ABC of rack and pinion!

[sgo]

There seems to be a lot of interest in rack and pinion steering so (xxxxxxxxxxxxxxxxxxxxxc) I'd like to start a thread on that topic, the ABC of rack and pinion mods!
Some of the basic principles that I think are relevant are:
B for bugger! -I'ts not legal or safe to cut and weld, heat and bend any steering                                                   component.If you're a metallurgist and engineer then there may be exceptions!
A for Ackerman-your workshop manual explains this but I think that seeing it mainly relates to the wheelbase of the vehicle and for the usual front end swap in most FE/FC's the difference in wheelbases is minimal , Ackerman has a minimal effect, so can be ignored!
S for steering arms-all (most?) early holden steering arms have the same bolt spacing and are different lengths.The ones to use would be the ones that are the same length as those on the rack that you intend to use. This will ensure that the movement of the wheels relative to the movement of the rack, ie steering effort, and turns of the steering wheel, is the same as what the designers of the rack intended.
T for tie-rod ends-the taper on the tie-rod end must match the taper in the steering arms, as you don't want these to separate when you're on the move!
P for parallel-the tie rods must be mounted parallel to the bottom wishbone to prevent bump steer. So when you have the steering-arms sorted this will give you the height at which the rack will be mounted at. When the bottom wishbone is horizontal the tie-rods should be horizontal as well, with one end connected to the rack and the other connected to the steering arm.
B for bump-steer: as your wheels move up and down over a bumpy road you don't want that movement causing your steering wheel to turn, if it does you have bump-steer!
S for shorten the rack- the rack is shortened on the opposite end to that of the steering column connection, by machining / duplicating the original end on the cut down end for connection of the tie-rod.
L for length of rack- this is critical to prevent bump steer. Imagine looking at your front-end from the back of your car (for a rear mounted rack), Draw a line from the inner pivot point of the top wishbone to the inner pivot point of the bottom wishbone, it will be at an angle, not vertical. If your bottom wishbone is horizontal, so will the tie-rod be and where the centre of the tie-rod meets our imaginary line through the pivot points will give you the position of the new rack ends.
M for mounts- duplicate the mounting brackets used on the racks original vehicle and add strong gussuts to stop sideways movement and to keep the engineer happy  and you're just about on the road!

[mcl1959]

sgo,  good idea to start a thread on this subject
Here are my thoughts  (by the way - I'm a mechanical engineer, and I understand the steering principles quite well.)
B - It is legal to cut and weld steering arms.  They must be done by a ticketed welder and must be XRayed for weld penetration)  An example is the steering arm for Mustang L to R conversion.  Hoppers Stoppers in Vic do this conversion regularly and in fact sell the cut and welded steering arms to other Mustang converters.  (These have been engineer certified).

A - Ackermann principal is the principle which makes the inside wheel turn in further than the outside wheel when cornering.  The theory is that if you draw an imaginary line from the lower ball joint through the outer tie rod end then continue through past the centreline of the car, the position that it passes the centreline of the car should be at the differential.  Clearly then the selection of steering arms other than HR will affect Ackermann and should only be attempted with experience.

S - Wrong.  the donor rack must be installed in the car to duplicate the exact position of the ORIGINAL steering unless IMPROVING the original steering of the car. Using longer steering arms on a HR front end for example will push the imaginary line above (Ackermann) back past the diff and you will scrub tyres.  Do not install steering arms on a vehicle just because they are the same length as the ones on the donor rack.

T - agree.  Note that it is not difficult to have steering arms re tapered to fit. An example of this is when L300 front ends are fitted to hot rods and HQ axles are retapered to fit the L300 ball joints.

P - parallel tie rods and B - bump steer.  This is rather simplistic, and does not guarantee no bump steer.  The idea  here is for the steering arm not to move in or out through the entire up and down movement of the suspension.  Once again replicating the original mounting position of the INNER tie rod end of the rack with the position of the ORIGINAL steering equipment is the best option.  This is generally just inboard of an imaginary line drawn through the two lower wishbone pivots.  Once again though, changes can be made so long as you are IMPROVING the bump steer characteristics of the original steering.

S & L - racks are shortened to meet the above requirement.  Generally the longer the tie rod, the smaller the affect of bump steer will be.  The down side is of course, is that the shorter the rack, the greater the turning circle will be.

M - fair enough, but be aware that OEM rack mounts are generally lighter than what an engineer would require.

An example of one way to improve original HR steering characteristics is to LOWER the mount height of the top wishbone.  This improves the body roll characteristic of the car during steering by tucking the top of the wheel in further.  Ever noticed how late model cars tend to lean the inner wheel in much further than a HR does during steering?

Sorry if this has been long winded but I will reemphasise my original point in a different thread.  If you don't understand it - DONT MESS WITH IT.

Ken

[Disappointed Bloke]

Ken
Thanks for clearing up those points made sgo in the previous thread it is an extremely useful comment and I was not aware of the concept of lowering the upper wishbone mount to help minimise body roll.  In case you are interested, regarding sgo’s statement “for those that don't mind sharing their experience and knowledge” please see my reply in “Power Steering V6” of today’s date.

