Shop can't balance drive shaft

I have an 87 Dakota with a two-piece driveshaft, bought it new. A couple months ago at 140,000 miles there came a chirping noise from the rear at acceleration from a stop. I changed the u-joints with new Moogs and had a new center support bearing pressed on at a driveline shop. Reinalled driveshaft same as it cam out. The u-joint at the diff was shot, the other two not far behind. The chirping vanished as expected, but was replaced with a slight vibration felt in the seat starting at 50-55 mph. I dropped the truck off at the driveline shop to get the driveshaft balanced. They put it on the balancer and called to say they couldn’t balance it, the indicator kept jumping around and wouldn’t stabilize. I asked them to reinstall it and came to pick get the truck. The guy who worked on it said that this was usually a u-joint problem. I asked what brand they used and pulled he out a Neapco u-joint box and said they use them exclusively and have never had any problems. I ordered Neapcos from RockAuto. Will replace the Moogs and see what happens. After they reinstalled the shaft I drove in the freeway and it acted exactly the same.

I was very careful when pressing out the old joints not to stress any of the yokes, applying pressure to the u-joint members at right angles to the cap being pressed out and not to the cap 180 degrees opposite. When installing the new joints, after inserting the clips (interior) I pressed all clips snug against the yoke. The joints all moved freely in all directions. Again, the shaft was replaced exactly as it came out.

Does anyone have any insight into what exactly would cause the indicator on a balancing machine not to stabilize?

When U-joints cause vibration they are usually totally shot on at least one cup. Is there any lateral free play of the cross in the cups? And are you certain that no needles were dropped during assembly?

Off center shaft will cause this. New drive shafts are made all the time but before you get one, try something with a big hammer. I have other dumb ideas involving big muffler clamps but nothing that should work in this universe. Next up is a random balance weight held on with duct tape and moved about until a semi-solution is found. Then you have it welded on. After the collateral damage lawsuits are settled you can be a happy driver again.

I’m going out now to check for lateral movement between the body and cups. That was my first suspicion

All three u-joints appear tight with no play, none that I could discern. The center support bearing has slots where the bolts fasten it to the frame with about 1/4 inch of play. I marked the extremes and tightened it in the middle. No change. The only thing left to try is to tighten it at either extreme. I doubt this will have any remediable effect as I’m sure they tried that at the driveline shop on the balancing machine. Looks like I have no option but to drop the driveshaft and try the Neapco u-joints when they get here on Friday.

I ran into something like this recently on my daughter’s '05 Mustang. During routine maintenance I noted the front joint was just a tiny bit loose so I replaced both joints with Precision brand from O’Reillys. (MOOGs not available)

After that the car was shaking itself so badly it was undriveable except at a crawl. A recheck showed everything tight, lined up as removed, no clips missing, etc.

A large driveline shop thought it was shaft imbalance but there was no shaking before. Once the shaft was removed the first question he asked was whether or not those joints were Precision from O’Reillys. Yes. Well, they’re junk; take them back and get your money back because we’ve seen this a lot he says.

So while I waited they installed a pair of new Spicers and smooth as silk ever since. The only reason I didn’t install Spicers in the first place was simply because (at the time) I could not find a local parts house that carried them.

ok4450, I thought the Moogs would be the best option for this truck. Maybe they are just not a good match. I will be getting the Neapcos on Friday and will report back with the results.

Did you place witness marks on everything showing the orientation of how it all fits together? And how it matches up with the transmission or xfer case output fitting and the differential input fitting? Before removing the driveshaft and replacing the u-joint? If not, one idea anyway, you may have put it back on the car with the wrong orientation. At least with my Ford truck there’s more than one orientation possible to install the drive shaft. If nothing else seems to work, you may have to try each possible orientation until you find one that works.

GeorgeSanJose, yes I placed witness marks. The center spline on this two-piece driveshaft is keyed so impossible to screw that up. The driveline shop tried to balance it off the truck and they could not get the balance indicator to stabilize so the problem is not at the pinion end or the transmission end. The only thing different is the u-joints.

Take it for what its worth and I don’t have much experience but twice I’ve had a problem with Moog. I know they are supposed to be good but I had a tie rod that snapped right at the casting that was only a year old. I also had a ball joint that was shot in a couple months and got my money back on that one. So just saying replacing them is a reasonable thing to do at this point.

