Castor corrected bushings vs. cranked radius arms - Defender Source
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  #1  
Old August 29th, 2011, 01:46 PM
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Mike Barnett
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Castor corrected bushings vs. cranked radius arms

It looks like it is time for me to address the driveline angles resulting from the lift, now that the driveshaft decided it didn't like it. So my question is what is the difference between these two options in terms of final results? The bushings are about half the cost of the radius arms, but I don't want to go that route if there are other reasons not to.
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  #2  
Old August 29th, 2011, 01:51 PM
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3rd option: redrill your swivel balls...

How many degrees do you need to correct?
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  #3  
Old August 29th, 2011, 02:40 PM
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never had to alter the caster on any of my landrovers but i prefer 1" to 1 1/2" Max as theres no need to go much higher, starts messing up the steering and transmission!
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  #4  
Old August 29th, 2011, 02:52 PM
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Daniel Chapman
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Lift messes up the transmission? Huh....

Doing this correctly involves both castor and pinion angle. You can't just add "caster corrected links" or "re-drilled swivel balls" to fix the issue. It's not one-or-the-other. It's both.
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Old August 29th, 2011, 03:02 PM
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How much lift are we talking?
You will really need to measure your caster to know what is wrong. Every rover seems different.

If it is just your drive line and the castor is not that bad... just get a DC shaft in front. That fixed my problems and with LR HD springs up front (previously OME 751).

I run OME 754's in the rear with rovertyme arms to correct the pinion angle, but mostly to get rid of the bushing bind.
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Old August 29th, 2011, 03:50 PM
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Quote:
Originally Posted by dchapman View Post
Lift messes up the transmission? Huh....

.

I think Marcus is referring to propshaft UJ's.
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  #7  
Old August 29th, 2011, 04:41 PM
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As someone that has used the bushings and the arms I'll say I wouldn't bother with the bushings again. The helped a little but nothing worth the effort involved.

The RTE radius arms helped a lot and were a hell of a lot easier to install.
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  #8  
Old August 29th, 2011, 05:40 PM
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Quote:
Originally Posted by diesel_jim View Post
I think Marcus is referring to propshaft UJ's.
correct!
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  #9  
Old August 29th, 2011, 07:32 PM
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Quote:
Originally Posted by ArmyRover View Post
As someone that has used the bushings and the arms I'll say I wouldn't bother with the bushings again. The helped a little but nothing worth the effort involved.
On top of that the castor corrected bushings seem to have little rubber on them... seems like a bad idea but what do I know??
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  #10  
Old August 29th, 2011, 09:10 PM
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Correct me if I'm wrong, but if you use bushings or new radius arms to correct the castor, doesn't this also correct the pinion angle? I'm after the pinion angle mostly, the steering has not been affected enough for me to worry with it. Truck has about 3" of lift (hard to tell since I replaced 20 year old shocks and springs). Steve, I already have a DC driveshaft from a Disco 2, but still seem to be experiencing some vibration - plus I think it's a little too short for the 200TDI. My spring setup is very similar to yours. Might have to bite the bullet on a Tom Woods...
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Old August 29th, 2011, 10:17 PM
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If you are going for pinion angle, you will first need to know what the pinion angles is vs the angle on the tcase output flange. For a standard driveshaft to work correctly with your lift, these 2 angles need to be no more than 1.5 degrees of each other. If you have a DC shaft, the pinion needs to be pointed directly at the tcase flange for it to work as designed.
Some of, or a combination of arms, bushings and swivel ball correction may be needed to get proper caster and proper pinion angles. I have roughly 3" lift with corrected arms, OME 2 degree bushings, and a DC shaft. There are 0 vibs at any highway speeds up to 75mph.
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  #12  
Old August 29th, 2011, 11:23 PM
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If the shaft is too short it can kill them. is your t-case in a different place?
After years of mucking around I finally bought Tom woods shafts. It is time for me to do the rear UJ soon but the front DC and rear normal made it through a year driving 30k in South America and another 20k states side in Baja and what not... no complaints!

If you are running 754's in an unloaded truck the rear pinion angle will cause vibes, at least is did on my truck. Good advise to check the angles and take the guess work out.
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Old August 30th, 2011, 04:57 AM
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Quote:
Originally Posted by D90user View Post

If you are running 754's in an unloaded truck the rear pinion angle will cause vibes, at least is did on my truck. Good advise to check the angles and take the guess work out.

LR used to supply some spacers for 4 cylinder 90's with HD suspension, that went in between the trailling arm bush and the chassis, which altered the pinion angle.

It was only 5mm or so thick, but enough to alter the geometry.
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  #14  
Old September 5th, 2011, 10:56 PM
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This is not an effort to advertise for Tom Woods, but there's a great write-up on his website about driveline (pinion) angles. It can be found here: http://www.4xshaft.com/driveline101.html

I've also added some information about castor angles to two of his images in an effort to clarify a few things with regards to this discussion (and many more here on D-90).

