I have just bought a beautifully restored 1967 Mk2 3.4 Jag. It has the rack and pinion conversion and i understand that some people have trouble with the steering geometry with this set up.
Does anyone have experience of this please?
I looked at another car on Saturday that had Vicarage kit fitted some time ago and the present owner had a bill of over £800 to get the tracking and toe-in set correctly. I did not buy that car but I wish i could have bought the engine - it was a lightened and balance 3.8 with E-type straight port head and twin HD8 carbs. Estimated to give around 260 bhp.

 

Any chance of a picture of what Vicarage did? With rack and pinion steering connected directly to the hubs it is impossible to get the Ackermann angles correct. Thus you suffer front tyre scrub. There are a number of threads on the subject here.

Lovely car!

 

Hi Glyn,
No I cannot get a photo of the installation but I understood that Vicarage had the correct set-up worked out. I guess it all depends on who fits the parts in the end
Bryan

 

It would require the fitting of an intermediate set of levers/idlers like the original design to ever get right. Likely only possible with a centre steer rack like the Opel Astra. End steer rack direct to hubs impossible.

 

It would be extremely difficult to convert a Mk2 to rack and pinion without losing some Ackerman and introducing some bump steer. By difficult I’m thinking of moving the sump, installing brackets suitable for a centre take off rack, and/or redesigning the whole front subframe and suspension to get rid of the trail. Keep in mind that a lot of great classic Ferraris and Alfas used steering boxes. BMW and Mercedes used them until fairly recent years on their larger models. Steering boxes can work well. The last power system on the Mk2/S-type/420 family is said to be good.

On the other hand, if it can work, a power rack is very nice. Most modern cars have reduced Ackerman (racing cars go negative) and, in consequence, tyre jump with stiff, cold tyres is now considered normal. Also, enough bump steer to give a little toe-out on bump is designed in to provide roll understeer for safe cornering.

The question is how well does it work on a Mk2? It’s clear from the varying reports that some upgrades are better than others or suit some drivers more than others. If you are looking at a car to buy, the only answer is to have a good, long test drive over a range of roads and see how it feels. Once you’ve bought it, if you sense excessive scrub or tyre jump, there aren’t any easy ways to increase Ackerman. It would be wise to start without any toe in. You could try a more flexible tyre wall: smaller wheels with higher profile tyres would help. However, that’s not possible with a Mk2 on standard wheels and tyres. If bump steer is a problem, you can stiffen the springs and anti-roll bar to reduce the wheel motion. That might also improve handling at the cost of comfort.

 

I don't see why anyone would want to go through all the design alterations to fit a rack and pinion steering when the original steering box system works fine. 99% of all classic Jaguars, Mk2s and S Types are used as Sunday drives. Off to a local classic car show perhaps. 1% are used for high speed driving on a track or on the roads where a more precise steering is required so if you are just off down to the local classic car show why change it? Seems a waste of time and money to me.

If you have non PAS then upgrading to the later Marles Adwest Variomatic power steering which was fitted as factory for low speed PAS assistance I can see the sense in. It uses all the same take off points and does not change any of the steering geometry.

Changing to a rack and pinion also makes the car less original. You may as well at the same time change the seats to XJ40 electric seats with head restraints, upgrade the engine to a V8 and change all the brakes to wilwood six pots. Why not go the whole hog and re shape the front end to make it more aerodynamic and fit air bags for safety. A diesel engine might make it more fuel efficient. Or, and this is really radical, you could go and buy a new Jaguar XF?

There's an old saying "If it ain't broke, don't fix it."

 

Just before lockdown a neighour up the road popped in to have a look at my Mk2 as it "brought back memories". Turns out he worked at Coombs, Guildford, mid to late-60's!!! Mainly did the rear spats, & modified the rear & front suspensions - apparently front springs came off the Mk10 with a coil cut off!!!
Had some great stories of what they used to get up to on the racers (like "wet weather bumpers" on the rear ... weighed down with lead for better traction racing in the rain!) but when asked what the one improvement he'd suggest to me was ... change to rack & pinion steering.

 

here in the uk Our latest ‘headline’ build is a Mk2 Jaguar, a project christened ‘Project Utah’ in homage to the prototype cars built and tested by Jaguar in 1952. The concept created by the factory was easily one of the most graceful prototypes of its era, albeit with clear signs of the Mk2 DNA we’ve all since come to know and love – both of which made it a perfect starting point for our own build.

We began by sourcing a suitable donor vehicle for the build, which was how we came to unearth a forlorn looking Mk2 from a local barn (complete with aftermarket wasp’s nest on the front passenger seat). This was subsequently used as a parts car for another, more solid looking example, one we’d actually previously worked upon as part of a partially completed Retropower project.
if you look at the build they have put on rack and pinion and say thay have looked at it and got it how it should be,
soyou could ring them and ask?

 

In VERY basic terms: Correct Ackermann steering for zero front tyre scrub ~ note relative position (increasing dynamic toe out that it is exponentially increasing with steering angle.) of front wheels. How does one achieve this with a fixed end steer rack with equal pull & push at both ends connected direct to the hubs when the centre of steer/turning circle is so far outside the bounds of the car. Jaguar achieves this with two idler arms (one being the steering box drop arm), a centre rod & two side tie rods with standard steering (PAS or Manual) & their respective angles from lock to lock in relationship to the hub arms.

This is only taking into account uneven front tyre wear & reduced front tyre life on our old girls and personal sensitivity to scrub/slip. For racing numerous other considerations come to the fore.

 

Bonzo,
Since your car has a rack and pinion conversion, would you keep us updated on how it feels to drive and any other experience of it?

