Caster over front pinion angle or front pinion angle over caster

EROCK

EROCK

TJ Enthusiast
Joined
Dec 1, 2018
Messages
183
Location
Arkansas
I use 4WD about 2 percent of total driving. Their seems to be two thought sets. The lifted guys say get the best caster angle first then front pinion. User manual says for a stock rig, get the best front pinion angle first and what ever caster you get is what you get.
I have a 5.5 in lift on Adjustable control arms. I prefer more castor over pinion angle because I dont use 4WD ,well, never so far but only would use it if I get stuck and need it on forestry roads. The jeep is used as a daily driver though I have a new truck. I just enjoy driving the jeep more. Haha
 
Caster angle always (!) takes a back seat to pinion angle. Put another way, pinion angle takes precedence over caster angle. An excessive pinion angle will cause driveshaft u-joint vibrations which will damage things like the u-joints, seals, etc. where insufficient caster angle just causes reduced steering return-to-center and makes the steering less stable on the highway.

This is right out of the Mopar factory shop manual in the alignment section... notice the yellow highlighted area in the Caster section.

Caster Angle Precedence.JPG
 
Last edited:
  • Like
Reactions: strumble8
One easy way to achieve this is to let your axle hang at full droop and turn the driveshaft by hand. If you feel it "catch", that is the ujoint binding, raise your pinion to the point you can turn the driveshaft freely. This will give you the most caster, but no vibes. The driveshaft is happy thruout its entire range of motion.
 
  • Like
Reactions: JMT and Octavio Lizarraga
EROCK said:
I use 4WD about 2 percent of total driving. Their seems to be two thought sets. The lifted guys say get the best caster angle first then front pinion. User manual says for a stock rig, get the best front pinion angle first and what ever caster you get is what you get.
I have a 5.5 in lift on Adjustable control arms. I prefer more castor over pinion angle because I dont use 4WD ,well, never so far but only would use it if I get stuck and need it on forestry roads. The jeep is used as a daily driver though I have a new truck. I just enjoy driving the jeep more. Haha
Click to expand...

What Jerry said...

I've never read where anyone knowledgable on any Jeep related forum recommended caster over pinion. Nearly always they say "as much caster as you can get without vibes." Most of the time you should be able to get a reasonable caster angle, since larger tires don't require quite as much caster as stock tires. And whether or not you use 4wd a lot has no bearing, unless you have installed lockout hubs to prevent the front driveshaft from spinning in 2wd
 
Last edited:
  • Like
Reactions: EROCK
tworley said:
One easy way to achieve this is to let your axle hang at full droop and turn the driveshaft by hand. If you feel it "catch", that is the ujoint binding, raise your pinion to the point you can turn the driveshaft freely. This will give you the most caster, but no vibes. The driveshaft is happy thruout its entire range of motion.
Click to expand...
Vibrations from excessive pinion angles aren't from the u-joint binding or catching, they're caused by exceeding the working angle of the u-joint and/or the front & rear u-joints rotating at different velocities that cause vibrations. U-joints can start vibrating well before they start binding.

A good explanation of it comes from Tom Wood's website. Go to the Tech Info page then to the Driveline Geometry 101 page. This is just part of the good information on that page...

Tom Wood.JPG
 
  • Like
Reactions: MaloStapalo, ElectricWizard and tworley
Jerry Bransford said:
Caster angle always (!) takes a back seat to pinion angle. Put another way, pinion angle takes precedence over caster angle. An excessive pinion angle will cause driveshaft u-joint vibrations which will damage things like the u-joints, seals, etc. where insufficient caster angle just causes reduced steering return-to-center and makes the steering less stable on the highway.

This is right out of the Mopar factory shop manual in the alignment section... notice the yellow highlighted area in the Caster section.

View attachment 73746
Click to expand...
Is this where I put the angle finder to tell the angle difference or do I us the spot on the bottom of what looks like a spindle by the wheel and the shaft u joint crown?

20190123_123237.jpg


20190123_123914.jpg
 
Put the angle finder on the back of the axle on either of the two round machined surfaces which are precisely 90 degrees from that of the pinion angle. Rotating the angle finder 90 degrees to counteract that 90 degree difference will allow the angle finder to directly indicate the pinion angle as shown.

Pinion angle, where to measure from.JPG
PinionAngleMeasuring1.jpg


PinionAngleMeasuring2.jpg
 
  • Like
Reactions: Octavio Lizarraga
Jerry Bransford said:
Put the angle finder on the back of the axle on either of the two round machined surfaces which are precisely 90 degrees from that of the pinion angle. Rotating the angle finder 90 degrees to counteract that 90 degree difference will allow the angle finder to directly indicate the pinion angle as shown.

