Front driveshaft angles issue - ‘12 2500

[FishinGuns]

I need some help gurus. It’s getting cold and snowy and I go to use my 4WD modes on my 2012 2500 Suburban and I’m vibrating a noticeable bit in 4 Auto (and 4 High) at highway speeds. More than I ever noticed in my 2011 Silverado 1500, I had previously.

I go to the local drivetrain shop thinking I probably need a double cardan joint front driveshaft. Most 4” lifts have that option, and I’m on a Skyjacker 3” lift with new knuckles and lower control arm drop brackets, diff drop, etc.

The shop (reputable) measures the angles of my front driveshaft and my front diff pinion angle is +3.3 degrees and my t-case front output is +4.4 degrees. I’m no drive line expert, but that’s my problem right there. Can’t disagree with their diagnosis.

Has anyone shimmed the front diff on an IFS? Can I custom cut axle shims on my trans crossmember?

Shop thought I’d be fine to drive it as-is, but if it can be done, I’d rather get’er in line.

Starting to figure out why nobody does this Skyjacker 3” lift…

 

[1stDeuce]

Man, I really like the engineering in that Skyjacker 3" lift, so I'm sorry to hear that it's causing you issues...

If I understand correctly, your u-joint angles are within 1.1° of each other, and the overall angles are not bad for a short driveshaft like the front... I would not expect much of a vibration issue with the angles you are reporting... I don't think shimming down the t-case will fix it, as the angle at the transfer case won't change much while the angle at the pinion will decrease. That makes the angle difference greater, which is not good. While rotating the pinion up will decrease both angles, it will take more angle out of the pinion end, which isn't too bad anyway. This would also make the difference in angles greater, which is no good. You could add angle at the differential end, which would match the angles, but being that you're only different by 1.1°, and you would be adding angle to both ends till they match, the resulting ~5° that you'd end up with at each end would seem to also be directionally wrong...

If I recall correctly, the slip yoke is part of the front t-case output on trucks with the magna transfer cases, so you can't have a driveshaft that's been assembled out of phase.

You may actually have a driveshaft that's out of balance a bit. The first thing I would try is to remove the front u-joint from the differential pinion yoke and re-install it 180° rotated. That may make enough balance difference to make the vibration go away. I have a truck that got new u-joints, and doing that at the rear pinion resolved a vibration issue I was feeling at 60+ MPH.

You may also want to remove the shaft completely while you're messing with it a do a good inspection of the u-joints themselves. One that's starting to fail can bind, which will cause a vibration. Given that the front driveshaft often spends months without turning, it would make sense that a u-joint that was a bit rusty inside for any reason couild start to lock up and lead to a vibration. You might even be able to feel it as varying resistance when you spin the driveshaft by hand in 2wd.

Good luck!!

 

[1stDeuce]

To be clear, if the angles you quoted were the u-joint angles, not the pinion and t-case angles, you do not have an angle problem so far as I can tell... Even Spicer's calculator torsional analysis calculator says you're good up to about 3200 driveshaft RPM, which is probably in the realm of 70mph. My experience has been that you're good quite a bit higher than the analysis would suggest, which should have you clear 4000 driveshaft rpm without issue. That's probably 85mph or so...




IF you were giving the angle of the pinion, and the angle of the t-case, not the angle that the u-joints are seeing, then the u-joint angles would be several degrees greater, which could start to cause issues with inertial effects...
Shimming is not going to fix that, as you're not going to shim much angle out of both ends. Shimming the differential to have more angle so they match will cause even higher angles at both ends, resulting in much greater inertial effects, and vibration from that...

If it's not balance or u-joints, my advice is to simply shift out of 4wd modes at higher speeds. This would not be uncommon advice for higher lift amounts on most vehicles... Driveshafts with high U-joint angles at both ends simply don't like to spin fast due to the torsional effects they generate...

I'd still be looking for an issue with the balance or u-joints as the primary cause.

 

[NatersXJ6]

Did you adjust your driveshaft length when lifting? If your slip yoke is pulled too far out for solid engagement you could have wear or wobble there causing an noticeable vibration as well. Same goes for a mid-shaft slip joint, although as stated above, your is likely a slip yoke.

 

[FishinGuns]

I’m 99% sure they quoted me the t-case and pinion angles and not the u joints angles. They told me it was crashing with both angles pointing up (I understood them as the t-case output and the front pinion “output,” if you will).

