Front suspension and steering Drawings

Looking for help I want to rebuild the steering and suspension on my GT40 . Has anyone got proper drawings of it that I could fabricate it from
 
What brand of replica do you have?
HI Bob it's a KCC kit with I think has a cortina front end . It under and over steered bad so I changed it and got it alot better. But it still not great so I want to rebuild it with more adjustability to get it to handle great.
Thanks
Nigel
 

Mike Pass

Supporter
It is probably Cortina Mk3 front end if it like the KVA early chassis. Does your car have the trailing arm rear setup like the early KVA? If so then the rear set up is more likely to be the problem rather than the front. Where are you based? This will be relevant for any advice.
Cheers
Mike
 
It is probably Cortina Mk3 front end if it like the KVA early chassis. Does your car have the trailing arm rear setup like the early KVA? If so then the rear set up is more likely to be the problem rather than the front. Where are you based? This will be relevant for any advice.
Cheers
Mike
Hi Mikemthe rear end is Forg Granada
 
It is probably Cortina Mk3 front end if it like the KVA early chassis. Does your car have the trailing arm rear setup like the early KVA? If so then the rear set up is more likely to be the problem rather than the front. Where are you based? This will be relevant for any advice.
Cheers
Mike
MIKE I'm in New Zealand the rear I set up with no camber or caster angle . I dont know if that's correct ?
 

Mike Pass

Supporter
OK. If you were in the UK I have some spare front wishbones so try another idea.
The first thing to check is what tyres you are using. As you complain of both under and over steer the tyres may have something to do with that.

The front suspension being Cortina Mk3 type does not have the best geometry as the typical factory settings are.
Toe in 0 to 6mm
Castor1.5 degrees
Camber1/2 to 3/4 degree
The Cortina Mk3 was petty understeery.

While it is hard to change the geometry the suspension can be improved a lot by changing the bushes from squishy rubber to polybushes. Change the wishbone bushes, the tie bar bushes and the antiroll bar and drop link bushes. This will stop the suspension from moving as much with better control. The anti roll bar bushes can be made of solid material such as nylon.
If the front shock absorbers are a bit tired replace with adjustable type. If you can get stiffer springs and anti roll bar from a similar model e.g. GT or V6 model that would help. The initial understeer is down to the front suspension.
However, when the suspension loads up in cornering the rear suspension then causes problems. The trailing arms have soft rubber bushes. When the cornering side loads act on the outside trailing arm the bushes deform and the outer moves back and the inner moves forward thus rotating the wishbone. It then gets toe out which is bad. Toe out makes the back end unstable and oversteery.
The factory setting for the trailing arm suspension is typically
Toe in 0 to 0.09"
Camber 0.1 to 0.5 deg
It is important to not let the rear wheel get toe out. It should remain et least straight ahead or better slight toe in. The trailing arms are mounted at an angle. This is so that the wheel gains camber as it rises. This is to compensate for the roll of the car body in cornering and keep the tyre flat to the road.
The Ford Sierra Cosworth used similar trailing arms but as it was a a high performance car it was improved to prevent toe out caused by hard cornering. At first glance the trailing arm bushes looked to be the same rubber bushings but inside the rubber was a solid steel ball joint. This prevented the bushings from compressing and causing toe out.
So the thing to do is to replace the squidgy rubber bushes with something better. If the two pivots are in line then a solid bush such as nylon would be OK. If they are not in line then a spherical bearing would be best. Make up a sleeve with outer diameter the same as the trailing arn hole and inner diameter the same as the spherical bearing. Make up two cones to clamp the spherical bearing inner in the bracket. Tack weld the fabricated outer sleeve to the trailing arm.

Try these changes with decent tyres. If it needs to be better then a more radical change will be needed.

Cheers
Mike
 
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