Fitting rack & pinion steering in your RX7 or other early RX

Technical info not specifically 1st gen RX7 related.
Post Reply
TOOL
Posts: 2513
Joined: Thu Sep 01, 2011 10:30 am
Location: Var, France (ex NZ, ex UK)

Fitting rack & pinion steering in your RX7 or other early RX

Post by TOOL » Sun Mar 08, 2015 8:34 am

I'm not professing to know too much on this topic, but let's get a decent thread going anyway.

The issue with most racks is that they're designed to mount in front of the cross member and connect to the knuckles from the front.
The RX7 and early RX cars have the knuckles at the back though.

So, you could swap the knuckles over to correct this, or according to Aaron Cake, you can fit a LHD rack in a RHD car to solve this too.
See here:

[/quote]

He has used a MX5 rack in his RX5.
Back in sunny France

TOOL
Posts: 2513
Joined: Thu Sep 01, 2011 10:30 am
Location: Var, France (ex NZ, ex UK)

Re: Fitting rack & pinion steering in your RX7 or other earl

Post by TOOL » Sun Mar 08, 2015 8:36 am

And we all remember this boat anchor:

Image

Image

Image

Image

Image

Image

This is a RHD FC rack fitted to the FB cross member and connected with swapped over knuckles.
Back in sunny France

User avatar
ian65
Posts: 5653
Joined: Wed Mar 30, 2011 12:11 am

Re: Fitting rack & pinion steering in your RX7 or other earl

Post by ian65 » Sun Mar 08, 2015 9:28 am

when changing to a rack, the fabrication is only half the battle... the real challenge comes when trying to perfect the geometry....
Changing to rack and pinion is definitely worth doing to dump the horrible steering box setup but it isn't as straight forward as it first appears.....
I looked into it and thought ' how hard can it be?' The answer is 'very' once you start becoming involved with Ackerman angles etc.

I'd love a R&P setup in my car but only if it was spot on...... and that isn't easy to achieve.

Great thread though Tool.... I'm very interested in this so keen to read other everyone elses views on it.
1986 Series 3 13B Turbo II
http://rx7fb.com/viewtopic.php?f=2&t=2400
1992 Peugeot 205 1.9 GTI
1975 Honda SL125 Street Scrambler

User avatar
ian65
Posts: 5653
Joined: Wed Mar 30, 2011 12:11 am

Re: Fitting rack & pinion steering in your RX7 or other earl

Post by ian65 » Sun Mar 08, 2015 10:09 am

What are the pros and cons of the FC subframe swap...... this would seem at first look to be a good starting point for a R&P conversion but how does the steering geometry pan out with that?
1986 Series 3 13B Turbo II
http://rx7fb.com/viewtopic.php?f=2&t=2400
1992 Peugeot 205 1.9 GTI
1975 Honda SL125 Street Scrambler

User avatar
ian65
Posts: 5653
Joined: Wed Mar 30, 2011 12:11 am

Re: Fitting rack & pinion steering in your RX7 or other earl

Post by ian65 » Sun Mar 08, 2015 10:16 am

it's a shame we never got to see how that boat anchor was installed... I can't quite picture it.... why was the rack fitted in front of the cross member instead of behind it like the stock drag link is?
1986 Series 3 13B Turbo II
http://rx7fb.com/viewtopic.php?f=2&t=2400
1992 Peugeot 205 1.9 GTI
1975 Honda SL125 Street Scrambler

apexheid

Re: Fitting rack & pinion steering in your RX7 or other earl

Post by apexheid » Sun Mar 08, 2015 10:26 am

longer link is better for the UJ, more smoother for turning,
I can pic it very well and canna write good about it! Ha

TOOL
Posts: 2513
Joined: Thu Sep 01, 2011 10:30 am
Location: Var, France (ex NZ, ex UK)

Re: Fitting rack & pinion steering in your RX7 or other earl

Post by TOOL » Sun Mar 08, 2015 11:20 am

ian65 wrote:it's a shame we never got to see how that boat anchor was installed... I can't quite picture it.... why was the rack fitted in front of the cross member instead of behind it like the stock drag link is?
The steering knuckles got swapped left to right, so the tie rods stuck out the front. The trick is how it was connected to the steering column.
Back in sunny France

