Ok, for you Terrain Tamers...caster shims or no caster shims??

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Ride Fly

Ride Fly

Joined
Oct 20, 2017
Threads
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Location
Lake Oswego, Oregon
This quote is from another thread I started awhile back about the different options I was faced with in lift kits. I opted for the TTs obviously 😎

The dilemma I have is whether I'll need shims. I read that the shims are needed because the shackles are longer on lift kits. Isn't the true cause, the actual height of the lift of the axle in relation to the previous point in space? Shackle length maybe the reason the axle height is higher, but the actual length of the shackle should be irrelevant.

My current shackle length is way shorter than my previous, which were 5.25" long. But my old springs were completely flat, so I hope I get a good 2-3" of lift from the TT.

Will I need shims? Did my fellow Tamers install shims during install? Or afterwards when you felt the loss of steering tracking? If shims, 2.5° or 4°?

jim land said:
2" skyjacker with shorter shackles , like 3.5" or 4" CtC max is perfect for 33" tires .
You will need a 2° or 4° caster shim for the front depending of the shackle size.

No presses clips on Skyjacker spring.
Click to expand...
 
Scott11cruiser said:
I shimmed mine 4* I think when I installed.
Click to expand...
Thanks for your reply Scott! Did you just do the front or rear also? I've seen the rear shim added when the lift stresses the u-joint, so raising the angle of the pumpkin alleviates that. How does the 40 steering tracking to center with the TTs as compared to before?
 
The shackle is 100% the reason shims are or are not needed to correct the castor angle.
All the springs do is create a higher ride height.
The shackles, while also changing ride height do so while only changing the height at one end of the spring, therefore dropping the front of the springs and rolling the axle housing forward.
They only have 1-2 degrees of positive castor to begin with, turn that into 0 or negative 1-2 degrees and the steering gets squirrelly real quick.
How many degrees of shim that is required, needs to be measured not guessed at. With manual steering, having extra degrees of positive castor is not a good thing, they will increase the effort required to turn the wheels.
 
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brian said:
The shackle is 100% the reason shims are or are not needed to correct the castor angle.
All the springs do is create a higher ride height.
The shackles, while also changing ride height do so while only changing the height at one end of the spring, therefore dropping the front of the springs and rolling the axle housing forward.
They only have 1-2 degrees of positive castor to begin with, turn that into 0 or negative 1-2 degrees and the steering gets squirrelly real quick.
How many degrees of shim that is required, needs to be measured not guessed at. With manual steering, having extra degrees of positive castor is not a good thing, they will increase the effort required to turn the wheels.
Click to expand...

That was an AWESOME explanation Brian! I have manual steering, but the next big project is to install power steering. You stated the shim degree needed needs to "measured". I'll be looking that up on YT next! Given my old situation with the 5.25" shackles replaced by the TT anti-inversion shackles which are probably 3" (can't measure them at the moment), do you think I'd not need them? I didn't have any shims with the previous shackles and it was a fairly squirrelly ride all the time.

Thanks again!



I'll be asking for opinions on air lockers vs e-lockers vs lunchboxes next. 😁
 
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Remove front drive shaft.
With a degree finder check the front output flange on the tcase( on level ground, in a perfect world should be 90*). This will be your "0".
Same degree finder, now check the front pinion flange.
The shim degree is what you need to match the pinion flange to the output on the case.
What you need is everything on the cruiser....ie, this won't work if all the weight normally there, isn't there.
The cruiser doesn't need to be perfectly level either, as the idea is to match what degree the output on the transfer is.
 
brian said:
Remove front drive shaft.
With a degree finder check the front output flange on the tcase( on level ground, in a perfect world should be 90*). This will be your "0".
Same degree finder, now check the front pinion flange.
The shim degree is what you need to match the pinion flange to the output on the case.
What you need is everything on the cruiser....ie, this won't work if all the weight normally there, isn't there.
The cruiser doesn't need to be perfectly level either, as the idea is to match what degree the output on the transfer is.
Click to expand...
You ARE THE MAN!! I learn so much from guys like you here on the Mud! Thanks a million Brian!!
 
