34 replies to this topic

[TerrA LX]

I would be looking at your diff mounts/bushes as the includes angle I eluded to before should be zero (under acceleration). If your diff is pointing down you would have to raise the back of the box to equalise that defeating the purpose.

[76lxhatch]

" Working Angle A = 4 - 1 = 3deg
" Working Angle B = 1 - -2.5(Diff down)= 3.5deg

That makes sense, so your angles are now almost equal which is good. However (as above) they are not opposite which would be more ideal.

[ls2lxhatch]

The gearbox and pinion angles have to move in opposite directions to cancel each other out. If you draw a picture with the gearbox and pinion in a straight line and the rotate paper so the gearbox is pointing down you will see the pinion is pointing up. If the gearbox is down 4 degrees then the pinion should be up 4 degrees for the angles to be canceled.

Typically you would make allowance for pinion angle changing between 1 and 3 degrees under load. This will vary depending on suspension design, bush material and vehicle use (eg drag racing, street driving). If the pinion rotates up 2 degrees under load, then the pinion angle would be set at two degrees up which becomes 4 degrees up under load. You should take your measurements with the suspension at ride height as the pinion angle can also vary during suspension travel.

Edited by ls2lxhatch, 16 August 2009 - 02:31 AM.

[76lxhatch]

If the gearbox is down 4 degrees then the pinion should be up 4 degrees for the angles to be canceled.

As I understand it, most cars will be set up the opposite (trans up, diff down). I know I still haven't managed to get mine right either due to restrictions with the gearbox and doing it this way is probably near impossible in the Torana. Anyway my question is... does this have ramifications with regard to traction? Seems like setting up the angles in reverse is like going from a drag racing setup to a drift setup?

[ls2lxhatch]

You often hear people say increase the pinion angle 3 to 4 degrees down for better launch traction.

What does the statement mean?

The statement saying increase the pinion angle 3 to 4 degrees down from the static canceled pinion angle not from 90 degrees.

Gearbox down 5 degrees, the static canceled pinion angle is up 5 degrees then this would be reduced to up 1 or 2 degrees.
Gearbox horizontal, the static canceled pinion is 0 this would become down 3 or 4 degrees.
Gearbox up 5 degrees then the static canceled pinion angle is down 5 degrees the is increased to down 8 or 9 degrees.

How does this improve traction on launch?

The statement assumes that the pinion is rotating up 3 to 4 degrees from the static pinion angle as the suspension is loaded on launch. Increasing the static pinion angle down 3 to 4 degrees allows for the diff rotation which then results in the perfect canceled pinion angle. The canceled pinion angle means no vibration on launch which means better traction. Once you back off, the load on the suspension is reduced, the diff will rotate down and the uni angles will no longer be canceled. This is not an issue on a dedicated drag car as the run is over.

On a street car the load on the diff when cruising at highway speed is significant less than the launch load. As the amount the diff rotates varies you have to decide what is more important. The perfect angle for drag racing or the perfect angle for cruising.

The amount the pinion angle changes under load depends on many factors. As a starting point from this website.

Factory bushings: Set Pinion Angle 3 degrees to 4 degrees downward.
Poly bushings: Set Pinion Angle 2 1/2 degrees to 3 degrees downward.
Solid bushings: Set Pinion Angle 1 degrees to 1 � degrees downward.

Edited by ls2lxhatch, 16 August 2009 - 01:08 PM.

[76lxhatch]

Aha, so I have misinterpreted the phrase 'degrees downward' (or taken it out of context). That makes a lot of sense, thanks for the explanation!