My beloved XJR has a problem with its power steering; I think!
Pre lockdown, I began to feel that the steering was requiring more effort than usual when parking and manoeuvering. There was clearly still some assistance, and it didnt take an untoward level of effort, just more than usual. The tyres were at the correct pressures, hadnt been changed recently, and I hadnt been undertaking any other work related to the suspension or steering. Everything was fine at speed, and there were no leaks or untoward sounds when turning the wheel.
I decided to replace the seals on the pump, which was relatively straightforward. The old seals seemed to still be functioning properly, but the new ones were clearly softer and more "full". The system was flushed and filled with new fluid. Upon reassembly, everything worked, and I managed to persuade myself that the steering was a bit better, but not yet right. Lockdown prevented any further use until now, when I have been able to drive the car and more fully assess the position.
The feeling at parking speeds is indeed that the effort required is greater than usual, and above say, 30mph everything feels fine. What I have also noticed however is that as I turn the wheel to make a slow turn there is a stiffness as the road wheels leave the straight ahead position which disappears as the car responds to the turn. It happens on both left and right turns, and the sensation at the steering wheel is as if the rack is sticking as it moves, and then releases as the wheels turn further. There also seems to be a very slight but noticeable reluctance to self centre as the turn is released.
My current theory is that the "issue" coincides with when the rack is being asked to do most work, and could be caused by wear in the seals allowing hydraulic pressure to blow by rather than ease the effort required to move the rack. The rack has provided sterling service for some 170,000 miles, and could well be feeling its age, but the lack of noises and leaking fluid is making me wonder whether there is a more likely cause.
As always, your advice and guidance would be appreciated guys.

 

Not on all X300 models there is a variable steering servo on the rack that is controlled by a module which is controlled by the left rear wheel speed sensor as the signal " goes through " the instrument cluster ( speedometer )

The way you can tell if you have this variable servo ( converter on the print ) is if you have the module just fwd of the 2 front windshield heater ( if equipped ) relays in the pic on page 19 of the LWB pdf below

In a bit I will recall how to trick the servo to actuate one way or the other to see if it moves effecting your steering " effort "

Also see the 2nd PDF on the ZF rack below

From the module socket the way you can tell if you have a open circuit on the servo ( different then open fluid flow path ) is by socket 2 ( Red wire ) and 5 ( Gray wire ) , See page 146 of the electrical guide

This servo ( or module ) may not fail until it warms up

http://www.jagrepair.com/images/AutoRepairPhotos/jagxj1996.pdf

The connector on the rack servo can get contaminated from oil leaks but is hard to get too under there

 

Parker,
Many thanks for your post.
I have checked, and I do have the servotronic module. I removed the relay, and it is dual branded ZF and Jaguar, jaguar part number LNA2100CB. No obvious signs of damage or corrosion on the terminals. The speedometer is functioning correctly, and my ABS and TRAC warning lights are off, so I am assuming the left rear wheel speed sensor is OK.
I am not clear from the electrical guide whether there is a way to test the module, or trick it into providing "full" assistance all the time, at which point I could tell whether the rack is ok, and this is an electrical issue?

 

I'm glad you posted about this as I have the same issue in my 97 but haven't diagnosed it yet.

BUT, I have diagnosed a 2004 Volvo S60 with similar ZF Speed Sensitive Steering controlled by a Servotronic Module (not relay) and solenoid on the rack (same as "transducer" for this discussion). I looked at the wiring diagram and rack design and it looks like this system is similar. The power steering in that car was fine when you were moving but for slow parking maneuvers it was very stiff. I characterized the issue best by sitting at idle and turning the steering wheel quickly left or right, when the system failed, the steering wheel would get very stiff after a few degrees of turning, as if it were a weak pump. My 97 Jag has the exact same issue, and only has 53k miles on it.

The issue with the S60 turned out to be a clogged "oil screen" on the rack solenoid. As you can see from the pictures, it clogged, and then burst, and then I think the solenoid itself clogged. You can also see from the pictures below that the Jaguar "Servotronic 1" system has the same oil screen (I assume that's what you have because that is what my Jag has?). But I won't jump to conclusions and say this is your issue too, especially since you want to avoid removing the solenoid if you can, the screws are very small and you risk stripping them out and I bet it would be very hard to find replacement O rings and oil screen. First you'll want to test the circuit, so let's talk about that.

The Servotronic Module has five pins. Wire colors WP/U/R/S/B (White+Purple/Blue/Red/Slate/Black). The black wire is ground. The WP wire is B+ which receives its power through a 10 A fuse in position 12 of the RH heelboard fuse box, this goes hot with "ignition on". The U wire is vehicle speed input. The R and S wires are the two leading to the rack solenoid.

The vehicle speed wire's (U wire) input changes depending on vehicle speed (shocker), but the way that it does it is confusing, someone might have to clear up what the electrical guide means by this: B+ @ 10 MPH = 20 Hz, 20 MPH = 40 Hz. I think that means it is a 12V signal AC with varying frequency. A voltmeter with AC voltage reading should pick this up.

