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Center Take-Off Rack & Pinion


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#21 Moist Lightning

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Posted 24 December 2017 - 10:11 AM

This has always been the confusing part of center mounted tie rod R&P. The civic one clearly has pivots only a couple inches apart. so did they make up for that design flaw with other suspension engineering?

Regardless i have wondered about machining big ole extension bars that thread into the center mount and place the pivot out at the standard location.

 

I don't know if anyone has mentioned it, but the distance between inner tie rod ends on the new rack needs to be the same as the distance between inner tie rods on the stock tie rod setup or you will create a bumpsteer condition. You could modify things to get it right, but it would be easiest to start with the proper width rack.

 

I guess i didn't explain that well enough in the first post.

 

The stock center takeoff are designed for mcphersons and the geometry(center pivot points) won't work with double wishbone.

 

We are just using the center take off rack and pinion to create something similar to the unisteer.

 

You have to build a new mount and extension bar that attaches to the rack where the tie rods use to connect.(if you remove the intrepid tie rods and mount from the rack you can then bolt the extension bar to it)

 

400px-Center_take_off_pics2.jpg

 

This build is almost exactly what im talking about. http://bloom.is-s.co...-n-Pinion.shtml

The civic build - http://www.fordmuscl...ack-pinion.html

The extension bar needs to be 22.75" 20" the length of the stock 620 center link. as i mentioned earlier my only concern would be flex in the bar due to the length.

 

That is why i also suggested converting the steering box to and idler arm. then you just attach the center link to the rack and mount the rack to the cross member right behind the center link.  Never mind the arc of the idler arms would make the center link pull away from the rack.



#22 flatcat19

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Posted 24 December 2017 - 01:45 PM

Yes they are mounted on the fire wall but they are front steer. 
 
You can see that the pillars are really far back.
 
7t4WNX3.jpg
 
Here's the diagram.
 
zNUVckl.jpg



Touche'


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#23 datzenmike

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Posted 24 December 2017 - 01:49 PM

Longer tie rods, say, from the center would be better than the stock ones. If they were infinitely long there would be infinitely small bump steer.


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#24 thisismatt

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Posted 24 December 2017 - 02:17 PM

Longer tie rods, say, from the center would be better than the stock ones. If they were infinitely long there would be infinitely small bump steer.

No. Longer tie rods means less radial movement of the outer tie rod end through the suspension travel compared to the radial travel of the LCA. Bump steer.
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#25 Lockleaf

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Posted 24 December 2017 - 06:12 PM

I hadn't ever researched anyone making an extension bar to create the proper tie rod placement. I've discussed this idea in other threads, but never seen that first link you posted. I think it's a fantastic idea.

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#26 Stoffregen Motorsports

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Posted 25 December 2017 - 09:14 AM

This has always been the confusing part of center mounted tie rod R&P. The civic one clearly has pivots only a couple inches apart. so did they make up for that design flaw with other suspension engineering?

Regardless i have wondered about machining big ole extension bars that thread into the center mount and place the pivot out at the standard location.

I've seen that done before. You need to support the extensions to avoid deflection.



#27 Moist Lightning

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Posted 25 December 2017 - 10:06 AM

I've seen that done before. You need to support the extensions to avoid deflection.

 

Thanks for the input.

I think i found a pic of a braced extension 

 

manual%20rhd%20mustang%20rack%20reduced%

I'll have to do some more research, as this brace looks like it could get dirty and wear fast.



#28 Moist Lightning

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Posted 25 December 2017 - 11:16 AM

I've seen that done before. You need to support the extensions to avoid deflection.

 

 

Thanks for the input.

I think i found a pic of a braced extension 

 

 

I'll have to do some more research, as this brace looks like it could get dirty and wear fast.

 

I've been looking around and it seems commonplace to have long extension bars with no brace. Both unisteer and steeriods do this. 
One of the longer ones i've found are the ford falcon unisteers

 

8001050-01-400x400.jpg

 

Could you elaborate on your experience? Did you or someone you know make one? did they have problems until they braced it?



#29 Stoffregen Motorsports

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Posted 25 December 2017 - 01:19 PM

Well, if you read it online, it must be true.

 

I think it would depend on a multitude of factors, but I would like to see all those factors addressed before I made that mod to a steering rack.



#30 Moist Lightning

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Posted 25 December 2017 - 03:02 PM

Well, if you read it online, it must be true.

 

I think it would depend on a multitude of factors, but I would like to see all those factors addressed before I made that mod to a steering rack.

