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Shims questions (newbie didn't do enough research)

822 views 6 replies 4 participants last post by  CrawlingForward 
#1 ·
Installed a BDS 2" plus 1" shackle lift on Saturday.

Ended up adding shims, not because I knew about pinion angles needed for my just-ordered SYE, but rather it was to keep the centering pin from bottoming out on the axle.

Here's where you get to point and laugh:

We needed them quickly, so I got them from the only auto store around where I was working: Pep Boys.

So now I have (2) 2* cast aluminum shims stacked on each leaf (for a total of 4* upward pinion angle change).

.....turns out that's not a good permanent solution, huh. :facepalm:

Keeping in mind that I'm in New England with salt, how long do you thing this solution is going to last before it bites me in the ***? A couple years? Months? Weeks, ha ha?

Also, when they do finally fail (even if it's tomorrow), I'm going to need to replace the u-bolts as well now that they've been torqued down, correct?

This is why we do things right the *first* time people. :brickwall


Lastly, we didn't get a chance to put in the t-case drop (I'm installing the SYE/CVDS soon anyhow) and going over 30mph felt like going over rumble strips (it was a fun 20 mile drive home on the highway with hazards flashing the entire way). I know shims don't help stock driveshafts, but could they actually make it worse? Just curious.
 
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#2 ·
Where to begin :(. First, shims will affect both CV and non CV drive line systems. The two systems have different angle requirements but improper angles on either type will cause drive line vibrations. CV systems require that the axle pinion be angled directly to the transfer case output yolk while on a non CV system the axle pinion yolk and the transfer case output yolk need to be parallel. The following diagrams were borrowed from Tom Woods drive shaft web site, an excellent source of drive shaft into.



It sounds like you have your pinion pointed too far upward toward the transfer case and that is causing the vibes. A shackle lift will will move the pinion up and then 4* of shims moves it further up. Check your angles.

Aluminum shims also have a nasty reputation for splitting at the centering pin hole. I recommend that if you really need shims to get some made of steel as soon as possible. If the centering pin is too long either grind it down or buy a shorter centering pin.

I hope that helps some. Good luck.
 
#3 ·
A shackle lift will will move the pinion up and then 4* of shims moves it further up. Check your angles.

I hope that helps some. Good luck.
Ah, that is new information to me!

Yeah, I've read through the whole 4xshaft.com information shortly after posting this and it said that torsional stresses also occur when pinion angle isn't parallel with output on stock shafts, so I'm sure that is a large factor in my current vibes.

The good news is that the plan was always to get an SYE and DC DV. I actually just ordered it from Tom Woods and it should be here next week. The Jeep is off the road and will just limp down the street to get the work done when the time comes. A bit of research suggests that the pinion typically needs to go up 4-6* with my life, so the current shims and shackles should put me right in that area when everything is changed over, but I'll obviously have to check it when the time comes and fine-tune.

In terms of the aluminum shims, I would not have been able to limp home without them, so they've served a purpose at least. What safety concerns are there in terms of them breaking? (Aka, wait until I see cracks or replace *immediately*?)

Thanks for the answers!
 
#4 ·
I personally have not used aluminum shims but do know that when they crack they can work themselves out and cause the axle to be loose on the spring. Is there an immediate concern? I don't know but would think they would hold up for at least a little while. If it were my jeep I would remove them as soon as I could get to it but I wouldn't do it in a panic. Others may have a different opinion.
 
#5 ·
my shims were aluminium, lasted till I swaped them out almost 5 years. no problems, swapped them due to the SOA...

as for vibrations with only that much lift AND A tcase drop you should have NONE, something else may be going on..... I used 2.5 OME springs and same shackle lift and had NO problems on mine before hte SOA... i used the tcase drop but did not really need it... I thinking hte shims are to mcuh and THAT is causeing the vibration NOT the angle from the tcase
 
#6 ·
You've really got to check your angles to see what's going on. My gues is that you probably did not need shims except for the pin problem you mention. When you shimmed it made issues worse that what they would have been. THe other thing is that you said you did not do the TC drop. you shaft could be a too much of an angle and your just binding. My BDS was slightly over 2.5 when I first put it on. Couple that with a 1" shackle and you might need the TC drop. Again check you angles.......

Of course if you're getting a SYE and DS then just wait and do it once, the right way this time :)

-jeff b.
 
#7 ·
Yeah, further research is suggesting that a 1" shackle lift generally contributes 1.5 - 2* on pinion angle. Combine that with the 4* shims we used to keep the locator pin from bottoming out and we're looking at a possible 6* pinion angle change (13* total?)

That's a *lot* for a stock driveshaft to handle at that steep an angle, so it's pretty reasonable to assume that's my issue.

It's off the road until the SYE gets put in, and I just looked at my angles and, while I still need to measure, it looks like my pinion angle is juuuust about right for SYE.

So end conclusion I think is:
1) Install SYE
2) If that cures vibes and the angles are right, then I'll leave the aluminum shims for a bit (a year, max) until I get a chance to replace them
3) If my angle is not correct, then I'll replace the shims with proper angle steel ones (and new u-bolts) this spring and make sure the job is done right this time. :cheers2:

Anyone see any major issues with that plan?

Thanks everyone for the insights. Really appreciate it!
 
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