Posted From: 22.214.171.124
|Posted on Monday, 18 August, 2014 - 01:41 am: |
As you know the brake pump has no seals and relies on a close almost transition fit. The pump moves quite fast.
The pump is easy to dismantle and assemble. Which is unlikely to damage it.
The brake distribution valve is tricky.
Because it moves not much and slower, the clearances are transition fit. Any tighter and the spool.would be to big for the hole.
This is why they are unavailable and no spares.
Transition fits mean parts cannot every be interchangeable.
The valve looks so simple and enticing to take apart. But in the front is a seal.
Normally a o ring there would extrude out of the valve. So this seal is special and now 40 years old.
One tiny tiny imperfection and the valve will probably leak worser. Which is why the valve is don't touch. If an internal leak occurs it will be obvious because the valve will leak back return and or leak to the caliper.
I think repair would be impossible. So no point in trying. But I not saying don't just be really care full.
The brake pump is more tolerant to imperfections.
£600 each for brake valves.
(Message approved by david_gore)
Post Number: 209
|Posted on Tuesday, 19 August, 2014 - 03:34 am: |
The pump has a seal, but without opening it, I must surmise that it is a seal like a piston ring, meaning steel, and not a o-ring seal. Correct? If this seal goes bad, how is it replaced? I assume it would be similar to any other ring job, but the ring itself might be hard to come by.
My manual (June 1968) indicates that at one time the distribution valves were considered sealed units, but subsequent policy recognized that there were field repairs possible. From Section G13, "The Brake Distribution Valves", Page G63, lower left, comes this text:
I keep telling you guys, that I do read the manuals...
For your consideration,
Posted From: 126.96.36.199
|Posted on Tuesday, 19 August, 2014 - 05:12 am: |
No the brake pump has no piston rings it has a plunger that is a near transition fit the clearance is less than the size of a dot molecules.
Although the brake valve is listed as take apart able. The seal is a dowty seal which unavailable.
Because this valve is very intolerant to dirt scratches etc.if it works it works and taking it apart could damaged the 40 year old dowty seal.
Often old bits were ok until it was serviced.
They cost $2000 for two second hand.
I am a retired grease monkey with 50 plus years vehicles and I can tell that you have no formal training as a grease monkey because even when you read the manual you misunderstand how cars work.
This is not being rude to you or any other non pro.
Before I went to university I thought every thing was obvious but it is far from obvious when it goes deeper.
Now go to page G30 and read how to test acv switches using the master cylinder and then tell me what this means about master cylinder circuit.
I am going to try to show you how to read between the lines of workshop manuals.
(Message approved by david_gore)
Post Number: 1443
|Posted on Tuesday, 19 August, 2014 - 08:18 am: |
Repeat after me very slowly and carefully:
Rolls-Royce Distribution Valves are made to conventional hydraulic system practice and rely on the use of individually selected matched parts to achieve the close tolerances required for the valves to function correctly.
For this reason, the DIY owner with a leaking distribution valve and without the necessary stock of new parts to match up to the specified tolerance MUST install a service exchange unit if ongoing problems are to be minimised. In this case, first cost is not always end cost and the final cost in time and money of trying to rejuvenate a faulty distribution valve without the right equipment and spare parts will inevitably be much greater than the upfront cost of a service exchange unit covered by a guarantee.
OK, we all like to tackle "mission impossible" and sometimes succeed but this is most unlikely when trying to recondition hydraulic valve banks such as the distribution valves. Just talk to any experienced hydraulic service technician and they will advise you accordingly and recount "tales of horror" where much time and money has been wasted on a quest that was doomed to failure right from the beginning.
Post Number: 212
|Posted on Tuesday, 19 August, 2014 - 08:44 am: |
How did we arrive at "Chris is going to take apart the distribution valves."? Not without understanding what I'm getting into, and so far my understanding is that I don't want to do this. And I have no reason to believe that I need to.
The manual says the seal is replaceable, but it doesn't say that the seal is available. I assumed it was some sort of o-ring, which is not too intimidating. Apparently this is not the case.
The entire question of the distribution valves is simple. Pressure can only exit the accumulator either back trough the ACV or forward through the distribution valves. If the accumulator sphere is not holding pressure, then it has to be escaping through one of these two avenues. I have rebuilt the ACV, so I know what to expect, and in another thread I'm trying to learn how it works internally, but I had no experience with the distribution valves, although I fully expected them to be "serviceable" parts. I think this discussion has dispelled that assumption...
Thanks for the help,
P.S. Bob, I have a hydraulic pump on my bench with a gauge, so the "on car" technique is very clever, but much more of a problem than simply removing the switches and testing them on my bench. It is absolutely brilliant for a grease monkey, which as you have pointed out, I am not.
Posted From: 188.8.131.52
|Posted on Tuesday, 19 August, 2014 - 08:48 am: |
Bang on money 100% correct.
I often do stuff that is meant to be fixed by specialist with special tools and got away with it. Every time it goes wrong the specialist says oh dear and whistle through his teeth and says I shouldn't have done what I done.
I don't do aircon, domestic gas and not £1200 dowty valves. Flying bits charge that much because I have worked on things like Red Head grinding spindle brgs. Which are for grinding stelite valve seats 10mm dia for dowty valves and 50 % scrap rate was the norm on a good day. The bearings cost.lots and lasted 100 seats before they got used in the less accurate stuff. Trouble was doing normal stuff they lasted years. And there was maybe £10,000 brgs in boxes that will never be used. SKF made loads of money from this.
Another is.RR V8 wet liners
Enough to give one a twitch taking liners out. When comes to stuff like this I get the willies.
Or as my mum said "the screaming abdabs" which is not a rock and roll band.
(Message approved by david_gore)
Post Number: 287
|Posted on Wednesday, 20 August, 2014 - 01:44 am: |
If there is a leak,and excess RR363 in the rat trap cover, it might be the little master cylinder that is leaking anyway. We should not but often do jump to conclusions which turn out to be erroneous.
Wouldn't a tech article on the brake control valves be interesting?
Dowty is still very much in business; anything that has been made can be made, but I understand demand would be somewhat limited. It is common to use seals, and other items such as bolts, lock rings, O rings, et al, which are a stock size and which are used in many similar products. Aircraft hydraulics come to mind here. I guess I don't easily take "No, it's not available" for an answer. Often I would be better off if I had.
Bob I hear you on "do not touch". Early on I am sitting with a technician from Solar Gas Turbines. "Now, this is the fuel control valve; it is a high-precision device; NEVER touch it." Then we proceeded to touch it. But he knew what he was doing. I still don't touch it.