How to install shims (already searched)

Just wanted to double-check that I am doing this proper. I've got the stock driveshaft with the 2" OME lift (which I've had nearly a year now) and I've had some very minor vibes on acceleration. I spotted some cheap (less than 10 bucks) shims and thought I'd give them a shot. My question is how do I want to install them? I want to rotate the pinion up, right? and to do this I want to put them fat-end towards the back in between the spring and the axle.

All my search came up with was discussions on CV and double-cardan joints. I know I could just put it in and see if it works and if not just switch it... but I hate having to do things more than once so rather than try to think it out I thought I'd ask. TIA.

pretty simple. you gotta pull undo the u-bolts that hold the leafs to the axle obviously. then take a C-clamp or two and clamp the springs so that when you remove the center pin they dont go everywhere, now slap the shim in thick side towards the assend of the jeep, reinstall center pin and put the rest of it back together.

Hunter

i wouln't use those cheapo shims. thet are aluminum and break easily after a little while. get some real steel shims that bolt in to a spring pack.

But with only a 2* shim, does it really matter? I thought it only really mattered if you had a large shim. I'm too broke to order "expensive" shims right now (the shims I got were free, I'm visiting my folks right now, and I was with my dad at a shop... so he paid for them ). These are aluminum, and the hole is too large to be used to attach them to the spring pack, without some work anyway, so are they really that bad?

"get some real steel shims that bolt in to a spring pack"

I second that!! One of mine did spit out, and it was pretty lucky findings that we spotted it before things got woggly for me on the ride home.

Doing the work correctly once in the driveway is way more better than fixing it on the trail.

STOP THE PRESSES

If these shims have too large a hole for the center bolt to capture it underneath the springpack and engage the hole in the spring pad, BAD THINGS will probably happen. If not as soon as you nail it, then about the first time you get on the binders hard. You will have an adjustable wheelbase Jeep!!!

Skip the thought of washers...get good steel shims and new center bolts to locate them.

I like Loctite Blue and lots of it.

Well, I misunderstood.... the hole is too large for the TOP bolt to capture it - it's the right size for the bolt at the bottom of the spring pack (which I couldn't see and forgot about, I assumed it was the same size). So it doesn't bolt in, but it is captured so that it can't move back and forth.

So I went ahead and installed it...took all of ten minutes. However, the pinion is now pointed perfectly at the t-case. The vibes seem to have only moved. Now they don't show up until I hit the thottle harder, but seem to be worse when that happens. Didn't take it to highway speeds.... so not sure about the deceleration vibes (seemed to only happen at high speeds.)

So what did I do wrong? I installed it fat-end back. Is the pinion supposed to be parallel to the t-case? Seems like that would only make the angle greater though....

I see I got here too late to express an opinion before the dirty deed was done, but I can always pile on ...

Aluminum shims are junk, and an accident waiting to happen. Now that you've satisfied yourself that they weren't the answer (the answer is an SYE), take them out and throw them in the trash before something bad happens.

If you are absolutely determined that you must run shims -- you should understand what they are trying to accomplish. The concept is that the operating angle of the front (transfer case) and rear (axle/pinion) u-joints should be the same, or within 1 degree of the same. The reason is to keep the u-joints "in phase." A double cardan joint has two u-joints in it, and they are automatically always in phase with each other -- which leaves the pinion u-joint always out of phase unless it has a zero operating angle. So with a double cardan joint you shim the axle to point the pinion parallel to the drive shaft.

If you still run a stock drive shaft with two single u-joints, what you should be doing is getting the pinion parallel to the transfer case output shft.

That's the theoretical ideal. In reality, under acceleration the pinion tends to "climb" the ring gear and make the pinion point up more than it does at rest. So in shimming the axle you might set the pinion to perhaps 1 degree below the transfer case angle, so that when the axle tips up under load they become parallel.

Well, I know a SYE would be best - and I will do that eventually. But for the moment, I am unemployed with few qualifications outside of my profession. I had to borrow money from my parents just to be able to afford gas to come visit. In other words, a SYE is near the bottom of my list. However, free shims that may save my u-joints are inticing. After a year of vibration I imagine they are getting a little worn, I can't afford for them to pop. That and I just got tired of the vibration. So that's why....