 

Sorry, didn't mean to say I didn't think it needed it. Just trying to get as much info as I can. However unisteer and steroids are commercial manufactures, not just "oh i found some dude who wasn't bracing them and it seems fine."

 

anyway you said you've seen it done and sounded like you had some experience, is there any more you could share?



#31 Lockleaf

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Posted 25 December 2017 - 06:51 PM

For more it seems more like a question of intent.

I don't race. I don't even really drive aggressively. I don't think i would have any issues with there being some deflection in the setup, so long as the final feel was tighter and more crisp than what i previously had. And the deflection was not so great that i believed it to be a safety concern.

But the more aggressive the use, the more deflection gets created AND the more you would be concerned about that deflection.

Street vs track to me, at which point the potential for wear on the reinforcement bars would be unimportant, as it would be monitored along with the rest of the car.

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#32 thisismatt

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Posted 25 December 2017 - 07:10 PM

What about using a normal rack and connecting the two ends with a bar you can mount your new pivots to?
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#33 wayno

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Posted 25 December 2017 - 08:21 PM

Is this about power steering or something else?

What year is your 620?


 

 


#34 Lockleaf

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Posted 25 December 2017 - 08:26 PM

What about using a normal rack and connecting the two ends with a bar you can mount your new pivots to?


Interesting thought. I hadn't considered this but it could be made to work well i think.

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#35 distributorguy

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Posted 26 December 2017 - 07:27 AM

I've been looking around and it seems commonplace to have long extension bars with no brace. Both unisteer and steeriods do this. 
One of the longer ones i've found are the ford falcon unisteers

 

8001050-01-400x400.jpg

 

Could you elaborate on your experience? Did you or someone you know make one? did they have problems until they braced it?

What's the point of center steer if you move the inner tie rod connecting point so far outboard that a traditional rack and pinion would not only work better, but be significantly simpler?  

 

I think there's some mis-information being spread here, not understanding the difference between Ackerman Angle and bump steer.  Moving the center pivot inboard will likely reduce extreme bump steer angles, but it WILL have an effect on Ackerman (the different angles the tires must turn in a corner to turn their respective radius.)  That has a bit more to do with the rack placement than the inner tie rod angle, but both are important.  We totally screw these all up anyway when we lower the truck, so whatever design you come up with will have to be sorted with the end ride height in mind.  

 

Simply offsetting the tie rod height will correct bump steer.  Ackerman is MUCH harder to fix, generally done by changing steering arm length and at least one control arm length.  

 

On any R&P, you can build extensions or cut the inner tie rod shorter.  I have a 2000 Chevy rack in my '49 Willys truck.  Just takes minor modifications to the tie rods as described above, and custom steering arms for front steer.  Chose the wrong rack and your steering wheel turns the opposite direction of your front tires.  Oops.  

 

MGB racks may be a viable option, and relatively tight ratio steering.  They are front mount and plentiful.  Too narrow, which is easier to fix than too wide.  



#36 Lockleaf

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Posted 26 December 2017 - 08:42 AM

The problem is that there are virtually no easily available racks that are narrow enough. They all start out too wide already. Those options that have been used are either difficult to find or expensive and custom.

Perhaps mg is the answer that has been missing, but up to now there hasn't been a magic bullet that didn't cost a grand.

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#37 Stoffregen Motorsports

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Posted 26 December 2017 - 09:38 AM

Sorry, didn't mean to say I didn't think it needed it. Just trying to get as much info as I can. However unisteer and steroids are commercial manufactures, not just "oh i found some dude who wasn't bracing them and it seems fine."

 

anyway you said you've seen it done and sounded like you had some experience, is there any more you could share?

I was just being cynical.

 

I have seen extensions done before, both with and without bracing. The bracing has been in the form of a pillow block style mount, but I am not sure how they addressed the wear issue. The comment about many variables, well the rack could possibly hold up to the stress of added extensions if the rack is very large to begin with and the extensions are of a strong material, but there are also suspension geometry factors involved. If the steering geometry is not perfect  to begin with, there could be built in deflection that would exacerbate matters.

 

Short extensions are pretty common, but I don't know at what point the extensions become too long. My thoughts are all theory, as I have never dealt with this, but I am "in the industry" so my mind is continuously going, looking for potential pitfalls and possible solutions.



#38 Stoffregen Motorsports

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Posted 26 December 2017 - 09:43 AM

I don't race. I don't even really drive aggressively. I don't think i would have any issues with there being some deflection in the setup, so long as the final feel was tighter and more crisp than what i previously had. And the deflection was not so great that i believed it to be a safety concern.

