Spridget VS MX5/Miata steering rack

[Hoghead]

Why one over the other, and what is the preferred route? I see postings with people choosing the MX5 over the Spridget but no rational as to why.

I have the Spridget kit in hand with a used rack, but now questioning which way to go. Both Spridget and MX5 racks are readily available rebuilt for about the same cost

If the Ackerman quasi cure is the goal, then one could use the MX5 rack and MGB arms as Jim has done

I cannot find any links on the MX5 mod other than the power installation by Jim. Is there a link on how to do this.

I also see that one can use a power MX5 rack due to the quicker ratio, and de-power it if one prefers manual steering.

 

[66TigerMK1A]

I really can't say what is the 'best' setup...

As far as the 3 racks, I have them all here... stock and Spridget on the bench... I've heard it said that the stock rack is 3.5 turns lock to lock but I get about 3 1/8 turns. The Spridget is 2 1/2 turns and the Mazda power rack ( in the car ) is about 2 7/8 turns. As far as the 'Ackerman' improvement, I think the MGB arms help 'some' but I think for my setup, the biggest gain in that area was ( because I have 'custom' brakes ) moving the whole caliper/rotor/steering arm outboard another 1/4" beyond what the stock location is. That's with a specific 14" wheel, Porsche 911 rotors ( adapted ) and Wilwood calipers

The only Mazda setup I saw before I did mine was a bit 'crude', on a race car and it had things like the pinion was quite vertical ( requiring 3 u-joints and the tie rods were 'welded' together . That got me interested enough and I refined it a lot by ( with some grinding ) rotating the rack so the pinion angle was about the same as stock and making some proper tie rod extensions etc. etc. I didn't modify the stock rack mount although that might have been an easier route.
I know of only those 2 plus Mal's and I talked to Cleo Shelby who has that Mazda rack on her car also and had promised pics from her 'people' but I never got them. I believe hers also runs a conventional belt driven P.S. pump but the rest use an electric pump ( mine is from a Toyota MR2 )
Most of the finer details are in my head ( I think, lol ) and I've sent many emails over the years explaining it all but have never sat down and done an 'assembly manual'

 

[Tiger tamer]

I rebuilt my original rack with a turned down midget rack inner and a pinion machined to suit. We also bushed the pinion end as well. On the bench it was fine but once fitted there was a little play in the rack. Sometimes this transferred through to the steering wheel. Nothing major but obviously something not quite right.
Also the steering was very heavy at slow speeds.

I decided to explore the power steering options.
I knew Jim had used the mx5 rack do I contacted him for some help. I used the mr2 pump as Jim did. Once fitted even before I had the pump wired the car was much better to drive. I think it's because it's a more modern design. Once the pump was wired it was a dream to drive.

The set up is basically the same with the midget rack and mx5. You use mgb steering arms. You do address the Ackerman angle issue to an extent. I found there was a issue with bump steer but using Minx spindles seems to have solved that.
I will also say I am not a engineer or a mechanic so these are my personal observations.

Cheers Mal

 

[Hoghead]

After some thought and speaking with Jim about his set up, I decided to go the Miata/MX5 power steering rack route, but de-powering the rack for manual mode. I do not want power steering and could have used a manual MX5 rack, however the power rack in manual mode gives what I think is a better ratio.

There is a lot of info out there on MX5 sites about de-powering the rack, but note there are different generations of MX5 rack. The 99-05 version I used requires welding on the pinion end and this is well documented.

Rebuilt MX5 racks are readily available I bought a "rebuilt" LHD rack from a big US rebuilder, however I find that the bearing is rough so I will have to rebuild it properly myself. Not a problem and removes the worry about harming the bearing when I weld the pinion to de-power

One can buy 55.00 USD plug kits for the oil holes, but it is easy and cleaner looking to weld up the holes in the MX5 rack

I have now made the mounts and machined the rack to fit.
Rather than use adapter brackets to mate the MX5 mounts with the Tiger, I decided for a cleaner look and machined the MX5 ears off the pinion end so that I can use a clamp on the rack and bolt directly to the Tiger crossmember. A similar procedure would apply if you are using a different generation of rack

The rack is made of an aluminium casting at the pinion end with a steel tube attached to the aluminium casting. As the steel tube is larger OD, my pinion end clamp is 2 piece aluminium.
The non-pinion clamp is 1 piece steel steel and I will TIG weld this to the rack once aligned and hooked up in the Tiger. One could split the steel clamp as well, but having the mount integral to the rack will make Re&Re easier in the future.

2 single J-joints are required and a length of 3/4 DD shaft to hook it all up.
3/4 DD x 5/8-36 on the pinion end
3/4 DD x 3/4-48 on the Tiger steering column end

Will post more info and pics when I have it installed this summer, but am confident that it will work as designed