924Board.org

[jmshistoric]

I’m currently rebuilding the front suspension on my 1978 NA race car which appears to have standard rubber bushes fitted.

I’m going to replace the wishbone and ARB bushes with Powerflex poly bushes but I’m not sure weather to go for the standard road/fast road grade or the motorsport spec bushes which are 25% stiffer. (Minimal price difference between them)

The car is used for racing and track days about 95% of the time so I’m not to worried about road comfort but I’m wondering if they might put too much stress into the chassis and wishbones causing them to crack. What do you guys think?

The car weighs approximately 1000kgs (2200lbs)

[MikeJinCO]

The only possible problem is that it might get very difficult to adjust the caster. I have delrin in front and poly rear, the delrin is rigid so I had to widen the holes in the front cross member to get the caster to adjust at all. I have to loosen the front then move the rear block in as far as possible to maximize caster then tighten the front. If you can afford it get the uniball units from Racers Edge, a much better solution. I have a spare cross member for when I can upgrade.

I have also reinforced the lower A arm. Boxed along the edge where the cross section is smaller and a steel wrap around the front bushing holder where they have been know to break.
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Mike


'67 MG Midget Dp
'71 Ocelot Dsr Kawasaki 1000(under rebuild)

[Cedric]

Ive run superflex polybushings for years, didn't chose delrin or other hard plastics for athe reason mentioned above, the front needs some flexibility due to caster adjustment. Will probably need to change them in a year or two, but i bought then 15 years sgo, so that's ok. It worked very well on track, and its really sharp in the front end. Racers edge ball joints would be very nice, but the costs are very high, not sure its worth it.
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1980 924 Turbo
www.instagram.com/garagecedric/

[jmshistoric]

Thanks for the feedback, I hadn't considered the caster adjustment!

From my quick bit of research Delrin seems to be 25% firmer then the Black Powerflex bushes so I think I will give the black powerflex bushes a try in the hope that there is still enough give in them to adjust the caster. Worse case as mentioned the front cross member holes can be ovalised to allow side to side movement.

[Karlio]

Change all the bushes to powerflex, purple or black, it will make the world of difference.
And there is no drama adjusting everything.