ScottishB: I haven't changed any of the control arms on the rear 4 link, and of course, the angle of the tranny hasn't changed. Should I start thinking about a double cardan shaft? I'd have to get shorter upper arms for the rear to point the diff up...

 

From what I've read, the double cardan is needed in that situation.

 

For either type of shaft, it needs to be properly aligned. The key to making the transition to a double cardan seems to be the overall shaft angle and length. I found on my '85 rear shaft that it was fine at stock length and 12 degrees, but when it was shortened for double cases and went up to ~15 degrees, it would not run smooth. So check the overall shaft/u-joint angle and if it is reasonable, then u-joints will work fine, given proper alignment. Not sure what angles you are running, you said it was checked but no particulars were posted. If the angles are too steep, then yes, a CV on the top end would help, *given* that you tip the pinion up in line with the shaft.

 

I just don't think it's that drastic of an angle. I'd take it to Driveline Service of Fresno to get checked, but they already said they wouldn't touch it 'cause of the rubber "balancer" that nobody seems to have heard of. Maybe I'll try another shop. Too bad. I've always heard solid reviews of them.

 

Seems that some makes of vehicles have harmonic/rubber type balancers on the drive shafts, but they seem to be external parts:


Wonder if the shop is thinking of the Toyota LWB pickups with the rubber-mounted center support bearing. Have they actually looked at the vehicle and shaft or did you just call/e-mail them?

 

The fellow from Drivelines laid under the truck. Said it was between the outer "shell" of the driveline and the core. Knowing little to nothing about it, I assumed he knew what he was talking about.

Question: If I threw the rear on jack stands and let it run in Drive, would I be able to visibly detect a driveline imbalance?

 

Alright, I put the rear end on the stands and let it spin. There's NO DOUBT that the vibration/rattle is coming from the forward ujoint. Give it a little gas with no resistance against it and it sounds awful.

 

What would the noise coming from the front ujoint (or possibly the new bearing the yoke sits in) indicate? Pinion angle?

 

Well, could be noise from the u-joint or it's bearings. Or it could be lack of alignment with the u-joint at the pinion end of the shaft. Both u-joints *must* be at the same angle for the shaft to run smooth. If the angles are different, you *will* get vibrations even with a perfectly balanced shaft due to the unequal velocity signatures of the two u-joints:
- http://www.4crawler.com/4x4/CheapTri...n-Measurements
Animation showing this below:
- http://www.4crawler.com/4x4/CheapTri...ies/ujoint.avi

Or the u-joint might be making noise because the slip yoke end inside the trans. is loose and letting it move around too much. Basically if there is any issue in the whole drive shaft system, it will show up at the weakest link in the system. So maybe the shaft is perfectly aligned, but not balanced; that vibration caused by the imbalance will show up someplace. Or a perfectly balanced shaft that is not aligned properly will vibrate and that will show up someplace. Or a perfectly balanced and aligned shaft that has a loose slip yoke or loose pinion flange will vibrate and that vibration will show up someplace.

I find loose vibrations tend to show up most as you back off the gas and are in that zone between acceleration and engine braking, where there is no load on the shaft and any looseness induced vibration will be apparent. Alignment vibration can often show up more or less under changes in throttle, so acceleration causing more vibration means the pinion angle is too high (pinion will tend to tip up under acceleration, even on a linked suspension like you have). Vibration under deceleration is a sign the pinion is too low. A linked suspension will have less angle change from acceleration than leaf springs, so you likely want to have a closer to ideal alignment than on a leaf sprung truck.

But with the drive shaft, you need to find out what is the cause of the vibration and fix the root cause. You might find a worn out u-joint and replace it only to find the vibes are still there. What that says is that something else is causing the vibes and the u-joint wearing out was simply a symptom of the vibration problem, basically it was the weakest link in the system and it wore out from the added stress of the vibes.

 

Thanks, Roger. I really appreciate the time and consideration you're putting in to this. I took your online advice and purchased the same angle finder you show on your website. Following the same article, I measured the two respective angles. As precise as I could get, I show between 9 and 10 degrees of angle at both ends of the shaft. When measuring, I noticed that the casing at the tip of the tranny, where the yoke plugs in to, was still pretty hot to the touch though it had been parked for some time. Feeling a bit further up the tranny casing, the temp was considerably cooler. This is leading me to believe that maybe there's something wrong with the bearing at the very tip of the tranny. Gonna get in touch with the shop that just changed that bearing and try to get it on a lift over there to witness what I'm seeing when it spins with no load/resistance. Again, thanks to all that have chimed in thus far. I'll be sure to post again when I'm done with this "chapter."

 

Basically a process of elimination to find the cause of the vibes. Sounds like the angles are indeed OK. And a bad output bearing might be the cause, not really familiar with the 2WD setup, but a loose bearing on the 4WD shaft can cause vibes as well. The thing to realize with drive shafts is that they always vibrate (unless the u-joints are exactly at 0 degrees). Normally you don't feel the vibes if everything is tight as the torsional flex in the shaft absorbs the vibrations, but have some weak point in the system and those vibrations can find another way out.

 

Ok, fellas, decided to do a little easy experimenting. To the naked eye, it looked like there might be more angle at the tranny output shaft than at the diff. Although I had checked with an angle finder, it still looked like it. Soooo.... I supported the rear axle on stands, supported the tranny with my floor jack and pulled the crossmember bolts. Lowered it about an inch, started it up, put it in Drive. LESS VIBRATIONS! Lowered just a tad more, VIBRATIONS GONE! Jacked it back up into original position, vibrations came back. In short, I'll be either spacing out the crossmember permanently or modding my tranny mount to sit lower. What do you think? I've just got washers in there now, need a more permanent solution either way.

 

Commonly done on the SWB Jeeps with lift kits. With the linked rear suspension and non-adjustable links, about the only way to change angles on the shaft. Many of the Jeep lift kits use spacers between the frame the the trans. cross member with longer bolts to lower it. With a 4WD, you would be making the front angles worse, but with 2WD, not a concern.

 

Sorry for the giant pics im barely getting the hang of posting pics like the first time learning how to drive stick. Anyway i took my drive line to get balanced and they said they couldnt balance it because of this dent. My question is are they exagerating and could this have a major affect like vibrations at 65-70mph Or this driveline still okay

 

Personally, I have had worse dents that didnt cause any noticeable issues when driving. But they may be saying either 1)We would rather balance a shaft that we put new tube, u-joints, etc onto so we can make more money and decrease chances of a comeback, OR 2)We literally can't balance it because its a bad dent.

Since its hard to tell the depth of the dent, it kinda looks like a scratch to me...

If you're around any other driveline shops, let them take a look and get some other opinions. If they all say they can't balance it, then let the first place retube/balance it. It's not crazy expensive I don't think. Cut the welds, new tube, re-weld, and balance. Providing all your u-joints are good.