Shortening a Miata rack
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Author:  Blackbird [ October 7, 2008, 1:15 am ]
Post subject: 

MonkeyNutZ, like mcfandango said it depends on your design.
Mine will be 20.5".

Pic of the shortened housing now available here -
http://www.locostusa.com/forums/viewtop ... 6902#46902


Author:  jazzguitarboy [ April 8, 2012, 8:19 am ]
Post subject:  Re: Shortening a Miata rack

I know this thread is several years old, but I wanted to contribute a better way to shorten the rack if you don't have a lathe. The normal disclaimers hold -- I'm not advising you to do it this way, and if you do it and it breaks, it's not my fault.

I was planning to weld the rack, but once I found that I couldn't cut it with a hacksaw, I didn't feel comfortable welding it, at least without knowing what alloy of steel it was and the proper filler rod to use. As previous posters in this thread have mentioned, if the welding process introduces any cracks, they'll be hidden where you can't see them.

You need a 5/8" cobalt drill bit ($10 on eBay) and a M17-1.0 tap ($23 from Enco -- it's a Chinese tap but it's well-made and will do the job). The recommended tap drill for M17-1.0 is 16mm (.630), and with the wobble you'll get drilling by hand or with a drill press, you'll end up at just the right size hole. Cut the rack to length, make sure the end is flat and exactly 90 degrees, drill out the rack about 1" deep, and then tap the threads. Simple.

A trick for shortening the housing: After you have both pieces of the housing cut down to length and have squared off the ends, put the rack back inside the housing, reinstall / loosely tighten the pinion shaft, and tighten down the cap that holds the spring-loaded bushing until the steering rack cannot move (this would be overtightened for normal operation). Then slide the end of the housing over the rack, line it up, and tack it securely. The rack will help to hold the housing straight.

Author:  JPS Europa [ April 8, 2012, 8:44 am ]
Post subject:  Re: Shortening a Miata rack

When I did mine I did not weld anything. The rack itself is case hardened, but carbide tools made short work of that. I had my local machine shop just remachine the ends to match the originals. I gave them drawings of what I wanted, but I would not want to reproduce the drawings. I had the rack where the tube was internally threaded. I feel totally comfortable with the safety of the work.
Paul Harhen

Author:  gryphon68 [ June 15, 2012, 12:11 pm ]
Post subject:  Re:

What is is the shortest rack possible with a 90-93 Miata rack as a starting point?

mcfandango wrote:
MonkeyNutZ wrote:
speaking of steering racks, is there any general length they should be for a book frame?

Depends on your front suspension design. IIRC, its usually ~18 inches for most designs.

Author:  fredvv44 [ August 12, 2012, 10:52 pm ]
Post subject:  Re: Shortening a Miata rack

i just found this thread and would like to offer my ideas. i'm building a 3 wheel JZR. i bought a Triumph Spitfire rack. these are easy as pie to shorten. the rack itself isn't hardened so can be cut on a band saw. the threads are outside threads and easy to cut on a lathe (std. American thread size). the housing is a steel tube that can be cut to length. there is a bushing in the right end that can be pushed out. after the housing is cut to length the inside has to be bored out to fit the bushing which was the worst part of the job.

the rack has a flat milled on both ends for cutting the teeth for both right and left hand drive. when i cut the rack i had to cut it into the flat section (i removed about 6"). i cut the new threads on the flat section but you could weld up the flat and turn it round. i felt that the flat was not a problem and it is just as strong as the original.

there is a flange on the right side of the housing that butts up to the rubber mount. i machined off the weld and removed the flange and welded it back onto the tube so it fits up just like the original did. i believe the MG Midget R&P would work the same way.
Fred V

Tr rack front2.jpg
Tr rack front2.jpg [ 89.36 KiB | Viewed 1033 times ]

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