Front Leaf Spring Caster Shim Install

[CJM72]

Hi All. Part way into install my 2.5" Tuff Country front leaf springs on my 72 K5, and I ran into a question related to the caster shims I have. As you can see in the pictures, the shims are slotted and slide over the center pin. The head of the pin barely clears the shim.

Should I install the longer bolt with the extra long nut with the nut facing down? The nut would have to be cut to length and it doesn't quite fit in the hole in the spring perch. I'd have to grind it to fit and then my alignment might be a little off.

Will the short little stub of the center pin be OK based on the picture? It's probably sticking out about an 1/8" or less. If everything is torqued properly, I can't see it popping out of the alignment hole.

If I slide the shim back so the thin section with the hole is over the pin, quite a bit of the sprint wont be touching the perch area. I don't love that option. I'd like to use these based on Hemi's comments about the approved tracking.

[CJM72]

My last idea was to find or machine a spacer that would go under the head of the center pin or find center pins with a longer head. I'm sure that's the most 'secure' idea, but I've never looked for something like that.

[Richard]

The most secure method is to get caster shims that bolt onto the spring pack with the center pin. They are available. Just looked at some spring shims I recently purchased for another use and they have the smaller hole for attachment to the pack.

Add with edit- The Skyjacker 8" lift springs I used on my last truck had the shims pre-installed on the front leafs to alleviate driveline angle. The decreased positive caster was a compromise I had to live with. Are you trying to increase caster, yes do it. There should be no problem with the CV clearance or driveline angle with the 2.5" springs. IMO if you are installing the shims to angle pinion up for the driveline, there is no reason to do it. After install of springs jack up truck put on stands and let axle hang. If driveshaft spins freely you are good to go.

[CJM72]

Originally Posted by Richard

The most secure method is to get caster shims that bolt onto the spring pack with the center pin. They are available. Just looked at some spring shims I recently purchased for another use and they have the smaller hole for attachment to the pack.

Add with edit- The Skyjacker 8" lift springs I used on my last truck had the shims pre-installed on the front leafs to alleviate driveline angle. The decreased positive caster was a compromise I had to live with. Are you trying to increase caster, yes do it. There should be no problem with the CV clearance or driveline angle with the 2.5" springs. IMO if you are installing the shims to angle pinion up for the driveline, there is no reason to do it. After install of springs jack up truck put on stands and let axle hang. If driveshaft spins freely you are good to go.

Thanks Richard. Yes I'm trying to increase caster to improve the handling. A few board members have done this with these small lifts and reported improved tracking and less 'dartiness'. I considered buying a different shim that just bolts on, but I have every thing apart and not sure I want to wait. I do have washers that fit the center bolt and the OD fits the slot on the shim almost exactly. I have to imagine that once bolted in with the U bolts, this shim won't move around. But I've been wrong before!

[hemi43]

First of all, congrats on using those angled shims. It's probably the biggest improvement you can make (anti-sway bar comes second) for stability, IMHO.
As far as the locating bolt; It's nice to have to line up the springs, but not totally necessary. Once the U bolts are tightened down, that locating bolt does nothing.
Assemble everything finger tight, and check your wheel base with a tape measure while snugging up the U bolts. You want both sides the same (assuming your rear axle is in the proper location).
If you want, you can stack a few washers under the head of the locating bolt and the grind the washers down to the same diameter then install.
I made my own shims and bolted them right to the springs like Richard was talking about. Funny part was that I had to elongate the hole in the spring perch 1/8" anyway because I couldn't get my wheelbase equal on both sides.
Please post back and let us know what you think of the extra caster.
FWIW, I'm running around 6-6.5 degrees of caster.

