Setting Caster

[[memphis]]

I understand Caster from a basic sense. I know the interwebs says it needs to be around 4-8 degrees to help with wander on the road.

Does wheel base length have any factor in setting caster? I will be running 86” wheel base and running leaf springs under the axle.

I am building a low slung willys like Rango running 2.5” YJ springs all four corners

The front axle is a passenger drop HP44 so I have a pretty blank slate. Essentially I am doing a basic cut and turn. I’m past the cut part and need to complete the turn.

I was thinking about setting the pinion at 90 degrees (referencing the machined flats on the housing) and Setting caster at like 10 to slightly compensate for rolling the pinion up if required?

I measured a JK Rubi axle (2 door if that matters) sitting in my buddies garage prepping for a swap and with the pinion at 90 degrees the caster is about 4.2 degrees. Doing a little googling that appears to be the factory spec?

I know there are a bunch of other factors… driveshaft type will affect pinion angle, vehicle weight, but I’m stuck in a bit of a project paralysis at the moment…

I have lock outs so I don’t think pinion angle is going to be super critical especially since I am not going to be sitting sky high… 10 might be a bit much, do I shoot for 7-8 and worst case it needs to go positive 2-3 degrees?

 

[reptillikus]

Wheelbase affects ackerman angle moreso than caster. You still want to shoot for 5-8º IMO to compensate for the bigger tires we all like to run. Most OEMs spec 3.5-4.5º IIRC.

Im running 7.5º and it handles great, but ive also got hydro-assist because of running a 42" tire.


You said YJ SPUA. Im assuming front-mounted shackle? Whats the plan for the front shaft, single joint or double cardan?
Theres probably a formula for how much to change the angle but im not that smart Is it possible to set the housing under the vehicle on jack stands, and then just kind of eyeball where you think the pinion angle should be? Thats basically all we did when we built my front D60.

 

[[memphis]]

Wheelbase affects ackerman angle moreso than caster. You still want to shoot for 5-8º IMO to compensate for the bigger tires we all like to run. Most OEMs spec 3.5-4.5º IIRC.

Im running 7.5º and it handles great, but ive also got hydro-assist because of running a 42" tire.


You said YJ SPUA. Im assuming front-mounted shackle? Whats the plan for the front shaft, single joint or double cardan?
Theres probably a formula for how much to change the angle but im not that smart Is it possible to set the housing under the vehicle on jack stands, and then just kind of eyeball where you think the pinion angle should be? Thats basically all we did when we built my front D60.

I’d like to get away without a double cardon shaft up front and I think I can with my lift height plus having lock outs… shackles are up front because I don’t want a long travel front shaft.

I’m building inside a shipping container and lack room so I want to be able to roll the frame in and out as required to work on whatever I need but I can’t get any real weight on it until it’s mobile…. But I shouldn’t set my angles because the engine isn’t in it… again project paralysis 😆

So if I set it aggressive, my logic was I could fine tune it to be perfect

 

[BDK]

My rig has a much longer wheelbase than yours (119"), but I am running a HP D44. I have early Bronco type radius arms. I ended up with the caster at 7.5* with 35" tires, early Bronco width axle.

One thing I ran into with my HP D44 is if you try to point the pinyon at the T-case output you lose a lot of compression travel. The top of that housing needs to stay flat. I used a JB Conversions high clearance yoke with a double cardan driveshaft on my Atlas II. No binding with 14" coilovers of travel.

 

[[memphis]]

My rig has a much longer wheelbase than yours (119"), but I am running a HP D44. I have early Bronco type radius arms. I ended up with the caster at 7.5* with 35" tires, early Bronco width axle.

One thing I ran into with my HP D44 is if you try to point the pinyon at the T-case output you lose a lot of compression travel. The top of that housing needs to stay flat. I used a JB Conversions high clearance yoke with a double cardan driveshaft on my Atlas II. No binding with 14" coilovers of travel.

So I might be on the right track keeping the pinion flat or at 90 degrees using the factory machined flats… the JK Pinion being flat really surprised me.

7.5-8 sounds like the meal ticket. I plan to run 35s but if I get off my wallet I’d like 34x9.5 swampers

 

[BDK]

If I pointed my pinyon at the transfer case, the yoke would be a few inches away from the engine cross member. I think 7-8 is the sweet spot. If you go over that the tires start to fold over and you lose your turning radius.

 

[Slander]

I’d like to get away without a double cardon shaft up front and I think I can with my lift height plus having lock outs… shackles are up front because I don’t want a long travel front shaft.

I’m building inside a shipping container and lack room so I want to be able to roll the frame in and out as required to work on whatever I need but I can’t get any real weight on it until it’s mobile…. But I shouldn’t set my angles because the engine isn’t in it… again project paralysis 😆

So if I set it aggressive, my logic was I could fine tune it to be perfect

I'm running front shackles on my Tacoma and don't worry about driveshaft travel. Mine only plunges like 1/2" from full compression to full droop. I'm running a single joint on each end. Good call on the pinion angle, I forgot to do that when setting my castor and wound up with a shitty angle, I'm running 8* of castor fwiw with no complaints.

