Well in my search to fit power assisted rack and pinion to my buggy I have learnt a lot about the subject. I did the reading and I bought the books... came up with my design and though all was pretty cool.

Then I found thsi picture of someone who has done it ......

Seems to me if thsi works then I have wasted many hours of my life ....

Hi

That looks like a Camira rack.

1302Steve

Not being rude but WTF. Go the bump steer

Bump steer and I reckon the 30" tyres he has on the front will hit his rack ends.

It is teh best pic I could find of one actually setup.

Anyone got any better ones ? I an not putting my rack in this position but would like info from anyone out there who is running rack and pinion if possible.

That set-up would have less bump steer than the original steering box. Having the tie-rods as long as possible is a good thing.

It looks like it was power steering but is bypassing to itself. LHD so not Camira.

I've done up this diagram to try and give everyone a bit more of an understanding of steering geometry and to try to explain why the rack and pinion setup shown will give significant bump steer.

This is a difficult topic to get your head around so if I don't explain it in a suitable way let me know and I will try and elaborate.

There are two triangles on the picture (A & B). Triangle B shows the geometry of the suspension and I will explain it's relevance first. Triangle A shows the geometry of the rack and pinion setup.

Triangle B
The beetle torsion bar suspension pivots along the torsion tubes (blue line). The torsion arms (yellow line) are a solid and run on bushes in the torsion bar. Therefore their geometry to the blue line cannot change. The point where the torsion arms attach to the steering knuckle travels up and down in an arc at 90 degrees relative to the torsion tubes. So as the suspension goes up or down the point where the red and yellow line meet gets closer to and further away from the front of the car but it's distance from the torsion tube does not change (the torsion arm is a solid object). Now if you imagine the triangle (B) to be a solid object you could take the point where the yellow and red lines meet and spin it around and around the torsion bar and the length of all three sides of the triangle would remain the same. IE. in real life you can spin a torsion arm around and around the torsion tube when there is no steering knuckle or torsion bars in the torsion tube.

Triangle A
Triangle A shows the geometry of the rack and pinion steering in this car. The yellow line is again the torsion arm, the blue line is the static line or pivot line of the steering, and the red line represents the tie rod. The first sign that this setup is not geometrically correct is that the blue pivot line is nowhere near the same location as the pivot line of the front suspension (Blue line triangle B). As a wheel travels through it's movement the torsion arm (yellow line) will pivot on it's arc around the torsion tube. As it moves up and forward the distance between where is meets the steering knuckle (yellow meets red) and the centre of the rack (blue meets red) needs to increase. Since the tie rod is a static object and cannot increase, the steering is pulled inward and therefore the front of the tyre will move outward. Bump steer.

The best geometry for steering is to be exactly the same as the geometry of the suspension. The geometry of the suspension is triangle B, so we need to make the geometry of the steering as close as possible to triangle B to eliminate bump steer. This could be achieved by having a rack and pinion setup mounted right up on the front torsion tube with it's tie rods pivoting where the red and blue line meet on triangle B.

If the rack pictured was moved all the way forward, flipped end to end, mounted on the torsion tubes, and had the tie rod mounts attached to the back (instead of the front) it would work well. Looking at the rack, the centre section may well be free to rotate and could be rolled over so the tie rods attached to the back.

Hopefully I've explained that correctly.

[Edited on 4-6-2004 by MikeM]

I sent the picture of the rack to my cousin who owns a power steering and transmission shop.

He said that the rack is very similar to the racks used on Camiras and some Audis. But obvisously Camiras and the Local market Audis have a RHD version.

The center section cannot be modified to mount the tie rods on the other side (back) as the center section on the Camira racks is cast alloy. What could potentially be done though is a piece of u chanel could be mounted over the center section to bolt onto the stock mount on the front but allow the tie rods to be bolted to the back. We'd have to confirm with a blue plate officer whether this would be acceptable.

This rack would be dead easy to mount on the front torsion tubes, it just depends whether we can come up with a way to mount the tie rods to the back and get it all approved.

Also my cousin mentioned that the shortest available standard rack (end mount not center) is actually a standard Commodore rack. These are around 20 inches long. Due to the number of varieties of commodores over the years the tie rods are available is many custom lengths so getting it the right overall length for the VW should be easy enough. I will look into this option a bit more as he has several commodore racks sitting in his workshop at the moment.