[CJM72]

Originally Posted by hemi43

First of all, congrats on using those angled shims. It's probably the biggest improvement you can make (anti-sway bar comes second) for stability, IMHO.
As far as the locating bolt; It's nice to have to line up the springs, but not totally necessary. Once the U bolts are tightened down, that locating bolt does nothing.
Assemble everything finger tight, and check your wheel base with a tape measure while snugging up the U bolts. You want both sides the same (assuming your rear axle is in the proper location).
If you want, you can stack a few washers under the head of the locating bolt and the grind the washers down to the same diameter then install.
I made my own shims and bolted them right to the springs like Richard was talking about. Funny part was that I had to elongate the hole in the spring perch 1/8" anyway because I couldn't get my wheelbase equal on both sides.
Please post back and let us know what you think of the extra caster.
FWIW, I'm running around 6-6.5 degrees of caster.

Thanks Hemi. Your feedback is what led me to buy the shims in the first place. I am installing the correct spring plates to install a second gen sway bar in the coming months as well. That will take some time because I'll have to fab some mounts for the cross member.

It hadn't occurred to me that I'd have to (or be able to) adjust the wheelbase by slotting the spring perch. Is that a common practice?

[hemi43]

Originally Posted by CJM72

Is that a common practice?

Not sure if it's common practice, but it was my way of getting the drive train as close to perfect as possible. These trucks had a large build tolerance, and I'm sure my truck was within spec but I wanted things as close as possible.

FWIW, another thing I did on the rear axle was to add a short lift block to have the ride height level. In those blocks I installed the locating pin 5/8" further back to center the axle better in the wheel arch opening. For some reason, GM put the axles too far forward which is real noticeable with larger tires. In fact, one side is 5/8" rearward and the other side is only 1/2" because of the build tolerance in either the body or frame.

[kwmech]

Toss that piece of cr.. aluminum shim and spend a little extra and get a bolt on steel shim. BUT first, are you sure you even need the shim for a 2.5 lift? If you need it to roll the pinion up for driveshaft you will lose caster alignment as these trucks like at least a 5-6 degree reading.

[hemi43]

Originally Posted by kwmech

Toss that piece of cr.. aluminum shim and spend a little extra and get a bolt on steel shim. BUT first, are you sure you even need the shim for a 2.5 lift? If you need it to roll the pinion up for driveshaft you will lose caster alignment as these trucks like at least a 5-6 degree reading.

Nothing wrong with that shim, and if you had read from the beginning, CJM is increasing the caster, not reducing it. Adding the shim has nothing to do with his 2 1/2" lift, and in fact these shims would benefit even with zero lift.

[Jiggers72-GMC]

Great info right here guys, thanks for sharing your knowledge........ working on my K10 wandering issue.

[hemi43]

Originally Posted by Jiggers72-GMC

Great info right here guys, thanks for sharing your knowledge........ working on my K10 wandering issue.

Not enough toe in or worn components will cause wandering. I'm running 3/16" toe in with 33" tires. I tried 1/4" which felt better, but I didn't want to destroy my tires.

[Jiggers72-GMC]

Thanks Hemi, great advice .......... I ordered a new (not reman) steering gear box yesterday then I'll check the measurements again, cheers

[BIG BLOCK JIMMY]

After 2+ years of staring at the 3 degree caster shims I bought from offroad design, I'm ready to install them. I'm attempting to cure the invigorating "dartiness" and I'm hoping the shims and an alignment will do it.

Questions:
Are 3 degree shims sufficent or should I get 4 or 6 degree shims?
I assume to increase caster the thick side of the shims points forward.
The shims came in a three pack, so the differential side will have one on the bottom and one on the top opposing each other, correct?

I also have the rear axle offset blocks to center the rear with the wheel well as HEMI stated. I'm sure there's a thread on that already, but I can't find one.

[hemi43]

Originally Posted by BIG BLOCK JIMMY

After 2+ years of staring at the 3 degree caster shims I bought from offroad design, I'm ready to install them. I'm attempting to cure the invigorating "dartiness" and I'm hoping the shims and an alignment will do it.

Questions:
Are 3 degree shims sufficent or should I get 4 or 6 degree shims?
I assume to increase caster the thick side of the shims points forward.
The shims came in a three pack, so the differential side will have one on the bottom and one on the top opposing each other, correct?

I also have the rear axle offset blocks to center the rear with the wheel well as HEMI stated. I'm sure there's a thread on that already, but I can't find one.

