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Chris Miller
Grand Master
Username: cjm51213

Post Number: 420
Registered: 5-2013
Posted on Saturday, 23 July, 2016 - 12:08 pm:   Edit PostDelete PostView Post/Check IP

Hi Folks,

Hydraulic system 1 will spontaneously de-pressurize over a relatively short period, like overnight or during the day and I am considering why and what to do about it. Pressure in the accumulator can only escape two ways -- the "non-return valve" in the ACV or through the distribution valves to the brake caliper system.

Periodically, in the morning, I will discover that system 1 has de-pressurized overnight, or in the evening, if it has been a particularly hot day, and I'm not sure which path is leaking. And why would a hot day have anything to do with it, that a hot, running engine would not? Does anybody have a good diagnostic for this? I have one idea, which is a lot of work, and that would be to swap the ACV and see if the de-pressurization follows the ACV or the distribution valves. If there is an easier way to do this, I'd like to hear about it...

If it is the check valve in the ACV ("non-return valve"), then I think the solution is to polish the seat and piston, so I know how to do this and it is an easy fix, but if it is the distribution valve, I don't know what options I have to renew the distribution valves. Additionally, I have another set of distribution valves that I could swap, but I don't know how to test them, so advice here would also be helpful.

I also don't really understand how the brake fluid flows on the brake caliper side of the distribution valves. The brake pedal, via the distribution valves, allows pressurized fluid into the calipers, but how is this pressure relived once the brake pedal is released? Where does the fluid go?

Thanks for the help,

Chris.
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Jonas TRACHSEL
Frequent User
Username: jonas_trachsel

Post Number: 94
Registered: 2-2005
Posted on Saturday, 23 July, 2016 - 03:16 pm:   Edit PostDelete PostView Post/Check IP

Chris
Marinus Rijkers has a superb webpage with animated hydraulic system and its components:

http://www.rrsilvershadow.com/EIndex.htm

Hope this might help you to understand the distribution valve.

Jonas
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Robert Noel Reddington
Grand Master
Username: bob_uk

Post Number: 1044
Registered: 5-2015
Posted on Sunday, 24 July, 2016 - 12:08 am:   Edit PostDelete PostView Post/Check IP

The distribution valves have 4 ports on early cars one for bleeding.
Later cars have 3 ports - no bleed nipple.
One port is pressure in second port is pressure to calipers and third port is dump or return to reservoir.

When the pedal is off or up the dump port is connected to the calipers port. When pedal on or down the port to calipers is shut off from the dump port and connected to the pressure in port. When pedal released the pressure in the calipers goes to dump port and back to reservoir. Which is why the circuit as far as the distribution valves is more or less self bleeding when the pedal is pumped. The bit from the valves to the calipers is not self bleeding because it's a cul de sac. However if the calipers pistons are allowed to extend on to thin pads and then retracted with closed nipples air will be pushed back via the dump port to the reservoir.
Also because when pedal up the caliper is connected to the reservoir via the dump line then the reservoir can be drained by merely opening a nipple(s)
Where does the pressure go to overnight.
My car holds pressure on no1 system overnight down to about 25 pumps from 90 pumps. No 2 doesn't because the ride height continually sips pressure trying to hold the car level while parked. The distribution valves also leak a bit to lubricate them.

As said last year or the year before. The distribution valves are 600 each and must not be taken apart.

My compressor loses air gradually, find the leak is impossible.
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Brian Vogel
Grand Master
Username: guyslp

Post Number: 2012
Registered: 6-2009
Posted on Sunday, 24 July, 2016 - 12:26 am:   Edit PostDelete PostView Post/Check IP

If you wait long enough I don't know of any of these cars that don't eventually depressurize the hydraulic systems, as the various valves themselves don't necessarily seal perfectly.

I know some people who, like Chris, will lose pressure in a system over the course of hours and others over days or a couple of weeks.

Unless you are losing pressure at such a rate that braking would be compromised in a stall situation you could spend a lot of time chasing internal slow leaks that have no functional impact when the car is running and for any short period after a stall. To me, that type of internal leak not worth a lot of effort to find. If your pressure readings are fine when the car is running and you do not see pressure bleeding off at the ACV at a rate you can notice within a very short span of time when the engine is shut off you do not have a system that has any compromise in braking ability or overall safety.

It's also an interesting test to keep the pressure gauge connected to the ACV over a span of hours to see what the rate of draw down is and when the pressure warning lights illuminate. They illuminate well before you've lost actual braking ability (which is a good thing, as if they didn't illuminate until afterward they're not warning you of anything except an impending crash if you're in motion).

