REPLACING TOP WISHBONES - TRUNNIONS

[Guy Lowe]

I have a 1990 S3 De Dion chassis with trunnions & some time ago I replaced the front top arms (see image) with  standard track top wish bones, new type ARB, new dampers and springs but retained the lower wishbones, trunnions & uprights. I had the car set up by a Caterham race team and everything seems good & I am very pleased with the cars handling on the road and track.

However I have now read somewhere on BC (for the life of me I can’t find it now) that this should not be done as it moves the top of the upright to a slightly different position altering the caster and more importantly, it puts additional strain on the trunnion and lower wishbone trunnion lugs.

Before I consider changing the lower wishbones, dampers, springs and uprights, does anyone have any knowledge of this upgrade or can point me to the post please?

Thanks Guy

[SteWi]

Perhaps this https://www.caterhamlotus7.club/comment/2178648#comment-2178648 ?

[Guy Lowe]

Reply #2

Thank you Steve, yes that's the the thread, I spent hours searching but couldn't find it

This is what concerns me:-

Officially it's only recommended with a change from trunnions to ball joints at the bottom because otherwise the upright is over-constrained, i.e. both the trunnion and the top wishbone try to set the castor, and they might not agree.

So it look like I need to change the lower WB's uprights etc. Better start saving.

[Jonathan Kay]

"... yes that's the the thread, I spent hours searching but couldn't find it"

Only just spotted that. Here's the search that I would have used:

https://duckduckgo.com/?q=site:caterhamlotus7.club+upright+caster+trunnion

Jonathan

[John Vine]

Works even better if you spell it "castor". 

JV

[Guy Lowe]

Works even better if you spell it "castor"

 

Seems you can spell it either way but as I was told never to argue with the teachers, you must be right John 

 

[John Vine]

Of course, all I meant was you get more search hits with "castor" than with "caster".

JV

[Tony Whitley]

You're talking Pollux

Castor is a British term for caster wheel, whereas caster is an American term for caster wheel.
 

Caster is a type of sugar.

[Guy Lowe]

Reply #7

Thanks John I really struggle with the BC search facility so your help is appreciated, a couple of very helpful threads there.

[Gridgway]

#3 to change the lower WBs do you need to mod the chassis for the front pickup point for the lower WB?

Also there is the "Triumph" trunnion conversion kit from Canley Classic that some have used.  I looked but decided to keep the trunnions after talking to them.  They didn't think the Caterham wishbones were right for their kit.

[Guy Lowe]

#10

"I looked but decided to keep the trunnions"

The more I look into this, the more I am leaning towards  doing the same.