Got alignment done after OME 2.5", have a couple ??? (1 Viewer)

[LFD2037]

I installed an OME heavy front/medium rear kit a few weeks ago w/out doing any cater correction. Ordered TJM rubber 2.5* caster correction bushings yesterday. Got my alignment done today. Caster is -2.0 on DS & -1.9 on PS. I know I need to be between +2 & +4. What confuses me is what people say about 2* bushings change caster 3.7*, 3* change caster 4.7*, etc. Am I pissin' in the wind installing the TJM 2.5* caster bushings? I guess I can get it checked again after I install the bushings to see what it puts it @ but don't want to waste my time/money if these bushings aren't going to get me where I need to be. To me, it seems I need @ least 4* plates but everybody says plates are for 4"+ lifts. Your thoughts?

***EDIT***
Added the TJM 2.5* rubber bushings & they changed caster readings by 4*.

DS before -2* PS before -1.9*

DS after +2* PS after +2.1*

 

[tarheel40]

I don't have a great technical answer for you - I read up on lifts, caster, etc. for months before installing my kit and there is certainly a lot of conflicting info so it's difficult to come up with a definitive answer. What I can tell you is that I found a lot folks that seem to think Slee's 3 degree bushings installed with Landtank's template work well with 850s up front, especially if you don't have much weight and end up with closer to 3". Most were comparing these to the 2 degree OME bushings, not the 2.5 degree TJM though.

I decided to follow what seemed to work well for many others, and installed Slee's 3 degree black bushings (using Landtank's template) when I installed my OME 850/860 springs and 315s in December. I don't have caster numbers post-install, but I can say the truck tracks straight down the road, does not wander at all, and I haven't experienced any driveline vibrations yet. It seems every truck is a little different, but this combo has worked very well for me thus far and I am extremely pleased.

Again, to the best of my understanding, plates will typically provide too much caster correction for 850s without spaces which will tweak your front driveshaft angles to the point that driveline vibrations are a real possibility. I hope this helps, as we appear to be in very similar situations, and I'm sure someone with a bit more technical knowledge can follow up.

 

[Pin_Head]

There was just a thread on this last week. 14 mm of total rotation of the axle will give you a 4.34 degree change. Measure the offset of your bushings. Multiply this number by 2. divide this number by 185, which is the center-center spacing of the bushings. Then take the invsine or arc sine or sine -1 of this number on your scientific calculator and you will obtain the angle in degrees. If your bushing is offset by 7 mm each, then 2 of them give you 14 mm of rotation which is 4.34 degrees. This is a close approximation of how much the rotation will correct your caster, but it is not exact.
4

 

[LFD2037]

There was just a thread on this last week. 14 mm of total rotation of the axle will give you a 4.34 degree change. Measure the offset of your bushings. Multiply this number by 2. divide this number by 185, which is the center-center spacing of the bushings. Then take the invsine or arc sine or sine -1 of this number on your scientific calculator and you will obtain the angle in degrees. If your bushing is offset by 7 mm each, then 2 of them give you 14 mm of rotation which is 4.34 degrees. This is a close approximation of how much the rotation will correct your caster, but it is not exact.
4

I'll do that when they get here!!! Here's some of what fuels my confusion:

From TheBigBoy:
Caster plates and caster bushes are named incorrectly and always get confused. 2 degree caster bushes dont add 2 degree's of caster correction. They take your caster from -2 to +3 (or suppossed to) = 5 degree's of caster correction (2.8" of lift). Its the same with 3 degree bushes, 5 degree caster plates etc...

I cant talk for the US. But here in aus where most of this originated from, they simply got it wrong (the name, not the product). For about 10 years it was hard to convince people from their veiws that 0 degree's was correct caster. In which the number kind of added up (Ironmans qoute that every 1" lift = 1 degree of caster correction). ie 4" lift = 4 degree's of caster correction (under the ussumption 1"= 1 degree change, and 0 degrees was correct caster numbers). They had no problems so never bothered getting their actual caster numbers checked. And scratched their heads when they did get caster number checked. They wont ever change the name though.


From surfpig:

OK I can see that. If 0 is correct (+3* or whatever), then it's off from correct by +/- whatever.


See my confusion?!?!?!?!?! I know a lot of people argue w/TheBigBoy when it comes to caster correction but he seems to know his stuff & has such compassion when he talks about caster correction that I almost have to believe him!!!!

 

[sleeoffroad]

The main confusion comes in that simple rotation of the axle and measured caster is not a one to one relation. What Pin Head explain is how to calculate the amount that the axle rotates, but when measured on an alignment machine it is not the same.

From your caster numbers, yes you need more correction to get back to stock specs. You are likely that low on caster if you used the heavy springs with no load resulting in higher than the expected lift where one uses the 2.5 degree bushings.

 

[LFD2037]

The main confusion comes in that simple rotation of the axle and measured caster is not a one to one relation. What Pin Head explain is how to calculate the amount that the axle rotates, but when measured on an alignment machine it is not the same.

