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steering rack
rocket - 13/7/05 at 08:10 AM

just into this part of my build and low and behold I have a alloy sierra rack!!

From what I've read here on the forum this isn't any good to me!

but inlooking on the net for picture of modified racks I came across a picture of this one which looks like the one MK uses.

It is from a skoda estelle ( used for a porche kit car.)
Rescued attachment s_rack_ref.jpg
Rescued attachment s_rack_ref.jpg


James - 13/7/05 at 08:27 AM

MK uses the alloy Sierra rack.

They chop out the middle and fit extensions on the end to compensate.

You've just got to make sure that the balljoints of the track rod arms are inline with a line drawn between the bushes of the top and bottom front wishbone.
This minimises bump steer.

Hope that helps,
James


Mark18 - 13/7/05 at 09:33 AM

Having said that, that rack does look like it'd be better suited - so long as it steers the front of the hub rather than the rear - any chance you could put up the dimensions and turns lock to lock?

Mark


NS Dev - 13/7/05 at 09:59 AM

the rack in that pic looks uncannily like a short escort mk2 rack!!!


MikeR - 13/7/05 at 12:12 PM

hmmm, i'm not sure, the turny bit for the steering column to attach to appears to be at an angle to the body of the rack. I thought the escort was at 90 degrees.


NS Dev - 13/7/05 at 12:45 PM

I thought it was angled? The splined shaft looks a touch longer than the escort one but the casting around that end of the rack looks very similar!


rocket - 13/7/05 at 08:08 PM

Got my grinder out and attacked rack!!

took 5" out of it and is now perfect fit!

Not as big a job as I thought, just got to weld the extensions on ( after I make wish bones and I know where everything lands!!)

My cars a bit "odd" as I'm making it fit a westfield body that I got cheap. So the top rails are wider but the bottom is as per book.

Rgds

Roger


NS Dev - 14/7/05 at 08:01 AM

bear in mind that the whole handling characteristics of the car are set by the difference in width of the chassis between top rails and bottom rails! (without going into further detail, but camber change etc is affected dramatically!)


britishtrident - 14/7/05 at 08:15 AM

Look at the picture carefully --- who can spot why it won't work :-)

Also it looks to me like a Hillman Avenger rack.

[Edited on 14/7/05 by britishtrident]


Mix - 14/7/05 at 08:26 AM

It's from a vehicle with the track rod ends attached behind the hubs.
Could always try crossing your hands

Mick


rocket - 14/7/05 at 08:51 AM

quote:
Originally posted by NS Dev
bear in mind that the whole handling characteristics of the car are set by the difference in width of the chassis between top rails and bottom rails! (without going into further detail, but camber change etc is affected dramatically!)


But surely this is set by the length of the wish bones?

If I shorten the top one to compensate for the extra with this should work yes?

rgds

Roger


NS Dev - 14/7/05 at 10:07 AM

That's exactly the point, you will have to horten the upper wishbone to get the wheel upright! The shorter upper wishbone then gives greatly increased camber change in bump and droop, affecting the handling. Exactly what effects I'll leave to the experts but it has a major effect. A basic rule is to have wishbones as long as possible, as this removes unwanted effects. The design of the generic "7" type chassis is based around the ratio of the upper and lower wishbone lengths, and the chassis then fitted to these lengths.

At the very basic level, if your wishbones are equal length, the wheel stays upright in bump and droop. If the upper wishbone is shorter, it takes on negative camber in bump and droop, and this is exploited in the "7" to roll on negative camber on the outside wheel when cornering. The shorter the top wishbone, the more negative camber is rolled on. Taken to the extreme, where the upper wishbone is reduced to 0 length, you end up with a swing axle where the wheel angle simply rotates about the bottom wishbone pivot (a la Imp)