Caster Correction

[RIBob]

Would like some assistance on how best to correct my Caster angle. Currently -0.3* on the front left and -1.6* on the front right.

1979 FJ40 with a 4” lift on 33” rubber. Spring perches do not appear to be modified. Based on the larger than stock tires I would like to shoot for about +2* of caster. Open to recommendations here.

The lead guy at Midas said I can only correct Caster on the vehicle by moving the axle forward and that a shim rotating the caster angle would not do it. If he were the guy sitting next to me at the bar I would dismiss this, but since he has 20 years at Midas, I am looking to see if his impresssion that Caster can not be corrected with an axle shim is correct.

Last piece of advice sought: I could put in a different thinkness shim on each side, though to more closely align the left and right side caster. E.g., 2* on the left and 3* on the left. What are your thoughts?

Thank you for your help.

 

[brian]

Find a different shop

 

[Mark Jennings]

Shims work, there are a number of threads on the subject. You’ll need approximately 2* per inch of lift to restore the original caster spec…0 to +1, for you that would be 4* shims as a starting point. I would also check your rear pinion angle….this is also affected by lift.

Also, I would be concerned with the difference between right and left, has that axle been tweaked off road use or in an accident? Not sure how that could be corrected.

 

[65swb45]

I’m with @brian on finding another shop. The odds of the two sides on an unmodified axle housing having different values are very low. IMO, if there were any noticeable difference, something obvious like the shackle angles would be different too.

 

[RIBob]

Shims work, there are a number of threads on the subject. You’ll need approximately 2* per inch of lift to restore the original caster spec…0 to +1, for you that would be 4* shims as a starting point. I would also check your rear pinion angle….this is also affected by lift.

Also, I would be concerned with the difference between right and left, has that axle been tweaked off road use or in an accident? Not sure how that could be corrected.

Thank you Mark. Previously took care of getting the rear pinion/TC angles in line with a shim. (Will check the front pinion/TC angles as well as I work through correcting the caster. It may be a balancing act. Hopefully I can get both in spec.)

Back to Caster. A previous owner has a shim installed (see pic), though it is not providing enough positive caster. Regarding the asymmetric caster measurements, what puzzles me most is that my measurements using a $12 angle finder, came up with -2* on the left (shop measured -0.3*) and -1* on the right (shop measured -1.6*). Not sure what to make of that, but will determine what degree that shim is, remove it and add a couple more degrees to make both sides have some degree of positive caster.

 

[RIBob]

I’m with @brian on finding another shop. The odds of the two sides on an unmodified axle housing having different values are very low. IMO, if there were any noticeable difference, something obvious like the shackle angles would be different too.

I’m with @brian on finding another shop. The odds of the two sides on an unmodified axle housing having different values are very low. IMO, if there were any noticeable difference, something obvious like the shackle angles would be different too.

Thank you. Shop had a brand new alignment machine. Apparatus mounted to the tires and not the rim. Lasers etc. Suspect it is a great machine but perhaps the two guys are still getting up to speed on its operation. I like your suggestion regarding the shackle angles. I will check those on level ground.

 

[pb4ugo]

I use the cheap angle finder also, making sure the vehicle is on level ground and tire air pressures are correct. I'll trust a simple angle finder over the fancy machine with an unknown operator. It is sort a balancing act with caster and pinion angles. I think caster is more important because of driving and handling. I can take my hands of the wheel going 65. Once I get the caster to my desired angle, I put the suspension in full droop to confirm there is no binding at the U joint yokes. I've clearance them a little in the past or you can install limiting straps to prevent any extreme angles. Or do a cut and turn. The actual frt pinion geomtery is not as important as it is in the rear. Usually the speeds when the frt is engaged are lower. Shackles will effect caster, I ended up shortening mine a bit to help the angle. When using the angle finder be sure to catch the edge of the lower bearing cap, and not use the studs or nuts. I'm currently running 6* shims with a 4" lift. That nets me around +3* caster.

 

[pb4ugo]

The differences in the angles from side to side is concerning, your angle finder #'s are more realistic. What is the condition of your knuckle trunion bearings? Have the knuckles been serviced lately?

 

[65swb45]

I use the cheap angle finder also, making sure the vehicle is on level ground and tire air pressures are correct. I'll trust a simple angle finder over the fancy machine with an unknown operator. It is sort a balancing act with caster and pinion angles. I think caster is more important because of driving and handling. I can take my hands of the wheel going 65. Once I get the caster to my desired angle, I put the suspension in full droop to confirm there is no binding at the U joint yokes. I've clearance them a little in the past or you can install limiting straps to prevent any extreme angles. Or do a cut and turn. The actual frt pinion geomtery is not as important as it is in the rear. Usually the speeds when the frt is engaged are lower. Shackles will effect caster, I ended up shortening mine a bit to help the angle. When using the angle finder be sure to catch the edge of the lower bearing cap, and not use the studs or nuts. I'm currently running 6* shims with a 4" lift. That nets me around +3* caster.

