Caster angle question

[drummerdad]

Sorry if this is a simple question. But I am in the process of building Isaacs truck ( https://www.pro-touring.com/threads/...(Isaacs-truck) ) and we are doing the IFS. I didnt go with an all out race suspension, with all the adjustability that you guys usually see. Its a simple IFS kit for the factory frame. It should suit the truck well. Its going to be a driver, not a racer.

The installation appears to going well, and we are about to install the upper shock mounts. This is going to give the truck +4 degrees of caster. I have searched and this seems to be okay. I have a manual rack with the kit, but I can upgrade later to a power steering rack. I dont think I need to, but we will see. My understanding is, the more positive caster I give it, the more steering effort it will need. It appears that +4 degrees will be good. There is NO adjustment for this though. After it is welded in, its done, unless I change a-arms or modify it some other way. So, does this sound okay? The instructions dont even mention caster angle.

[andrewb70]

I would say that 4 degrees is okay, but more is better. You are right in noting that more caster will give higher steering effort. I have 5 degrees of caster in my 67 Cougar and with manual steering the steering effort was pretty high when standing still.

Also, the fact that you have no way of adjusting caster is not optimal. Caster will change somewhat when you change rear ride height. Caster is also generally slightly different on the left and right in order to keep the car tracking straight with the crown found on most roads. So you definitely want adjustability!

Andrew

[drummerdad]

I dont see how it would be adjustable with these parts. The upper a-arms have camber adjustments. But I dont see any caster adjustments, unless it can be done with the ball joints. I had not thought about the caster changing when I adjust the rear ride height. It needs to go up maybe 1" to 1-1/2", maybe 2" but no more than that. That will change it, maybe 1/2 degree to the negative. Again, this is all just preliminary, but it should be close.

[andrewb70]

If you shorten the A-arm mounting tube, then washers can be stacked on either side to move the arm forward and back, giving you some adjustability.

Andrew

[drummerdad]

If you shorten the A-arm mounting tube, then washers can be stacked on either side to move the arm forward and back, giving you some adjustability.

Andrew

Im thinking of doing this while I have the chance, and everything is apart. Is there any rules of thumb or anything I need to watch? Im thinking just find a few thin washers that work with the bolts, and stack them up, measure the thickness, then remove that much material. Does that sound right? Maybe remove material front and back, and add washers to both sides? We have a mill at work that would do it pretty easy.

[oleyeller]

You have the ability to adjust castor and camber with the threaded urethane rod ends on the upper A arms. If you screw one in and one out, it changes the position of the upper ball joint relative to the bottom one. Are you looking at castor angle with that angle finder stuck on the spindle as in the last photo? If so, that is not how you measure castor. Castor is measured with the wheels turned 20 degrees in each direction. Just give yourself plenty of anti dive angle on the upper A arm, square everything and weld it up, you will be fine for a driver.

[andrewb70]

You have the ability to adjust castor and camber with the threaded urethane rod ends on the upper A arms. ...

You can do some of that, but only a little, because it will put the poly bushings in a bind.

Andrew

[drummerdad]

You can do some of that, but only a little, because it will put the poly bushings in a bind.

Andrew

I thought about that too. Thats why I didnt mention it as a viable option. But shortening the upper bolt tubes would work, if needed.

On checking the caster angle, yes that where I was getting the angle. The upper ball joint is behind the lower, so I measured it there. The installation doesnt even mention this as critical. He has me measure from below the bolt tube to the ground. Either way, it looks like its right where it needs to be, according to the instructions. I just dont want to mess this up. Its kind of important. I guess if need be, I could upgrade later to better A-arms and spindles.

The upper shock mounts have 3 degrees of anti-dive built in, according to the instructions. The forward most adjustable end is higher than the aft most on both sides, so they are pointed upward toward the front, slightly.

[CSG]

You can machine the pieces that hold the bushing and use shims on either side for castor adjustment.

[drummerdad]

You can machine the pieces that hold the bushing and use shims on either side for castor adjustment.

So how critical is it to be able to adjust the caster? The kit apparently is designed to install without an adjustment. Im okay machining it, and it seems like a good idea, but should I install it and see how it works first? Im sure if I machine these parts, there wont be any warranty replacement parts.

[dhutton]

So how critical is it to be able to adjust the caster? The kit apparently is designed to install without an adjustment. Im okay machining it, and it seems like a good idea, but should I install it and see how it works first? Im sure if I machine these parts, there wont be any warranty replacement parts.

Based on your description of intended use it is not critical imho. 4 degrees is plenty good for a cruiser.

Don

[drummerdad]

Based on your description of intended use it is not critical imho. 4 degrees is plenty good for a cruiser.

Don

That seems to be the popular opinion. If in the future it seems to need more, or I update to power steering, and want more positive caster, I can do the mod discussed above. Shouldnt be too bad. I think Ill just install it like it says, and see how it works then go from there.

[andrewb70]

I don't really know what the "best" way is to do this. Someone may have better suggestions.

Andrew

[Shawn0331]

Is that a mustang II spindle? If so i remember they're somewhere around 10-12 degrees of SAI, i think the general rule of thumb is to split half that with your caster so 4 degrees would be fine and perform decent. I personally would want more but that will do fine if you dont feel like trimming it down.