have depressed the brake enough to engage them. I hope that makes sense.

As I write this, it doesn't seem to make sense that it would be possible to stop the drive to the wheels, and so i have another theory... Could it be that the brakes are going on more than I expect initially when I first touch the brake, then contrary to what one would expect, as I depress the pedal further somehow coming off a little.

Anyway, it's a bit disconcerting to suddenly find yourself speeding up as you are expecting to brake. I hadn't thought much about it until just now when I read that the braking system can fail if the hydraulic system etc hasn't been replaced in the service interval. I have no idea if mine has or not. I suspect it hasn't, or I'm sure I would have been told about it. (There is a note to check over the brake system in the recent service sheet, but that doesn't necessarily mean much.)

So my question is: What trickery is afoot? Is this a normal quirk of the marque? Am I inadvertently tripping a power switch and just need to adjust my braking technique, or do I have the makings of a more serious problem. I was more than slightly concerned to discover that the braking system on these cars can fail completely when the car is being driven, and without any warning too! Yikes!

Any thoughts on this are definitely most welcome

many thanks in advance

Stumbler
 

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Stumbler said:
I drive slowly and always brake early and very gently to slow the car down in anticipation of traffic. The idea being to avoid stopping if at all possible. On a couple of occasions as I've barley tickled the brake pedal I've noticed that I seem to have taken the car out of drive, but the brakes haven't yet been depressed enough to come on. The car feels like it goes into a momentary freewheel until I depress the brake a bit further, at which point the brakes behave predictably. The overall sensation is quite subtle but noticeable.
My guess is that you have an insufficiently bled system with air in it. These systems, unlike others, can tolerate a bit of air in the system but, when it's there what you get when the brake system is activated is a short period where the initial rush of pressure is taken up compressing the air and, after it's as compressed as it can get, the system kicks in as would be expected.

After I had replaced all of my hydraulic lines I had a problem similar to this. I would press the pedal and get very minimal application of the brakes until the travel was at least 1/3 of the way down, and then the brakes would make a pronounced "grab." It was due to air in the system. After the system was re-bled the problem went away.


Anyway, it's a bit disconcerting to suddenly find yourself speeding up as you are expecting to brake.
This is, I think, an illusion. You have every reason to expect that you should be slowing down immediately and, when you don't, your brain automatically kicks in with the (entirely rational, I might add) fleeting panic reaction, "Oh, *#($*^_, I'm not stopping!!." Once the brakes engage that panic goes away, but you are still unnerved because it should never have happened to begin with.

You should definitely check out
Marinus Rijkers' Rolls-Royce Silver Shadow Pages with particular attention to the section on the hydraulic system. The braking system in these cars is unlike most others, except the Citroen cars on which the Rolls-Royce system is based, and you need to understand how it works. The previously noted site is the best explanation, with animations as well, that I've ever found.
 

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Discussion Starter · #3 ·
Brian,

Many thanks for your response, needless to say, this was an issue that was keeping me up at night. In fact it was while 'bed surfing' at 3am unable to sleep because of it, that I came across that site you mention. I agree it's a wonderful explanation of the system.

I will get my brakes bled, and take a good look at the hydraulics to see if there is any evidence of a recent rebuild. If not, I think I'll start planning the overhaul myself. It would certainly give me peace of mind to know it's been done.

Unfortunately, the service history of my car was lost by a major car auction house. Apparently, it's not an uncommon occurance if the car doesn't sell, in which case they lose interest and just dump the paperwork!
(Lesson: Don't give them the original, or keep a copy of everything.)

As a result I am having to start from scratch, and the learning curve is steep!

Best

Stumbler
 

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Discussion Starter · #5 ·
Thanks Brian,

I had seen that article before, but having searched so many forums since, couldn't remember where. I didn't realize it was right under my nose.

I will have a go at a diagnosis to see what I can find.

One question though, in the article it mentions using a 'proper pressure gauge'. Is this a special tool that I would have to hire, or something I can buy new and cheaply on the net?

Many thanks once again.

Stumbler
 

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Discussion Starter · #6 ·
Thanks Brian,

I had seen that article before, but having searched so many forums since, couldn't remember where. I didn't realize it was right under my nose.

I will have a go at a diagnosis to see what I can find.

One question though, in the article it mentions using a 'proper pressure gauge'. Is this a special tool that I would have to hire, or something I can buy new and cheaply on the net?

Many thanks once again.

Stumbler

PS. Just had a stroke of luck, I called up a local independent Rolls service company about coolant fluid, and they knew my car really well. They have about £20k worth of bills for it from 2000, and are going to copy them all for me. They said it was a very nice looked after car. So in the next couple of weeks I will get about six years of service history!
 

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Stumbler said:
Thanks Brian,

One question though, in the article it mentions using a 'proper pressure gauge'. Is this a special tool that I would have to hire, or something I can buy new and cheaply on the net?
It is a special tool that can be purchased from:

Hyphen Repairs, Inc. – Ralph Curzon & Tony Curzon [EPW, Clouds, & Shadows, plus others]
1146 Westport Crescent
Mississauga, ON L5T 1G1
Phone: (905) 670-3656
e-mail: [email protected]

or, I would have to presume, other Crewe-era RR/Bentley motorcar specialist suppliers. Since you're in the UK, you would be very well advised to consider joining the Rolls-Royce Enthusiasts' Club (UK). I am sure that the folks at Hunt House and the membership will be able to help you in the search for this tool and with many other issues.

These gauges are not inexpensive and one must never use on that's been used on an RR363 system on a mineral oil car and vice versa.
 

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Corniche with possible braking issue

Agreed with all previously said. From what you describe it sounds definitely like air in braking systems, if these cars aren't used much they have a tendency for air to get in system. Another way to check is to drive the car somewhere safe off road preferably and stamp on the brake pedal you will probably get a clonk from under the pedal area. Bleeding the brake system will cure it. make sure you use RR 363 brake fluid assuming the chassis number is pre 50000
 

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Discussion Starter · #9 ·
Having driven the car much further now, I can say that there has been no recurrence of that strange braking behaviour. And I have now come to the conclusion that it was actually caused by a slight tightness on the pedal which somehow managed to trick my senses into thinking stranger things were happening.

I'm going to see if there are any obvious joints to drop some oil on. I now recall that simply oiling the gas pedal wire in my old Porsche made a huge difference to the feel of the pedal.
 
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