Question about pinion angles, shims - with pic (1 Viewer)

[MDH33]

I have a '73 fj40. With the addition of some 4" Downey lift springs and slightly longer shackles, I think I need to add shims to get the pinion angles right. The rear axle had a 2.5˚ shim which I kept in place. I took some measurements which are below:

From searches and asking club members, I think I would need an 8˚ shim in front and a 6˚ in the back, which would point the pinions down .5˚ front and 2˚ in the rear.

One thing I was wondering about; will the springs settle/flatten significantly as they break in to change the angles?? They have a ton or arc right now.

Does this sound right?? Just want to make sure I get it right before I bolt it all back together. Thanks!

 

[Deep South Cruisers]

I put 6 degree shims in the front and nothing on the back when my 4" TPI lift was installed. Your shackle length might be the difference in the rear.

Yes, they will settle out some after break in but not enough that you would need to change the shims again.

 

[Pin_Head]

It sounds OK, but you didn't list the angle at the transfer case flanges. Is it 90?

A couple of things to check:

If you point the front down, you may be getting close to exceeding the maximum operating angle of the joint when the suspension is at full droop. If so, cutting and turning the knuckles and pointing the pinion up might be a better option.

If the rear isn't vibrating, why fool with it?

 

[Deep South Cruisers]

Also:

My ujoints were WELL worn in the stock position and created vibes in the new position. I went a head and put all new Toyota OEM joints in and got rid of some of the vibrations.

 

[MDH33]

It sounds OK, but you didn't list the angle at the transfer case flanges. Is it 90?

If the rear isn't vibrating, why fool with it?

Yes, the flanges at the transfer case were 90˚ - or 0˚, depending.

There's no vibration in the rear, but I assumed that the angles should be within a certain tolerance?

The front is obviously pretty far off, and may be affectng the steering. How close to parallel do the flanges on the pinions and TC need to be (in an ideal setup)?

 

[Pin_Head]

How close to parallel do the flanges on the pinions and TC need to be (in an ideal setup)?

Within about 1-2 degrees.

 

[MDH33]

Thanks for the replies.

If you point the front down, you may be getting close to exceeding the maximum operating angle of the joint when the suspension is at full droop.

What is the max angle for the front drive shaft?

 

[Degnol]

Since you don't usually use the front drive at any speed, I don't know if you should worry about pointing the pinion down. I would think that the longer shackles in the front ( if they are longer in the front) would have a more deleterious effect on your caster. If you have tracking problems or death wobble, you may need the shims in the front or a cut and turn like PH said.

GL


Ed

 

[MDH33]

Yeah, I noticed a difference in how the steering tracked after adding the longer front shackles. No vibration that I can tell, but some wander. I haven't engaged the front drive shaft yet with the longer shackles to see if it will vibrate.

How is caster measured??

My only reservation about cutting off and rewelding the spring perches after rotating the axle, is that if I want to take it back to stock spring height, it will be off then.

 

[Degnol]

Yeah, I noticed a difference in how the steering tracked after adding the longer front shackles. No vibration that I can tell, but some wander. I haven't engaged the front drive shaft yet with the longer shackles to see if it will vibrate.

How is caster measured??

My only reservation about cutting off and rewelding the spring perches after rotating the axle, is that if I want to take it back to stock spring height, it will be off then.

Imagine a line that goes through the center of the trunion bearings on the knuckles. Caster is the degree from vertical. Stock is 1 or 2 * positive caster, meaning leaning slightly back when viewed from the driver's side. Longer front shackles will rotate the caster to 0* or worse yet, (-) caster, leading to steering and tracking and wobble problems.
Mark W, I think, posted about using a grinder to remove some material from the yoke that mates to the pinion flange to gain some U joint clearance.
Do you really need the longer shacles in the front?

GL

Ed

Search "Caster" on the forum and you'll find a lot. I posted a diagram on one thread that may clarify what I just tried to say....

EDIT: Found it, go to post #48

https://forum.ih8mud.com/showthread.php?t=115946&highlight=caster

 

[MDH33]

Great info there. Thanks.

 

[Pin_Head]

The maximum recommended operating angle is approx 19 degrees. It will operate at higher angles which is OK on the front, but a few more degrees and there will be binding due to interferance with the yokes and this will lead to breakage. You can check this at max axle droop by rotating the shaft.

 

[MDH33]

hmmmmm, yeah I bet it's going to be close at full flex/droop. I'll get it on the jack and measure.