 

I have made some very minor edits above to improve clarity. I too would be interested in Bonzo's feedback. I am very sensitive to tyre scrub but others don't seem to notice it.

My interest in Ackermann, Anti Ackermann, Parallel etc steering has always been in terms of racing where I have some interesting white papers on the subject. They are not definitive in this regard but do prompt some fascinating questions where tyre wear is of less importance & other matters require consideration for best performance in corners.

 

Very nice car Bryan. Given your stock wheel/tire setup I'm guessing you'll be very happy with the steering conversion.
Dave, I've been in touch with the folks at Retropower and they were willing to sell the billet steering arms they've designed - I never followed up regarding cost. The lower takeoff for the steering link is key to minimizing bump steer with a rack.

 

I did read that they made some mounts for the rack to mount it in a better place but till its on the road we will not no if its better?

 

Its always a contentious subject but from my own experience I had a 1966 S-Type with an M&C Wilkinson conversion on it and it was fine to drive.

My current 3.8 Mk2 has the manual steering box and I don't like the feel of it, its just too low geared for me.

The next MK2 will have another XJ6 conversion.

What would be interesting is if anyone has ever had one of these conversion fitted and disliked it so much they have removed it?

I personally think a lot of the problems are just theoretical and not noticed in the real world, as an example there was a very interesting thread on one of the mini forums where someone was trying to fix a percieved problem with the ackerman angles on the long wheelbase minis. Apparently this is because the steering setup is exactly the same on the saloons as the vans estates etc.

Over the life of the cars there were well over 500,000 long wheel base minis made and i've owned a few myself, I never noticed any problems with the steering and I doubt anyone else did.

 

Yes. The Manual Mk2 steering was 4.3 turns lock to lock. The first S Types were 3.5 turns lock to lock & final models with Marles Bendix Varamatic steering were 2.8 turns lock to lock & feel great.

The Mini was a noisy, high NVH vehicle that suffered torque steer & other maladies. What I don't like about driving R&P converted Mk2's & S types is the sound of front tyres tearing away at one another in sharp turns, especially on the quiet S type & the resulting uneven tyre wear.

 

The attention to detail that the guys at Retropower do on their builds is phenomenal so I have an extremely high degree of confidence they have designed a great setup and it would be nice that they make that a kit available to others to purchase. My car is so modified like Doug's but I have the XJ rack and we were able to make that work well and I do not have any issues with the handling but I have done a lot of other mods for my unique build. The car is so much more enjoyable with power steering and I have no issues with tire wear.

 

Some of the folks here clearly know a lot more than I do about steering geometry. One thing I do know is that I've installed a fixed end rack in a Mark 2 with no noticeable bump steer or tire scrub. I've attached a plot of my front left tire at center and full locks (the right side was identical within my measuring tolerances). If my high school math is correct the inside tire is turning about 5 degrees more at full lock than the outside tire. Does anyone know how this compares with a target or proper Ackermann effect for a road car? I'm guessing this isn't too bad since I went from a lot of tire scrub at full lock with my initial setup to little or no scrub after a lot of sorting. This included a shortened rack, moving the rack farther rearward and dropping the steering arm pivot points about an inch. The only downside I see for the rack is an increased turning circle - my rack is 4" shorter than the XJ6 racks commonly used so I'm certain the reduced travel is not helping. It would be nice to know the steering angles for the stock gear and the XJ rack. Regarding bump steer I can't locate my measurements of toe change from full compression to full drop, but I know we got it down to a fraction of an inch measured 6' out from the wheel center (we never calculated the degree change). FWIW
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As it is wheelbase dependent your question regarding a normal road car can't be answered. You are certainly achieving some way towards Ackermann steer. I've always believed that it would be easier to achieve with a lot of fiddling & a centre steer rack. Easier to buy a set up where all the calcs have been accurately done for you. That's why I was interested to see what Vicarage had done.

The few R&P converted Jags that I have driven have certainly not got it right.

"By using Ackermann steering, the wheels of a vehicle will never be forced to skid. This increases energy efficiency and reduces tire wear." ~ WORCESTER POLYTECHNIC INSTITUTE, Worcester, MA

https://www.researchgate.net/publica...anism/download

Download pdf. Institution of Mechanical Engineers UK. I've tried posting the pdf and the forum does not like the .pdf extension. Go figure?

Only read the early part of the paper. The introduction of a geared mechanism will be of little interest & is really going overboard.

 

Out of curiosity I measured the steering angles on my wife's BMW sedan - 7.3 deg of Ackermann at full lock vs 4.7 deg on the Mark 2. Wheelbase is 117" vs 107" respectively, so the higher number makes sense. The BMW also has a much higher max steering angle - about 33 deg vs 24 deg for the Mark 2. Glyn mentioned exponentially increasing toe with steering angle, so I'm still clueless whether I have too much or too little Ackermann on the beast. I promise to get a life and let this go now - I think it's this damn virus.

 

Doug, Glyn is a fanatic when it comes to Ackerman. You built a great car, just drive the crap out of it and the more miles you drive you will know if there are any issues that show up in the real world as HomerSimpson said. It sounds like you have it close enough not to be noticeable and the real test is miles on the car to see the tire wear and feel of the car. I am already closing in on 150,000 miles since completing my Jaguar restomod, Doug you need to get at least 10,000 miles on it before you make excuses to keep working on it, especially when you have done such quality work. We tweaked my car's suspension a few times after putting miles on it and the car tracks great with no tire issues and the car handles so much better than stock. Drive it Doug Heck right now with the pandemic it is the best time to seriously shake down your car. The last few months I have hammered down the Jaguar to 110 to 125 MPH consistently when the coast is clear and I am having so much fun driving this car!