: Driveshaft reindexing?



Castro
12-17-10, 12:16 PM
Hey guys I posted earlier on a bad vibration I'm getting between 22-30mph in any gear after having my snow tires and driveshaft coupler replaced. My thinking at this point is that it is probably a driveshaft indexing issue. I searched and didn't find the exact answer I'm looking for. Two questions- (1) a misaligned driveshaft can cause this type of speed sensitive vibration right? Shifter vibrating badly, wub wub wub noise feel at only these speeds, and accelerating through it it goes away (more torque changing the harmonics?) and (2) assuming the shop did not properly index it and reinstalled it wrong, how do I know? I believe there is a marking on the diff side of the connection right? Is there one on the trans side? If not how can you reindex it? I'm not sure if they had to drop the whole thing or just the front to do the coupler swap. Ideally I'd like to crawl under there and know before I call to bitch about it. Please help!

darkman
12-17-10, 01:55 PM
See attached:

Here is a description of the operation of the propeller shaft:

Propeller Shaft Description and Operation (CTSV)
The propeller shaft is a tube with rubber couplings at both ends which do not require periodic maintenance, that transmit power from the transfer case or transmission output shaft to the differential.

Propeller Shaft Description
A center bearing assembly is used to support the propeller shaft connection point, and help isolate the vehicle from vibration.

Propeller Shaft Phasing Description
The propeller shaft is designed and built with the yoke lugs, ears, in line with each other. This produces the smoothest running shaft possible. A propeller shaft designed with built in yoke lugs in line is known as in-phase. An out of phase propeller shaft often causes vibration. The propeller shaft generates vibration from speeding up and slowing down each time the rubber coupling goes around. The vibration is the same as a person snapping a rope and watching the wave reaction flow to the end. An in-phase propeller shaft is similar to 2 persons snapping a rope at the same time and watching the waves meet and cancel each other out. A total cancellation of vibration produces a smooth flow of power in the drive line. All splined shaft slip yokes are keyed in order to ensure proper phasing.

Center Bearing Description
Center bearings support the driveline when using 2 or more propeller shafts. The center bearing is a ball bearing mounted in a rubber cushion that attaches to a frame crossmember. The manufacturer prelubricates and seals the bearing. The cushion allows vertical motion at the driveline and helps isolate the vehicle from vibration.

Based on my reading of the Service Manual the phasing is controlled by the postion of the splines particular to each of the two halfs of the driveshaft. If you are disassembling the halfs you are instructed to mark each one so that upon reassembly the original postion can be maintained. Based on reports in this forum, I gather that the factory marks may, or may not still be on the shaft. If that is the case the process is pure trial and error to see which spline alignment minimizes vibration.

heavymetals
12-17-10, 02:36 PM
Are the snow tires balanced?

Castro
12-17-10, 02:39 PM
I gather that the factory marks may, or may not still be on the shaft. If that is the case the process is pure trial and error to see which spline alignment minimizes vibration.


Hmmm that's the part I heard. Thanks again Darkman your input is always appreciated. Strangely enough on the drive back to work this afternoon it was gone, totally gone. Bizarre. I noticed my tire psi readings were +2 psi at the time, and after the warm up drive the other day it also seemed to disappear. I'm going to "overfill" my tires after work a bit and see what happens. I can't believe this could all be a matter of +/- 2 psi though, we'll see. If not I'll jack her up and hope I have markings that aren't lined up.

heavymetals
12-17-10, 02:50 PM
You might have developed a "flat spot" on the tire(s) depending on how they were stored.

I had the same problem on Mr. Vette when it sits for awhile.

Would go away after the tires "warmed up".

Castro
12-17-10, 03:17 PM
You might have developed a "flat spot" on the tire(s) depending on how they were stored.

I had the same problem on Mr. Vette when it sits for awhile.

Would go away after the tires "warmed up".

So were they permanently flat spotted or did it go away as long as it wasn't sitting for a long time? Did they have to warm up every day?

heavymetals
12-17-10, 03:34 PM
The flat spots would go away after the tires warmed up, but it took awhile.

Since your problem is doing the same I would not blame the indexing.

How did you store the tires?

Leaned up against a back wall or stacked?

Castro
12-17-10, 03:57 PM
They're new Sottozeros, I had the shop order them probably from tire rack

kevm14
12-18-10, 09:32 PM
I'm not sure you'd feel flat spotted tires through the shifter, unless it was the whole car + shifter.

Castro
12-20-10, 09:37 AM
the whole car + shifter.

Yes that. I put more miles on and definitely narrowed it down to a cold issue, meaning as soon as it's up to temp the issue is gone every time. I put 34psi all around (36psi when warm) and it helped slightly but it's still there from 22-30mph every morning. I'm calling the shop this morning to see about returning the tires for a replacement set.

Castro
12-22-10, 03:30 PM
What I heard from the tire guy was that these high speed rated snow tires have a lot of nylon in them and tend to be temperature sensitive. It sounds like they will continue to flat spot when parked on cold surfaces for extended periods (like overnight). Or maybe it's just this set. It does seem to be improving as I put more miles on them, and if I drive aggressively it goes away pretty quickly. After a few miles it seems to be gone. Not very happy with this outcome, I wonder if others have had this issue with Sottozeros?

heavymetals
12-22-10, 03:37 PM
Sounds like a reasonable answer and you are just another victim of the cold weather.

Since the "problem" goes away in short order, I think you are just being fussy.

You should be happy you didn't screw around re indexing the drive shaft.