From your caster numbers, yes you need more correction to get back to stock specs. You are likely that low on caster if you used the heavy springs with no load resulting in higher than the expected lift where one uses the 2.5 degree bushings.

So your 3* caster correction bushings will change the caster numbers by how much(as in your casting bushings will turn my - 2* caster to???????)? I went heavy in front because I'll be adding your Shortbus bumper and 12K winch as money allows. Thanks.

 

[landtank]

You can't just say X spring lift = Y caster correction. That is do to the fact that any additional weight will effect the ride height and it's actually the change in ride height that determines the change in caster.

So it's quite possible that your 2.5" springs on a stiock truck will yield the same "ride height" as a 4" spring on a heavily modified truck.

Along the same lines people will neglect to figure in any addition gains in ride height from spacers.

It's not about the springs per say, but they are the major contributor in changing the ride height.

I use a formula for determining which correction to use. I measure the distance from the hub center to the bottom of the flare, lets call it H2F

then

H2F - 20.5 x 1.75 = amount of correction

as an example: 23.25 - 20.5 x 1.75 = 4.8125

Now it's not an exact number but with a 2* target to hit it has worked out well.

 

[sleeoffroad]

I have not had the time to do a pre and post measurement session with the 3 degree bushings. As Pin Head calculated, they rotate the axle approx 4.5 degrees, but I am sure that is not what we are going to measure pre and post install on the alignment machine.

Here is a case study of a truck we did with caster plates and it might help you a little.

Stock Truck before any work was done.

Stock 80 Series
==========
Caster
Left = 2.5° - Right = 2.1°

Hub to fender measurement
LF = 19.88" - RF 19.88"
LR = 20.27" - RR - 20.27"

After we installed the 4" lift, but before any caster plates were installed
==============================================
Caster
Left = - 3.4° - Right = -3.8° ----- Caster Loss - Left 5.9° = Right 5.9° -> 1.5° per inch of lift.

Hub to fender measurement
LF = 23.81" - RF 23.81" / GAIN = 3.93"
LR = 24.88" - RR - 24.88" / GAIN =4.61"

After installing SLEE caster Plates
======================
Left = 2.4° - Right = 2.0° ----- Caster Gain- Left 5.8° = Right 5.8°


Observations
=========
The correction is right where we expected it.

The caster loss per inch of lift is lower than what most people have calculated the angle of loss to be. The common wisdom is that it is 1.76° but that is a purely axle rotation calculation and does not take into account how the caster is measured.

One should not negate the caster effect that having the rear lift more than the front has on the caster loss. We are going to be working on that and seeing how that effects it, but quick measurements has show us that you can loose as much as a degree of caster for every inch that the rear lifts more than the fronts.



==========

 

[LFD2037]

You can't just say X spring lift = Y caster correction. That is do to the fact that any additional weight will effect the ride height and it's actually the change in ride height that determines the change in caster.

So it's quite possible that your 2.5" springs on a stiock truck will yield the same "ride height" as a 4" spring on a heavily modified truck.

Along the same lines people will neglect to figure in any addition gains in ride height from spacers.

It's not about the springs per say, but they are the major contributor in changing the ride height.

I use a formula for determining which correction to use. I measure the distance from the hub center to the bottom of the flare, lets call it H2F

then

H2F - 20.5 x 1.75 = amount of correction

as an example: 23.25 - 20.5 x 1.75 = 4.8125

Now it's not an exact number but with a 2* target to hit it has worked out well.

Ok, my DS is 23.25 & PS is 23 so:

23 - 20.5 x 1.75 = 4.375 for +2* or 5.375 for +3*

According to that my only option is caster plates but EVERYBODY says plates are for 4" & up lift. Not to mention I'd rather be closer to +3* than +2*. There's not a bushing on the planet that'll give that much correction & plates are too much so what about this:

I install the 2.5* caster bushings which leaves me w/needing/wanting 2.875* more difference(assuming the TJM correct caster by 2.5*). So then I'll need to do the 'washer mod' & move the hole down 9mm(.354") to give me 2.78* more caster & 'should' put me @ 5.28* caster correction.

-2*(what I'm @ now) + 5.28*(how much I'll change)= +3.28

Is this all correct? Jeez, I reeeeaaally tend to overthink/overcomplicate things(OCD) but I just want to have to do this once! I'll add spacers after bumper/winch install so the caster will remain a constant. Thanks for your patience!

 

[landtank]

Ok, my DS is 23.25 & PS is 23 so:

23 - 20.5 x 1.75 = 4.375 for +2* or 5.375 for +3*

According to that my only option is caster plates but EVERYBODY says plates are for 4" & up lift. Not to mention I'd rather be closer to +3* than +2*. There's not a bushing on the planet that'll give that much correction & plates are too much so what about this:

I install the 2.5* caster bushings which leaves me w/needing/wanting 2.875* more difference(assuming the TJM correct caster by 2.5*). So then I'll need to do the 'washer mod' & move the hole down 9mm(.354") to give me 2.78* more caster & 'should' put me @ 5.28* caster correction.