[Edited on 4-6-2004 by MikeM]

I never said it's good. Just probably better than stock.

Sure as it travels each wheel will toe out, be it will be even amounts.

The stock set-up weaves on big bumps cos the short tie rod and long tie rod are changing the toe different amounts on each side, causing it to make the car want to turn on big bumps.

If you have (and I know you will) a copy of Jeff Hiddard's book baja bugs and buggies, have a look at page 66. In a box on the left All about bump steer I use this when I set up a car with howe or wright racks and have on prob's. maybe It can help you to..

one more thing ????? while talking steering geometry. how do you guys go with the ackermans angle on your short wheel base Buggies

something to look into if your making front stubs but

I see Bump steer as a much bigger issue than Ackerman. As long as the Ackerman angles are close to stock (which they would be with the rack mounted on the torsion tube or just behind) I don't think it would be a concern.

http://www.auto-ware.com/setup/ack_rac.htm 

Here is a cool reference on car handling. Actually relates to RC model cars, but hey a Manx is just a big toy car

http://rctek.com/handling/index.html 

This is pretty cool, gives some info on how Ackerman can be set.

http://rctek.com/handling/ackerman_steering_principle.html 

This is actually a bit simplistic as it does not take into concern the arc travelled by the pitman arm or the steering knuckle.

Having now read a bit of info on Ackerman I believe that putting a rack and pinion on the humble VW may actually fix the Ackerman rather than make it worse. Is the Ackerman on a VW actually correct? It will be at one point, but probably not at all points due to the swing of the pitman and the issues with a short and long tie rod. At full lock I'd say a VW has incorrect Ackerman.

If I get enthusiastic I will look into this more. There must be some equations relating to this somewhere.

[Edited on 4-6-2004 by MikeM]

love this stuff

mmm looks like some people have gone and gotten some big words........ hehe

If all goes to plan I should have a Power assisted R & P on a ball joint front end in the next few weeks. Just sorting out exactly what the engineer wants before he will approve it.

The above does make for very interesting reading though... so where are all your pics of setups though ??

Cool

What's that going on Brad? Last I checked the Mega manx was using Link Pin?

the center mount race rack no good Brad .I know where there is two of them .Not power but very good $$ :alien

This is the pump its not the best pic but I will replace it later with a better one and also one of the rack and servo..

Quote:

Originally posted by Buggy Brad

now that's a steering damper!

FWIW that first picture IS using the same rack setup as Camira. Remember Camira is an Opel and was sold all round the world as the GM "J" car, so you can do the same setup here using the camira rack. JD and JE were available with power steering.

Hey Mike, I know where you got that photo you posted...... lol

the Wright place

A fellow Eureka owner has used a R & P out of a Hyundai not sure on how legal it is but I'll see if I can get pics.

There was an old 1980's vintage article on R & P steering for VW based kit cars. Go to the Nova site here

http://www.nova-international.net/home.htm 

then on the left bar click ‘data’ when the page loads, scroll down the Right hand side and click ‘The chassis’ then when that loads scroll down to "an alternative steering system to the VW"

Hey Brad I don't know if this will help you but a long time ago when I was fitting racks I made a toe beam. What’s this you ask, it one step up from a tape measure...lol. I got a 25mm piece of Polly pipe 6" short of the inside of both front tyres (about 1100mm long) then a 12” bit of broom stick and a 24mm spring that was about 10” long. Drill a hole in the stick 2” away from the end and put a bolt though it. But the broom stick in the pipe with the spring between the bolt and the pipe. On the broom stick at about 5” and up to 7” mark it off in millimeters this is where you read your toe change. Take you torsion bars out and use a jack to lift and lower the front of the car to check the bump steer. With the rack tacked you can move the rack up, down, back or forward to get the right bump steer before you weld it. This cool backyard tool can be used as a bodgie wheel aligner as well. When the car is back together but it at the front of the wheels then roll the car forward till the toe beam is at the same height at the back this will give you your total toe reading e.g. the difference between the to reading. Bodgie but it works. (I use a laser aligner now to setup but it takes longer).

Moose
:thumb