FJ40 rear axle shims (1 Viewer)

[ukboneman]

OK, so I think I have a pretty good understanding of the need for caster shims on the front axle. I am doing a 4" Skyjacker lift with shackles on both front and back that are 1 1/2" longer than stock. What about the rear axle. Obviously, caster is not an issue, but pinion angle is. Some say that the pinion should be parallel to the transfer output flange (e brake in this case). In that case, the high part of the shim would point towards the rear. Others say that the shim should increase the pinion angle so that there is less likelihood of the universal joints binding or the shaft vibrating, so the thick part of the wedge will be on the front. Opinions?

 

[rkymtnflyfisher]

I installed the shims on the rear of my 40 thick end to the rear to make the flanges parallel.
same setup, 4" Skyjacker, extended shackles. Before I had a helluva vibration form the rear, even wiped my rear diff bearings.

 

[C6H12O6]

I have 4" Hell Creek springs on my 40 and used 4° shims in the front, and 2° shims in the rear. I used the measure app on my phone to check angles before I added the shims after the lift and that seemed about right to make the flanges parallel. No vibrations after the shims and everything sounds great. I was getting a little bit of a weird hum from somewhere in the rear before the shims. Totally gone after.

FWIW, 4° on the front might not be enough, depending on your shackles, your truck's weight, and the tires you're running. They're pretty cheap, and fairly easy to swap out for 6° shims if you plan ahead and have center pins in your springs that will work with the taller shims if you need them. Mine is ok, and I haven't had the alignment checked at a shop to get a really accurate caster measurement yet, but it feels like I could use a little more caster even with the 4° in there.

 

[ukboneman]

I have 4" Hell Creek springs on my 40 and used 4° shims in the front, and 2° shims in the rear. I used the measure app on my phone to check angles before I added the shims after the lift and that seemed about right to make the flanges parallel. No vibrations after the shims and everything sounds great. I was getting a little bit of a weird hum from somewhere in the rear before the shims. Totally gone after.

FWIW, 4° on the front might not be enough, depending on your shackles, your truck's weight, and the tires you're running. They're pretty cheap, and fairly easy to swap out for 6° shims if you plan ahead and have center pins in your springs that will work with the taller shims if you need them. Mine is ok, and I haven't had the alignment checked at a shop to get a really accurate caster measurement yet, but it feels like I could use a little more caster even with the 4° in there.

Thanks. I am assuming that the rear shims have the thick part in the back tilting the pinion back down?

 

[ukboneman]

I installed the shims on the rear of my 40 thick end to the rear to make the flanges parallel.
same setup, 4" Skyjacker, extended shackles. Before I had a helluva vibration form the rear, even wiped my rear diff bearings.

thanks. Super helpful

 

[1911]

What about the rear axle. Obviously, caster is not an issue, but pinion angle is. Some say that the pinion should be parallel to the transfer output flange (e brake in this case). In that case, the high part of the shim would point towards the rear. Others say that the shim should increase the pinion angle so that there is less likelihood of the universal joints binding or the shaft vibrating, so the thick part of the wedge will be on the front. Opinions?

From a recent thread - this will explain all:

Driveline Geometry 101 - https://4xshaft.com/blogs/general-tech-info-articles/driveshaft-angles

 

[ukboneman]

From a recent thread - this will explain all:

Driveline Geometry 101 - https://4xshaft.com/blogs/general-tech-info-articles/driveshaft-angles

seems like more of a 301 course to me... thanks.

 

[snaggletto]

The deal with castor shims is to offset the difference in longer shackles vs. stock length shackles. Theoretically, if your lift springs were properly made, and you used stock length shackles, you would not need castor shims. The reality is that shims are useful front and back if you are running longer than stock shackles, especially on a street driven vehicle, even if you are still on stock springs. The fat part goes toward the shackle end as it simply negates the angular error added by the longer shackle. I used 4 degree shims with my 4" lift springs and longer 1.5" shackles. I did not measure with an angle finder, but it certainly did reduce/eliminate vibes from the rear end.

I would STRONGLY recommend only using STEEL castor shims, not aluminum. I had aluminum initially, and the u-bolts would not stay tight.

 

[macdaddy59]

Put 4" steel shims from Georg at Valley Hybrids on front and back on my 4" HFS lift.

 

[Groucho263]

Just so you guys don't install it wrong like I did and have to redo it...here are some pictures. The fat part of the shim is towards the front of the vehicle...you want the driveline to be relatively straight or inline. I had read a bunch about the fat part of the shim towards the shackle...so I did that first and made the problem worse. So...fat part on the rear axle towards the motor. Before and after pic:

 

[snaggletto]

With stock joints, the goal is not to point the pinion at the transfer case. It is to make the pinion flange and transfer output flange parallel. Run it how you want, but you had it right the first time.

 

[cruisermatt]

Just so you guys don't install it wrong like I did and have to redo it...here are some pictures. The fat part of the shim is towards the front of the vehicle...you want the driveline to be relatively straight or inline. I had read a bunch about the fat part of the shim towards the shackle...so I did that first and made the problem worse. So...fat part on the rear axle towards the motor. Before and after pic:
View attachment 2982744View attachment 2982745

Your driveshaft is completely out of phase which is much more likely the cause of any vibrations you may be having

 

[Brian/99uzj100]

Just so you guys don't install it wrong like I did and have to redo it...here are some pictures. The fat part of the shim is towards the front of the vehicle...you want the driveline to be relatively straight or inline. I had read a bunch about the fat part of the shim towards the shackle...so I did that first and made the problem worse. So...fat part on the rear axle towards the motor. Before and after pic:
View attachment 2982744

Hope this helps.

 

[Groucho263]

Well...I'll be...I only took that driveshaft off to measure the angle and marked it with white chalk to make sure I put it back on the same as I took off. The PO must have done that. Do I just unbolt, twist one of the ends of the driveshaft and rebolt?

 

[Brian/99uzj100]

Well...I'll be...I only took that driveshaft off to measure the angle and marked it with white chalk to make sure I put it back on the same as I took off. The PO must have done that. Do I just unbolt, twist one of the ends of the driveshaft and rebolt?

The driveshaft will slide apart at the sleeve yoke, it's splined.

I was going to tell you to flip your entire driveshaft front to back, because mine is the opposite. I looked at the driveshaft picture in the FSM and MINE is incorrect. It's only been that way for 20 years...sheesh.

 

[Brian/99uzj100]

@Groucho263 I forgot to mention it's a good time to clean and re-grease the sleeve and splines.

 

[Groucho263]

Thank you @Brian/99uzj100. Looks like I remove the axle side...pull the driveshaft apart, rotate 90 degrees then reinstall the sleeve. If I am a tooth or so off, will that affect it?

 

[Groucho263]

With stock joints, the goal is not to point the pinion at the transfer case. It is to make the pinion flange and transfer output flange parallel. Run it how you want, but you had it right the first time.

@snaggletto Now I'm more confused. When I had the shims with the fat part towards the shackle (pointing aft), the truck was almost not drivable because of the vibration...at like 5 mph (I didn't go faster than that). When I changed it to the current setup, the vibrations went away...there was a little vib, but based on the out of phase thing, it might be that. Not sure what is right now...

 

[fjc-man]

So, do the driveshaft correction first.

 

[pb4ugo]

Thank you @Brian/99uzj100. Looks like I remove the axle side...pull the driveshaft apart, rotate 90 degrees then reinstall the sleeve. If I am a tooth or so off, will that affect it?

Yes,