There are some excellent YouTube videos that explain, and illustrate the concept of universal joint phasing. Here’s one video, but there are quite a few:



There are also videos that explain how to measure pinion angles.

The engine in an FJ40 is angled down front-to-rear, so the transfer case rear output shaft angles down. IIRC, 3º is typical for automotive applications. I’m going to use that number for explanatory purposes, though it may, or may not be correct. Assuming no double-Cardan or CV joint in the driveshaft, if the transfer case output shaft angles down at 3º the rear axle's pinion angle should angle up at 3º so the two are parallel.

But, that also means the transfer case’s front output shaft angles UP 3º, and to create the same parallel but offset angular relationship, the front axle’s pinion should angle down 3º. Using CV joints changes things. If a CV joint is installed at the transfer case end, the axle's pinion should be aimed at the transfer case.
 
Augustiron said:
You don't shim the front for driveshaft angle, you do it to fix caster to steer properly after a lift.

Yes, the shims negatively affect driveshaft angles But the trade-off for better steering is worth it and effects on a drive shaft are massively outweighed by correct caster
Click to expand...
Pinion angle can affect caster angle no?

From previous discussion and watching that YT vid, I understand that caster angle changes depending on the length of the shackle. Stock shackles have had all the proper geometries figured out by the manufacturer, but when introducing a lift kit with longer shackles, I can see how the extra movement forward of the front axle can turn a properly set caster angle to a more negative angle, causing the steering to not want to return to straight tracking. I can also see how the changes in input/output angles affect their respective shafts which will cause the changes in rotational speed. The part that I don't really understand is how all the changes introduced by a lift kit are remediated to work back in perfect synch as the manufacturer intended. Going back to my question at the top, does the pinion angles have to be corrected so that the caster angle only changes depending on the shim to compensate for the shackle length? (I'm not sure if I'm making myself clear 😎)
 
On your solid axle, rotating the axle with shims or otherwise, affects both caster and pinion angle. That's why you hear of guys doing a "cut and turn".
 
Your pinion and your axis of rotation of the knuckle for caster are fixed to each other unless you do a cut and turn on the axle.
Any rotation of the axle from a lift from just springs, or shackles, affects them both.

Caster is more important to the vehicle, which is why when you lift, you do something to correct the caster.
In this case with leaf springs it is shims to get the access of rotation for the knuckle back on spec for caster,
on the 80 series and trucks with radius arms it is offset bushings, aftermarket offset arms, or drop brackets for the rear mount of the radius arms.
 
Also, front drive shaft angles for a part-time 4-wheel drive vehicle with a two and a half inch lift are not really ever going to be an issue to cause vibrations.
You are not lifting the vehicle so high that you need a double cardon drive shaft, or a cut and turn to point the pinion towards the transfer case.

Tried and true solution for the last 50 years 2-4" leaf spring lift is just to put the shims in.
 
aztoyman said:
. That's why you hear of guys doing a "cut and turn".
Click to expand...
The cut&turn is most commonly associated with the spring over axle mod.....which radically alters drive line geometry.
 
Just because you added lift springs does not mean additional changes are necessary or required. Over the years my rig has run stock springs, Burbank lift springs, OME lift springs and I've never had to add shims or do a cut and turn on the axle housing. My current setup is ARB/OME CS001F (stock/light load) and CS001R (medium load) springs with Ironman anti-inversion shackles. I also converted it to Saginaw PS along with SBC with NV4500 and Warn 8274 winch and home built spare and gas can/cooler carrier. It all rides on 33-12.5x15 tires on 10" wide rims with toe-in set at 1/8". It tracks straight and true as speeds into the triple digits.

Now I mention this because I can't be the only one out there to have a mystical rig that does this. I also know that depending on how they are configured affects handling because of weight balance front to rear and side to side. Tolerance stacking with parts/components is also a part of the equation and will be different for everyone. Verify that everything is in serviceable condition and adjusted properly and make any changes to bring things into spec. This can be a lengthy process or the corrective measure can come quickly. If you can't handle the task on your own then have the good sense to seek out someone who can.

Good luck on resolving your issue(s).
 
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