Now, the problem with aluminum shims. The problem is that they may crack, yes? Now, this is because aluminum has a lower fatigue strength than steel, yes? So how long do they last? If they do break, what happens? I guess I just thought that a 2* shim wasn't enough to be a big deal.

Now, the problem I have now is that the pinion is too high - but it was too high to begin with. So I want to turn the shim around to get rid of the vibes. If for no other reason than to determine that the shim will or will not solve the problem (I bet I could convince my dad to pay for a "real" shim ). Is that right?

EDIT: btw - I thought aluminum would be alright for a 2* because rubicon express' sells aluminum 2*, but everything larger is steel.

The only bolts that really matter here are the ones that are holding the leafpack together...Round headed, with the shim on bottom...fat side back.

and the (four) big U-Bolts that hold the axle tight to the axle. There will be the plate atop that, with a centered hole that allows the spring bolt/washer/nut to pass through... a lockwasher is OK on this and... the center bolts ought to fit pretty tight in the hole through the springs...but no washers on the spring bole sandwiching the top plate to the leafs.

A washer below the U-Bolt nuts is OK though

:dunno: smart/verbal folks feel free to bail me out if this isn't clear?

Has everyone forgotten that he does not have a double-cardan u-joint? You only rotate the pinion up if you have a double-cardan because the drive shaft does not experience acceleration and deceleration that a single u-joint equipped shaft does. The u-joint at the pinion does not have to cancel out the speed changes in a double-cardan u-joint system so it needs to be pointed directly in line with the u-joint. When adding lift to a stock driveshaft equipped XJ, you need to rotate the pinion down and make the u-joint at the pinion about 1* less than the angle at the t-case. IE: if your t-case u-joint is 135*, your pinion u-joint should be about 134*. The 1* is to take up for spring wrap when under power, because you pinion moves upward as you accelerate.

Steve

Apologesia

Didn't read the specs on your rig (and process the info effectively) it's a '00 XJ with a 2" OME...and I am way out of element advising on one of those...

except since you have done the axle shimming and if you want the pinion down, put the fat side forward.

If I had vibes in a LP 30, I'd pull the front shaft out (4-1/2" or 13mm at the tcase and 4-5/16" or 8mm at the pinion) and drive it. If the problems subsist, go further, but if they dissapear...

The vibes don't seem related to the front driveshaft. For clarification: I have no vibes at any certain speed. It is under acceleration at low speed and deceleration at high speed. About a year ago when I first posted about this, I was told all I would need was a little shim to fix it - but I never got around to doing it because it was so minor. I probably would not have bothered except I saw an opportunity for free shims! When you're a moocher like me, you begin to spot these opportunities.... maybe someday I'll have a real job again and won't have to worry about 30 bucks to properly fix something...

thanks for putting up with me. I'll turn it around tommorrow morning at see if it works. I looked around the net, and I couldn't find anyone that sold steel 2* shims. Rocky Road would make custom sizes for 40 bucks though, and although the ad seemed to indicate sizes from 3*-7* only, I can't imagine they wouldn't make a 2* shim...? Of course, that's still 40 bucks less than I have...

First,fat end forward is very typical for a single joint shaft(especially shackle lifts).
Second,there is "no" substitute for measuring.
Third,I agree with Woody(check the front shaft,mine's junk,only 17k miles).
Fourth,been there done that.

Willis said:

Has everyone forgotten that he does not have a double-cardan u-joint? You only rotate the pinion up if you have a double-cardan because the drive shaft does not experience acceleration and deceleration that a single u-joint equipped shaft does. The u-joint at the pinion does not have to cancel out the speed changes in a double-cardan u-joint system so it needs to be pointed directly in line with the u-joint. When adding lift to a stock driveshaft equipped XJ, you need to rotate the pinion down and make the u-joint at the pinion about 1* less than the angle at the t-case. IE: if your t-case u-joint is 135*, your pinion u-joint should be about 134*. The 1* is to take up for spring wrap when under power, because you pinion moves upward as you accelerate.

Steve

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Thank you. I thought I said that, but I guess I wasn't clear enough in my explanation.

An update, and more questions...