I did crawl under it last night to look if shimming would even be possible, and I’m not seeing how I could even correct the front pinion without major custom bracketry work. I did notice what I thought may be some play at either the t-case output yoke (there’s a boot on it) or that u-joint at the yoke. Should there be some movement there if I push up at the u joint? I pushed at the pinion end u joint, there’s no play at all.

Im wondering if I have a failing u joint now that you guys pointed all that out. Compounded by the odd angles at this point as well.

I did run the 4WD on trip up north April 1 last spring that I recall hearing some vibes, but just chalked it up to the new-to-me 3/4 ton drivetrain. Could have been that u joint starting to go, in hindsight. I’ll see about pulling the front drive shaft tonight and checking it out more (marking it first, for reference). The front t-case output yoke (is it a slip yoke with a boot?), is there a range of engagement I can measure with a tape measure while I’m under there?

 

[ramblinChet]

Driveshaft vibrations are always fun to chase down. I guess a few of the questions I might have first off are what gear ratio and tire size does your vehicle have. As @1stDeuce pointed out above driveshaft vibrations are related to RPM and higher gear ratios invite vibration problems.

When discussing measurements there are two additional considerations that are easy to overlook. One - in many lifted vehicles you must calculate using compound angles at both ends since many times the front axle is offset laterally post-lift. This is most apparent on solid axle vehicles with lateral track bars but there is no harm in taking this measurement to verify the joints are aligned in this plane. Two - worn bushings can permit the axle to rotate an excessive amount under load thus increasing the angles. This is easy to visualize when you imagine a rear driveline under hard acceleration as the pinion wants to "climb" as the wheels rotate in the opposite direction. On lifted Jeeps we intentionally set the pinion low while static so it comes up into the proper while dynamic.

My suggestion is for you to contact the lift kit manufacturer and ask for a copy of the suspension installation directions and make sure everything is in proper order. They may have recommended a longer driveshaft, installation of shims, etc. If everything looks to be in agreement with the instructions I would then begin hunting down where the vibration is actually coming from. Right now it seems like we are all guessing it originates from the front driveshaft. You still have axle bearings, axle shafts, pinion bearings, etc.

Good luck and keep us posted.

 

[FishinGuns]

Also good points! My diff was moved laterally to the passenger side 5/8” because that’s how thick the CV Axle spacer on the driver side is. There is no spacer on the passenger side. Bushings seems decent to me, I had approx. 50,000 miles on the odometer when we installed the lift. I’m at 57,000 now.
We did install with Skyjacker’s instructions printed out and we referenced it quite a bit. I did call them first and got absolutely no where. I bought a lift for a 2500 truck knowing there would be some differences, but I knew the front end and front frame was the same. What I ended up figuring out, is the torsion bar crossmember is hung from the top of the frame on a 2500 Suburban, and can articulate (swing) a bit. Truck cross members are riveted to the bottom of the frame. I had to buy a truck torsion bar cross member and drill holes in my frame. Worked out fine, surprisingly, with my luck! Regardless, Skyjacker Tech Support doesn’t care in the least about this since I put a truck lift on a Suburban… and they haven’t done that. Click.

They’re great…

So, I did verify last night that my diff spacers were installed per their instructions. They did not mention a longer drive shaft or shims in the least. A longer drive shaft sure makes logical sense to me, though. My t-case was not essentially dropped. The trans crossmember was dropped to make room for the torsion bars that got dropped, but the trans/t-case had spacers to put it back up in the same spot. So, my t-case output didn’t drop, but my diff did, and it moved laterally 5/8”. Probably working against me in my situation as well.

I’m factory 3.73 gears and 255/80R17 Toyo AT III’s (33x10). If anything the driveshaft revolutions should have decreased, right?

I plan to pull the driveshaft tomorrow after work and start checking that thing out. I figure I should measure length while it’s out to determine if I need it lengthened. I’m assuming I should try to push the yoke into the t-case as much as possible and then measure. What parts of the yoke is it preferred to measure from for driveshaft length?

 

[1stDeuce]

Actually, your front diff was moved to the side 5/16", not 5/8". The spacer has to be double the offset because they're making up the extra width on one side only. 5/16" is not enough to mess with anything. At 5/16, you added less than half a degree to the overall operating angle of both u-joints.

You really shouldn't need a longer driveshaft either. I doubt the driveshaft needed to be more than 1/2" longer to reach the diff in it's new location, and there's plenty of travel in the slip to handle that.

