420 Steering rack conversion help

I have a 1967 420 with the original Adwest power steering. I replaced the seals and fixed the leak on the end plate. Now the new seal at the input side leaks. I read a rack can make the handling feel less knumb too.

Does anyone have info to do a conversion without spending $5000.00 ? I see the moss kit, but heard negative feedback from fitting issues and the rack was bad out of the box. Somewhere I saw a mounting bracket available for a rack. If I had that I would modify a rack to fit.

I fitted a rack to my 3.8S a number of years ago. My shop obtained the bracket, and I bought a ZF rack used on a later XJS. Advantages: very positive steering and no leaks, disadvantages: reduced turning circle and tire scrubbing on tight turns with earlier tire wear, Job was way less than $5000 US as I recall. The rack IIRC was less than $1000 US. Ran it on the standard generator mounted pump. Lower column had to be shortened as I recall but splines matched the rack. New hoses made up by a hydraulic shop with some of the original ends. Your prices may vary, not sure where you are located. My understanding is that the 420 used the Marles Variomatic steering box which, if it doesn’t leak, is highly regarded.

Thanks John!
I’m located in IL. My current box is leaking, but not so bad as not to drive it, but enough to be annoying having drops on the garage floor.
I was looking at pictures of the bracket and if I can’t buy one, it can probably be made locally.

First I need to replace my brake servo. It has been giving problems with the rear circuit not releasing. The piston is hanging up in it. It was fine for 100 miles and then last night it acted up. I carry a 7/16 wrench to crack rear brake line to bleed pressure off. It’s difficult to drive and not touch the brakes!! At least I was close to home.

Thanks again for the input!

You might want to try an old shade tree remedy for minor leaks Add a quarter cup of DOT 3 or DOT 4 brake fluid to the power steering fluid, Brake fluid tends to cause seals to soften and seal better. Also always good to list your location and car on your forum info, Might help in future responses to your posts.

Hi, Yes my 67 420 Marles matic PS was leaking and as Dick Maury, of Coventry West, told me that rebuilding of the original PS was not feasible I installed the XKs steering rack conversion. I had to do some modifications on the subframe, get custom hoses to install to the original PS pump. Not $5000.
I think I paid $1100 for the rack about ten years ago. Your turning radius will definitely be restricted and the car tracks nicely.

The ideal rack for the mk2 is too narrow for a power unit - as far as I know, all the conversions kits are too long, I think by about 4". I developed a manual rack design for my mk2 and had Unisteer make it to my specs. I believe it was about $600. The brackets bolt to the original subframe mounts, and e-type urethane rack mounts interface. The steel pan requires some dimpling on each side. It does require some steering effort when parked, and I’m thinking of switching back to 5" rims when I next change tires, but not bad. I have no bump steer or significant scrubbing.

How is the handling? Is it improved?

I see moss sells the same kit as XKs, since they own them. It’s $1300.00.

Hi, it really has no impact on steering. It does require many more K turns with the turning radius being noticeably reduced.

It is my contention, but I have no proof, that the reduced turning radius is not due to the amount of right to left travel of the steering rack but more due to the loss of the Ackermann angle effect that results in the tire scrubbing on tight turns. This prevents the car from tracking freely from the angle the rack provides to the swivel pins.

I am about to fit my own PAS rack conversion to my Mk2 Jaguar using a BMW E21 3 series PAS rack, the narrowest PAS rack I could find in my stock, I did a dry build and managed to find a rack position where I had NO bump steer and full travel lock to lock with four turns of the wheel, I found that I had to drop the rod ends by about 18mm so am using rose joints with spacers, hopefully I can test out my theory in the next few weeks,

Would like to see photos of this installation. With the Jaguar rack (I’m using one for and XJS) I do not know how a narrower one would fit as the pinion tower can not move inboard any further as it would foul the sump, as least it would on an S Type.


It is tight for a short rack. If you switch to a steel Mk2 pan, you can make it work. As I noted above, I had to dimple the sides of the pan as well.

With my manual rack, I don’t find the turning radius particularly long, but then I don’t really remember what it was like before the conversion, it has been so long. I have to get the car out for a drive, so maybe I’ll measure it to see. Perhaps if I do that, someone with the kit conversion could offer a comparison?

As to handling, my car handles very well, although I think I need a bit more castor for better straight line tracking - car is a bit twitchy - that’s not a rack issue. The Unisteer rack is a bit fast - I don’t remember the exact ratio, but I think it was something like 2.8, so I switched back to the stock steering wheel from the smaller Motolita, and it’s much more comfortable both for turning and straight line.

Really interested in how that BMW rack works out. I’d rather have PAS, and have considered adding electric assist. Too many projects for now, though.

I will take more pictures, my car is RHD so I did not have the exhaust to worry about, I cut a corner out of the alloy sump and got a mate to tig weld it back in further forward, not a hard job to do at all, I would rather do a bit more work than suffer tyre wear and “bump steer” .

I assembled the front suspension one side without the spring or bump stops, I could then cycle the suspension through its full travel and check if the toe altered as the suspension was raised and lowered, I got it to the point of zero toe alteration moving full travel, on the road travel would be 1/3 or less as it is limited by the bump stops and shocks, after I found the sweet spot I tried different positions for the rod end, with the rod end on top of the steering arm the one wheel toed out 44mm on full upward travel, 20 mm in the normal position and zero with the position I settled with, all that difference with just moving the position of the rod end relative to the steering arm!

The BMW rack is still too wide, if I had narrowed it to the correct length it would have only had half the lock!

I inverted the upper witsbone pivot and that gives more negative camber as the suspension compresses, as a side effect of that the toe moves in at the same time, this counteracts the toe out caused by the longer rack,

On my mk2, I did the same thing with a spare front suspension and subframe and found the ideal rack width to be 20 7/8" which gave zero bump steer. How wide is the BMW rack?

When measuring the rack width from what points do you take that measurement? I’m guessing between the inner ball joint on both sides?

If the leak on your power steering is ‘not too bad’, I’d suggest trying a bottle of ‘Trans X’. I used it on my 1967 Mark 2 fitted with the Marles Varamatic power steering setup last August. In the last ten months, it hardly leaked more than a few drops.

I’ll try that. I ordered a seal kit so I can replace that input seal again. But I’ll try that stop leak first.

Thank you!

UR welcome. Good luck!

correct, inner pivot to inner pivot.

So on my manual rack conversion, my diameter of turn measured outside of wheel to outside of wheel is 41 feet or radius of 20.5 feet. Not ssure if that is a standard way to measure turning radius, but that’s how I did it.