TOOL
Posts: 2513
Joined: Thu Sep 01, 2011 10:30 am
Location: Var, France (ex NZ, ex UK)

Re: Fitting rack & pinion steering in your RX7 or other earl

Post by TOOL » Sun Mar 08, 2015 11:41 am

ian65 wrote:What are the pros and cons of the FC subframe swap...... this would seem at first look to be a good starting point for a R&P conversion but how does the steering geometry pan out with that?
Here's a thread off RX7club.com:
82transam;10768774 wrote:Hey guys, been meaning to do this writeup for a while, but I've just haven't had the time. I've gotton a number of pm's asking for more detail so I figured it was time to make a thread about this. A quick note, when I build a car, or do a project I like to make it look stock, so that if someone who is not familiar with the car were to look at it, they would think that it came that way. With that in mind, I wanted the wheels to line up in the fender well, I did not want the wheels to stick out so far that I needed flares, and I did not want there to be a bunch of easily seen cuts/bends/welds etc. I also did not want to go with coilovers at this time - retaining the stock FB strut/spring/sturt hat etc was important. My point is - there are other ways to do this, this is just how I went about it :)

First a bit of history. I've wanted to do a FC subframe swap on my T2 FB for many years, but for various reasons (other projects taking up my time etc) I just never go around to it. About this time last year I decided it was time to start getting serious about it and started doing research. Like many of the people pm'ing me I found that the information on here about the swap is very scattered, and many of the build threads were never updated with the end result. It wasn't clear if those people just didn't finish the thread, or if the swap itself had never been completed. I knew there were at least a few people who had finished the swap, but in many cases they were on track only cars, or widebodies or some other setup where it didn't matter as much if it looked stock - it just needed to work. Anyway, after much comparison between the FB parts and FC parts, it became obvious that this was going to work, and work well, so earlier this year (end of March, early April) I went ahead and started wrenching. The end result is exactly what I wanted, you get an easy way to mount the FC engine/steering/brakes and the way I did it, you still retain the abilty to use FB shocks and springs (I already had a good set of Eibach springs and Tokico blues) The wheels don't stick out of the fenders (although the track width is wider than the FB, they don't rub) and other than a few welds that you wouldn't notice unless you were really looking, it looks like it belongs there!

Ok, onto the pics and info. Just a note, this is not intended to be a step by step writeup. If you are planning to do this work then you should already be familiar with how to take the front end of an FB apart, and should be able to cut/weld/modify things. I'm really just showing how I went about the swap, and to give you guys some ideas on how to go about it. Again, there are other ways of doing this, but this is how I went about it :)

Pffew this is a lot of typing lol.

Ok, we'll start with the subframe (good place to start eh? lol) The Subframe needs to be moved back 1 inch. If you were to bolt it up using the existing front hole in the subframe and existing front stud on the FB it will sit too far forward and the wheel will look silly and rub the fender well. Seems that many guys on here just remove all 4 studs from the FB and replace them with bolts in the correct spot. While there is no way to get around the need for a new bolt or stud for the rear of the subframe, you can use the existing front stud if you modify the subframe itself. Again going with my theme of making it look stock, I wanted to keep the modifications to the FB as minimal as possible, this means keeping the front stud. So, to get the subframe moved back the 1 inch it needs to be, I simply drilled a new hole 1" forward on the FC subframe. Now if you look at a FC subframe you'll see that this is dangerously close to the front edge of the frame itself. So once I drilled the hole I made a new extension (whatever you want to call it) out of 1/4" steel that extends the subframe forward and reinforces the whole area. I also made a similar tab out of 1/8" steel to go on the bottom to level out the whole area (the front of the subframe has a stamped curve to it, hopefully the pics make this clearer) The end result is a very solid section of metal, and with some careful grinding and welding it smoothed out to the point that it almost looks stock.

