Thrust angle adjustment, how many threads? (1 Viewer)

[jellis]

I finally got my alignment properly done after redoing the steering rack and adding @Delta VS 6" lift radius arms and 5" panhard bracket in the rear:

I'm pretty stoked on these front caster readings, looks like those Delta arms are doing their job (~5.5" lift on 37s)! But it looks like my thrust angle is off ~0.6 degrees. I have fully adjustable LCAs/UCAs (Dobinson's), anyone happen to have any idea how much I need to adjust them (length and/or threads) to correct a 0.6 deg toe in/out on the rear?

Thanks,
~Josh

 

[BILT4ME]

I finally got my alignment properly done after redoing the steering rack and adding @Delta VS 6" lift radius arms and 5" panhard bracket in the rear:
View attachment 2793247

I'm pretty stoked on these front caster readings, looks like those Delta arms are doing their job (~5.5" lift on 37s)! But it looks like my thrust angle is off ~0.6 degrees. I have fully adjustable LCAs/UCAs (Dobinson's), anyone happen to have any idea how much I need to adjust them (length and/or threads) to correct a 0.6 deg toe in/out on the rear?

Thanks,
~Josh

On an 80 series, there is no adjustment for Toe on the REAR axle. It is a solid, non-steering axle.

You either have something bent, or the technician didn't get the machine set up properly. My money is on the latter.

 

[jellis]

If I crank the threads IN on one side of my LCA/UCA, and OUT on the other side, there is no amount of setup the technician can do to correct that. That is what has happened in lessened form according to the rear measurements (one side + other side -).... If both were negative or positive, THAT would be a problem.
I have fully replaced every single positioning element of the rear axle with adjustable equivalents....and they appear to need adjusting! Just wondering how much to adjust, posts on here sure saved me a lot of guess work when installing LCAs!

 

[bigredmachine]

adjusting your upper and/or lowers will not change your toe angles, just your pinion angles. if you pinion angle is good do not change where they are at, you will be wasting you time. with a lift you would need an adjustable panhard bar, the higher the lift the more the axle will shift. you would need to lengthen the bar to recenter the axle

 

[bigredmachine]

so did they do any adjustments or did they just roll it to check the numbers, your toe is still out

 

[smritte]

Measure inside edge (back edge) of front rim to inside of rear rim (front edge). make sure the tape measure is centered.
Adjust as necessary. A common issue on alignment is the tech not pulling the vehicle on straight. The machine is calibrated to the rack.
If the distance between your rims side to side is the same, that's your issue.

 

[jellis]

I believe my toe on front is where I want it for 37s. The limits on the sheet are for an 87-90 FJ62 not a '90 HDJ81.
If I only adjusted uppers as a group or lowers as a group independently, that would change pinion angle. If I change left/right CAs as a group, that will adjust rear toe. Panhard likely works in conjunction with CAs....probably all relative, screw with one and tweak them all. My panhard was way off to start with, then I put in the Delta bracket, then I replaced LCAs because one was really bent....
I'll measure shortest rim to rim and try to split the difference, that makes sense. I'll report back with results when I get around to it......

 

[Njck22]

Say positive thrust is considered the right side of the axle is back more. Multiply the sine of the thrust angle by the distance between the axle control arm mount and the center of the axle housing. Then divide this by 2 times the cosine of the angle between the upper control arm and the horizontal, and multiply by the TPI of the control arm . This is the number of turns to make the right upper control arm shorter and also the number of turn to lengthen the left side. go back and divide by 2 times the cosine of the angle between the lower control arm and the horizontal, and multiply by the tpi again. This is the number of turns to adjust the lower control arms.

 

[bigredmachine]

A common issue on alignment is the tech not pulling the vehicle on straight. The machine is calibrated to the rack.

depending on how crooked it is on the rack its not that big of a deal as the turn plates will move and allow the truck to center up a bit

I believe my toe on front is where I want it for 37s. The limits on the sheet are for an 87-90 FJ62 not a '90 HDJ81.

having a little more positive or negative toe will help give the vehicle some stability driving down the road

 

[smritte]

depending on how crooked it is on the rack its not that big of a deal as the turn plates will move and allow the truck to center up a bit

That's if the tech is trained properly, actually cares or is not in a hurry. When I read a post that starts off with "My vehicle didn't pull until after the alignment", I ask to see the rear before and after numbers. Sure enough, it starts with the rear toe pointed to one side or the other and ends with it straight.
If I'm close then yeah, I pull the rear plate pins and scoot the back over. I still prefer doing them on the ground with a bubble gauge and string.