[mcl1959]

Thanks DP,  your comments are appreciated.  I've read your comments in the other thread, and I understand your position.
Please don't feel disheartened, my experience of the chat line has shown that most people are quite generous and helpful when spoken to in person, but a strange phenomenon of typing words into a PC tends to dehumanise people to the extent that they say things on the chat line which they would not say in person.
We have had a couple of instances now of people getting carried away with badly thought out responses & the results are not good.
My message to you DP is to stay happy and keep up the good work.
My message to everyone else (including me) is to think twice before pushing the "Post" button.  Ask yourself whether what you are about to say is really in the best interests of all concerned.

Hope this helps    Ken

[sgo]

Just some more info, taken from another site!
A couple of years ago automotive engineer Ted Robinette, the technical writer for Australian Street Rodding magazine, wrote that front mounted racks on HRs are a compromise. He said you can't get the steering geometry perfect.
My next door neighbour fitted a 351 Cleveland to his EH. He used a CRS front rack and I could see what Ted was talking about. The problem was it is not possible to get the Ackerman principle correct so the toe out on turns is out.
Lines drawn from the lower ball joints through the tie rod ends should meet in the centre of the diff in order to get steering on turns correct. Front mounted steering systems have the tie rod end mounted outside the lower ball joint for this reason. On the HQ for example if you draw a line from the tie rod ends through the lower ball joints you will see it goes towards the diff. centre.
On a HR you can't do this. CRS supplies bent steering arms to take the tie rod ends out but you can't bend them out far enough because the wheel gets in the way, hence the compromise.
This does not affect the car in a straight line but it does on corners.
I think the racks CRS uses are also shortened to get the inner ball joints on the rack pivoting on the line extended through the upper and lower inner bushes to prevent bump steer. I think this shortening also has a detrimental effect on the turning circle.
This system is not ideal but it does a reasonable job and is necessary because that is about the only way you can get a V8 into a HR.

[Burnsy]

It is two years on from the last post on this thread and I was just wondering whether there have been any developments.  Particularly in relation to power steering and the comments made by Ken as to a Volvo unit that was used on a HR frontend by Hopper Stoppers and on any L300 front end conversions that people may have seen/undertaken?

[sgo]

In the past two years it seems that the concensus was that it's too hard to shorten a power rack to fit a HR front end.
One sleepless night  it occurred to me that if you can't make the rack fit the front-end, perhaps you can make the front-end fit the rack?

I have a cross-member where one of the lower pivot points is stuffed, so in repairing that I may as well move it outwards so that it lines up with the corect position for a power rack.
To keep the track and camber as normal the lower wishbone needs to be shortened.
Anyway thats the theory and if it works I'll keep you posted!

[GM]

Hi guys, my 2 bobs worth. rear mounted rack is the best way to go, even if its only for the turning circle. I am running a nissan rack and pinion and it works great. The steering was heavy with 225 tyres, but went to 205s and made all the difference. I did have a picture a  while ago on modification help. It was under ' F.C. 308'.
[If you weld  steering arms etc. shouldn't  they be stressed relieved?]
                          Cheers Glenn

[Burnsy]

I am interested in use of the L300 front end, I found these pictures ages ago and can't remember where.  You don't hear much about these front ends other than them being used on rods but I would be interested to know if anyone has experience with them.  I figre there is a fair bit of fabrication required to mount them but when you consider the fabrication required to adapt a HR fornt end with R&P it may well be worth it?

[Glenn 'Stinky' Stankevicius]

Judging by some of the post on the Hot-Rod Internet forum, it is no big deal to shorten the L300 front-end to suit whatever application.
Jag front-ends seem a popular choice too.
http://www.hot-rod.com.au/benchracing/viewtopic.php?t=2374

[FC229]

I had an early Commodore rack fitted to my wagon a few months ago and while I am reasonably happy with it, the turning circle is not as good as it was. It's a rear mounted CRS kit and we ended up using a Commodore column to make the connections easier. Playing with combining an H KTG column with the Commodore column was frowned upon by the engineer. Makes sense I s'pose.
The top bearing of the commodore column was modified so the original indicator mechanism could be refitted, combined with a sports wheel it does not look too out of place, though it is a lot closer to the dash than the original. I quite like the fact its so far away, feels more like a hot rod.
The main reason for this post is to try and get clarification re the steering arms. The mechanic who fitted suggested trying different steering arms, citing (I think it was) HQ's that had different length arms. I think it was to do with power steering, but apparently made a good difference when changed to non power steering vehicles. Sounds odd, perhaps someone can clarify that.

Can anyone tell me if the early commodore arms will fit the HR front end? Even better if they have fitted them and suffered any consequences. I think the Ackermann principle is only 1 part of the equation, and camber and castor which don't change must play a major role in any tyre wear problems. "The Ackermann angle compensates for the fact that the inner wheel on a bend must turn through a greater angle than the outer wheel to follow a curve of shorter radius"
I can post a copy of the diagram that goes with this quote if anyone is interested. Looking at it it seems to me that the further back the imaginery line intersects, i.e. past the diff, would be betterI wonder really whether the conversion is over rated, and if fitting the H KTG column (which gives a collapsible column), and having the rest of the gear in tip top condition wouldn't do the job. They don't go too badly when they're nice and tight!!
I've heard there's also the possibility of Toyota Crown power steering box fitted to the H KTG column.