Caster Correction for Dobinson C97-146VT 2.5" Springs (2 Viewers)

[Mojo Jojo]

I bought a 97 LC with 267k miles back in Aug 2023, been lurking on Mud since then but first time posting a thread. I put in the Dobinson 2.5" VT lift kit this past Christmas and went with the 2.5* polyurethane caster correction bushings. Currently running 35s but plan to go up to 37s. When I went in to get it aligned the caster measured right at 0*, which is obviously not enough. Drives OK in a straight line but feels a little jerky when transitioning from one turn to another.

So I'm looking into caster correction plates and am weighing two different approaches:
- Keeping the 2.5* caster correction bushings and adding plates with around 3* or 4* of caster. The perceived advantage to me is the current caster with the 2.5* bushings is a known quantity (0*) so adding the plates will fine tune it to where it needs to be. I know a lot of people prefer the ride quality of the OEM rubber bushings, but I'm personally fine with the poly bushings. I searched and didn't see anyone that has combined bushings and plates, so not sure if that is a no-no.
- Replace the 2.5* caster correction bushings with OEM bushings and put in caster correction plates with a higher degree of caster. I'm guessing I would need around 6*, but not really sure what the caster is with OEM bushings, so it's a little bit of a guess. Assuming I installed the 2.5* bushings correctly, in theory the caster would be -2.5* with OEM bushings, so 6* plates would theoretically give me 3.5* caster.

This is my first time working on a straight axle front end, so pardon my ignorance. My gut tells me the second option is the better way to go but curious what the collective wisdom out there is.

 

[Mojo Jojo]

Here are some pics

 

[Mojo Jojo]

Forgot to add this pic

 

[landtank]

There is nothing better than stock bushings in the front arms for longevity.

I’d install OEM bushings and then add plates.

If you measure from the center of the front hub to the underside of the flare and subtract 20.5 you will get a good idea of what the lift is and your correction needs are.

 

[77mustard40]

I had the Landtank 2.5” plates which were fine up to that lift height, then purchased some Gen 1 VT-146(7) coils from someone wanting to go smaller. I ended up at roughly 3.5” of lift and the 2.5” plates were insufficient. The other issue at that height were my front driveline angles. I ended up with the DVS 4” control arms and a Landtank DC driveshaft and it’s been a super setup.

You need to determine how much lift you are getting on your truck with those springs before tackling the problem, and it may involve a DC front driveshaft. Properly sized plates with OEM bushings will work, but if you’re headed for 37’s you may want to open your wallet for control arms.

 

[Mojo Jojo]

I’m measuring 23.5” on the driver side and 24.25” on the passenger side. I don’t have the fender flares so factoring in an assumed 0.5” distance between the flares and fenders, that would change the 20.5 reference point to 21.0 and give me a 2.5” and 3.25” lift on the D and P sides, respectively (which is interesting because they were the same height right after the install, could they be settling at different rates?).

FWIW, the P rear is also 0.75” higher than the D rear. I had hoped the new lift would equalize the D and P sides, so at this point not sure what is causing the difference.

At any rate, assuming an average 3.0” lift in the front, what caster plates are recommended? Any ideas on what might be causing the difference in lift height between P and D side? Shocks and panhard bars were also replaced.

 

[Delta VS]

Don’t sleep on this thread: Compiling/comparing lift and caster data - https://forum.ih8mud.com/threads/compiling-comparing-lift-and-caster-data.1099600/ had a customer just yesterday tell me they used it to figure out what kind of correction would be best for them by finding a similar setup in the spreadsheet

 

[landtank]

I’m measuring 23.5” on the driver side and 24.25” on the passenger side. I don’t have the fender flares so factoring in an assumed 0.5” distance between the flares and fenders, that would change the 20.5 reference point to 21.0 and give me a 2.5” and 3.25” lift on the D and P sides, respectively (which is interesting because they were the same height right after the install, could they be settling at different rates?).

FWIW, the P rear is also 0.75” higher than the D rear. I had hoped the new lift would equalize the D and P sides, so at this point not sure what is causing the difference.

At any rate, assuming an average 3.0” lift in the front, what caster plates are recommended? Any ideas on what might be causing the difference in lift height between P and D side? Shocks and panhard bars were also replaced.

you might have the springs installed backwards, that's a rather big difference and it could be the rears as well. You want the taller springs on the left (DS) of the truck.

 

[Mojo Jojo]

you might have the springs installed backwards, that's a rather big difference and it could be the rears as well. You want the taller springs on the left (DS) of the truck.

I’m positive they’re installed correctly. All four were labeled, plus I measured them and confirmed the driver side springs were longer. At the time of install, the ride height at the front was equal on both sides.

 

[Mojo Jojo]

Don’t sleep on this thread: Compiling/comparing lift and caster data - https://forum.ih8mud.com/threads/compiling-comparing-lift-and-caster-data.1099600/ had a customer just yesterday tell me they used it to figure out what kind of correction would be best for them by finding a similar setup in the spreadsheet

Thanks for this link, I hadn’t come across it in my prior searching. I’ll check it out tonight.

 

[landtank]

I’m positive they’re installed correctly. All four were labeled, plus I measured them and confirmed the driver side springs were longer. At the time of install, the ride height at the front was equal on both sides.

I have no experience with these springs but that doesn't seem right. With that 3/4" difference your axles aren't parallel and the truck won't track straight. I'd get some shims and level that truck out. I think you'll end up around 3" of lift.

 

[77mustard40]

If you are going with plates I’d recommend Landtank’s 4” plates.

 

[Mojo Jojo]

If you are going with plates I’d recommend Landtank’s 4” plates.

I think that's what I'm going to do. If I were to buy the Delta radius arms now with 35's I'd need the regular ones, but would need to buy the long ones when I switch to 37's, so I'll wait until then to buy the long arms so I only have to buy one set. I can weld shut the holes I have to drill in the brackets for the caster plates when I get the new radius arms. Thanks for everyone's help, once I get the plates installed I'll get the alignment checked and report back with the new caster number.

 

[landtank]

looks like there is something going on with the front left wheel. Look cat the camber reading. Might check the wheel bearings.