Hydraulic system help

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- Hawk GT
  
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posted
20 years ago

Thu, Jul 17, 2003 6:55 AM

Hello Jag owners and lovers!

I own an '88 XJ40 3.6L. I spent the winter tinkering with and working all the little problems out of it and have enjoyed a summer of driving it in the Colorado sunshine! Recently I have noticed a pulsing fluid sound emitting from behind the dash above the brake pedal, that disappears when any pressure is applied to the brake pedal. From a little investigation I noticed the rhythm of the sound matched the movement of the high pressure hose coming from the hydraulic pump to the valve assembly. Being short on spare time I decided to take the car to the local Jaguar dealer for this repair. After 5 days and over $700 in parts and labor, I drove the car home still with the problem. The service technician recommended and replaced - relief valve (part no. CCC-3832 - $70) and high pressure switch (part no. CCC-3834 - $350). When these did not correct the problem, he threw up his hands and said there is little documentation on how to trouble shoot these cars and we would have to just keep replacing parts in the hydraulic system (which by the way are not returnable) until we find the bad part. The car has had the self-leveling suspension converted to non-leveling shocks, so the hydraulic system only runs the brake boost. I am hoping that someone has experienced the same problem and can point me to the cause and solution to the problem without costing me a small fortune 'trying' more parts.

Thanks in advance for any help or suggestions!

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- webserve
  
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posted
20 years ago

Thu, Jul 17, 2003 12:09 PM

Hawk, From the XJ40 book on

formatting link

7.3 - 'Pulsing'

"If you can see the pressure lines pulsing, and hear a knocking sound which varies with engine speed, you might have a sticking charge switch. That's the switch on the accumulator with the yellow-black and black-pink wires.

When low pressure is detected the switch closes, supplying a ground to the charge valve (unloader), which directs high pressure oil to the accumulator.

If the switch sticks closed the pressure builds up until the pressure relief valve opens.

You can check it by measuring the resistance to ground of the yellow-black wire when the pulsing occurs. If it is grounded then the switch is closed and that's where your problem is.

It is worth trying unscrewing them and cleaning."

Total Cost: $0

You should nread the book and Never, never, never, never, never (did I say never?) take your car to adealership for repairs. There idea of auto reapair is to simply replace what ever they happen to think is wrong at the moment. Doesn't matter if they are correct or not -- you pay the tab.

Webserve

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posted
20 years ago

Thu, Jul 24, 2003 3:50 AM

Thanks for the great link and advise Webserve!

With the engine running I tested the yellow-black wire for a ground. What I observed, as the hose from the pump builds pressure the yellow-black wire receives a ground, as the pressure relief valve opens, the ground is removed from the yellow-black wire. I'm not fully clear by the wording below:

Since the yellow-black wire does receive the ground during the pulse, but it is not a constant ground, is this my problem? I will be removing and cleaning the charge switch tomorrow night and re-test it if I'm understanding it correctly.

Thanks! Hawk

accumulator.