wishbone fabrication/rosejoint query

wishbone fabrication/rosejoint query

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craig hughes

Original Poster:

17 posts

205 months

Thursday 16th June 2005
quotequote all
I sprint a Scimitar SS1 (not the V6 hearse, the little X19/TR7 thing!) which has pushrod top front wishbones actuating the coil over dampers. The std wishbones are derived from vauxhall Chevette with a triangulated upper pushrod welded on.
I intend to remake them in steel tube to reduce the weight and increase strength and wish to use rosejoints inboard to mount to the chassis and outboard on the upright. Im worried what spec of rosejoints to use as the single outer rosejoint will be suspending the weight of the car and dealing with the springing and damping. Also what type (CDS etc) tube do i use? and what diameter wall thickness etc?
Any thoughts ladies and gentlemen.....

Mutant Rat

9,939 posts

215 months

Thursday 16th June 2005
quotequote all
To be honest, I wouldn't bother replacing the outer ball joints - they are a metal-on-metal joint anyway (so very little play when in good condition). Also, a ball and socket joint will be safe, whereas it is possible to push the ball through an overloaded rose joint where you are placing an axial load on the inner ball.

The big gain is to be made by replacing inner rubber bushes with Rose joints, and since these will be arranged so that the loads are at 90 degrees to the bolt axis (sorry - easier to explain with sketches), the loading is much safer.

As a rule of thumb, for a conventional double wishbone design with outboard springs, you'll usually find that 1/2" bore x 1/2" thread Rose joints will be adequate size and strength for most light sports cars and 3/4" x 16g seamless (CDS) tube will be about right. The geometry of the wishbones/pushrods has a big influence on the stresses, though, so the only safe way is to do the calculations. Rocker arrangements, in particular, can be subjected to very high bending loads. True pullrod arrangements (ie. the rod in pure tension) are pretty good, because steel is very good at resisting tensile loads.

I'm afraid I'm not familiar with the Scimitar pushrod arrangement, though, so I can't give any useful advice specific to the Reliant set-up.

craig hughes

Original Poster:

17 posts

205 months

Friday 17th June 2005
quotequote all
Thanks for the info. Can i email you a couple of pics to give you an idea of the setup?
Cheers,
Craig