I'm redoing some stuff, but have run this setup since 2016 and have been happy.

 

[94toytruck]

My old rig was like 2* and I moved it to 4 and noticed a change. My current rig which is a buggy is at 8 IIRC and handles awesome.

I'm not sure what affect wheelbase and caster play to each other.

 

[[memphis]]

I'm running front shackles on my Tacoma and don't worry about driveshaft travel. Mine only plunges like 1/2" from full compression to full droop. I'm running a single joint on each end. Good call on the pinion angle, I forgot to do that when setting my castor and wound up with a shitty angle, I'm running 8* of castor fwiw with no complaints.

I'm redoing some stuff, but have run this setup since 2016 and have been happy.

How’s that ride up front? Looks like that’s sitting at ride height on its own weight but your spring is darn near flat. Shallow shackle angle too! I used Wilson’s formula.

 

[Slander]

How’s that ride up front? Looks like that’s sitting at ride height on its own weight but your spring is darn near flat. Shallow shackle angle too! I used Wilson’s formula.

I built it wrong at first so the steering was almost hitting the oil pan, so it was sitting on airbumps, so it sucked. Im pushing the axle forward so I get it off the bumps and some uptravel/ride quality back. It rides like a leaf sprung truck.

 

[Skinny]

IMO you absolutely cannot set the caster and pinion angle without the truck being finished on the ground. I mean you can but if you don't get it perfect or close you will ABSOLUTELY have to compromise one of them.

Of course this is for a street rig that you want a useable front axle at higher speed.

If you don't want a CV front shaft consider setting it up for a broken back or W arrangement. You'll see this on Rovers. May not be great but it gets the pinion up higher which gets the driveshaft up further and less angle on the joints then a normal Z configuration.

I think 6-8 degrees is a good number. Stock most vehicle will be less but I believe a little more then usual helps with larger tires and generally poor handling characteristics of what we drive.

I just got my new project up and running. Noticed that it doesn't have great or any return to center. Caster is like 2 to 2.5 degrees so I think some more would help.

I don't believe wheelbase changed anything. From what I was taught the only spec difference "back in the day" for caster was steering options. Manual steering spec trucks had less caster spec then power to make it easier to turn. That's all I'm aware of.

 

[[memphis]]

IMO you absolutely cannot set the caster and pinion angle without the truck being finished on the ground. I mean you can but if you don't get it perfect or close you will ABSOLUTELY have to compromise one of them.

Of course this is for a street rig that you want a useable front axle at higher speed.

If you don't want a CV front shaft consider setting it up for a broken back or W arrangement. You'll see this on Rovers. May not be great but it gets the pinion up higher which gets the driveshaft up further and less angle on the joints then a normal Z configuration.

I think 6-8 degrees is a good number. Stock most vehicle will be less but I believe a little more then usual helps with larger tires and generally poor handling characteristics of what we drive.

I just got my new project up and running. Noticed that it doesn't have great or any return to center. Caster is like 2 to 2.5 degrees so I think some more would help.

I don't believe wheelbase changed anything. From what I was taught the only spec difference "back in the day" for caster was steering options. Manual steering spec trucks had less caster spec then power to make it easier to turn. That's all I'm aware of.

Do you mean build a 2pc front drive line?

With how low everything should be on this willys I think I’ll have a hard time running a front double cardan. If I had a real shop with space this would be so much easier and I’d install the motor et al. I need to roll this thing out of the way…

 

[Skinny]

Nope 1 piece

W is basically a standard single ujoint arrangement except you rotate the pinion up past the angle of the driveshaft itself. May be a better option then a CV in your situation.

Tell me about it, I just built my S10 in a storage unit. Not an easy task but better then being outside.

I would save the front axle fabrication then till last.

 

[pinchegringo]

Caster affects more than return to center. It is the single most important angle for safety and stability. Cars had zero caster before power steering was invented and 55mph was scary.4.0 is the absolute minimum and I think the jk would handle better had they used more caster. Most common these days is around 7.0. That's usually what I aim for with the pinion at 90 degrees plus whatever angle the transfer is sitting at. So correct pinion angle is actually pointing down a bit.

 

[gt1guy]

The manufactures try to get away with as little caster as they can so that the average person with T-Rex arms can turn the wheel of a bone stock vehicle. Take the factory setting and just forget it, it no longer applies. After we have cut and hacked everything on the vehicle, added tires that are a foot taller and wider, wider axles, wheels with different back spacing, wheel spacers and whatever else we throw on it............caster becomes your friend.

I built 12* or 15* (can't remember) into my axle. Full hydro and I plan to street drive it.

20*+ might be a bit much for what we do, but there are dragsters and other types of vehicles running even more.

