Reply to "STEERING RACK"

Dick,

I have recently done some work on Jonathan Root's car. One of the things I was asked to look at was the steering and alignment.

Jonathans main gripe with the steering was the low gearing and the way it grabs, pulls and tramlines.

After studying the front end for quite a while I realised the Mangusta's biggest problem is excessive positive scrub radius. I measured it at 6" (150mm) this is alarming to say the least!
The only way to reduce the scrub radius is to redesign the upright. This would then require longer A arms or relocated pick up points on the chassis - probably both.

The Renault rack is actually very well made, way better than the Pantera rack. On the turn plates I measured one rotation of the steering wheel achieves 13.5 degrees of rotation at the road wheel. For comparison a Pantera achieves 18 degrees.
On a road car changing the rack on the Goose for one with a quicker ratio would actually exaggerate the scrub radius problem and make the steering wheel grab and pull even more than before due to the fact the driver effectively has less leverage at the steering wheel.

I decided the best course of action was remove all the play from the steering system and align the car. I also modified the steering arms and replaced the outer tie rod ball joints with a Rose joint (Heim if your American) This enabled me to completely remove all the bump steer. I calculated the ball joint (now Rose joint) needed to be raised 8mm on the right side of the car and 5mm on the left. It would be possible to achieve the same thing by raising the rack but I dont like to do it that way.
I bought the extra long M16x1 Rose joints from http://www.mcgillmotorsports.co.uk/ The proprietor says he had them specially made for another car and thinks he is the only source for that particular size world-wide. A normal M16 Rose joint would have a thread pitch of 1.5 not 1mm.

I replaced the two Hook joints in the steering column. This was the source of all the play on this low mileage car. The original joints had bronze bushes. I was able to buy direct replacements with needle roller bearings and grease nipple! They are very expensive at approx £80 each!!!! I got them from Roger Brotton rogerbrotton@btinternet.com

The rag joint between the column and the rack had no play in it at all so I did not touch it.

Alignment:

I found the castor to be 4,3/4 degrees on one side and 6 degrees on the other. I set them both to 6 degrees positive.
The camber was already correct at 1/2 degree negative.
I set the toe in at 1/4"



Regards, Johnny