620 Rack and Pinion

[Jester]

posting to keep myself reminded of updates (even though im RHD)

 

this is something i want to do with my 620 one day .

 

I thought about aquiring a RHD Hardbody PS box and trying to mount it inside the left frame rail. 

[Lockleaf]

Ok fellas, some additional info. Please take these measurements as close estimates. The guy who helped me wasn't completely aware of how a Rack and pinion is put together, so he wasn't necessarily measuring exactly where we might have wanted. Regardless, I would just like to give a big shout out to Mark at Mercedes Benz in riverside, ca, for working with me.

 

Here's what he gave me.

Rack length with inner tie rods attached - 41 3/8" or 41.375"

 

Inner tie rod length (described by him as a measurement from the end of the outer tie rod to where the rubber boot ends on the rack) - 16"

 

Assuming there was an inch not measured, that was threaded in to the outer tie rod, we get 17"

 

Assuming the boot is attached to the rack one inch in to the rack, we lose an inch again, so 16"

 

And assuming the rack travels 3.5 inches and steering was centered, we lose another 1.75 inches, so 14.25" (I have no reason to assume that amount of travel, just spit balling)

 

And assuming the pivot is one inch from where the tie rod meets the rack, we lose one last inch, now having inner tie rods that effectively measure out at 13.25"

 

13.25" x 2 (two inner rods) = 26.5"

 

41.375" - 26.5" = 14.875"

 

Inner pivot to Inner pivot = 14 7/8"

 

The reality is that it could be a few inches wider, or small possibility, a little narrower.

 

Spacers could be easily fabricated to create the exact distance desired for whichever front steer chassis this was used on, be it 620, 720, or maybe even 521 and older stuff.

 

I personally think It is the perfect option. But I don't have to gamble my money on it.

 

And Greiggy, these came in RHD so if it works for us, really good chance it will work for you with an rhd rack

[orangie]

It sounds about an inch to small.  Pivot to pivot should be about 16 to 16.5 depending on how high you set the rack.  I know the design theory, but I can't tell you what you can get away with before you start to experience bump steer or at least bump steer that's scary to drive.

[Lockleaf]

Too small is easy. You fabricate a spacer that threads in to the rack and the inner tie rod threads in to it, moving the inner pivots outward. Problem solved.

[Jester]

As much as I too appreciate Marks efforts, at this point it sounds like pure speculation. Way too many assumptions. We need exact, correct measurements. 

[orangie]

As much as I too appreciate Marks efforts, at this point it sounds like pure speculation. Way too many assumptions. We need exact, correct measurements. 

That is very difficult to do without the right measuring tools.  If you have enough adjustment in height and width you can compensate with tweaking.  The width of the pivot points are dependent up the height of the rack placement.  It's like an upside down trapezoid.  If you mount the rack at the height of the lower control arms, the width needs to be approximately 16 inches  The higher you go, the wider the pivot points need to be. I'll see if I can find a picture to post.  I could never find any write up on how far forward or backward you could get away with on the rack placement.

[G-Duax]

Keep in mind that the inner tie rods on most racks share the same thread as many other cars.

So if a different length is needed, just do some digging.

[Jester]

In order to get around having a custom width rack built, I think I would probably go this route. You could put your inner tie rod ends where ever the hell you want.

Everything I have read so far says the best spot for the rack to be mounted is with the tie rods level AT RIDE HIGHT. You should end up with everything between the steering arms in a straight line just as above.

 

Also, a RHD, rear mounted rack could be flipped around and mounted in front. 

[Laecaon]

I disagree about the level control arms/tie rods. 

 

You need to calculate the angle based on roll center, and center of gravity. Control arms pointing down at the wheels will raise the roll center a bit and make it better inline with the CG. Of course this all changes on ride height. 

[Icehouse]

Ackerman is one thing you will loose by changing to rack and pinion.  We recently learned this on our 510 crossmember we are building.  We also had the issue of it turning slower.  With trucks already steering slow this may not be an issue.  

[Laecaon]

Is that still using 510 knuckles that you loose ackerman? I can imagine steering angle due to reduced throw of the rack, but not ackerman... 

 

Im not using 510 knuckles or ZX knuckles on my car. I should have plenty of ackerman and steering angle. 

[Icehouse]

What knuckle are you using?  Seems like any knuckle off a steering box car will do the same thing.  The steering box, idler arm arc adds lots of ackerman it turns out.  Just look at the difference in these two steering knuckles.  It will apply to the 620 as well.  

 

 

 

[Laecaon]

S13...

[Lockleaf]

Hey jester, ep3 civics came with that style rack as an electric assist. Rsx had a hydraulic version. But as it is rear steer it would still require a flipped rhd rack.

[5t341tH]

it's been about 4 years. Anyone done rack and pinion yet?

[]2eDeYe]

I have seen one done recently. I was told it was a 'pinto' rack.
 

I requested more info, but haven't had any response. 

 

 

 

[5t341tH]

On 11/30/2020 at 2:52 PM, ]2eDeYe said:

I have seen one done recently. I was told it was a 'pinto' rack.
 

I requested more info, but haven't had any response. 

 

 

 

guess not many are interested in this. I just hate the sloppy/slow steering these trucks have

[datzenmike]

A pinto rack is in front of the front wheels so this might just work.

[Moist Lightning]

Datzenmike - I know the post you are talking about, i visited the page of the shop that did the conversion. All they said is that is was a custom rack.

A shortened pinto rack is 18.5" pivot to pivot so still too long unless the did something else to shorten it more.
https://www.flamingriver.com/fr1501-2-pinto-style-5-inch-narrowed-rack-and-pinion
PDF under instructions

[Moist Lightning]

Forgot to mention that the company that did the conversion said they might make a kit.

Also another option ive been looking into is a circle track R&P.

[Icehouse]

38 minutes ago, Moist Lightning said:

Forgot to mention that the company that did the conversion said they might make a kit.

Also another option ive been looking into is a circle track R&P.

 

 

pics of the conversion!

[Lockleaf]

What about NA and NB miata racks?  They come with steel cases threaded into an aluminum "steering box" section.  Guys narrowed those up to 8 inches with just steel welding and some drilling and tapping.  They are front steer vehicles.

[Moist Lightning]

5 minutes ago, Icehouse said:

 

 

pics of the conversion!

[Moist Lightning]

3 minutes ago, Lockleaf said:

What about NA and NB miata racks?  They come with steel cases threaded into an aluminum "steering box" section.  Guys narrowed those up to 8 inches with just steel welding and some drilling and tapping.  They are front steer vehicles.

Hmm sounds like ill have to look into that thanks.

Edited December 3, 2020 by Moist Lightning

[Icehouse]

So rad!