Driveline vibration?

[jeromio]

Can someone confirm my seat of the pants impressions? I think I may have messed up on the driveline alignment. I spent many hours trying to get it right, but at speeds above 85mph or so, there is a vibration that I feel, coincidentally, in the seat of my pants. It's high frequency and gets worse as the speed goes up from there.

 

I really wish I had a lift (or was Mikelly's neighbor ) since it would make fixing this so much easier. I also need to re-do the exhaust.

[Mike kZ]

Did you check Pete's write up on the subject?

http://mywebpages.comcast.net/pparaska/drivelinemods.htm

also this:

http://drivetrain.com/driveline_angle_problem.html

[jeromio]

Yeah, I read Pete's drivetrain section about a thousand times. Not sure exactly where I went wrong. I may have just goofed in a measurement when fabbing or mounting my tranny mount or something.

 

That other link is a very good one. Don't think I'll be buying any of them fancy tools though. When I checked, I used the vertical planes of the trans output shaft and the diff pinion flange. I used an angle finder tool from HomeDepot. Tried to make the two surfaces parallel to each other, which I believe is correct. I think I just have a bad measurement someplace and I need to go back and re-measure and make adjustments.

 

I guess it's just the fact that I did spend so much time on this that makes me question whether it really is the driveline causing the vibration - even though it is glaringly obvious

[Mike kZ]

Tried to make the two surfaces parallel to each other' date=' which I believe is correct. I think I just have a bad measurement someplace and I need to go back and re-measure and make adjustments.

[/quote']

 

They can be parallel to each other as long as the max angle is 3 degrees or less. You can slightly raise the diff nose up and/or the tranny tail down to decrease the angle.

[Pop N Wood]

Have you looked at Ron Tyler's page concerning driveline vibration?

 

http://www.home.earthlink.net/~rontyler/rontyler.html

 

He is of the strong opinion that a properly balanced aluminum driveshaft is the answer.

 

I am a big fan of laser pointers. It would seem to me that if you were to take an old tranmission yoke and diff yoke, cut them off then firmly attach a laser pointer to each, you would have the perfect tool for aligning the trans and diff. Hook these things up on both ends and place a piece of thin paper (mylar) stretched inside a cardboard frame in front of both laser pointers. By looking at the two laser dots on the mylar page you could measure the offsets very precisely. Just align the trans or diff so the dots are exactly the same distance apart on both pages. Maybe lined graph paper would make this even easier.

 

The smaller the distance between the two points, the smaller the U joint angles. If you measure the distance between the two pieces of paper, then you could easily and very accurately compute the angle as the arctan of the distance between the dots divided by the distance between the pages.

 

Ideally the laser pointer should be perfectly perpendicular to the yoke flange, but it doesn't have to be. Spinning each yoke(s) will cause the beam to rotate about the true axis. Trace the circle on the mylar pages and the point in the center of the circle is the exact centerline of each shaft.

 

This is certainly more accurate than placing an angle finder against the case of a transmission and hoping it is parallel to the output shaft. I have also heard of using a solid driveshaft, but a laser beam is lighter and avoids the issue of the drive shaft not being welded perfectly straight.

 

Maybe someone should manufacture plastic cups matching the output shaft splines on one end and a laser pointer insert on the other. You could probably sell such kits for $25.

[johnc]

Does it vibrate more or less under power, neutral load, or decellerating?

 

At those speeds any number of things can contribute to the vibration you're feeling. I would focus more on a balance issue then a driveline misalignment. Have the driveshaft balanced to 9,000 rpm, have the halfshafts balanced, check and make sure your u-joints are in good shape, and look for other things like loose engine, tranny, and diff mounts.

 

Are the driveshafts and halfshafts fully seated to the diff pinion and the stub axle respectively? Did you throw a weight off the driveshaft? What kind of diff are you running (open, LSD, welded)?

 

A simple fix might be to unbolt the drive shaft and turn it 180 degrees in relation to the diff pinion and bolt it back up. If that doesn't work do the same with each halfshaft.

 

Set aside misalignment issues and look for more simple solutions.

[Guest cbrunberg]

Just a thought but check your u-joints, drive axles and tires for balance also. My tires on my truck wound up the problem. I thought it was a u-joint. It was tred separation.

 

Hey!!!

 

I just saw the above comment writen while I wrote mine. Sorry to be redundant.

 

Carl

[jeromio]

Hrm. Well, I ASSume that the driveshaft shop balanced the driveshaft when it was shortened (since that's part of what I paid for). There's only one shop in the area though, so, no 2nd opinions are possible. You know, now that I think about it, I don't actually recall whether there even are any weights on the DS. I guess it couldn't hurt to carry the shaft back to the shop and have him re-balance it.

 

The vibration seems to be there at 85mph+ during accel/coast/deccel. It's not a huge vibration, just an annoying, high frequency sort of buzzing vibration. It doesn't seem to get worse as speed goes up. All very unscientific impressions.

 

Diff is an open 4.11. This problem did not exist pre-swap. I did remove the driver's side half shaft during the swap. I have ZXt CVs and flanges with the 240 stubs. Pinion and adapter were well seated and locktighted. I'll check these when I try that 180degree dealio.

 

Thanks for the tips.

[Tim240z]

Jeremy,

have you checked the balance of your rear wheels?

Tim