I have an 88 XJ6 with an ABS problem. It seems to be different than other ABS problems I have read on this forum. Occasionally before driving the Brake Low Pressure message is displayed. This disappears after a few seconds. Then the Anti-Lock Failure message is displayed. This is followed by a repetitive clunking at about 1-2/sec. it seems to be coming from under the center of the dash. It increases with engine revs, but never gets faster than 2/sec. The brakes are a little soft but seem to work fine. Most times there is a repetitive clunk coming from the RF wheel when starting out. I have not seen any obvious problem with the disk or sensor when I lift the wheel and rotate by hand. The noise continues while driving. Any ideas? I cannot find the actual hydraulic pump for the brake boost. Where is it? Apparently it is engine driven according to Haynes. The tank shows a green float. Any assistance is greatly appreciated. Thanks.

 

Hi British Ride,

Welcome to the Jaguar Forums! It's great to have you with us.

It's been a while since we owned our '88 XJ6, but I think I recall that the brake system hydraulic pump, valve body and accumulator sphere are mounted in the front right of the vehicle - I think you have to partially unfasten the wheel arch liner for access. The location of these components could have something to do with the noise you are hearing from the right wheel area.

In addition to the Haynes manual, I would highly recommend that you order the appropriate XJ40 Service Publications DVD-ROM from the Jaguar Daimler Heritage Trust (jaguarheritage.com). The DVD contains the original Jaguar Workshop Manuals and other resources. The Supplementary Information DVD-ROM contains additional valuable info, such as the Electrical Guide that shows all the schematics for the car.

Another good resource is jaguarclassicparts.com, the parts service of the JDHT. There, you can view part diagrams and look up part descriptions and part numbers. For example, here's the diagram for your ABS pump/valve block, accumulator and combined pressure and warning lamp switch:



The diagram is from this webpage:

http://www.jaguarclassicparts.com/uk...lator-and-pump

For some helpful information on diagnosing problems with the hydraulic brake boost and ABS system, the eBook at Jag-Lovers.org is worth studying. You will have to join to view the contents, but it's free:

Hydraulic system:
Jag-lovers' Ebooks

ABS Warnings:
Jag-lovers' Ebooks

Do you know if your car has the Self-Leveling Rear Suspension (SLS)?

Regarding the clunking noise you are hearing from under the center of the dash, does it sound mechanical? Could it be a relay latching and unlatching? Have you tried turning off the A/C blower fans and radio to see if the sound goes away? Off the top of my head, I can't think of anything associated with the brake system that would make noise in that area.

Can you hear the sound while standing beside the engine bay with the hood/bonnet up and the engine running? A common issue on the earlier XJ40s is hardening of the rubber fuel line at the fuel rail, which can cause a soft "helicopter" like sound inside the passenger compartment that cannot be heard in the engine bay. But the frequency of the sound is usually faster than 2/sec because it's related to fuel injector pulsing, so it doesn't seem as though that is your issue.

Please keep us informed.

Cheers,

Don

 

Don, thanks for the info. I will check further. The clunking sounds are both mechanical. When I start the car the first seems under the dash. When I start moving the dash clunking is less obvious and the wheel sound starts as soon as the wheel starts rotating. I am suspicious that the dash clunking is actually reflecting and coming from the engine compartment. I will prove that today. I cannot feel anything obvious when I rotate the wheel by hand and I do feel a slight pulsing in the brake pedal if I touch it lightly once moving. I do not feel anything if I brake normally. I wonder if the pump may have low pressure since I get a Brake Pressure low alert occasionally upon engine start. Ron.

 

Ron,

The Brake Pressure Low alert is fairly common while the pump pressurizes the system, especially if the accumulator is not holding pressure as well as it once did. You might do the simple accumulator test outlined in the eBook.

Regarding the clunking at the right wheel, have you checked for play in the wheel bearing? Very common on these cars and not too difficult to correct, even if you need a new bearing. Also check the dust shield on the brake rotor to see if it is coming into contact with a moving part. If the clunking is more pronounced going over bumps, suspect the top shock bushings. There's not a lot that can clunk in that area: ball joints, steering rack tie rod end, control arm bushes, exhaust heat shields.

For the clunking under the dash, perhaps an engine mount or the rear engine/transmission mount could be allowing the bell housing to contact the transmission tunnel or an exhaust heat shield, or a front subframe rear pivot bushing could be failing....

We'll be curious to hear what you learn upon further investigation.

Cheers,

Don

 

Don, finally had a chance to do a little more work. Good news and mediocre news. I found the overvoltage relay had a bad fuse. This is a car that sat for a number of years. It has new battery so a jump start and spike would not be too hard to imagine. The fuse is 8A and is a microfuse (electronic use only). I installed an old VW style fuse since the microfuses fuses are at work. The Antilock Failure message has left the Jag. Fantastic. Now the mediocre news. The pressure valve you referenced is the source of the repetitious mechanical clunk. It is pulsing, there is a clunk followed by a pulse of fluid in the valve body. Disconnecting the electric line eliminates the noise. I am afraid to drive it this way since there may be excessive pressure-not sure how the system works. You asked previously if the car had SLS-it doesn't to my knowledge. Can't see lines. The shocks are a little soft and there is no leveling action with weight in the trunk. I have topped up the hydraulic fluid since I thought it might be low pressure at first. It did take almost the whole 1/2L (quart) but no change noticed. Progress has occurred though and thank you for your help. It is great to get rid of the Antilock message. Ron.