So I switched them around this morning so that the shims rotated the pinion down. However, the pinion is still pointed up at a slight angle. I don't have an angle finder - but my eye tells me it's only a few degrees, for whatever that is worth. At any rate, the vibes are better than they were with the shims the other way - but they are only marginally better than they were before I put in any shim. It doesn't vibrate under deceleration now, and it takes a little more throttle to get it to vibe - but it does nonetheless.

Concerning the front driveshaft, that couldn't be the problem because it only vibes under throttle in 2wd (well, it might in 4wd as well, but I've never noticed) - and since the front driveshaft isn't receiving any torque in 2wd, it wouldn't vibe under accel and not under speed....right?

Of course, it is possible that something else is causing the problem - but it very much feels like a driveline vibration to me. If it's supposed to be paralell to each other - then I need a larger degree shim, right? But doesn't 4 or 5 degrees sound a little high for such a modest lift?

Now, last question, what about a t-case drop? I know that I would lose ground clearance I can't afford to lose... but what if I got a t-case crossmember with a built-in drop that does not sacrifice clearence? (like rusty's) Does that cause any other problems? Would that fix the vibes, or even let me go a little higher in the future (by a little I mean 3/4" or so with a spacer and a shackle)?

Obviously, it will be a little while before I could afford even this option - but it is alot cheaper than a full SYE and CV driveshaft - and my crossmember is starting to get a little beat up anyway... does anybody have experience with this option?

So when I go to install the tapered 2.5" blocks from RE that I just ordered I should put the fat end towards the front because I have a stock driveshaft?

Drewlee77 said:

So what did I do wrong?

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You didn't measure your angles. You can dance around this all day and maybe never solve your problems.

The only advise you should be getting here is:

"Sorry, I can't help you without knowing what your angles are."

Your u-joint angles may be fine. The lack of a SYE may be the problem. Sure, you can't afford one right now, but measuring the angles will tell you whether or not you should be saving for one or messing with shims or drop kits or ...

OK, I tried my best to measure my angles... but since all I have is a tape measure and a calculator, I'd say my margin of error is around 1*....
My driveshaft is at a 14* angle while the pinion is at a 3* angle. This is with the 2* shim rotating the pinion down. So, I'd have to use a 6* shim to properly angle the pinion, but this would place my driveshaft at an 18* angle, right? Which is well beyond the 15* maximum suggested by Tom Woods (I did some reading and I think I understand why I need the pinion and tcase parallel) A 1" t-case drop would put my driveshaft somewhere in the neighborhood of 12* and send the pinion down a little... so perhaps a 3* or 4* shim and a t-case drop would be enough for now if I managed it...

A shackle lift would rotate the pinion further up and make things worse though... so I'd be stuck until I got a SYE, eh?

What I don't understand is how I could have perfect u-joint angles and still need a slip-yoke. I thought that the problem with the slip-yoke was that it shortened the driveshaft and made for worse angles.

Drewlee77 said:

OK, I tried my best to measure my angles... but since all I have is a tape measure and a calculator, I'd say my margin of error is around 1*....
My driveshaft is at a 14* angle while the pinion is at a 3* angle. This is with the 2* shim rotating the pinion down. So, I'd have to use a 6* shim to properly angle the pinion, but this would place my driveshaft at an 18* angle, right? Which is well beyond the 15* maximum suggested by Tom Woods (I did some reading and I think I understand why I need the pinion and tcase parallel) A 1" t-case drop would put my driveshaft somewhere in the neighborhood of 12* and send the pinion down a little... so perhaps a 3* or 4* shim and a t-case drop would be enough for now if I managed it...

A shackle lift would rotate the pinion further up and make things worse though... so I'd be stuck until I got a SYE, eh?

What I don't understand is how I could have perfect u-joint angles and still need a slip-yoke. I thought that the problem with the slip-yoke was that it shortened the driveshaft and made for worse angles.

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Trying your best would be plunking down $10.00 for a cheap angle finder and measuring your angles..

Your numbers don't ring true, but based on what you said, it sounds like you'd be better off without any shims. Your assumptions don't add up. You've yet to mention your output shaft angle. A t-case drop would not send the pinion down a little, or any at all.

Get an angle finder. Buy one. Borrow one. Make one.

Measure your angles.