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 Post subject: Spitfire rack
PostPosted: July 16, 2020, 10:35 am 
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Joined: December 24, 2007, 5:11 am
Posts: 1112
Location: Seattle area
My shortened, de-powered Miata rack has some slop that I can't seem to get rid of and was considering replacing it with a Spitfire/GT6 rack. Has anybody here have experience with these?

TIA

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 Post subject: Re: Spitfire rack
PostPosted: July 16, 2020, 10:52 am 
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Joined: June 15, 2010, 8:29 am
Posts: 606
Location: Duxbury, MA USA
Hey Larry,
What is wrong with your Miata rack? I also have a shortened, depowered Miata rack in my Seven and there is exactly zero slop.
In any case, my Europa has a Spitfire rack with tie rod extensions. What are your questions?
Paul

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 Post subject: Re: Spitfire rack
PostPosted: July 16, 2020, 3:00 pm 
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Joined: December 18, 2010, 3:29 pm
Posts: 129
De-powered by welding or epoxying the spool valve or just 'de plumbed?' The spool valve is built in slop and has to be fixed or you really don't have any of the benefits of the de-powering.

Alex


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 Post subject: Re: Spitfire rack
PostPosted: July 16, 2020, 8:27 pm 
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Location: Seattle area
Paul,

I have close to an inch of free play before the wheels start to turn. That and a lack of castor makes driving more of a chore than a pleasure. The castor is being taken care of (new UCAs) but the play in the wheel I'm just not sure of. All seems tight right down to the rack. I have tightened up the adjustment and it didn't help. So I was going thinking about changing the rack. The Miata rack is all but un rebuildable so looking for an alternative and the Triumph unit looks like a likely choice.

Alex,

I have read somewhere else that a depowered Miata rack will have some play that won't go away. I shortened and depowered following Keith Tanner's example. Don't know anything about the spool valve. Probably didn't do anything about it. at least not on purpose. Another usual suspect is the lower u-joint but mine seems tight. It turns with shaft ok.

Thanks gents for the replys.

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 Post subject: Re: Spitfire rack
PostPosted: July 16, 2020, 9:14 pm 
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Joined: July 17, 2008, 9:11 am
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Location: West Chicago,IL
It should be fairly easy to figure out where the slop is. I would vote for that over changing the rack. Without knowing, you maty not fix the problem. The second thing is, it might be easier to just shorten another Miata rack if the current one cannot be "fixed".

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 Post subject: Re: Spitfire rack
PostPosted: July 16, 2020, 9:42 pm 
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Joined: December 18, 2010, 3:29 pm
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Here's a quick video I made years ago to show how much slop is in a depowered spool valve. Hydraulic pressure from the pump effectively 'stiffens' the valve so it really is way worse when you just disconnect it.

https://youtu.be/_4DiSopjNfo

Alex


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 Post subject: Re: Spitfire rack
PostPosted: July 16, 2020, 11:33 pm 
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Joined: September 30, 2005, 1:28 am
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Location: Sunny-Okanagan, Canada, eh?!
I have a Triumph/Midget rack in my Locost. I shortened it 7-1/2". The challenge was re-threading the ends to a thread size I couldn't get a die for. I forget what it was - something silly like 13/16 super-ultra-mega-fine or something.

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 Post subject: Re: Spitfire rack
PostPosted: July 16, 2020, 11:42 pm 
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Joined: December 24, 2007, 5:11 am
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Location: Seattle area
Been digging into this more, which I should have done a long time ago. Tanner's method didn't address the spool valve at all. Just watched another guy doing his rack and he demonstrated the spool valve action. He had barely a 1/4" play which I thought wasn't enough to be causing my problem. But wait! I said to myself. He is showing that on a 3/4" shaft. How much will that be in a 14" steering wheel?

That may very well be where I'll find the slop. I'll be checking that tomorrow.

Thanks again.

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 Post subject: Re: Spitfire rack
PostPosted: July 17, 2020, 12:21 am 
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Joined: March 19, 2011, 10:22 am
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Location: Holden, Alberta, Canada
Yeah I heard of guys welding the spool valve up to make it solid like a manual rack. Thats one of the must does when converting a power rack to a manual rack.

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 Post subject: Re: Spitfire rack
PostPosted: July 17, 2020, 12:36 am 
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Surprising that Keith Tanner's write up didn't address that. Paul, did you do anything with yours?

Cheers!

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 Post subject: Re: Spitfire rack
PostPosted: July 17, 2020, 1:13 am 
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Location: Holden, Alberta, Canada
Here's a write up on de powering a Miata rack and welding the spool valve.
https://motoiq.com/project-miatabusa-part-5-de-powering-the-steering-rack/

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"If you can't build it safe, don't build it."

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 Post subject: Re: Spitfire rack
PostPosted: July 17, 2020, 3:39 am 
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Thanks Perry. I was just reading that one. Sure sounds like my cure. I'll look at that tomorrow. Got some welding coming up. Get it all done while you can.
Doing some modifying to the UCAs. They are in interference with coils springs if I crank in enough castor to make me happy.

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 Post subject: Re: Spitfire rack
PostPosted: July 17, 2020, 9:44 am 
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Joined: June 15, 2010, 8:29 am
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Location: Duxbury, MA USA
Larry, I completely disassembled my rack and removed anything that had to do with power steering. Machined up parts to make it shorter and all solid. Like I said, no play.
I have no complaints. How much caster will you have with new UCA's? I have 6.5°. Car tracks very nicely and steering is plenty quick. Front end really sticks. Only time I have any sketchy moments are caused by bumps with live axle out back, and sometimes too much right pedal.
Paul

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 Post subject: Re: Spitfire rack
PostPosted: July 17, 2020, 2:38 pm 
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Location: Seattle area
Paul,

I originally planned on 7* however between mock up and weld up I somehow lost 6*. So the new UCAs will allow 7*. The way the ICAs are now any movement of the spindle and I'm hitting the spring.

I was following Flyin Miata's tutorial on shortening and wasn't even aware of the valve on the pinion. The play is about a 1//4" at the bottom u-joint and I'm unable to find any slack anywhere other than at the rack itself.

Thanks!

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 Post subject: Re: Spitfire rack
PostPosted: July 19, 2020, 1:25 am 
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Was planning on doing the rack today but a medical problem arose and I haven't had a chance yet to act on all the good advice. The video that Perry sent a link to is going to be my first task. Chuck's advice to fix what I have is making more sense the longer I think about it.

Once I get the rack apart I might find some friction sources that are making the steering heavier than what I think it should be. We shall see.

Thanks again for all the suggestions. I will post results when I get them.

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