 

Yes!!! That's great, Ron.


Just thinking out loud, but is it possible that the valve body or accumulator are in contact with part of the body and normal noise is being amplified and carried into the passenger compartment? Is the valve body mounted with rubber isolation bushings, and if so, are they in good condition or deteriorated?

Don

 

Thought it was about time I reported my findings thus far. I ordered a new Charge switch from Welsh Ent. It arrived quickly, unfortunately it was the wrong part. They are out of stock for about two weeks. Sigh. Here is what I found and why I ordered a new Charge Switch. I checked the pressure, bought a cheap 2000psi gauge and fittings. The pressure rises to 1500psi according to the cheap gauge. It is supposed to have a pressure relief at 120bar. (1740 by my calculations). Then the pump output line pulses periodically according to engine RPM. Approx. 3per sec is the max I could hear for normal in town driving-any higher revs make the noise hard to hear. When the pressure is high the switch was closed. It is supposed to open and release the charge solenoid to allow fluid to bypass to the reservoir. I proved the operation with a cheater switch. Close the switch and the pressure rises till pressure relief. Open the switch and the line does not pulse. Leave it long enough and the low pressure warning comes on. Hold the switch on and the low pressure warning disappears. The Charge Switch is located on the lower port of the Accumulator. This is located on the RH side of the subframe in the engine compartment. Only visible from under the car. By the way the XJ6 uses 0.125" Molex pins for the electrical connectors. These are available from Jameco Electronics and are cheap-I mean inexpensive. You will need a proper crimp tool or patience and a standard crimp tool to put them on the Welsh Ent Charge Switch. Thanks to Don B and all who assisted with this problem.

 

I believe now that all is well and that nothing further can go wrong....Hopefully I can summarize the solution. I ordered a charge switch from Welsh Ent. for $175 plus 55 shipping with a further $20 for customs. The switch was incorrect in pressure and contact activated. After some frustration with the supplier and against better judgement I set to make the switch work. This involved connecting to the NC position of the switch and not NO as shipped and adjusting the pressure. This is a PDI switch that sells for $50 from PDI or suppliers. It also has a $20 adapter for the Jaguar threads. Note: remove system pressure before opening any fluid connection-you will know if you don't. Even a little will spill a few ounces of fairly expensive and hard to find hydraulic fluid. I removed the epoxy on the switch head to access the contact wire needed. It needs to be re-epoxied for protection. The pressure adjustment is located near the center end of the switch body. There is a 3mm allen plug with the 3mm adjustment screw located underneath. The XJ40 hydraulic procedure manual from Jagforums is invaluable for the adjustment pressures and testing procedures. I set it for 83Bar activate. It will pressurize to 100Bar (1450psi) before opening and bypassing the pump to the reservoir. This is normal. I found the line would still pulse intermittently. The pressure relief was activating at 1450. This valve can be removed. I drilled out the brass fitting where it is punched to hold the adjustment screw. Only drill the outer shell and be careful not to drill the adjuster. I did not test pressures afterward but this is what I found. At 100Bar it was relieving pressure. 1/4 CW turn of the adjuster resulted in occasional pulsing. 1/4CW more eliminated the pulsing. It is likely set below the factory spec of 120Bar (1750psi) but I am Ok with that. If you are not simply use a pressure gauge to verify and adjust accordingly. Hope this all helps someone experiencing what seems to be a fairly common 88-90 XJ40 problem.
PS: In a previous post I reference the 0.125" molex pins used in the Jag connectors. This should read Mouser Electronics not Jameco as I stated above.

 

Ron,

That's a tremendous report, and congratulations on sorting it all out!

Did you take any photos as you were modifying the switch? If so, please post them when you can because they will no doubt be very helpful to others who may face the same issue in the future.

Cheers,

Don

 

Jaguar issued Publication S73 for info on the Power Hydraulics system. The 88/89 are VERY different from the 1990-1994 MY cars.

bob gauff

 

This picture is of another brand of switch. My apologies for not taking pictures. This will get the message across though. The OEM (Lucas) switch and any other replacement hydraulic switch that is adjustable will have the same basic layout. Contact wires with an adjustment port, usually on the opposite to the threaded end. The Suco Co. switch above has an adjustment screw on one side. The Lucas switch adjustment is visible once the boot is removed and sits on one side of the end face. The switch in my XJ6 had a hole close to the wires. This hole had a 3mm Allen set screw plug. Once this was removed access to the 3mm adjustment screw was possible. Any hydraulic switch will work as a charge switch if it can be adjusted to 83Bar and has a NC (normally closed) contact. Any hydraulic switch will work as the low pressure indicator if it has a NO (normally open) contact and can be adjusted to 50Bar. The Lucas switch has a port that adjusts CCW to raise pressure. The switch I was supplied adjusts CW to raise the pressure. You will need a 2000psi gauge in the circuit to adjust the system properly. The overpressure mechanical relief is also adjustable. Be sure to remove the complete relief valve to remove the adjustment locking dimples in the fitting. CW will raise the pressure relief point. (120Bar is spec). These values are fairly critical. You will see intermittent errors if any of them are misadjusted. Ask me how I know.
Hope this helps.