 

[White Stripe]

I finally got my alignment properly done after redoing the steering rack and adding @Delta VS 6" lift radius arms and 5" panhard bracket in the rear:
View attachment 2793247

I'm pretty stoked on these front caster readings, looks like those Delta arms are doing their job (~5.5" lift on 37s)! But it looks like my thrust angle is off ~0.6 degrees. I have fully adjustable LCAs/UCAs (Dobinson's), anyone happen to have any idea how much I need to adjust them (length and/or threads) to correct a 0.6 deg toe in/out on the rear?

Thanks,
~Josh

I would say shorten the right side arms by one full turn. It's not out by much and likely does little to affect any handling as is. Technically this should be done on the alignment rack.

 

[bigredmachine]

I still prefer doing them on the ground with a bubble gauge and string.

our rack automatically unlocks all of the plates so were pretty good unless its way off. and when we do trucks that are too long for the rack well just do a thrust line alignment instead of a 4wa. when its trucks that big were pretty much limited to just toe adjustments and steer ahead anyways

 

[smritte]

our rack automatically unlocks all of the plates so were pretty good unless its way off.

only one of our four have that. Its also the only one that has a hunter aligner. My personal favorite.

 

[Super80]

ajustar la parte superior o inferior no cambiará los ángulos de los dedos de los pies, solo los ángulos de piñón. si su ángulo de piñón es bueno, no cambie su posición, estará perdiendo el tiempo. con un elevador, necesitaría una barra Panhard ajustable, cuanto más alto sea el elevador, más se desplazará el eje. necesitaría alargar la barra para volver a centrar el eje

H What is the correct rear sprocket angle? Thanks

 

[bigredmachine]

only one of our four have that. Its also the only one that has a hunter aligner. My personal favorite.

hunter has a great machine and their usually the first to get specs for vehicles, if your going to be spending money on a rack then you might as well buy the best

 

[bigredmachine]

H What is the correct rear sprocket angle? Thanks

im not sure what the spec is for toyota but usually its around the 4* mark. whats more important is keeping your angles in phase meaning its has equal angles at the t-case and at the rear diff. very flat or very steep angles will cause accelerated u-joint wear and may cause vibrations depending on how sever the angle is.

heres some reading form people that know more than me on the subject

Driveline Geometry 101

Driveshaft Angle Explained This video will demonstrate the proper angles for a drive shaft in a stock Jeep or Truck and how the rules change when you add a suspension lift. The video below demonstrates what is happening to the shaft at different angles, how improper angles can cause speed...

4xshaft.com

and for calculating out the shaft angles

Spicer Driveline Operating Angle Calculator

Measure the angles of each component in your drivetrain, then use the Spicer Driveline Operating Angle Calculator to find the operating angle of each u-joint in your drivetrain.

spicerparts.com

 

[Super80]

im not sure what the spec is for toyota but usually its around the 4* mark. whats more important is keeping your angles in phase meaning its has equal angles at the t-case and at the rear diff. very flat or very steep angles will cause accelerated u-joint wear and may cause vibrations depending on how sever the angle is.

heres some reading form people that know more than me on the subject

Driveline Geometry 101

Driveshaft Angle Explained This video will demonstrate the proper angles for a drive shaft in a stock Jeep or Truck and how the rules change when you add a suspension lift. The video below demonstrates what is happening to the shaft at different angles, how improper angles can cause speed...

4xshaft.com

and for calculating out the shaft angles

Spicer Driveline Operating Angle Calculator

Measure the angles of each component in your drivetrain, then use the Spicer Driveline Operating Angle Calculator to find the operating angle of each u-joint in your drivetrain.

spicerparts.com

Thanks. Now I will study the information.

 

[bigredmachine]

no worries