-2*(what I'm @ now) + 5.28*(how much I'll change)= +3.28

Is this all correct? Jeez, I reeeeaaally tend to overthink/overcomplicate things(OCD) but I just want to have to do this once! I'll add spacers after bumper/winch install so the caster will remain a constant. Thanks for your patience!

I take the tallest side run the numbers and then that is the amount of change in caster that I need.

so 4.85 or round it up to 5.0 degrees.

as Christo has pointed out the resulting change in caster is less than the amount of actual change in rotation.

so most refer to caster solutions in there results such as

OME 2* or Slee's 3*

with a number of 5* it's plates.

 

[driveshafterw]

pinion

YILHVLIFG

 

[sleeoffroad]

One of the other variables is what is a stock height truck measurement. I have it at between 19.5 and 20". Looks like Rick has it at 20.5".

On our spreadsheet of truck measurements it is at 19.81" for all the 80's we did the last 4 years. That puts you at about 3.5" of lift. Also, you might have had a truck that had low caster right off the bat.

 

[landtank]

One of the other variables is what is a stock height truck measurement. I have it at between 19.5 and 20". Looks like Rick has it at 20.5".

On our spreadsheet of truck measurements it is at 19.81" for all the 80's we did the last 4 years. That puts you at about 3.5" of lift. Also, you might have had a truck that had low caster right off the bat.

It's what I use and it serves me well. I wouldn't over analyze it.

but feel free and use your numbers, the truck now needs 6.5625* of caster correction.

 

[86tuning]

Ok, my DS is 23.25 & PS is 23 so:

23 - 20.5 x 1.75 = 4.375 for +2* or 5.375 for +3*

According to that my only option is caster plates but EVERYBODY says plates are for 4" & up lift.

I install the 2.5* caster bushings which leaves me w/needing/wanting 2.875* more difference(assuming the TJM correct caster by 2.5*). So then I'll need to do the 'washer mod' & move the hole down 9mm(.354") to give me 2.78* more caster & 'should' put me @ 5.28* caster correction.

If you're going to slot the holes and do the washer mod then just skip the bushings all together. Stick with the stock bushings for more compliance and flex.

Also, when you slot the holes, consider moving the holes towards the rear of the car to effectively lengthen the control arm a little bit.

There's a good writeup on how to do this here somewhere. Just slot, then go get the caster measured again and adjust as needed, then weld the washers.

 

[LFD2037]

Got my TJM 2.5* caster bushings in. From the best I can measure is the hole is moved .375" which is a change of 9.525mm. Using the above equation each bushing causes 2.95 degrees of rotation.

2.95 x 2 = 5.9 degrees of rotation

This should put me @ a caster correction of about 5.5* so I should be @ about + 3*!!!!!! I think what I was having a hard time comprehending is a 2.5* bushing will actually change 2.5* but since we use one front AND rear(on the control arm) then the actual change is twice what it's advertised as. I'll report back after install & alignment w/new numbers for anyone interested.

 

[LFD2037]

Just installed 2.5* rubber caster bushings & now I have a vibration on the highway. WTH? All u-joints seem good & wheel bearings. I had no vibration prior to installing the bushings. What would cause this?

 

[86tuning]

Just installed 2.5* rubber caster bushings & now I have a vibration on the highway. WTH? All u-joints seem good & wheel bearings. I had no vibration prior to installing the bushings. What would cause this?

Front propshaft? It's joints are now running at different angles....

 

[LFD2037]

Front propshaft? It's joints are now running at different angles....

Bit it didn't vibrate before lift or after lift. Only after lift when caster was more correct. I'm hoping I just threw a weight(s) off the wheel. Going to get tires balanced again Tuesday. If its not that I'm lost!

 

[landtank]

If its not that I'm lost!

no you are just not understanding.

we have a radius arm setup and the operating angles don't change much at the pinion even after a lift until you rotate the axle to correct for caster. These new angles can cause vibrations that weren't there before because the joints are now traveling through a different range. A range that now doesn't match the previous one worn into the spiders.

 

[LFD2037]

no you are just not understanding.

we have a radius arm setup and the operating angles don't change much at the pinion even after a lift until you rotate the axle to correct for caster. These new angles can cause vibrations that weren't there before because the joints are now traveling through a different range. A range that now doesn't match the previous one worn into the spiders.

I read this 3 times and on the 3rd time I had an "Ah-Ha" moment. Never understood this concept of how/why it changed. Yes I knew its radius arms but the way they change for a lift compared to correcting for caster is what I didn't get. Thanks!!!!!! So, besides a DC shaft, what's my options? Truck handles like factory now except for the new vibe.

Btw, I'd of used one of your templates but you don't make one for the TJM caster bushings.