Many years ago, one of the guys in my bike club owned a tire shop with a fancy computerized alignment machine. I was swapping around tires and wheels a lot in those days. One day when I was over there getting a crappy tire dismounted from a stock rim, he offered me a $20 alignment on my 45 because his alignment guy was bored and needed the practice. I agreed.

After determining that my toe in was incorrect according to the machine, the guy took his wrenches and reached for the relay rod coming down from the center arm. I had to stop him to explain that THAT was not the correct rod for adjusting toe in.

When I left his shop, as soon as I hit 40mph I had a terrible case of death wobble. Had to take surface streets all the way to my shop. I reset the toe in with a tape measure; problem solved. And lesson learned.

 

[peesalot]

Mark, I vaguely recall years ago this issue came up and it was offered that Toyota had a slight diff in caster to account for road crown, is this a real thing or myth as far as you know ? FWIW my stock 1970 drum axle had a slight diff from the factory, I dont think it was as much as op's difference but never the less it was different by 1/2 deg IIRC.

 

[65swb45]

Mark, I vaguely recall years ago this issue came up and it was offered that Toyota had a slight diff in caster to account for road crown, is this a real thing or myth as far as you know ? FWIW my stock 1970 drum axle had a slight diff from the factory, I dont think it was as much as op's difference but never the less it was different by 1/2 deg IIRC.

John,

No, I have not heard of this. The possibility is not only interesting, but intriguing. I would be genuinely interested to read about it if you found some links.

In the one minute I have had to consider this, I have to wonder IF it were true, did they also creat a reverse offset for ROW vehicles that drive on the other side of the road? And if so, what of the early 1970s, when ROW vehicles ended up being shipped to the US when demand outstripped supply (the grey and orange ones)?

 

[peesalot]

I will search, these would have been threads from early 2000's, 03. 04, 05 and I think Pardi had some input as well as Mark H in AK.

 

[Mark Jennings]

As far as an offset caster, the FSM doesn’t show anything, both side should have equal caster….and camber. And as far as front end adjustment to make up for road crown, changing caster angle just doesn’t make sense….you would think an offset tow or even a slight axel repositioning on the springs (move the crown side, the left side ‘aft’ a bit to force a bit of left turn)….just enough to overcome right drift caused by road crown.

And I think the FJ40 caster angle (+ 1*) is a compromise anyway, just enough to keep you on the road AND maintain a good pinion axle on the front differential.

If the alignment results from above are accurate, I would suspect a tweaked axle. Or maybe even a bent rim.

 

[serenity]

Mark, I vaguely recall years ago this issue came up and it was offered that Toyota had a slight diff in caster to account for road crown, is this a real thing or myth as far as you know ? FWIW my stock 1970 drum axle had a slight diff from the factory, I dont think it was as much as op's difference but never the less it was different by 1/2 deg IIRC.

You do find one side pushed forward on modern ifs vehicles, the front tyres on my Hilux rub the mud flap on the drivers side but not the passenger side.
However the difference must be in the control arm mounts as there is no variation of caster between sides.

 

[65swb45]

You do find one side pushed forward on modern ifs vehicles, the front tyres on my Hilux rub the mud flap on the drivers side but not the passenger side.
However the difference must be in the control arm mounts as there is no variation of caster between sides.

And you are RHD correct?

 

[jim land]

That Midas guy is wrong and should keep working on newer car , never let your 40 in ignorant hands

 

[Grayscale]

The knuckle bearings are known weak spots on these live beam axles. Because the axle beam has to hold the knuckle bearings close to the axle housing, it takes only a little wear on these races to cause a big angle change in caster, and camber. The truck came with like 28-inch diameter treads, so running 33s kinda dwarfs the stock equipment, or makes the 'moment' of road forces/bumps much greater thru increased leverage against these bearings - just my opinion, however, I'm inclined to look for wear at these points.

No offense to the alignment shop, but, their tooling, and reporting of data, is for IFS cars. Maybe measuring knuckle bearing preload (FSM fish-scale measurement with tie rod disconnected) will reveal inadequate bearing pre-load? Either way, if there is service to be done, it probably is at the knuckles, where they are known to wear.

 

[serenity]

And you are RHD correct?

Yes RHD, the same thing seems to happen to the Tacoma but on the opposite side of course.

 

[pbgbottle]

Mark, I vaguely recall years ago this issue came up and it was offered that Toyota had a slight diff in caster to account for road crown, is this a real thing or myth as far as you know ? FWIW my stock 1970 drum axle had a slight diff from the factory, I dont think it was as much as op's difference but never the less it was different by 1/2 deg IIRC.

I remember reading about this also back when I was leaning how to do my cut n turn. Hmm.

 

[pbgbottle]

My buddy 35 year mechanic brake and muffler shop. They got a new alignment machine last year super expensive and fancy and all that and he said it is horrible every time they use it the customer comes back he has gone back to using their original probably 30 year old alignemt setup. He hates the new alignment machine. He said way to complicated just to get it setup correctly. Even before taking measurements,, hmm.