Jaguar Power Steering

Hello,

I am looking to sort out my power steering on my Jag MK2 3.8, it came to me with a very crudely fitted rack & pinion power steering set up, this not only looks horrendously bodged but fouls & rubs etc, the rack from the research I’ve done is from an XJS, my dad has a Daimler series 2 and the rack looks identical apart form the tie rod rack ends, the rack brackets are home made and not square etc etc, I’m thinking get a jag xj6 series 2 subframe cut off the factory brackets and make good to fabricate to the mk2 existing subframe once all lined up and made good, making sure wheels aligned, I have read stories about cutting column, tie rod ends etc, anyone who has done this or knows the pitfalls any help, pictures etc would be greatly appreciated, regards Paul.

My 1965 3.8S has had a rack fitted for 20 years or so. The shop that did the work in the San Francisco Bay area acquired the bracket which fits well. I do not know their source. I acquired the rack from a supplier in San Diego and specifically asked for a ZF rack as from my years in Jaguar warranty I knew these late XJS racks were more reliable and less leak prone than the earlier ones which I think were Adwest. The steering column did have to be shortened slightly but the splines matched up to the rack OK. I run the standard generator mounted pump which powers the rack with no issues. New hoses had to be made up by a hydraulic shop to connect to the rack. The downside of an rack on a Mark II, S Type or 420 is that you loose the Ackermann effect that the old pitman arm and linkage provided, This results in some tire scrubbing on turns, more severe the tighter the turn. My research indicates there is no solution for this. Due to the loss of the Ackermann effect the turning circle is reduced and early tire wear on the inner edge of the tires is an issue if you drive the car a lot and more if on twisty roads, The up side is there are no leaks and the car steers with the precision of a modern vehicle with no play in the system. Moss Jaguar sells a complete kit to convert, hoses, mounting bracket, rack, tie rod ends, etc to do the complete job. Search Moss Jaguar, early sedans, steering for full details. Not sure what type of rack they include.

I have had M&C Wilkinson rack conversion since 2002. See:


It has been OK, with same downsides John described. The kit was not so complete in those days, I kept original dynamo & pump. Later I put Dynamator in, original pump still working.
Köpi

Hi John, thanks for the reply, it’s a shame you don’t know where the brackets came from, yes I think mine is the ZF rack, if the column is shortened how about the horn assembly in the column tube, my column was cut down to fit the rack & UJ and they fitted an aftermarket horn on a crude cheap plastic rocker switch under dash! Turning circle on mine, tyre scrubbing and bad handling were many of it’s issues as well as bump steer etc, do you happen to have any photos of the rack on the car to get an idea of how it’s positioned on the subframe and how it sits in general with regard to position near chassis legs and suspension setup, any pics would be greatly appreciated John, Regards Paul.

Many thanks for the reply Kopik, I have requested fitting instructions to see what’s entailed, there kit is a lot cheaper than others I have seen available, interesting to hear your kit has been fitted a long time and all ok, again is there any chance of any photos of your kit fitted on the car, to gauge an idea of how it looks position wise etc, it would be greatly appreciated, regards Paul.

If you call Mc Wilkinson they might sell you the brackets, I know a garage that did.

Thanks Phil, I’ll give them a go, regards Paul.

Sorry I do not know where the shop I used obtained their bracket but I may have come from XKs when they may have sold a bracket as a separate part from the complete kit. There was no issues with the horn since all the column modification took place forward of the firewall in the engine compartment. The horn (at least on my 3.8S) is fed by a wire that attaches to a contact through a oval hole in outer column casing just above the floor boards. The whole horn operation set up is a bit complex (I know, I have, over the years, had it apart a few times). You will have to study the WSM to understand how it all works.

I’ll attach a few pics of my rack mounting but some are really poor photos. I need to take better ones when the car is on a lift. It all works without anything fouling other components.

.Center of vehicle with Rack installed, small

Paul Shields, Further to my earlier comments here is a picture of the inner column and the horn components and wire in the column, As I said it is a bit complex and takes a while to get your head around how it all works. BTW, you have not identified where you are located in your header.

Paul Shields: And still more photos.