View attachment 73756View attachment 73757

View attachment 73758
Click to expand...
Awesome!! Thanks Jerry! Are we going for a "0 degree" difference or is there 1 or 2 positive degrees allowed?
 
EROCK said:
How do you know what my rear drive shaft looks like? The pictures are of the front differential.
Click to expand...
Whoops you're right it's the front DS. As above, the answer to your question on the correct front pinion angle is more complicated. The correct front pinion angle is the one that gives as much caster angle as possible without it causing vibrations on the front driveshaft.
 
Jerry Bransford said:
Whoops you're right it's the front DS. As above, the answer to your question on the correct front pinion angle is more complicated. The correct front pinion angle is the one that gives as much caster angle as possible without it causing vibrations on the front driveshaft.
Click to expand...
Really !! Great, so I'm at 6.5 degrees of caster and have no vibrations so I'm good??
 
Jerry Bransford said:
Is your rear driveshaft still stock as it appears to be? With a 5.5" lift I hope not but...
Click to expand...
This raises a question though. Here's a pic of my rear drive shaft. Does it look right. I have 1 degree pinion diffence and 1 degree difference on the other end if I remember right. Also my rear lift measures 5in and the front is 5.5in

20190123_135819.jpg
 
EROCK said:
This raises a question though. Here's a pic of my rear drive shaft. Does it look right. I have 1 degree pinion diffence and 1 degree difference on the other end if I remember right. Also my rear lift measures 5in and the front is 5.5in

View attachment 73785
Click to expand...
That pinion angle not right at all, someone didn't know how to set up the pinion angle for the factory single-cardan driveshaft. That will cause vibrations. The pinion angle for that style driveshaft should be parallel to the transfer case's output shaft angle.

With 5.5" of suspension lift your TJ absolutely (!) should have a SYE kit installed into the transfer case and your rear driveshaft needs to be replaced with a double-cardan (aka CV) driveshaft. Those should be installed once the suspension lift height reaches 4" or taller. At least if your TJ is the SWB model. You can get away with a bit more lift before needing the SYE/DC driveshaft if you're driving the longer wheelbase Unlimited which has a longer rear driveshaft.
 
Last edited:
Jerry Bransford said:
That pinion angle not right at all, someone didn't know how to set up the pinion angle for the factory single-cardan driveshaft. That will cause vibrations. The pinion angle for that style driveshaft should be parallel to the transfer case's output shaft angle.

With 5.5" of suspension lift your TJ absolutely (!) should have a SYE kit installed into the transfer case and your rear driveshaft needs to be replaced with a double-cardan (aka CV) driveshaft. Those should be installed once the suspension lift height reaches 4" or taller. At least if your TJ is the SWB model. You can get away with a bit more lift before needing the SYE/DC driveshaft if you're driving the longer wheelbase Unlimited which has a longer rear driveshaft.
Click to expand...
Yayy!! This PO did nothing right. I wonder if it would just be easier and less money to swap the crap 6in springs and RC shocks to Bilstein 5100 shocks and 4in springs.. and pass on the SYE and Double cardan shaft. Also do you think I could get away with just the Double cardan shaft without the SYE being that it's only 5in of lift in the back and only 1in over the 4in lift cutoff?
 
EROCK said:
Yayy!! This PO did nothing right. I wonder if it would just be easier and less money to swap the crap 6in springs and RC shocks to Bilstein 5100 shocks and 4in springs.. and pass on the SYE and Double cardan shaft. Also do you think I could get away with just the Double cardan shaft without the SYE being that it's only 5in of lift in the back and only 1in over the 4in lift cutoff?
Click to expand...

Get the Rancheros RS5000X. They are a good price and ride great. The Bilsteins are made for heavy trucks and such. Also,are you sure the springs are 6in? take a tabe measure to them to see exactly how long they are.
 
  • Like
Reactions: MaloStapalo
EROCK said:
Yayy!! This PO did nothing right. I wonder if it would just be easier and less money to swap the crap 6in springs and RC shocks to Bilstein 5100 shocks and 4in springs.. and pass on the SYE and Double cardan shaft. Also do you think I could get away with just the Double cardan shaft without the SYE being that it's only 5in of lift in the back and only 1in over the 4in lift cutoff?
Click to expand...
1" too tall is 1" too tall. As said above, anything 4" or taller requires a SYE and double-cardan driveshaft. Bilstein 5100 shocks are too stiff for me, not many like them. Rancho's RS5000x would be a great choice.

And a SYE is required to install a DC driveshaft due to how it needs to attach to the type of output you get only after installing a SYE kit. The factory connection between the tcase and OE driveshaft uses a slip yoke. A DC driveshaft does not connect to a slip yoke. SYE stands for slip yoke eliminator.
 
  • Like
Reactions: MaloStapalo and Brad W
Top Bottom
Back