Maybe just re-do all the u-joints is the best plan. Since the only difference is the u-joints. It doesn’t cost or take that much time to replace them all. I’ve done u-joint replacements on my Ford truck’s rear drive shaft several times over the years. As I recall it has 2 u-joints on the transfer case side, and two on the differential side. The double u-joint arrangement is a sort of poor man’s constant velocity joint. That’s needed b/c of the angles, there’s quite a drop in elevation from the transfer case to the differential, something associated with Ford 9 inch differentials. The input flange is down quite low to the ground on those. It is a two-part drive shaft like yours, splined in between. A free floating unit, there’s nothing supporting it in the center.

To replace the u joint, I just use an appropriate size socket and a hammer to pound them in and out, not even a press. I purchased my replacement u-joints at NAPA, and asked they give me the best quality brand they offered. I think it was a NAPA branded u-joint I ended up with in fact. The first set they gave me didn’t work out so well. It was obvious once I had it sitting on the floor next to the driveshaft, it didn’t fit. That was b/c they gave me the wrong part number … lol … a quick return to NAPA for an exchange and I was in business.

A couple of fine points on u-joint replacement: Make sure it is exactly centered in the yoke, by comparing the clearance on one side compared to the other. And be really careful to double-check the needle bearings in the end cylinders don’t move out of position and get all skewampus in the process of doing the install. It’s very easy for that to happen. Best of luck.

I really appreciate all you guy’s input. I have some things to try tomorrow. I will report the results.

GeorgeSanJose, I will try what I can while I wait for the Neapcos to arrive sometime tomorrow. here is my list:

  1. Rotate the shaft 180º at the pinion, inspect needles bearings in the two free caps
  2. Smack each u-joint cap with a hammer and socket to eliminate any play
  3. Isolate the metal frame of the center support bearing from the truck frame with rubber bushings
  4. Stick pins in a voodoo doll shaped like a u-joint

When I pressed in the new Moogs I made sure they all moved freely by pressing on the two pins of the body that were 90º to the cap being pressed outward. This pushed the circlip in the groove of the cap against the machined face of the yoke. I had to do this to get the joints to pivot freely after pressing them in. The way I pressed the old joints out and the new ones in, it was impossible to stress the yoke. I didn’t want to risk deforming anything.

As soon as I finish this mug of hot tea, I’m out there.

Smacking u-joint caps with a socket and hammer to eliminate any play - no effect
Isolating the metal frame of support bearing from the truck frame with rubber - no effect
Rotate the shaft 180º at the pinion - seemed to be less vibration

BUT… I was able to eliminate the vibration by moving the center support bearing to one extreme of the allowable range of the bolt slots. First I put it to the drivers side extreme and the vibration got noticeable worse. I moved it to the other extreme and the vibration was gone. The allowable range is no more than 1/4 inch. I’m going back under with a 5 point laser level and a plumb bob to see if the center support bearing is in line with the drive shaft at the pinion end and the tranny end.

While under the truck with the laser level and plumb bob and finding out that the two piece drive shaft was not in a perfectly straight line, I recall reading that it is not important for DS to be in a straight line, only that the pinion shaft and the transmission shaft are parallel. At this point, I don’t care much what the theory is, only that the vibration is gone. Hallelujah.

Good for you. Have another tea or better.

Wow! That Was Easy, Eh? :wink:

It’s beer time now, Bing. All things in their time.

Too easy, CSA. I get suspicious when things are too easy.

I had a carrier bearing that just started to chirp once, and u joints, but they usually had a clunk first.

if you had this since new, I d be curious as to how many times you ve had to do the u joints and carrier bearing…

I ve had a couple of 75 fords with the two piece shaft and carrier bearing and I ve changed a fair number of u joints and one carrier bearing. I learned quickly to change all three u joints if one went bad…

I ve never had a problem afterwards tho, and I m pretty sure that I put the rear shaft back on in a different position once…, or maybe twice.

probably the u joints

but is there any chance it s a brake shoe rubbing?

or the rear?

It sounds like the shop didn’t mount the driveshaft correctly, when they were trying to balance it

Sounds like a very basic mistake, maybe even a beginner’s mistake