My latest Mk2 had the Wilkinson system installed when I bought it and initially I was quite impressed however a couple of points worth noting.
it is not a progressive system despite their claim. the electrically operated hydraulic pump would normally be connected to the vehicle ECU to receive the relevant signals. What I think they did from tracing the wiring is simply connect the alternator out to the pump thus giving some kind of signal as speed increases (capped at 14.5 volts) which gives a totally undetectable variance in steering assistance.
Secondly you do get uneven tyre wear as has been stated above.
Lastly and this is the reason I removed it all, try driving it quickly on a twisty road and I just didn’t feel I was in control, you get very limited feedback through the steering and the steering feels ‘dead’ which I don’t like.
one other consideration you must inform your insurance company of the mods and in theory given the extent of the modification you should have to obtain an MOT every year.
I reverted to a totally original manual non power steering using a higher geared mk 1 steering box and love it. its a pig to park as the steering is heavy but on the road I just love it. This is all very subjective and depends how you want your classic to behave and feel.
best regards
Phil D

Thanks for the info Phil, I was looking at the Wilkinson kit last night, we have decided going to try make what we have work but obviously a whole lot better, as the kits are so expensive and a shame to throw away what we have, if we can re-engineer whats already with the car, regarding tyre wear etc it seems all the kits have similar traits and it is just a case of compromise to get the best drivability possible, regards Paul.

Thanks John for all the pictures really close up and can see the lot, really gives a good indication of what’s required, we are going to speak to MC Wilkinson about brackets if no joy there my brother is going to make templates and fabricate them, your pictures are a real good indicator of what’s needed and how it should look, as for the horn like you say a real complex goings on, I initially had all my column apart to see whey wasn’t working then found out column had been chopped for steering rack as well as lots of parts missing of it, I now have a replacement column which will remain untouched any mods will be done after column on the u/j’s, Sorry I am based in the UK, regards Paul.

I am thinking of fitting PAS to a non PAS RHD car, I have a rack from a BMW E21 323i, why? because I worked on BMW’s for 40 years and have a pile of parts, plus it is a quite narrow rack and I am hoping that will reduce the problems with bump steer and loss of self centering etc. From my understanding the bump steer issue is caused by the rack being too wide compared to the wishbone pivot points, ideally they should share the same line, most racks are too wide,
I also have an XJ6 pas pump, one piece with reservoir that I am looking to mount above the dynamo position, it is a very compact pump and should fit in front of the exhaust manifold,

I have a 240 that had a seized engine so I have bought an XJ6 ser3 3.4 engine, will the 240 oil filter assy fit onto the XJ6 block?

My car is all in pieces right now so looking for advice…

Can anyone with a rack fitted tell me the distance between the centres of the side rod ball joints, i.e. the pivot points for the side rods?

Pat Essex UK

I like the idea of using an XJ front subframe adapted to the S type or 420 but when I measured the two I found it would take a lot of cutting and welding to fit. IIRC it would need to be narrowed and that would then raise questions about just what Jaguar rack might fit. Even with the subframe narrowed I have to wonder how well all this would fit in the earlier body work. If anyone has actually done this I would like to hear how he did it.

In those pictures of the rack installed you can see the reason for the bump steer and tyre wear, imagen where the side rod ball joints are inside those gaiters, they should be in line with the wishbone pivot but they are 3 or more inches out making the side rods much shorter than the original Mk2 Jag… as the suspension compresses the short side rod travels through a larger arc and shortens in relation to the wishbone, the tracking must toe in a lot on compression.

My understanding of “bump steer” may be different than yours. You do point out an interesting fact that the ball joints inside the gattors are not in alignment with the pivot points of the lower A arms. I went out and palpated the gattors on my car and the ball joints are in fact about 2 inches outboard of the center of the gattor in my earlier photos (1st and 3rd photos of my November 10 post) which was taken with the steering in the straight ahead position. (this may account for the difference in track on my 3.8S to an XJS as noted below) It seems this would only be an issue when one side of the suspension is compressed and the other relaxed which would in turn change the angle of the tie rod from the inner steering ball joint to the outer steering ball joint. So this should not be an issue if the car’s front end is level as when maneuvering slowly in a level parking lot. So the issue you point out cannot be the full problem. After much, much thought, measurements etc. I believe the issue is that a rack moves the wheels at equal angles when turning side to side. Thus the Ackermann effect is lost causing the tires to scrub when off center as in a turn. So in effect in a turn the wheels SHOULD be increasingly towed out the sharper the turn. This permits the outer wheel to scribe a larger diameter circle than the inner wheel. How this is achieved is beyond my inadequate engineering and geometry abilities.