The rear needs some work as well, If looking at the car from the side, the FB frame rails are straight, where the FC ones get thicker and dip down in the back near the firewall, and as a result the FC's subframe is not level (if you look at the subframe from the side its not flat across the top). You will need to construct some large spacers around the rear mounting holes on the FC subframe so that the subframe is level when bolted into the FB. There is some debate on here about how large that spacer needs to be. My initial measurements came up with 1/2", which is what I went with, but if I were to do it again I'd go with 5/8". The 1/2" spacer has worked out fine, but in reality it should be a bit taller. I know Peejay went with a 1" spacer and said it sits flush in his FB, not sure why there is such a difference between our two FB bodies, but either way, whatever gets the thing in there level is what you should make ;) Also, Peejay welded his spacer to the body itself, I welded mine to the subframe, again I wanted to keep the FB body as untouched as possible. (within reason obviously)

Image

Once you have all the above work done to the subframe then its time to do some work on the FB's body. If you're going the same route as I did then you will leave the front FB stud in there, and just remove the rear stud. It's just held in with a few welds, cut them and out it comes. You will then need to get out of a set of duckbill pliers, or a hammer and dolly, or just a hammer and a block of wood, whatever you prefer, and do some bending on the pinchweld along the bottom of the FB's frame rail. You will see in the pics where you need to bend, its just a few spots around where the FC subframe bows out, nothing major. Once those areas are bent you can put the FC subframe on the FB's front studs and hold it there with some nuts (be sure to support the rear with some stands or something as well) If you've done your measuring correctly then it should be lined up and sitting in there correctly. Make sure you measure constantly throughout this process to make sure its sitting in there straight and level! Now you can go ahead and mark where you're going to drill for the rear studs/bolts. Be warned, the new rear studs go basically right through the middle of where the stock FB steering box and idler arm go, there are multiple layers of metal and some tubes to support the idler arm/steering box. How you go about drilling these holes is up to you, just be careful not to go balistic and damage a bunch of surround metal or yourself! I only say that because I was using an incredibly powerful corded drill with a unibit to get through the FB box's support tube, it caught and almost broke my wrist from the force lol, so be careful. Anyway, once the hole is drilled where you want it, its time to reinforce the area. I used 8" long 1/2" grade 8 bolts, so get some thick tubing that those bolts will slide through (I found it at Lowes) and some 1/8" steel plate. You basically want to have the tube go through the frame rail to keep it from collapsing when you tighten the bolt, and you want the 1/8" plate on the top of the frame rail to support that tube, and keep the sheet metal from deforming. Once that is all weded together and painted to prevent rusting go ahead and bolt the subframe in! Double check your measurements etc and thats literally it! Now it's time to put the rest of the puzzle pieces in place....

Image

I don't have a pic offhand of the bent sections of the frame rail, I will get one and post it, its very simple though so don't sweat that part :)

Ok so the subframe is in, now what? Well, the FC control arms, spindles, hubs, brakes (the FB master cylinder runs the T2 brakes just fine, and presumably the NA FC brakes as well) and steering rack are all just bolt in items. Obviously now is a good time to replace worn parts like ball joints tie rods and bushings, sandblast and paint things etc, but thats entirely up to you. A quick note, the S4 (86-88) control arms are preferable because they have replaceable ball joints, but the S5's will work as well. Also, if you're running a re-speed sway bar, which already has solid heim jointed links then all you need to do is make a simple brakcet to attach it to the control arm. If you want to run the FC sway bar then you will need to make some way to mount it to the FB body. I did not go this route (I used the re-speed bar) so I'm not 100% familiar with the mods needed, however the "legs" on the FC sway bar are shorter than that of an FB bar, so it needs to be mounted closer to the subframe to work. I know its been done on several other swaps, and is probably just a matter of drilling and reinforcing a few holes in the FB frame rail and bolting it in. So once all that is taken care of, you have the steering colum and the strut assemblies left to build, and you guessed it, more cutting and welding!

