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post #1 of 11 (permalink) Old 06-21-2014, 02:31 PM Thread Starter
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Brake bleeding

Having replaced all caliper pistons and seals, all flexible hoses and 10 sections of bundy tubing I have today attempted to bleed the hydraulic circuits; no leaks so far but the following problem.

The upper pistons of the rear calipers are not getting any fluid delivered to them. The brake pressure limiting valve which supplies these pistons has been bled and although the flow from its bleed nipple was a bit slower than I expected, all air was cleared from the system and clean fluid collected.

I suspect that there might be a blockage within the valve; either deteriorated seals or a stuck ball bearing blocking the outlet port.

Has anyone experienced this problem; I am considering giving it a few taps with a hammer, but if not then its drain down time again.
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post #2 of 11 (permalink) Old 06-21-2014, 03:26 PM
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Does your car still have a master cylinder? I cannot recall at what chassis number the master cylinder was deleted.

If it does, you will almost certainly have to either pressure or vacuum bleed the master cylinder circuit. Take a quick look at Flush and Bleed Your Silver Shadow/Bentley T Hydraulics/Brakes the Easy Way.

You could certainly have crud somewhere in the system that's restricting fluid flow. If I recall correctly you posted that this car had been in storage for a long time before you began your revival on it.

Brian

The opposite of a correct statement is a false statement. But the opposite of a profound truth may well be another profound truth.
~ Niels Bohr


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post #3 of 11 (permalink) Old 06-22-2014, 09:25 AM Thread Starter
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The car is a very late series 1 and does not have the master cylinder.
You're right, the car has been stood for 8 years, but as the fluid and reservoir were clean and full, I thought I would replace the obvious first such as hoses and any suspect pipework, and give it a go.
I have filled it with straight DOT 4 fluid to flush it and to test the basic operation of everything, then I plan to fill it with RR363 once I am happy everything is good.
The plan was working until I found this problem with the pressure limiting valve.

I am going to make up a blanking fitting to stop off the feed to the valve so as to minimise leakage, then remove the valve and fit new seals.
I should get away with just bleeding the front /front calipers and I will blow out the line to the rear calipers from their upper bleed nipples using compressed air to remove any potential blockage before reconnecting and bleeding them.
I attempted to re-bleed the pressure limiting valve last night but noticed a few small black particles in what was otherwise clean fluid, so I have concluded that the seals in the valve have gone; parts of which must be blocking the feed to the upper rear pistons.

Everything else has bled easily and there has been no sign of contamination in the fluid. I have not yet had the accumulators refurbished as I want to see how they are (they were replaced just before the car was laid up).

It's all good fun and becoming easier to understand as I get into the job; the rear suspension is working, I have no leaks (so far) and the brakes are actually stopping the car and releasing, so I'm getting somewhere.
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post #4 of 11 (permalink) Old 06-26-2014, 03:51 PM Thread Starter
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I have now replaced the seals in the G valve and bled the circuit and the brake are working, but I am clearly going to have to get the accumulators sorted.
The pressure is depleted by 10 brake operations, and the front reservoir is rising in level over night which I assume is due to the check valve in the front control valve passing fluid.
So I am in the market for either a rebuild or recharge of the accumulators (8 years old but not apparently perforated), and a rebuild of the control valves.
I have found several posts regarding DIY recharging, but can't justify the cost of the equipment; so wonder if there is anyone in business who does this.

I have attempted to contact William James Motors Ltd who have an active website offering the best deal on rebuilding accumulators; but their phone number is not recognised and they do not respond to emails; are they out of business?
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post #5 of 11 (permalink) Old 06-26-2014, 06:18 PM
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You should download the RR & Bentley Parts, Repair, Restoration & Other Resources Compilation and search for "GENERAL PARTS and SERVICE DIRECTORY (UK)". Also, "the usual suspects" in the UK, Introcar and Flying Spares, do accumulator rebuilds and ACV rebuilds.

You're definitely in a part of the world where Rolls-Royce and Bentley service is much more easily obtainable than elsewhere.

The Accumulator Control Valves (ACVs) are really not all that difficult to rebuild and generally need nothing more than to be thoroughly cleaned out and the seals replaced. If, however, you have pitting on the surface of the bore into which the bobbin fits you would have to have the ACV sleeved.

