26 replies to this topic

[alpder]

Does anyone know if the caliper bolts on the disk-brake type of hub are exactly parallel with the "king-pin" (swivels) on the hub? (Parallel only in side-elevation, obviously.) Reason I ask is that - on some cars - it's easy (and cheap ) to accurately measure the angle of the caliper bolts and so know the caster angle, because the two are parallel. Can I do the same on a Mini, or are the calipers fixed at some random angle onto the hub?

Edited by alpder, 13 March 2024 - 09:07 AM.

[Ethel]

Interesting idea, not sure I'd trust Rover to be that accurate if it wasn't essential.

[nicklouse]

The ball joints are at different angles to each other. 
 

I can’t see how what you are suggesting would work on a Mini set up.

 

what other cars does it “work” as it is hard to understand what you are measuring.

[stuart bowes]

as I understand it (not fully to be honest) the correct method is turning the wheels 20 degrees each way, taking camber measurements at each, then doing some maths to work out castor

 

presumably you want some way of measuring camber anyway, so use that same equipment and work out caster at the same time I guess

[GraemeC]

Deleted now I’ve read the question properly!

Edited by GraemeC, 09 March 2024 - 09:21 AM.

[Spider]

Yes, they are parallel and I have made such a 'device'. It's a simple angle bracket on to which I have a magnetic protractor to put on it and directly measure the angle off. I found this tedious and made another similar 'adaptor' that goes over the upper and lower ball joint nuts. Being spaced further apart, it's a wee bit more accurate too.

 

With these gadgets, there's no need to check it 20⁰ either side, though, that's a good idea to check after setting it in the straight ahead position.

The 20⁰ (or you can use any angle) steering angle each way is used when all you have is Camber Angle Measuring gear. Using a formula you can then work out what the Castor Angle is.

 

The formula here is    Caster⁰ = (180 / 3.1415) x (( Camber 1⁰ -Camber 2⁰) / (Turn-angle 1⁰ - Turn-angle2⁰))

[stuart bowes]

So just to clarify, a theoretical zero degrees castor would be the two caliper fixing bolt centres at 90deg to the floor?

And the same question for the ball joint pin locations I guess (to confirm that you could do some fairly accurate setup before assembling hub and putting a wheel on)

Or would you need the wheel on and weight on the wheels.. I'm thinking that would affect camber but not sure about caster

Having 2 ways to measure and double check can't be a bad thing (or having an extra option depending on what gear you have available)

Edited by stuart bowes, 08 March 2024 - 05:37 PM.

[alpder]

So just to clarify, a theoretical zero degrees castor would be the two caliper fixing bolt centres at 90deg to the floor?

That's what I'm hoping. So if you want (say) 3 degrees castor then - with the wheels straight-ahead and the car on the ground - a simple angle-gauge can measure the angle between (a long straight-edge laid on the floor) and (a line between the centres of the heads of the caliper bolts). That should measure 93 degrees (i.e. sloping backwards from vertical) to get the desired 3 degrees.

It's a quick job to design a 3DP gizmo which will clip onto the caliper bolt heads and extend their line towards the floor for ease of measuring. And any cheap digital LCD angle-finder will measure the angle between this and the straight-edge on the floor accurately enough. The only other ingredient needed is a nice flat garage floor. And, lucky me, I have one of those.

I've read of this being done on Mk3/4 Cortina, for example. But it all depends on the orientation of the caliper bolts to the line through the swivels when viewed side-on. There's no engineering reason it should be parallel. But engineers don't add complexity without cause so they'd probably have simply made them parallel unless something got in the way and forced the calipers to be positioned further round the disk. And, even then, if we knew what that angle was...

[Spider]

So just to clarify, a theoretical zero degrees castor would be the two caliper fixing bolt centres at 90deg to the floor?

And the same question for the ball joint pin locations I guess (to confirm that you could do some fairly accurate setup before assembling hub and putting a wheel on)

Or would you need the wheel on and weight on the wheels.. I'm thinking that would affect camber but not sure about caster

Having 2 ways to measure and double check can't be a bad thing (or having an extra option depending on what gear you have available)

 

Yes. There is a small error (academic really) measuring from the Ball Joint Nuts, but in my view, the important thing with castor in particular is not to get it to the nth degree, but getting both sides the same is probably more important, so rather than outright accuracy, repeatability is more important.

 

I'll just add here though,,,,,,,,,,,,,,,,,,,,

It's years since I bothered to use this gauge.

These days, with adjustable front ends, where it comes to Castor Angle, I start off with the Rods set at stock lengths, then dial in more until I get what I'm after by driving. Turning both sides the same keeps it all in the ball park, then when it has the right feel, I'll keep dialing in one side only until I start to feel it pull that way. Then I'll back it off 1/2 a turn at a time (keeping count here !) until it pulls the other way. Finally, I'll set that side 1/2 way between the 2.  This is WAY more accurate in a final over all setting than any zillion dollar machine can ever give as it takes everything in to account and doesn't just look at one angle in total isolation.

[alpder]

Yes, they are parallel and I have made such a 'device'. It's a simple angle bracket on to which I have a magnetic protractor to put on it and directly measure the angle off. I found this tedious and made another similar 'adaptor' that goes over the upper and lower ball joint nuts. Being spaced further apart, it's a wee bit more accurate too.

I am firing up Fusion360 right now I fancied using the caliper bolts as reference because they're already virtually vertical (side-to-side). Whereas using the balljoints the gadget has to remove the king pin inclination - more faff than I'm willing to take just to get a reasonable idea of side-to-side differences and whether I've got 1 degree or 5 degrees caster at the moment. (Given that the car gives up on self-centering with about 1/2-turn of the steering-wheel still to go, I suspect the former.)

 

Thanks everyone.

[alpder]

The gizmo...

 IMG_20240309_172016x.jpg   45.67K   1 downloads

 

The gizmo fitted - just pushed onto the boltheads...

 IMG_20240309_172120x.jpg   34.6K   1 downloads

 

First result (0.45 degrees :-( )...

 IMG_20240309_172524x.jpg   46.24K   4 downloads

 

But at least they match (0.6 degrees)...

 IMG_20240309_172829x.jpg   53.93K   2 downloads

 

[stuart bowes]

nicely done I might have to copy that idea when I get to it

 

as Spider points out, even if just to make them equal to one another

[alpder]

Here's the STL:  CasterGauge v5.zip   19.54K   14 downloads .

Tip: Although the gauge can be jiggled into position with the steering straight-ahead, this method is easier: Turn steering all the way to the right, clip the gauge on the RHS caliper, straighten steering (slowly, carefully), check the gauge doesn't foul CV boot or tie-rod, take measurement several times, (to gauge roughly the error margin). Repeat in mirror for the LHS. Obviously, DON'T clip the gauge on the RH side and then steer left: it would foul the boot. And (uber-obviously) remove the gauge before driving.

Edited by alpder, 10 March 2024 - 11:07 AM.

[stuart bowes]

cheers :) definitely save that for future use

[Spider]

Nice work !  With a result !!