Brian
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Robert Noel Reddington
Grand Master
Username: bob_uk

Post Number: 1045
Registered: 5-2015
Posted on Sunday, 24 July, 2016 - 04:46 am:   Edit PostDelete PostView Post/Check IP

This is the reason why hydraulic parking brakes are forbidden.

Try this.
Start engine run for 5 mins.
Pump until light comes on and no more.
Apply brake and observe pads which should still grip the disc.
If not the switch pressure is to low.

I had the pipe from the pump to acv blow. No 2 light came on. I was 1 mile from home. So I carried on and got home and still had good brakes. The pipe cost 100 . Grr oh the pain of it. This means my lights are correct.

I read somewhere that at 40 lb of pedal pressure the pressure at the calipers should be 500 psi. Don't quote me because I forgot to write down in my shadow note book.

So using a pressure gauge in the caliper bleed nipple hole this can be checked with both engine running and engine not running with light just come on.

My car if you stamp on the pedal the front wheels lock at any speed. You can't really get better than locked wheels.
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Paul Yorke
Grand Master
Username: paul_yorke

Post Number: 1591
Registered: 6-2006
Posted on Sunday, 24 July, 2016 - 04:59 pm:   Edit PostDelete PostView Post/Check IP

Here is the simple diagnostic: First thing to do would be to narrow down which it is, remove the flex pipe from acv. replace with a bleed nipple.

Run engine and wait. If the light still come on, it can't be distribution valves.

There is a flow chart in the manual that gives a test plan.

The distribution valves are incredibly reliable.


Also check that the switches do not have any crap inside on the contacts. That can bring on random waning lights.

I would say that as long as you have at least 20 pumps AND it doesn't come on within a couple of hours I would live with it until the accumulator needs replacing. Then change the accumulator valve and accumulator together.
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Robert Noel Reddington
Grand Master
Username: bob_uk

Post Number: 1048
Registered: 5-2015
Posted on Monday, 25 July, 2016 - 04:18 am:   Edit PostDelete PostView Post/Check IP

The switches also could be another reason to use RR363.
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Paul Yorke
Grand Master
Username: paul_yorke

Post Number: 1593
Registered: 6-2006
Posted on Monday, 25 July, 2016 - 07:28 am:   Edit PostDelete PostView Post/Check IP

Just the rubber diaphragm touches the brake fluid so it probably won't help in this case. ??
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Chris Miller
Grand Master
Username: cjm51213

Post Number: 423
Registered: 5-2013
Posted on Wednesday, 27 July, 2016 - 03:15 am:   Edit PostDelete PostView Post/Check IP

Hi Jonas,

Thanks for the link. I was aware of that site and I should have not needed to be prompted, but thanks, just the same. This, in conjunction with Bob UK's explanation is quite helpful and I appreciate the assistance.

Thanks for the help,

Chris.
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Chris Miller
Grand Master
Username: cjm51213

Post Number: 424
Registered: 5-2013
Posted on Wednesday, 27 July, 2016 - 03:23 am:   Edit PostDelete PostView Post/Check IP

Hi Paul,

Brilliant! Yes. That is the easiest way to eliminate one branch! The big problem with the hydraulic system is that some of those lines require that I empty the reservoir to prevent it all from running out! Your technique requires that I dissipate the pressure, but I don't need to open and empty the reservoir, and it completely divides the problem so I can get a clear diagnosis.

Assuming my distribution valves are leaking, what are my repair options? Simply replace?

How can I test to find out if my replacements are any better than my current? I suppose I could hook up an accumulator on the bench and pressurize it and wait... That actually doesn't sound like a horrible strategy, and I have everything I'd need to do that.

Thanks for the help,

Chris.
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Robert Noel Reddington
Grand Master
Username: bob_uk

Post Number: 1055
Registered: 5-2015
Posted on Wednesday, 27 July, 2016 - 04:55 am:   Edit PostDelete PostView Post/Check IP

The valves are unlikely to be the problem. An external leak will be obvious.

Internal leaks. If the leak is from pressure in to pressure out then the front brakes would come on. If the leak is between pressure in and dump or return then disconnecting the dump line would mean fluid coming out of the dump port of the valve. This line is connected direct to the reservoir so fluid will issue from the pipe but not the port in the valve.

If the pressure is holding for say 2 or 3 hours then the car is safe to drive, even 5 mins is enough to stop the car but 5 mins is pushing the limits a bit.

I suspect that your acvs are not good due to constant dismantling.

The valves are 600 each.
The valves should leak a drop of fluid for lubrication.

Chris try not to look for faults that aren't there and read the workshop manual and use the proper test procedures. Do not make your own up because you will confuse your self. The proper test procedures are designed to be quick and easy with the minimum of dis assembly.

Note the rat trap mechanism is set up in the factory using gauges etc. These settings should not be interfered unless they are obviously wrong having been interfered previously.

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