After doing all the suspension work on the '95 VDP I felt comfortable letting my daughter take the car on a 200 mile roundtrip this past weekend, and it went great.

However, today she reports that the steering is suddenly too heavy for her to operate it at low speeds. We had this issue before, but it was cured using some Lucas Power Steering 'syrup' so it was likely the internal seals were dodgy in the rack.

I would guess then that either the Lucas additive has broken down and/or the seals have now deteriorated beyond the ability of the additive to work. So I need to either rebuilt or replace the rack...

...but looking at several threads there seem to be numerous stories along the lines of 'replaced the rack, then the pump, then...etc.'

So my question is how do I diagnosis the system so I am replacing the right part and not just throwing parts at it?

 

check first the pressure of your pump, second open up the rubber boot at the steering end and see if there are fluid coming or accumulated on both side. Rack and Pinion can be repaired cheaply than buying a remanufactured one, that is if you have the time to do the project. If the pump is leaking seals are also available but if the pressure is below the specification (see indication of BAR pressure on the power steering pump assembly name plate.

 

Mac,

I don't know if this ZF Servotronic repair manual covers the rack in the X300, but just in case it may be helpful, you might want to have a look:

http://forum.bmwland.ru/index.php?ac...=post&id=26967


Cheers,

Don

 

How would I go about testing the pressure of the pump?

 

Mac Allan, to test steering pump pressure, adopt/put an oil pressure gauge on the line that comes out of the pump leading and in between the racks. Start engine and check the reading on the gauge.

 

Perhaps this is a stupid question, but doesn't the pressure get to 1000psi or above?
An oil pressure gauge doesn't generally cover those ranges.

 

I've been unable to locate anywhere locally a steering pressure tester or to be able to bodge one together. I can order one for about $90, but it's on the East Coast which will add another 10 days, plus it isn't a tool I need to add to my inventory long term.

Is there a way via driving and testing the car itself that tends to point to one of the three causes?

IOW, "if it acts this way, it's the pump" or "if it does this, it's the rack"

I'd love to not have to order the tester if I could. Thanks!

 

The first thing I would personally do is to measure the resistance across the contacts of the Variable Assist Power Steering (VAPS) transducer or solenoid, which is mounted on the steering rack pinion housing. The repair manual I posted the link for states that the correct resistance should be in the range of 7.5 ohms +/- 0.4 ohms. I think I recall reading somewhere else that for some models the correct resistance is closer to 5 ohms, but I may be wrong. In any case, resistance near 0 would indicate the transducer coil is shorted; or a very high or unlimited resistance would indicate the coil is broken.

As far as the pump goes, I have never done this, but a basic, if messy method of checking the pump's operation might be to disconnect the hose from the pump to the rack at the rack fitting. Aim the hose into a suitable container (a clear, narrow-mouthed 2-liter soda bottle might be good). Wrap rags around the hose to help prevent fluid from splashing out of the container. Top up the fluid in the reservoir with new fluid. Put on your protective eyewear. While holding the hose and bottle tightly together with both hands, have a helper start the engine briefly so you can observe the stream of fluid that emerges from the hose. Do not run the engine long enough to empty the fluid reservoir. By this method you may be able to tell visually if the pressure/flow seems low or the fluid is full of bubbles that could indicate aeration due to cavitation.

The document at the link below might give you an idea of things you can rule out with a basic inspection, such as binding in the steering linkage or suspension components, kinks in any of the hoses (including the cooler hoses), etc.:

http://www.kse-racing.com/TechDocs/K...ng%20Guide.pdf

Cheers,

Don

 

Thanks Don,

Testing the resistance is a good idea. Your link to the ZF info was very helpful, but I've been torn in various directions and are acting a bit the noob on this because my attention has been elsewhere.

I got my first opportunity to really test the car this afternoon, and it seems to drive fine unless you are going *really* slow or close to stopped.

 

You might look up how the VAPS is supposed to work, but I believe it is supposed to be most effective when you're moving very slowly. The transducer/solenoid is supposed to open a valve that provides for additional power assist for parking and low speed maneuvers.