Bigger tires slow driveshaft speeds for a given vehicle speed. 3.73's would also lower driveline speeds compared to 4:10's. (I'm still bummed that they went to 3.73's standard when the 6L90E came out... Our '09 would be a much better truck with 4:10's)

Driveshaft length matters not, only spline engagement at the slip. You should have at least 2" of engagement IMO. I think a stock truck has about 1" of travel in the slip before the shaft bottoms out. I'd probably see where you are in terms of that. If you have more than 1.5" or so, then a slightly longer driveshaft might be in order, but that's not going to do much for anything IMO. I'd guess it's fine, since there's nothing in the instructions about lengthening the driveshaft, and your driveshaft would be no different than the one on a 2500 pickup that the lift was designed for.

You will probably get a little more NVH through the solid mounted torsion bar crossmember, but not so much that it would be really obvious. The isolated crossmember was to make the suburbans and Tahoe's feel less like a truck...

Do pull the driveshaft out, and mark the diff end. That way if you find nothing wrong, you can put it back in the opposite orientation and see if that helps.
Let us know what you find!!

 

[FishinGuns]

I appreciate your knowledge very much! Will report back soon.

 

[FishinGuns]

Got the drive shaft out in time help put the rug rats to bed. Win.

Marked it up first. Took some pictures. Short video of the play I noticed previously. It may just be the slight play in the slip yoke, I don’t really know to be honest. Tried to upload but 15sec. was too big. I could take one hand and essentially rattle it back and forth. Feels like it’s at the u joint, but I know it could be the yoke too.

The u joints seem to move fine with the DS free from the Suburban. I’ll try to slip out tomorrow and take to a driveshaft shop here in SE MI.

There’s close to 3” engagement of the splines of the slip yoke into the t-case, so I’m doubting that’s much of an issue. Looks like I’m missing the rear-most boot retainer though. I’ll find one of those while I’m out.

 

[1stDeuce]

The third picture appears to show the plastic starting to ooze out of the yoke ear on the slip end of the shaft. Those should look like the rest, not stick out like that... That is usually a sign of excessive heat. Does that U-joint feel tight or notchy? If so, replacing that u-joint would be the next step. (May as well do them both, as that's obviously not a desert truck...)

Everything else looks good. The slip boot on my stock 2009 2500 looks to be extended almost identical to that, so I'd say your driveshaft length is fine. Most of them are missing the clamp at the back, as it has to be removed to remove the driveshaft, and nobody puts a new clip on. I have a long zip tie double wrapped on my truck presently and it seems to work fine. It at least provides some peace of mind that less grunge is getting in. Put some moly grease on the splines when you re-assemble.

If you think everything checks out ok, then re-assemble the front yoke opposite your marks. I never believed that should make a difference, but as I said above, I had a truck where it did, so its worth trying...

If all else fails, it might be worth jacking up the back of the truck, placing the axle on stands, unplugging the front axle 4wd actuator while in 2wd, and running the truck in 4wd to actually watch the driveshaft spin slowly to ensure it's not bent. If that reveals nothing, you could run it up to 60mph or so to see if you can see anything out of sorts.

 

[FishinGuns]

I have a good DS shop down the road at work. Dropped it off this morning to have them check balance. They thought it would be worth while to replace the same joint you mentioned. I told them I don’t have a press, just do them both.

I’m going to reinstall after I get it back, both ways to test. Just to learn it, if anything. They were thinking maybe this afternoon or Monday.

 

[FishinGuns]

Alright, driveshaft shop calls and tells me, u-joints we’re getting there, but weren’t bad enough to cause vibration. Driveshaft itself was way out. 30+ thou on one end and was worse than that on the other! Lols!! They could try to repair it or I could buy a new one. Easy decision since I walked out of there with a new one for $159!

Got home after work, greased the new splines, and got her in there. Toight like a tiger… Test drove it, slightly better, definitely no vibes in 2WD now, she still vibrates pretty good above 65mph. Under 65, it’s no worse than my XJ. I don’t need to run auto or 4 high above 65, so I’ll be happy with it. While I was wrestling under there, I really can’t see how correct both up angles of the t-case output and pinion. Maybe could get 1-2 degrees out of each if I was really lucky, but I’d have to tear it half apart, so I’d definitely want to do it on a lift. But it’s still a big if…

At 58,000 could it be the diff mounts, trans mount, maybe engine mounts breaking down too much?

I’m thinking back to the only time I used 4WD before the lift was Up North at the beginning of April. I recall some vibes then, same as I have now under 65, so I think it was there before I did anything. I didn’t really think to put it through it paces at higher speeds then. Wished I would have now, to better compare.

Another thought I had, is there bearings at the front t-case output that are shot from the original driveshaft being that wonky?