These trucks like around 6-7 degrees of caster. Around 3 degrees is already built into the axle itself, so you want to add 3-4 for that final number. Adding 6 will be too much IMO.

The thick side needs to go towards the front to increase caster. This could cause issues with higher lifts (4 inch+) because it may put too much U-joint angle, but for a 2" lift there's no issues.
You will only need 2 shims. They go between the axle perch and the spring.
Odd that they would come in a 3 pack.
As far as an alignment, don't waste money getting it done by a shop. The only thing adjustable is the "toe". This can easily be done at home on flat ground with just a tape measure. As I mentioned before, with 33" tires, aim for around 3/16" toe IN.

[BIG BLOCK JIMMY]

Thank you Sir! This is what the retailer states for the reason on the three shims:

"Kingpin GM, Dodge and Ford D60 front axles have a spring perch built into the differential side and because of that, if you put a shim under the front springs, the big u-bolt (Ford applications) or the studs (GM/Dodge) don't sit on the same plane as the u-bolt plate. To fix that, you can put a third shim on the top of the differential side spring pointing the opposite way, that makes sure everything sits square. For that reason, we offer our shims in sets of three."

I do have a 4" lift with 35" tires.

I will adjust the toe in myself now, thank you

[BIG BLOCK JIMMY]

I forgot to add the picture from their website

[hemi43]

My only concern about your application is the 4" lift. If you don't do too much 4-wheeling you will be OK, but double check your front U-joint angle just to be safe. unfortunately increasing caster with shims also increases your U-joint angles.
Let me know how you make out.

[litebulblsc]

Are we sure the thick end goes towards the front? That would push the front of the axle down rotating the pinion up decreasing castor

[hemi43]

Originally Posted by litebulblsc

Are we sure the thick end goes towards the front? That would push the front of the axle down rotating the pinion up decreasing castor

Yup, we are sure! will do the reverse of what you say.

[litebulblsc]

Originally Posted by hemi43

Yup, we are sure! will do the reverse of what you say.

What am I missing?

[Richard]

Originally Posted by litebulblsc

What am I missing?

CJM72 wants to increase caster for handling. The caster adjustment has nothing to do with pinion angle. Thick end towards back of vehicle will increase caster on front axle, spring over axle.

[litebulblsc]

Originally Posted by Richard

CJM72 wants to increase caster for handling. The caster adjustment has nothing to do with pinion angle. Thick end towards back of vehicle will increase caster on front axle, spring over axle.

I understand he wants to increase caster.

If you are shimming at the leaf spring to increase castor, you are going to change your pinion angle. For some people it is easier to visualize pinion angle than castor angle.

I questioned Hemi saying thick side forward to increase caster, and he said no. That is why I asked what I was missing.

[BIG BLOCK JIMMY]

Originally Posted by hemi43

My only concern about your application is the 4" lift. If you don't do too much 4-wheeling you will be OK, but double check your front U-joint angle just to be safe. unfortunately increasing caster with shims also increases your U-joint angles.
Let me know how you make out.

I don't do any 4-wheeling in the Jimmy. only joy rides on dry sunny days. It will be a couple weeks before I can get to this, but I will follow up with the results. Thanks again for your help..... and I'll be putting the fat end forward.

[hemi43]

Originally Posted by litebulblsc

Are we sure the thick end goes towards the front? That would push the front of the axle down rotating the pinion up decreasing castor

My apologies !

I forgot that the springs go above the axle tube on the front of the Blazers.
I have a truck in the shop right now that I'm doing suspension work on that has the springs below the axle and that's what threw me off. My bad !!

[Richard]

Originally Posted by litebulblsc

I understand he wants to increase caster.

If you are shimming at the leaf spring to increase castor, you are going to change your pinion angle. For some people it is easier to visualize pinion angle than castor angle.

I questioned Hemi saying thick side forward to increase caster, and he said no. That is why I asked what I was missing.

Okay, get it. I do know the changing the caster will change the pinion angle. My wording was bad. Meant, the reason he is using the shims is not for pinion angle. Ujoint bind should not be a problem with the small lift and increased caster, none the less I would still check.