One of my concerns with deflection is wear in the rack, not solely performance. A manual rack will take more abuse than a power steering rack, but still, there could be a longevity issue with deflection.



#39 distributorguy

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Posted 26 December 2017 - 12:41 PM

I wish I could climb under my MGB and take measurements right now, but its -10 outside and the front spoiler is a lightweight fiberglass race setup - likely brittle in this cold.  It looks about right, likely having to make an adapter for the outer tie rod ends.  The distance from inner to inner pivot looks damn close to stock Datsun.  A Midget rack would be narrow yet, and quicker ratio.  The best part is that they never wear out.  The bad part is that factory steering (column) joints are too light for a truck.  



#40 Moist Lightning

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Posted 26 December 2017 - 02:08 PM

I was just being cynical.

 

I have seen extensions done before, both with and without bracing. The bracing has been in the form of a pillow block style mount, but I am not sure how they addressed the wear issue. The comment about many variables, well the rack could possibly hold up to the stress of added extensions if the rack is very large to begin with and the extensions are of a strong material, but there are also suspension geometry factors involved. If the steering geometry is not perfect  to begin with, there could be built in deflection that would exacerbate matters.

 

Short extensions are pretty common, but I don't know at what point the extensions become too long. My thoughts are all theory, as I have never dealt with this, but I am "in the industry" so my mind is continuously going, looking for potential pitfalls and possible solutions.

 

Thanks for sharing. I've done a bit more research on deflection. I also think i've got a solution but i'll start with deflection.

 

• Front steer tends to be the stronger than rear steer because when cornering the outside tire takes exerts the most force due to body roll/momentum pushing out. In a front steer vehicle the tie rod on the outside of the corner will be under tension not compression. This is why rear steers tend to bend rods more than front steer.

 

• I was also playing around with a deflection calculator but im not sure how much force is normally exerted on the steering. probably differs per vehicle.

 

Although, i've come up with a method that will keep the stock geometry as well as keeping the center takeoff close to stock config.

 

Earlier i mentioned the idea of replacing the steering box with an idler arm and attaching the center link to the rack. I quickly realized that the center link would pull away from the rack  as it rotates around the idler arms radius.

 

The solution is to use the center takeoff with cententral pivot points to connect the idler arms to the rack.

 

the next problem is that the stock tie rods off the center takeoff rack are too long. the solution is a short extension bar with some 10-11" tie rods. It would look like this but the tie rods would connect to two idler arms.

 

550px-Original_cavalier_inner_tie_rods.j

 

I just need to check if an idler arm will bolt up in place of the steering box or if a custom mount needs to be made.
 

 

What's the point of center steer if you move the inner tie rod connecting point so far outboard that a traditional rack and pinion would not only work better, but be significantly simpler?  

 

I think there's some mis-information being spread here, not understanding the difference between Ackerman Angle and bump steer.  Moving the center pivot inboard will likely reduce extreme bump steer angles, but it WILL have an effect on Ackerman (the different angles the tires must turn in a corner to turn their respective radius.)  That has a bit more to do with the rack placement than the inner tie rod angle, but both are important.  We totally screw these all up anyway when we lower the truck, so whatever design you come up with will have to be sorted with the end ride height in mind.  

 

Simply offsetting the tie rod height will correct bump steer.  Ackerman is MUCH harder to fix, generally done by changing steering arm length and at least one control arm length.  

 

On any R&P, you can build extensions or cut the inner tie rod shorter.  I have a 2000 Chevy rack in my '49 Willys truck.  Just takes minor modifications to the tie rods as described above, and custom steering arms for front steer.  Chose the wrong rack and your steering wheel turns the opposite direction of your front tires.  Oops.  

 

MGB racks may be a viable option, and relatively tight ratio steering.  They are front mount and plentiful.  Too narrow, which is easier to fix than too wide.  

 

As lock leaf mentioned there is no stock rack narrow enough and modifying a center takeoff is easier than shortening a rack.
You can look for one but many others have tried without success so far. I would love to be wrong.

 

However, the solution above would keep the stock geometry because the outer tie rods are still connected to an idler arm. solving the problem of akerman angle and bump steer.

 

And in regards to lowering i totally agree. additionally lowering without drop spindles also ruins the roll center because if the negative wishbones. Im working on ball joints and coils and though i might as well do R&P while i'm at it.