Image

Both the strut assemblies and steering column are similar in that they use FB "upper" parts and FC "lower" parts. There are many ways to go about the suspension, but what I did was take a set of old blown FC shocks, and cut pretty much right below the spring perch. Once you cut all the way around the strut itself will come out and you're left with basically a tube with mounting ears on it. Now take a set of FB spindles and CAREFULLY cut the spring perch off. You just want ot cut the welds, do not cut into the strut tube itself! You want to use both the spring perch and strut tube so don't damage either of these parts. Once the spring perch is off grind the rest of the weld smooth on the strut tube so that the perch can slide past where it used to sit. Next cut the spindle portion off so that you're left with just the tube part of the FB assembly. Conveniently the inner diameter of the FC tube you have, and the outter diameter of the FB tube are the same so they slide together nicely, almost as if it was made for this lol. Basically what you want is the tube to be the same height as the FB's original one (so the FB strut insert will go in correctly) and the spring perch to be the same distance from the middle of the spindle (so the bottom of the spring is the same distance to the middle of the FC spindle, as it was to the middle of the FB spindle) this ensures you have the same ride height you did before. Once all that is figured out then you just weld it all together. I drilled a few holes in the side of the FC tube so I could do some rosette welds, along with the bead I ran along the top, just to give it some extra strength. The end result is a FB strut/spring/spring perch/strut top with the mounting ears to bolt it to the FC spindle. There are other ways to do this obviously, but I'm very happy with the result!

Image

The steering column: You will be using mostly FB parts for this, the FB steering tube/support and the upper half of the FB steering column (you just drill out the plastic shear pins and leave the lower half of the column in the stock box and toss it) You will then need the lower half of an FC steering column (again held with similar shear pins) as well as a short section of the FC's steering column tube with its carrier bearing at the bottom. The FB and FC columns are almost the same size, but not quite close enough to just slide right together (can't be too easy now can it lol) so you will need to take a bit of material off the FC's lower column so that it slides into the FB upper. I used a dull flap wheel on a angle grinder (dull so that i didn't take too much off at a time) and just slowly ground away until it was right. I decided to that there is enough collapsable stuff built into this system that I didn't need to bother making the column collapsible (if you want to, go right ahead) so I just welded the two halves together. Once the column is one piece (be sure to measure 3 or 10 times before welding lol) then you put it into the FB upper and weld the FC lower bearing and its tube to the FB part. They are the same diameter luckily so its not difficult. The only thing left at this point is making a way to hold the bottom of the column in the car. If you have an 84/85 then there is a reinforcment plate around the hole in the firewall that the colulmn goes through, it wouldn't take much to make a small brakcet off two of these studs. If you're doing this on a 83 or older (like me) then you need to get more creative. I made a bracket that goes on two of the brake booster studs, and used the bracket off the bottom of the FC column, to bolt it all together.

Image
Image
Image
Image

Hopefully that answers some of the questions you guys have about this swap, and gives some alternate methods on how to go about doing it. I completed this swap in the beginning of April and have put several thousand miles on it already and so far no issues at all! Other than the pair of 8" long 1/2" grade 8 bolts and the few pieces of flat stock and tubing needed to reinforce the frame, everything comes from the FC donor car. If everything from the FC is usable then you really don't need to buy much. In my case I spent some time sandblasting and painting the parts, and replaced the bushings, ball joints, tie rod ends and tie rod boots. Otherwise it was all stuff I had. In the end I spent less than $400. I also chose to use a 15:1 rack and depowered it, there is a thread in the FC section on how to properly do this, it involved taking the rack completely apart, removing a bunch of seals and running a few welds on the pinion shaft.

Any questions, fire away!

Sean
You'll end up with issues such as positive camber which may be able to be corrected with camber tops if it's not excessive.
You'll also get 5x114.3 hubs on the front with more negative offset to compensate for as well as needing new front wheels too. In theory, you'll need to modify rear wheels or convert the rear end to 5x114.3 as well.

Ramon did this, and is one way to go if also fitting a Tii motor.
Back in sunny France

User avatar
ian65
Posts: 5653
Joined: Wed Mar 30, 2011 12:11 am

Re: Fitting rack & pinion steering in your RX7 or other earl

Post by ian65 » Sun Mar 08, 2015 10:28 pm

good info... I'd prefer to keep the Fb s3 hubs though to retain the stock s3 wheels..... can I modify the FB struts to us them with the FC subframe and rack?
1986 Series 3 13B Turbo II
http://rx7fb.com/viewtopic.php?f=2&t=2400
1992 Peugeot 205 1.9 GTI
1975 Honda SL125 Street Scrambler

Post Reply