The image I've attached called "stock castor angle" (hover over it to see the name of the attachment) has a red line that I've drawn through the differential showing what the stock D90 castor angle might resemble, it's around 3 degrees as I've noted in the image. Note the slope of the line through the differential in this picture and think of a bicycle or motorcycle fork... if you angle the bottom of the fork outwards (increase the castor) you generally stabilize the wheel and it wants to more easily track straight.

Now look at the picture called "cranked radius arms or bushings." This second image will show you what your angles will look like if you use modified radius arms and/or bushings. In this second image, Tom Woods has also shown that if you use modified radius arms and/or bushings, you must run a double-cardan shaft to ensure that the pinion angles will not cause driveshaft vibration. That's all fine, so what's the problem, right? To understand the potential problem in doing cranked radius arms and/or bushings with no other modifications on a D-90 look at the red line in this picture. You can see that it stayed the same in relation to the differential BUT, the castor angle itself has now been reduced because it is tied to the angle of the differential/pinion. You can see that if the stock one used to be 3 degrees then the cranked radius arms/bushings have just taken the castor angle down to 1 degree (or less). The closer you get to 0 it becomes progressively easier to turn the wheel (very desirable in some situations) but also can cause the wheel to want to turn on its own (very undesirable in some situations - e.g. wandering/wobbles on the road). If you want to fix this to make the wheels snap back to straight easier (as they did when it was stock) you'll need to figure out some way to detach the castor angles from the pinion angle. One of the most common ways of doing this on the D-90 is by slotting the bolt holes in the swivel balls so that you can "clock" them back to return the castor back to ~3 degrees as it was in the stock setup while leaving the pinion pointed up to accommodate the DC shaft. To visualize this in the second image, imagine rotating just the red line counter-clockwise so it looks more like it did in picture #1.

I'm running RoverTym springs that have given ~4" of lift on my ST, using the cranked radius arms (to point the pinion up towards the t-case) with a DC shaft, and then cranking the swivels back to put the stock castor at roughly stock angles. This results in no driveshaft vibrations (thanks to the DC shaft and proper pinion angles) and no speed wobbles/wandering on the freeway (thanks to proper castor angles) all the way up to 80mph - won't go any faster, lol. Hope this little explanation helps. I have no experience with the bushings, but I'm extremely happy with the combination of radius arms and swivels. As has been mentioned before, with under ~2" of lift, you can still get away with stock radius arms and stock swivels because the pinion angle is still nearly parallel to the t-case angle.
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  #15  
Old September 5th, 2011, 11:04 PM
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Quote:
Originally Posted by RiftRover View Post
Correct me if I'm wrong, but if you use bushings or new radius arms to correct the castor, doesn't this also correct the pinion angle? I'm after the pinion angle mostly, the steering has not been affected enough for me to worry with it. Truck has about 3" of lift (hard to tell since I replaced 20 year old shocks and springs). Steve, I already have a DC driveshaft from a Disco 2, but still seem to be experiencing some vibration - plus I think it's a little too short for the 200TDI. My spring setup is very similar to yours. Might have to bite the bullet on a Tom Woods...
Just a clarification... bushings and/or radius arms correct the pinion angle, not the castor angle. They actually mess up your castor angle (unless you want near 0 degree castor for off-roading or something). It's the swivel ball slotting/"clocking" that then corrects the castor angle after the bushings/radius arms messed it up as a result of them correcting the pinion angle for a DC shaft :-) Did that make sense?

In other words, if you correct your pinion angle to accommodate the DC shaft, you inevitably decrease castor angle thus possibly adding speed wobbles and/or wandering on the freeway. However, it's important to understand that each truck is a little different and each person drives a bit differently. The reduced castor angle may not be an issue for you, it depends on your driving. But if it is an issue, you may need slotted swivel balls.
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  #16  
Old September 6th, 2011, 01:24 AM
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I did all 3 to my truck when I put the rovertym lift on. Since it was on tired suspension to begin with, it jumped up 3" easy. New radius arms got the pinion angle pointed up, a tom woods double cardan shaft dealt with that, and then new swivel balls to get the castor correct.

I drove it without the new swivel balls just to test it out, and it was scary. Like have a religious experience scary. Crazy understeer and then all of a sudden nothing else except the feeling that you were going to flip or something. It's hard to explain.
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Old September 6th, 2011, 09:20 AM
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Quote:
Originally Posted by navydevildoc View Post
I did all 3 to my truck when I put the rovertym lift on. Since it was on tired suspension to begin with, it jumped up 3" easy. New radius arms got the pinion angle pointed up, a tom woods double cardan shaft dealt with that, and then new swivel balls to get the castor correct.

I drove it without the new swivel balls just to test it out, and it was scary. Like have a religious experience scary. Crazy understeer and then all of a sudden nothing else except the feeling that you were going to flip or something. It's hard to explain.
bingo :-)
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  #18  
Old April 17th, 2015, 11:23 AM
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Great thread! Lots of good info. The coils I put on we're supposed to give me 1.5 inch lift but ended up being 3 inches. On my first highway drive last night it tracked straight but I had similar experience as Neill. Previous to the new springs I rebuilt the front end and had it aligned and all was well. But these new springs really changed things. I might take it for an alignment and see what the numbers are.
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