In my Volvo (Servotronic 2 or later), the solenoid was actuated by a variable AC signal from the module. It looks like on these Jag's it is a varying DC voltage (easier to diagnose). For some reason the diagram doesn't label which of the wires going to the solenoid are which on the module, but for the sake of testing it won't matter. It states one is "negative transducer signal" and one is "positive transducer signal". The "negative" wire is 2V @ idle and decreases with vehicle speed. The "positive" wire is 9V @ idle and increases with vehicle speed. This means that at idle, the solenoid sees a total voltage of 9V - 2V = 7 Volts. And at speed, the solenoid sees a total voltage of potentially 14V - 0V = 14 Volts (could be slightly less, the guide doesn't specify what exactly "increases" and "decreases" means).

So all of this summed up, it it my understanding that the module works by taking a varying frequency AC voltage from the instrument cluster. It then varies the voltage to the solenoid between a total voltage drop of either 7V to 14V depending on vehicle speed. If I were you, I would do this:

1. Check the fuse, make sure it is a 10A and not blown.
2. Make sure the ground at the Servotronic connector has continuity to ground.
3. Make sure the Servotronic connector has B+ at ignition on.
4. Check for a short-to-ground in both wires leading to the rack solenoid (one lead on wires, one lead on ground, should be very high resistance or open).
5. Check the rack solenoid for corroded pins (might need to remove a few things in the engine bay to get to it.
6. Visually inspect that circuit for breaks.
7. If that is all good, then we can get more in depth.

One of the bummer's with these systems is you cannot just "jump" the solenoid to make it "full assist" at all times, their signals are more complex and I think it is best to try and actually fix the system. As you can see by more of my pictures, I eventually built a little extension harness for the module (they are harder to get to on the Volvo's) and this allowed me to do more in depth testing. This isn't necessary for you yet.

 

Off the top of my head the module is an amplifier and at one end of the range puts out 11 DC or so volts

So simply putting that on the pin 2 and 5 , I don't see as being a problem

A servo connector clean may be your solution but then its up high on the rack like in the Volvo pic but more stuff in the way

By the fact that it gets warm to the touch lets you kmow the amplifier is at least alive

You can tap into the wire on pin 5 to see the voltage increase from 9 volts with increase in speed as you test drive

Wire on pin 2 should decrease from 2 volts with increase in speed

That will let you know if the servo is getting the correct command from the amplifier / module ( whether it's getting enough current to force the servo is a different question ? test lamp from a spare brake lamp illumination ? )

 

Rustbelter,
Thank you very much, that is interesting and helpful. The fact that Jaguar and Volvo were both owned by Ford in the mid nineties could account for the similar systems, although ZF had pretty much cornered the market too.
My module has a ZF part number on it as well as the Jaguar one, and it is the same as your Volvo one apart from the last 3 digits; mine are 245 rather than 278.
Parker,
Thank you again too.
Frustratingly, I have just started another small project (fuel injecting a Triumph Stag, yes, I know, glutton for punishment!) so cant get the Jag on the lift at the moment to check out the servo. In the interim, I will check out the fuse and the earth for the module. I have been searching the net and have tracked down the correct Jaguar module for £50, and will try googling the ZF part number. At a low enough price it is tempting to buy one for a spare and to test by replacement, as the servo doesnt sound like an easy fix.
I will keep you posted, and thanks again

 

Some small project that turned out to be! Note to self, don’t try retrofitting fuel injection to an old car again; the anguish and bewilderment are not offset by the successful outcome!
Anyway, back to my beloved XJR at last, and having been under the car at last, the rack looks like new, and not a drop of fluid has leaked anywhere. Cleaned the electrical connections for good measure, but all to no avail, situation unchanged, steering heavier than I recollect it should be when parking or slow speed manoeuvring. Something else I noticed is that the steering is sometimes a little reluctant to return to the straight ahead position after a sharp turn. Nothing drastic, but again, noticeable.
This last development has set me wondering about the joints in the lower steering column, between the bulkhead and the rack. If they were dry, could they be causing a degree of resistance to the wheel being turned? I dont recollect seeing anyone post about this and am curious whether anyone has any experience of problems in this area before I take the plunge and take the lower column off.
As ever, all input appreciated.

 

Before looking at the rack manual the 2 outboard most seals can be smashed too tight by the end cap .so by backing it off a turn or 2 may help relieve the grip

This can be also from a incorrect sized outboard most ring seal

To get to the many internal piston seals would be a complete overhaul

 

Thanks for the manual, LadyP!
I'm just trying to find seal part numbers to stanch the leak at the servo......So far unsuccessfully....guess i'll just have to dis-assemble and take the old out on a scavenger hunt....at least it is off-vehicle....but the one in-service on the gold car is beginning to leak worse than the take-off unit....

 

There was a whole rack seal kit in a picture that has a kit #

https://www.jaguarforums.com/forum/xj-xj6-xjr6-x300-26/x300-steering-rack-replacement-52224/

See post # 8