As to getting a shorter rack I am not sure how the pinion side would clear the engine sump see the 3rd photo in my Nov 10 post. I have spent much time looking at the suspension of the XJ and XJS series cars trying to determine what is different on them from the one on a Mark II or classic S Type or 420. The front track on an XJS is 58.6 inches, a 3.8S, 55.25 and the XJS wheelbase 102 and an S Type, 107. Unfortunately transplanting the XJ/XJS front suspension in its entirety is major surgery which I do not choose to undertake. I wonder however, if the issue might be related to the steering arms attached to the upright might be part of the issue. If so, can the complete upright from an XJ be transplanted to a Mark II or 3.8S? I welcome continued discussion although at the end of the day my car does drive, steer and handle quite well with the exception of the tire scrubbing.

based on my knowledge of what has been attempted with MKX

The bolded is the fundamental problem and ruins the Ackerman angle

even a very small change at that point has significant negative affect on steering

It should not be attempted, and that is just fitting XJ uprights and brakes, let alone the rack mod.

I have never heard of anyone having success, except they grafted the entire XJ subframe

Hi John,

Let me give a bit of background so you know where I am coming from, I have run my own business repairing and modifying and restoring classic BMW’s for 40 years, now retired, I restore and rebuild vintage and veteran Matchless motorcycles and have modified a few vehicles in my time, not great on theory or calculations though!

Many years ago I built a camper that would carry a couple of motorcycles, it was based on a diesel Bedford CF1 bus, I fitted LDV front discs and callipers, that had the effect of widening the track, then I fitted a PAS rack from a BMW, it was a lot too narrow for the vehicle so I lengthened the side rods, it drove so badly I came straight back into the workshop and worked out the error of my ways, it suffered from bump tracking deviation, I removed the shocks and got some staff members to bounce it up and down, the tracking varied from toe in to toe out by say an inch when bouncing up and down! that would in turn produce bump steer depending on what wheel had better grip at any point in the cycle,

Basic Akcermann angle is set by drawing a line from the centre of the king pin to the middle of the rear axle, the steering track rod end centre should be on that line, so further in if the steering gear is behind the axle and further out if in front, that will make the inner wheel turn a sharper angle when steering so avoiding tyre scrub on cornering,

Try to visualise a steering rack much longer than yours with very short side rods, as the suspension compresses the short side rod goes to a much steeper angle so effectively shortening relative to the wishbones altering the toe angle a lot, and the opposite when going over a hump back bridge, factory suspension / steering stays relatively straight, we could set the basic tracking with a vehicle up on a lift and the suspension hanging and it was very close to spec when dropped to the ground, if you try that with yours you will find it changes a lot,

For basic setting we used an 8 foot light tube placed in contact with the tyre and eyed it up with the rear tyre (assuming the same track front and rear)

The Bedford CF1 was fitted with a BMW 635CSi engine and box… bit quicker than the 2.2 diesel!

Please don’t take this as a personal criticism I am just trying to pass on hard won knowledge! and solve the issue for myself!

Pat

Pat, you have obviously had more experience engineering these steering changes and I much appreciate your salient comments. If I understand you correctly the outer track rod ball joint must be on a line from the centerline of the rear axle to the kingpin. So, it appears that for me to regain the Ackermann effect on my 3.8S I would need to have a shorter rack and a different steering arm (what Jaguar calls in their parts books, a tie rod lever)![LH side with rack installed|690x461] would move the outer tie rod ball joint on each side inboard from where it is now as shown in my photos above. A shorter rack seems impossible to achieve, at least on the driver’s side as if you look at the photo (my car is LHD) you will see the pinion housing is quite close to the engine sump. I see no way with any kind of rack to move it more inboard. Of course a different (non Jaguar) rack would also entail a different mounting bracket attached to the rear of the front subframe. A different tie rod lever could achieve part of this but such an animal does not exist to my knowledge. I will have to look at how Jaguar achieved this on the 1969-1987 XJ and XJS cars. Perhaps my shop will have one on a lift at some point.