Post Number: 10
|Posted on Saturday, 18 November, 2006 - 16:11: |
I'm really upset. A little over a year ago I purchased a rebuilt accumulator + valve for the #1 hydraulic system from a company in Surrey, UK. When I received the assembly I wrote to tell them that there was some embedded dirt where the fittings screw into the assembly, which to me would indicate that it hadn't been cleaned properly. The company wrote back to say that it was probably dirt from their testing appartatus. Yeah, right.
I went ahead and installed the assembly and everything seemed fine until a couple of months ago when the #1 pump intermittently started making too much noise. I bled the system several times but the noise continued.
This evening I tested the accumulator/valve by attaching my gauge to the high output port, attaching an overflow hose to the short steel portion of the line that normally would go back to the resorvoir, and then I blocked off the rubber portion of that line so fluid would not flow back out of the resorvoir.
When I started the engine the gauge went to about 2250 psi in a couple of seconds and then stayed at that pressure. At this point the accumulator continually pumped excess fluid into the overflow bottle (this normally would have gone back into the resorvoir). Applying the brakes did not affect the pressure which stayed at a constant 2250 psi.
If I understand the manual correctly, this indicates a problem with the valve assembly. I tried hitting the assembly with a hammer, but that didn't help (although it made me feel better.)
I don't want to return the assembly or have anything more to do with the dealer in Surrey, and would be very grateful for advice on the following:
1. Is my diagnosis correct about the valve assembly and do these readings indicate that the accumulator sphere is also bad?
2. Although the manual indicates otherwise, is it possible for me to rebuild the valve assembly while the accumulator sphere is still attached and fully charged?
Thanks very much. I'll calm down now.
Post Number: 1133
|Posted on Saturday, 18 November, 2006 - 20:45: |
1. It sounds as if the valve assembly is doing its job properly. Leave it alone.
2. Removing the sphere is a trivial job, and makes handling the valve body much easier in the unlikely event that the valve body needs attention. The o-ring between the sphere and the valve body is best replaced at every opportunity anyhow.
My guess is that the sphere's diaphragm has ruptured and that the valve body is just fine. The fact that the pressure rises rapidly to over 2,000psi suggests that the accumulator's sphere diaphragm has ruptured.
- If the diaphragm is intact and the nitrogen fully charged, the pressure will jump to 1,000 psi then rise gradually to over 2,000psi over a minute or so.
- If the nitrogen is low, it may jump to 500psi then rise gradually to over 2,000psi over a few minutes.
- If the diaphragm has ruptured, there is no gas to compress, so the pressure usually jumps up there to over 2,000psi in a hurry (over a few seconds) and the pump will make lots of noise as the pressure pulsates. This sounds to be your scenario.
Post Number: 1135
|Posted on Saturday, 18 November, 2006 - 21:25: |
ps: have a look at the manual on this site for Silver Shadows. The same principles apply broadly for all post-1965 cars (SY and SZ alike). It bears out the statements in the previous posting.
Select Chapter G, section G6: see page 38 of the PDF document of section G. It is broadly correct except that:
- a steady reading of between 2,000 and 2,800psi is acceptable with the motor running. There is always some error in the gauge reading, and some tolerance in the actual pressure is to be expected.
- The document is ambiguous one one issue: with the motor running the pressure will stay high with the brakes applied and the diaphragm ruptured. However, with a ruptured diaphragm and the motor stopped, the pressure will drop to zero as soon as the are brakes applied.
Post Number: 23
|Posted on Saturday, 18 November, 2006 - 21:51: |
With your gauge connected and registering 2250 psi, does turning off the engine cause the gauge to drop to zero ?
This would confirm Richard's diagnosis.
Because of the intermittent nature of the noise are you sure it is coming from the pump and not a tappet ?
Post Number: 11
|Posted on Sunday, 19 November, 2006 - 08:36: |
Richard & John - thanks for your thoughts. I'm not absolutely sure that the noise is not tappet-related, but it seems that the tapping occurs when demands are placed on the braking system. The noise seems to be coming from the front pump. This tapping happens on start-up (as expected) but then probably every minute or so depending on whether the car is just idling or is actively being driven.
Regarding Richard's diagnosis, the gauge stays at 2250 psi when the engine is shut off and the brakes are applied. I didn't monitor the gauge very long after the engine was shut off, but it stayed at that pressure for at least 2-3 minutes.
Post Number: 624
|Posted on Sunday, 19 November, 2006 - 09:30: |
Have you any brake warning lights showing on start up after the the vehicle has been standing.
If so which one?
Post Number: 24
|Posted on Sunday, 19 November, 2006 - 09:56: |
It does not seem you have a problem with the accumulator. To confirm this run the engine for a few minutes, switch off, turn on the ignition and see how many times you can pump the brake pedal before the warning light comes on. It should be at least thirty.
Regarding the noise, can you bring it on by pressing or pumping the brake pedal while in idle ?
Check that both hydraulic reservoirs are up to the mark.
You may be able to determine the noise source by placing the blade of a long handled screwdriver on the pump body with the handle end to your ear (careful !)
Posted From: brig-cache-4.server.ntli.net
|Posted on Sunday, 19 November, 2006 - 01:02: |
Run engine for 4 mins.
Turn ignition on do not start engine.
Pump brake pedal. Over 90 pumps is a good accumulator less than 20 is dangerous.
No pumps and lights come on indicates ruptured diaphragms.
Leave car for 3 hours then check again with out starting engine.
I do the above once a week ( I try 30 pumps no lights and I am happy )
On my car No1 lasts 3 days and No2 lasts 10 hours. ( if the car is sat in or rocked No2 depletes quicker via the rear suspension hieght valves)
A good sign is that the power brakes will bleed with out running the engine-- the stored pressure must be driving the fluid.
Also if fluid squirts out of the valve body/ accumulator bleed nipple ( 3/8 UNF thread )with engine off then the accumulaors must have a charge.
If the accumulators are completely discharged the fluid pressure will force the diaphragm up agianst the charging valve and causes a nick in the rubber which will fail when the accumulator is recharged so if this has happened fit service exhange accumulators.
(Message approved by david_gore)
Post Number: 625
|Posted on Sunday, 19 November, 2006 - 22:14: |
If all the above is ok you may like to check that the flex feed pipes to pumps are not restricted as the pump in question could be sucking some air.
Note do not let any fluid get to the hot exhaust.
Post Number: 12
|Posted on Monday, 20 November, 2006 - 11:45: |
Thanks everyone. Got to work for the next few days and then I'll get back to it.
Post Number: 13
|Posted on Thursday, 23 November, 2006 - 15:40: |
Yep, looks as if it is the accumulator sphere. Thanks to everyone for the advice - it was very helpful and appreciated. The unit is now off and will soon be on its way to a dealer.