2002 E21 steering rack swap questions and details.

[3lack Sheep]

Hey guys, I'm new here and looking for a few specifics to get me started on my rack swap. 

I'm doing a K24 turbo with a Getrag 260 swap in a LHD '75 2002, and unfortunately the rebuilt OEM quick ratio box isn't going to work with our build, (it will crash with the AC compressor) so I've cleaned the OEM steering and motor mount bracketry off the crossmember in preparation for new motor mounts and rack mounts. 

I've already got the new motor mounts done and I'm trying to figure out the steering rack mounts for an E21 manual rack. 

I've read through a lot of threads, hear and on other sites, of doing this swap. Most of it has just been a lot of fluff, staying how difficult it is, without a lot of constructive information. 

I'm a mechanical engineer, with a trade background in fabrication and welding. I have also done many other custom car and motorcycle builds, however this is my first BMW car, and my first dealings with a steering rack. I have designed and built custom 4X4 suspensions so I have an understanding of the importance of getting everything lined up properly for function. 

I've read that the steering arms on the shocks need to be modified by shortening them 50mm, which won't be an issue. But I would like to know how far back from the crossmember to set the rack for its mounts? Is there a distance that works well, or do I just make everything line up as much as possible once the arms are shortened with the tierods being perpendicular to the wheels when the wheels are straight? 

Are you chopping off the colum at the fire wall and routing it with 2 U-joints to mate with the rack?

I also read that due to the length of the rack being wider than the inner control arm mounts there will be inherent bump steer. 

I am sure there are also some aspects to this swap I am not aware of, and could use a little guidance. 

 

Please, if you have any experience with a rack swap i would greatly appreciate your input or information so i can continue making progress on this build. 

[Georges]

I've always been scared to swap racks, but I did a F22C swap into my 2002 and kept the Honda A/C. Wouldn't it just be simpler to move your compressor? Then your only problem will be pullies and a belt to run the moved compressor.

[3lack Sheep]

Unfortunately it doesn't appear so with the manifolds we are using. We are already relocating the water pump so we can free up space for the compressor too. From what I've seen, it looks like the F22c would have been an easier swap. 

[Georges]

Easier, but too expensive. I'm actually super psyched to follow your build because if I ever blow my engine I'll K-swap. What engine management will you use?

[3lack Sheep]

We'll use either an infinity or a Haltech, we've got plenty of experience with them, and we have a great local tuner who only does stand alone units. 

[Tommy]

You do seem to know the pitfalls of this swap which is good. Usually people starting a rack swap thread don't have a clue.

9 hours ago, 3lack Sheep said:

But I would like to know how far back from the crossmember to set the rack for its mounts? Is there a distance that works well, or do I just make everything line up as much as possible once the arms are shortened with the tierods being perpendicular to the wheels when the wheels are straight?

The location does affect the dynamics of turning the wheels - ackermann steering. Usually rear mounted rack is located a bit forward from the perpendicular position - around inch or half. Being a mechanical engineer maybe you could make a CAD-model and see how it effects. Rack width and the turning arms length and angle affect ackermann too so it's not easy to figure out the outcome when many things change. 

 

9 hours ago, 3lack Sheep said:

I also read that due to the length of the rack being wider than the inner control arm mounts there will be inherent bump steer. 

I am sure there are also some aspects to this swap I am not aware of, and could use a little guidance.

This is why I wouldn't do this swap. I can't say how bad the bump steer effect is but it's hard to avoid using E21 rack because it's too wide. I would try to look for rack that fits better to the width. Or somehow, by modeling/simulating, assure myself that it's not too bad.

 

When I designed suspension with rack steering to my racecar I started by choosing the rack.  Then I made suspension pickup points according to rack width. I went with forward mounted rack because my engine was mounted further back so it doesn't help you to know that I chose Opel Ascona rack. 

[tzei]

I made mine with E21 crossmember with modified front fixing points = shortened to suit, rear holes fits 02 chassis holes. So i use E21 rack location although i replaced oe steel camp/bush thingie with solid u-clamps. Steering arms are made from 7075Al which has E21 dimensions but not as much trailing kpa line (to suit 02 strut). Moog used to have online measurements for rod ends: i have used Subaru & Ford inner bits. 

[3lack Sheep]

Tezi, did you have to utilize the E21 arms as well or did the 02 suspension parts work with the E21 crossmember?

Thanks! 

[tzei]

I use tube arms as found in FIA homologation #1663.

 

Edited October 24, 2023 by tzei

[TobyB]

So, the original drag link setup, the tie rods are the same length as the lower control arms,

and crucially, are in plane with them.

 

If you want to avoid bump steer, you must duplicate that geometry- and the E21 rack doesn't do that.

Also, the distance from the ball joint centerline doesn't much matter- EXCEPT as it affects

the motion ratio of the outer ball joint.  And that is determined by the forged arm that attaches

to the bottom of the strut.  

 

t

 

[Ian]

On 10/24/2023 at 12:42 AM, Tommy said:

When I designed suspension with rack steering to my racecar I started by choosing the rack.  Then I made suspension pickup points according to rack width. I went with forward mounted rack because my engine was mounted further back so it doesn't help you to know that I chose Opel Ascona rack. 

I'm interested in your opel rack conversion.  Any more info or pictures?

[Tommy]

3 hours ago, Ian said:

I'm interested in your opel rack conversion.  Any more info or pictures?

There is some in my racecar project blog. I'm not sure if you can call it a conversion as basically the whole suspension was reworked based on e28 parts.

 

[markmac]

My race car started out with QR box, but then R&P was homologated for Gr2 cars so Alpina switched to that.  The tire/wheel combo is so massive I don't know how anyone could have really steered the thing in a normal 50 lap race let along a 4,6 or 12 hour race - it would have been brutal.

 

After having a number of people monkey around with it over the years I took it in to have the steering completely gone through.  We used an e-21 motorsport QR rack that had to be shortened like 2.5" and then all new fabricated pieces.  They had the thing up on a jig with various measuring equipment etc.,  The guy doing the work told me it had the worst bump steer he had ever seen and would have been outright dangerous to drive.  All fixed now, professionally done, safe - but my gut still hurts four years later after paying the bill.  I have some pics somewhere and will post if I can locate them.

[Ian]

Another option is to get a custom rack from Woodward Steering.  Not cheap, but probably less than paying for fabrication if you don't want to weld.  I spoke with them, and they are very knowledgable and can make just about anything if you give them the measurements. They mostly make  power steering racks, but they've got a few manual steering racks that can b e used in rear-steer applications.

[markmac]

They have some good information there, especially the link to the 'basic R&P tech'.  Not engineer here but there are a lot of nuances to making it 'right' aside from just the rack.  I know when the shop was done with mine, they told me....'DON'T TOUCH IT', don't adjust it, move it etc., it should be perfectly set up the way it is.  Good by me, of course it has yet to be driven/tested.