Thread: Alternative suspension / conversion to springs

Off the following thread:

Chooks Defender 110

A mate of mine has a Jap wagon (old Nissan Pathfinder) that has rear leafs.

He's looking for more articulation in the rear, so he's designing a home-made coil conversion.

He's thinking of using trailing arms from the existing FRONT leaf spring mounts as basically lower outer control arms, then using the REAR leaf spring shackle mounts for either a pair of upper inner control arms, or else an A-arm / triangular system mounted on the top of the centered diff housing. So the outer/lower arms would be trailing and the upper/inner would be forward facing, if you follow.












Then John Bush65 had the following comment:

"It will work if the details are executed properly. How well it will work in terms of anti-squat and roll steer I can;t say from the information and I don't have a pathfinder to measure.

Obviously the stock leaf springs locate the axle assembly in the longitudinal and transverse direction and prevent it from rotating. So there is no reason to think appropriate links can't do the same.

A free body has 6 degrees of freedom. Three translations we assign X, Y, Z coordinates to, and three rotations about those coordinate axii.

The suspension for an axle assembly has to constrain 4 of those, 2 translations and 2 rotations, so the axle can only move up/down (1 translation) and articulate (1 rotation).

To do that 4 links, and only 4, are required. If there are less than 4 it will be under-constrained and will have either an unwanted translation or rotation. Now some vehicles such as coil sprung patrols and cruisers have 5 links (2 uppers, 2 lowers and a panhard). The flexible bushes allow the the axle to move as required up to the point where the bushes bind - because the upper links are close together they are able to achieve more travel before the bushes bind

With Land Rover radius arm in the front suspension, each radius arm takes the place of 2 links (one from the chassis mount to one of the bushes at the axle and the other from the chassis to the other axle bush. The panhard is a 5th link, so again we have an over-constrained system which only works because of flex in the radius arm bushes. This is why it is so difficult to get the front to flex as well as the rear.

So back to the proposed system, it has the right number of links, but the geometry and strength of the links should be checked and it should be tested to check that the links don't bind or hit other parts of the vehicle over the full range of travel."

And Slug_Burner:

"I am a bit concerned that as the TAs move through their arcs and the A frame does the same, it will want to roll the axle and therefore make the pinion angle move about. I expect that to a certain extent this happens with any suspension, but to what degree?"

Having had another look at it, it would seem as if the trailing arms (TA's) and the A-frame would both need to be on the SAME side of the axle, otherwise how would any upward / downward movement be handled? I assume SOME lee-way can be had by way of a shackle system on the axle mount for A-frame, but then surely you'll have instability?

Originally Posted by roverrescue

........But where there is a will...

.....and cash