Brian

The opposite of a correct statement is a false statement. But the opposite of a profound truth may well be another profound truth.
~ Niels Bohr


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post #6 of 11 (permalink) Old 03-04-2016, 04:22 PM
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Hi Brian,

I'm about to use your brake/hydraulics bleeding method but - if I got it right - you do not mention bleeding the accumulators as a part of the process. Could you explain me why ? Many thanks.

Jean-Christophe - Silver Shadow 1, 1976, SRH25085
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post #7 of 11 (permalink) Old 03-04-2016, 05:57 PM
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Essentially, the accumulators self-bleed.

If you have any air in the accumulators it is the first thing pushed out toward the end points when you have the brake pedal partially depressed and are opening the bleed screws. They also "self burp" during the initial fill cycle in most cases - the air gets pushed out by the incoming fluid and returned to the reservoir where, of course, it simply escapes.

If someone wants to be really, really cautious, then do your first pressure accumulation, turn the car off, return the key to the run position, and do the brake pedal test until your brake warning light(s) illuminate plus maybe 20 or 30 more presses. This completely empties whatever is in the accumulator and when it refills any air that might have been between the reservoir and the input to the ACV was pushed out long ago by the initial pressurization, and nothing but fluid goes in.

I've actually not bothered to bleed the accumulators when I've done this job myself. All indications are that it's not necessary and, if I really want to ensure the accumulators are bled I'd rather do a depressurize/pressurize cycle with the brake pedal. I have no great love for either RR363/YAK363 or HSMO/LHM and the messes that can come about during bleeding, particularly at the accumulator, if your hand slips or the tubing comes off the bleed nipple somehow. Been there, done that, was "slimed".

Brian

The opposite of a correct statement is a false statement. But the opposite of a profound truth may well be another profound truth.
~ Niels Bohr


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post #8 of 11 (permalink) Old 03-05-2016, 05:28 AM
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Very clear. I love knowing why and how things are done -or not- when applying a step by step.

By the way "self burp" : saying the same in my latin language would take half a dozen words

English is efficient

Thanks again.

Jean-Christophe - Silver Shadow 1, 1976, SRH25085
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post #9 of 11 (permalink) Old 03-05-2016, 11:48 PM
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Hi, about the best deal on rebuilding accumulators this William James Motors offers, how much is their price? As far as I know, $300 is about the average cost for one accumulator rebuild. and the shipping is in addition to that.


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Originally Posted by vincentbob View Post
I have now replaced the seals in the G valve and bled the circuit and the brake are working, but I am clearly going to have to get the accumulators sorted.
The pressure is depleted by 10 brake operations, and the front reservoir is rising in level over night which I assume is due to the check valve in the front control valve passing fluid.
So I am in the market for either a rebuild or recharge of the accumulators (8 years old but not apparently perforated), and a rebuild of the control valves.
I have found several posts regarding DIY recharging, but can't justify the cost of the equipment; so wonder if there is anyone in business who does this.

I have attempted to contact William James Motors Ltd who have an active website offering the best deal on rebuilding accumulators; but their phone number is not recognised and they do not respond to emails; are they out of business?

75 Silver Shadow LRD21XXX
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post #10 of 11 (permalink) Old 03-06-2016, 12:17 AM
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Covenant,

Given the range of work you've already done I have no doubt that you would have no difficulty rebuilding your own accumulators. It's not difficult to put together your own charging station for very little investment. Another option is to check with the mechanics at your local airport, as they use accumulators in all sorts of applications and will often charge your accumulators for a small fee.

If you do decide to go the rebuild it yourself route I can say that the Flying Spares redesign for the primary seal is much better than the original ball bearing seal. I have had "bad luck" with the original secondary (plastic ball) and tertiary (O-ring) sealing system as well, and now omit the plastic ball (but keep the O-ring) but use hydraulic/pneumatic thread sealant, e.g., Loctite 542, on the cap threads instead.

I know I've posted both here and on the Australian forums about rebuilding my accumulators and many have posted photos of the pin wrenches they've designed and used to separate the accumulator for rebuild.

Brian

The opposite of a correct statement is a false statement. But the opposite of a profound truth may well be another profound truth.
~ Niels Bohr


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