Axle castor angles ?

[super noob]

The standard diff angle on the series landrover is 12* giving 3* castor http://forums.lr4x4.com/index.php?showtopic=40996&hl=defender axle conversion&page=2

However I'm lifting my series by 3" so with this in mind how do I calculate the new angle needed as I'm not quite sure how to go about it

Thanks

 

[chevy2]

Castor is usually the amount of degrees of layback in the front spindles to help with high speed stability and steering self centreing,
Whereas pinion angle is the angle of the nose of the rear differential in relation to the road below,

Which is it?
If changing the rear axle pinion angle, on leafs the usual fix is to fit a tapered shim of the correct degree between the axle and leaf spring to alter the angle.

 

[super noob]

Well the series springs sit back at 3* and the seat on the series axle sits perfectly flat so the spring sets the castor

Pinion angle on the diff is 12* to get the angle to be 3* castor if you measure up using the diff as the datum point


The rear axle is already shimmed but I've just been given a pair of disc braked axles off a coil sprung 90 on, plan was to chop off the coil mounts then weld on leaf mounts so everything is being done from scratch really

 

[ben8vgte]

I don't quite get what your describing really as you'd need a lot more information to work it out, but it would be a simple case of taking some measurements and working it out with trig. Plenty of online calculators to make the trig part easy.

 

[chevy2]

To calculate the correct pinion angle needed is to get the vehicle mocked at the intended ride height at the front and rear,
Most rear wheel drive systems have the gearbox output shaft lower than the front crankshaft centreline,
Fit an angle finder to the rear of the gearbox and note the angle, for example 3degrees downwards,
The differential input shaft (pinion) should be the opposite of this and so should point upwards at approx 3degrees,

Mock the axle in place on the leaf springs and rotate the axle to the correct angle, tack the brackets to the axle,
Remove the axle to fully weld and refit, job done!

 

[super noob]

Well the standard set up is to have the diff nose pointing at 12* when you weld on the mounts. This leaves you with the 3* castor angle but what I want to know is if I raise my suspension another 3" what do I then need to change my diff angle to in order to keep the 3* castor as there must be some kind of general formula

Usually you add castor corrected radius arms of about 4* on a coil sprung axle IIRC so would that be an extra 4* added to the diff angle on a leaf sprung?

 

[super noob]

To calculate the correct pinion angle needed is to get the vehicle mocked at the intended ride height at the front and rear,
Most rear wheel drive systems have the gearbox output shaft lower than the front crankshaft centreline,
Fit an angle finder to the rear of the gearbox and note the angle, for example 3degrees downwards,
The differential input shaft (pinion) should be the opposite of this and so should point upwards at approx 3degrees,

Mock the axle in place on the leaf springs and rotate the axle to the correct angle, tack the brackets to the axle,
Remove the axle to fully weld and refit, job done!

This is a 4wd set up so the transfer box sits perfectly level, as far as I can tell from looking its all set on the axle end of things on landrovers. The output is still lower than the crankshaft though as the transfer is slightly rotated so the output flange sits lover than the input on the gearbox

 

[chevy2]

Is this the front axle you're referring to as thought it was the rear?

 

[chevy2]

If its the front then the most important thing is not the prop angle but the correct castor.

 

[super noob]

Well its both axles I need to know about but I presume its the same on either end no matter what I do just do the same to the other, its the same castor angle all round on the landrover at 3* but if I lift it I need to know how much to adjust it by in order to keep it right as theres no castor correction radius arms you can fit when running leafs

 

[Woody.v8]

I cant see how you could change the castor on a non steering axle? As you rotate a non steering rear axle,all you are changing is the pinion pitch as Chevy rightly said.

 

[chevy2]

The only way know for sure is to use an angle finder.

 

[chevy2]

I cant see how you could change the castor on a non steering axle? As you rotate a non steering rear axle,all you are changing is the pinion pitch as Chevy rightly said.

Yeah that,
Castor only relates to either kingpin or spindle inclination (layback)

 

[super noob]

Right will have to see if I can borrow or find one! My plan was to just cut a triangle at 12* out of MDF and slide it under the diff nose

 

[chevy2]

Right will have to see if I can borrow or find one! My plan was to just cut a triangle at 12* out of MDF and slide it under the diff nose

That'll work,
Make a board so the edge goes flat on the floor and clamp the pinion to the 12 degree layback to set it up,
It'll save on buying an angle finder for only one job.

 

[Woody.v8]

This is the one I use

 

[super noob]

That'll work,
Make a board so the edge goes flat on the floor and clamp the pinion to the 12 degree layback to set it up,
It'll save on buying an angle finder for only one job.

Excellent thanks!


However on last thought, in theory as its leaf sprung if I drop both ends by the same amount rather than just the one like some people do with extended shackles only and not modifying the dumb irons I may actually be ok given that the spring angle wont change it'll just be lowered overall to raise the height?

I'll make the triangle big enough to slide under anyway and will make sure its definitely set at 3*

 

[chevy2]

This is the one I use

Got a similar one but for chassis work that has to be more accurate i use this type which is accurate to 0.05 degrees.
http://www.ebay.co.uk/itm/Pocket-Di...quipment_Lab_Equipment_ET&hash=item19e4e49179

 

[Woody.v8]

I have one of these also ,But was trying to keep the cost down for the OP

 

[chevy2]

Excellent thanks!


However on last thought, in theory as its leaf sprung if I drop both ends by the same amount rather than just the one like some people do with extended shackles only and not modifying the dumb irons I may actually be ok given that the spring angle wont change it'll just be lowered overall to raise the height?

I'll make the triangle big enough to slide under anyway and will make sure its definitely set at 3*

Thats right, as castor is the angle in relation the level road surface below,
So as you say if you space both ends of the leaf spring by the same amount then the castor angle will not change,
thats assuming you raise the rear by the same amount?