Driveline or Torque Converter?
 

Just replaced the rear main seal in '93 940 turbo wagon. While trans was out, replaced seals & transmission mount; U-joints & center-bearing with shock mount. Also put in rebuilt torque converter, just because it was "never going to be easier" which has lead to my dilemma. I now have a serious vibration starting at about 25 mph.

While driving @ 50 mph, I've shifted into neutral and vibration is still present, only intensity changes not the frequency. When I rev the engine or when I shut engine off vibration doesn't change. This seems to indicate problem is not TC. The only other test I can do is the "stationery in-gear-foot-on-brake acceleration (got it up to 2500 rpms) and that doesn't create the vibration.

The machine shop that pressed in the u-joints & bearing says there's no indication of missing weights or damaged shafts. Could it be that the old, deteriorating bearing shock mount was absorbing effect of an out of balance shaft?

I'm in a real quandry but REALLY don't want to pull that tranny again for no reason at all. TD

did you mark the drive shaft and reassemble it in the same orientation?

its phased and balanced as it came from the factory. if you assemble it in a different orientation, it WILL vibrate.

I marked the sliding spline on both half shafts in the middle and the machine shop says they marked the yokes when they installed the new u-joints. If they messed up, does that mean sending the whole shaft to a driveline shop for re-balancing?

I hope you are agreeing that it's probably not the torque converter? TD

the torque converter is still spinning in neutral, and is driven at engine RPM, not road speed, so yeah, I don't think its the TC.

You just lifted my spirits out of the pits! That all makes sense. Could it be that the flanges where the drive shaft bolts to the output of the trans and/or the differential are 180 degrees off? I didn't mark those when I removed the shaft because I didn't think they were clocked. If the clocking of the flanges isn't the culprit, I guess it's back to the machine shop and if they insist it can't be their fault, it's off to the driveline shop? TD

I don't think the flanges at either end are 'clocked'.

maybe put the back end of the car up on *sturdy* jack stands, and put it in gear, and inspect the moving driveline for any obvious wobble ?

I'll do that before I head back to the machine shop. Thanks. Here's some fun car-tunes to listen to. https://tomellendemarest.bandcamp.co...ings-car-tunes

You can listen without downloading & purchasing. TD

Thanks Pierce. Driveline vibration solved. Took the shaft to a exclusively driveline shop 40 miles away and they discovered two u-joints had snap-rings that weren't seated in the grooves and those cups had started to back out of the yoke. Could have been a disaster if either had moved much further during my test-drives at 50 mph! I'll be presenting the local shop with the bill from the driveline shop tomorrow and give them a chance to do the honorable thing. Very disappointing as they've done lots of good work for me over many years.

The saga seems to be resuming although to a far lessor degree. The good news is that the local machine shop gladly paid the bill from the driveline shop and driving around town I thought all was well. First trip on the interstate yesterday indicated all is still not right. Assuming that the driveline shop did their work correctly, what could be the cause of this vibration? It is greatly improved since getting the shaft from the driveline shop but this vehicle rode as smooth as glass before this "repair". I don't feel it in the shifter at all and it doesn't change when I shift into neutral at 60 and rev the engine or shut the engine off. These kinds of mysteries drive me up the wall!!!

next step would be getting your tire balance rechecked. even driving a few miles with a severe drive train vibration could conceivably have caused uneven wear on a tire.

Well the tires are all off and back from the tire shop balanced. While the car is up I decided to replace all pads (ceramic) & e-brake shoes, install new rotors all around, and gas shocks. Might as well have it safe and handle well even if it still has a drive-train vibration, right?

None of the old pads Girling front, ATE rear, had any of the "blue brake-quiet" that I used to use all the time in my shop years ago. The rear pads had double shims so is that supposed to quiet the brakes better than the brake-quiet? Also the new rear pads have shims glued to them and the surface is like fine-grade sandpaper. I'm thinking nothing should be put over that surface? Ain't it great when the box contains no directions at all other than "Don't eat, lick, turn into a powder & inhale, and don't microwave!"

i still use rubberized red goop on the back of the pads to avoid squeaking.

Tires are balanced, brakes & rotors new, plugs & wires new, motor mounts checked out, but vibration is still there. Took it to a transmission shop for a test drive and he suspects an out of balance re-built torque converter or possibly the wrong converter for this car. He mentioned torque converts being internally balanced as opposed to externally balanced? He's not a Volvo guy but could that be a possibility?

At any rate, I'm preparing to pull the engine this time as I'm just to bloody old to be working underneath this thing anymore. I will be taking the torque converter back and want to be sure I get the right one & a good one. Should I think new maybe instead of rebuilt? Just one more example; "These old Volvos, they never die. They just get newer part by part!" TD