Your symptoms suggest that the VAPS isn't working properly. I think the Workshop Manual explains the operation - there's a Steering Control Module (SCM) and its operation depends on a speed signal from the left rear wheel speed sensor via the Instrument Cluster (I think). I would think the most likely problems would be either in the electrical connectors, wiring, associated ground points, the wheel speed sensor or the transduscer.

The only Diagnostic Fault Codes (DTCs) I can think of that could be related to the VAPS system would be for the vehicle speed signal or a wheel speed sensor issue, but it might be worth checking for stored codes with an OBDII scanner just in case the problem lies in one of those areas. You can download the DTC Summaries manual and the Workshop Manual either from this forum or jagrepair.com.

Cheers,

Don

 

Hi Guys
I have the same problem and so I will be checking this post on a regular bases for any cules or solutions
Thanks folks

 

Just thought I'd pass this info on as it might help some members!

I had the same low speed steering problem on my 95 Sport and was puzzled as to why it only happend at parking speed but was fine once underway.

After much investigation involving the electronic and mechanical systems it turned out that the pipe from the PS reservoir to the cooler in the radiator was collapsing under load.

Close examination of the pipe (part no MNA3990AC) showed it to be slightly oval in profile and I could feel it move when under load (engine running and a 'helper' moving the steering). It wasn't obvious just looking at it and there were no leaks it was simply restricing the flow of fluid to the pump when it neede it the most (during parking).

I removed the pipe as it was the original 20 year old reinforced rubber hose so, being fairly cheap, I replaced it with a new item, refilled the reservoir and crossed my fingers!

After a week of mixed town/country driving including parking my steering is back to its easy, relaxed, Jaguar original.

Hope this helps!
CBXSIX

 

That's an interesting idea and simple to do...... I will do that check
Thanks again

 

Just got inside from examining that hose on my car. It is also in an oval shape and a little more flexible than it should be. However, I couldn't really see or feel it collapse, though I could feel vibration in the hose when the wheel was turned.

I took the cap off the reservoir to observe the fluid level as the wheel turned. My expectation was that if that hose is collapsing or partially blocked, that the level would drop. It didn't that I could observe.

I'm trying to think if that hose could create a back pressure situation, that would cause the pump not to draw fluid from the reservoir...?

Also, does anyone know if the reservoir has a filter or screen built in?


I should also update on what I've found regarding the VAPS system. The workshop manual has a good supplement on the system, and I was able to test the pins coming into the PSCM. The transducer tests well above the 7.5+/- ohm threshold, it has proper power and ground. I believe that if there is an issue with the speed signal, it will light the anti-lock warning on the dash.

The PSCM is a small relay looking unit, and there have been some reported failures. I found a known good one for only $15 so I thought it was a very cheap way to eliminate that as the culprit. Alas, swapping it out made no difference.

 

The reservoir HAS a built in filter that can clog. If the filter clogs, the supply hose can collapse from 'suction'. The pump can move more fluid than is supplied so the intake/supply hose collapses. This will normally cause pump cavitation and the groaning noise like a low fluid level.

The pump can also wear and not move enough fluid at low speed to cause heavy steering.

The internal valves in the rack can leak and cause 'heavy-steering' at low engine speed.

My first guess would be clogged reservoir or worn pump. Most of the times I have found this fault I replaced the pump and everything returned to normal.

It is probably less expensive to replace the pump than the rack.

You can test the reservoir by disconnecting it and pouring ATF through it into a clean jar. If it flows/drains quickly, then it is probably NOT the problem.

bob gauff

 

I had the same problem on a client's car, although they never mentioned it. I noticed the steering was heavy as slow speeds. I swapped out the pump (was still under warranty) and still had heavy steering. What I eventually found was the wires to the solenoid had burned and rubbed against the exhaust. I fixed that and had the steering back to normal. So I figured I had a good pump still and my own VDP had tough steering at slow speed. I swapped the pump and sent my own back as a core. My steering was fixed too!

Same problem, different fixes.

I think early cars had the module go bad more often than other parts but that could be my hazy memory fooling me............

 

I'll post an update to close out this thread.

I narrowed the problem down to a failing pump, and finally had a chance yesterday to install the replacement. Now everything works fine.

Thanks for all the suggestions and help. This issue got pushed to back burner as I needed to deal with a radiator re-core on the XJS, so apologizes that I couldn't update this sooner.