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Rack and pinion exploration. Building a bolt in conversion


Icehouse

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Sam, James and I set out about a year ago to build a bolt in rack and pinion conversion.  First we wanted to model the stock suspension on the computer and find out exactly what was going on.  We've all heard that the "amazing 68-69" crossmember holds the key to an ultimate race car build!  I've always wondered if it was true.  Once we found out how the factory stuff is setup we wanted to hopefully make it even better with rack and pinion and less bump steer.  Anyways we are going to do a very fancy write-up when we are done.  For fun I want to share a few things we have done so far.  Plus you guys can help us think of good ideas.  Such as what motor mounts would be best to run.   

 

 

We drew everything in the front suspension in Solid Works.  It took hours!  Looks cool now though!  

 

 

steering%2Bmodel.PNG

 

To make sure the model was right we took bump off a stock setup.  Since we are doing this for mostly education purposes and are in no way in a hurry to get anything done.........Why not check bump on all 4 possible combination.  So we did!  Who would have thought the early crossmember sucks!  I'm not sure how important roll center.  Maybe very.  Nissan didn't seem to think so.   I'm sure when racing and every little bit counts and maybe you are allowed to shim the tie rods to fix the bump on the early crossmember.  

 

IMG_5818.JPG

 

 

dials%2Bon%2Bfront%2Bclip%2Bjig.jpeg

 

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So it turns out Wagon's have the least amount of bump from 68-72 they all used the lower LCA pivot points ("late X-member") and a steering arm with matching idler arm that drops the drag link 6mm.  This combination provides very little bump.  The problem is if you swap the 68-69 crossmember into a wagon (or column shift auto, they have the same steering arm and idler) the bump goes through the roof!!!  An easy way to tell if you have this very bad setup is, well without checking part numbers is to see how close the LCA nylock nut is the the drag link/ drag link joint.  I've driven ton's of 510's over the years and I always asked myself this question.  "why do some of them just drive so bad?!?!"

 

 

 

 

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Here is the chart for those who are interested and later we will have more and are doing a writeup as we speak.  Right Sam! :)

 

 

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Roll center is important when compared to the location of center of gravity. The farther apart they are the bigger the "lever" momentum has to roll your car on the suspension, aka body roll. To counter this, people use bigger sway bars and stiffer springs. If you tune your geometry to get those two closer together, you don't need the harsher riding stuff. This will also smooth the weight transfer "curve" and make the car less jumpy and grip tighter at the edge of control.

 

Very nice work. That is an awesome comparison between the possible factory options.

 

Have you guys determined a rack to try yet, or established a basic length of rack you are looking for?

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It's been a while since we updated this thread.  We've made some really good progress and are about to put our 3D model to the test.  According to the model this setup should have really low (less bump than even the wagon) bump steer.  Sam, James and I got the crossmember assembled and hopefully we will have time to put it in the test front end and pull some real life numbers.  I'm super excited to see what we get.  here are some photo's of the progress.  

 

 

rack%2Bcrossmember%2Bparts.jpeg

 

rack%2Bcrossmember%2Bassembly.jpeg

 

 

 

 

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rack%2Bcrossmember%2Bgetting%2Bcloser.jp

 

 

 

 

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rack%2Bin%2Bcar%2B.jpeg

 

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Very nice looking setup. Am I correct in assuming it relocates the factory control arms somewhat? Is this design optimized for factory ride height or for a specific dropped height? And am I allowed to ask what rack you guys chose to install?

 

Are you developing this new crossmember for sale as a bolt in kit?

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Very nice holmes i can model that front end in my suspension program and it will give me bump steer numbers ya"ll did it the hard way! But good for you!

 

 

haha yeah but doing it the hard way we were able to model the front crossmember and get a shop to cut the puzzle pieces for us :)

 

 

Now do a 210 next for me

 

 

You do the 210 :)

 

Very nice looking setup. Am I correct in assuming it relocates the factory control arms somewhat? Is this design optimized for factory ride height or for a specific dropped height? And am I allowed to ask what rack you guys chose to install?

 

Are you developing this new crossmember for sale as a bolt in kit?

 

 

Yeah it moves them forward slightly that plus shortening the TC rods adds a bit of caster which also makes the car feel and drive nice.  

 

 

It's designed for a lower ride height.  Who wants factory height....... :) 

 

We decided to go with the MR2 rack, since it is used in a few different applications it seems like it will be the somewhat available.  I wish there was a rack off a newer car.... Countless trips to the wrecking yard and nothing....  

 

yeah the plan is to sell them later, if all goes well and we like it.  Some welding will be need to hook up the column.  I've just always hated the idea of running a top mount turbo because the steering box is in the way.  Seem like such a better idea to upgrade the suspension while keeping the reliability of factory turbo components.  Steering boxes are IMO the 510's week spot.  With rack and pinion and Byron's rear camber/toe brackets it completely changes the feel of a 510.  I can't wait to see how this setup feels on the road!  

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Yeah for KA, SR and CA swaps.  I don't think it will work for VG's but maybe.   We've thought about making brackets for you rear sump guys but instead we think you should buy the MK2 510 front sump pan :)  

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Buy the MK2 510 front sump pan? :confused:

 

Please enlighten me as to what this is please.

 

77-79 510 oil pan and pickup tube. It's a front sump for the L-series. Or if you can find one, I think the 77-79 200SX uses the same pan. 

 

Pretty much any late 70s car that came with an L20b. 

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So how did the cross member and rack workout? thought due to the length the pivot point of the MR2 rack was longer  than that of 510 lower control arms?

 

 

Visually looking at suspension to make a "guess" on how it works out is impossible it turns out.  Yep it's wider but we were able to get the bump steer much lower than the factory sedans bump early or late.  We are going to prove the model by checking the bump hopefully this weekend with the prototype crossmember.  

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