 

[[memphis]]

My rig has a much longer wheelbase than yours (119"), but I am running a HP D44. I have early Bronco type radius arms. I ended up with the caster at 7.5* with 35" tires, early Bronco width axle.

One thing I ran into with my HP D44 is if you try to point the pinyon at the T-case output you lose a lot of compression travel. The top of that housing needs to stay flat. I used a JB Conversions high clearance yoke with a double cardan driveshaft on my Atlas II. No binding with 14" coilovers of travel.

Do you have a part number handy for that yoke?

 

[Bebop]

Wheelbase affects ackerman angle moreso than caster.

Akerman ratio, not angle.
Angle is a factor of the steering geometry.

You still want to shoot for 5-8º IMO to compensate for the bigger tires we all like to run. Most OEMs spec 3.5-4.5º IIRC.

agreed

You said YJ SPUA. Im assuming front-mounted shackle? Whats the plan for the front shaft, single joint or double cardan?
Theres probably a formula for how much to change the angle but im not that smart Is it possible to set the housing under the vehicle on jack stands, and then just kind of eyeball where you think the pinion angle should be? Thats basically all we did when we built my front D60.

I would install the axle first then turn the knuckles to setup the caster properly.

 

[BDK]

Do you have a part number handy for that yoke?

JB Conversions, Inc.

www.jbconversions.com

 

[Skinny]

Akerman ratio, not angle.
Angle is a factor of the steering geometry.

Well I should throw out all the books I had in college and all the books I used to teach college because every one of them references Ackerman as an angle and not a ratio.

Maybe there is a ratio to be had but the line going through the arms intersecting the rear axle is an angle.

 

[[memphis]]

JB Conversions, Inc.

www.jbconversions.com

Sorry I misunderstood. I thought you meant the yoke on the axle side. Thanks for that link though... I forgot how expensive those things are

 

[Bebop]

Well I should throw out all the books I had in college and all the books I used to teach college because every one of them references Ackerman as an angle and not a ratio.

Maybe there is a ratio to be had but the line going through the arms intersecting the rear axle is an angle.

I typed a big ass paragraph about the difference between akerman angle and Akerman level (or ratio), then I deleted it.

Feel free to search but both terms exist.

 

[RustyC]

I would advise to follow the correct order of operations to build out the front.
Set the front pinion yoke angle to match your t case yoke angle if a 2 joint shaft is used. If CV then point the pinion yoke straight at the tcase.
This will require moving the leaf spring mount on the axle tube.
Then set the castor angle of he knuckles to 6-7 degrees AT RIDE Height.
Build driveshaft, steering and shock mounts.

 

[BDK]

Sorry I misunderstood. I thought you meant the yoke on the axle side. Thanks for that link though... I forgot how expensive those things are

I thought it was a cheap fix for driveshaft binding before full rebound.

 

[[memphis]]

Well the consensus here makes it sound like the motor has to go in so… I guess I’ll shove the axles off to the side. Its time to start saving for the body since I don’t really know where it sits… yay more shit in the way

 

[Slander]

Well the consensus here makes it sound like the motor has to go in so… I guess I’ll shove the axles off to the side. Its time to start saving for the body since I don’t really know where it sits… yay more shit in the way

Next time don't cut the knuckles off until last, that way you can move it around

 

[triple_fcked]

For what it’s worth, I had a customer I was walking through having death wobble on a 3 linked Toyota mini truck, and the ticket for him was actually dialing back his caster from 7°-8° to 4° after chasing down all his worn heims and such.

I’m not an expert on steering geometry, but I imagine there is a point where Bigger caster number ≠ better necessarily

 

[[memphis]]

Next time don't cut the knuckles off until last, that way you can move it around

The previous owner of the housing already did that… I guess some hack wanted the outers so they cut the c’s right where the ball joints press in… I just made it passenger drop 😆

 

[gt1guy]

For what it’s worth, I had a customer I was walking through having death wobble on a 3 linked Toyota mini truck, and the ticket for him was actually dialing back his caster from 7°-8° to 4° after chasing down all his worn heims and such.

I’m not an expert on steering geometry, but I imagine there is a point where Bigger caster number ≠ better necessarily

I'm pretty sure it was the chasing down all the worn heims that cleared up the death wobble, not reducing the caster. In fact I'd think if you are having DW issues, reducing caster would make it worse. The caster trail is trying to keep the tires straight which could mask "some" DW symptoms.

The biggest drawbacks to high caster #'s is higher steering wheel force to turn the wheels, and that as the wheels turn, the caster becomes camber. The outside tire will go -camber and the inside tire will go +camber. In the dirt, that isn't a bad thing, it helps the tires bite. There are also jacking forces involved, but those only really become important on performance street vehicles, not our mushy piles.

 

[RustyC]

It may be best at this point to tack weld the front spring perches and inner c's just to get it on it's feet and allow you to move it or install engine, ect.
Then tune in the driveshaft angle and caster later.