Todd, good point. There is a great PDF floating around published by Dana/Spicer that does a great job illustrating all possible drive line issues.

Andrew

 

Andrew - yes! 3.55 times slower in my case - tires that is. I got enamored with the flat spot theory when I measured runout. But it's much more of a 'buzz the car' and less 'thump/thump'. Thinking the DS shop will help solve the mystery.

Toddoky - Tranmission/Engine in same 'horizontal' location as the 5.0L before it. Carefully measured and replicated -- crank centerline offset 1/2" to passenger side, tranny in same location/mount/x-member. It is possible that a small existing horizontal angle is combining with a slightly larger vertical angle to cause an issue, but I don't think so. The nature of the vibration (increasing with speed, no accel/decel issues) seems to point to some sort of fundamental imbalance issue with the DS. In any event, I'm going to slightly lower the back of the tranny and raise the pinion - maintain parallel and reduce vertical angle some. That will minimize any combined angle potential issues.

 

It's good you have some adjustment to play with, especially if it reduces the operating angles.

I'm my GTO, I have the opposite scenario. The pinion is higher than the transmission output shaft so the front operating angle make a shallow V. My front operating angle is actually 6 degrees, which is why I run a CV driveshaft.

I don't think the angles are your issue. I suspect your driveshaft might be out of balance.

Like I said, I love a good mystery!

Andrew

 

Remove the tyres from the equation, put the car in the air, remove the wheels and run it up to speed.

If the vibration is still there you know it isnt the wheels/tyres

 

No change with drive to Cars&Coffee this morning. Don't think this has anything to do with wheels/tires -- frequency is too high, and I was on some newly paved asphalt - things are butter smooth up to about 55-60 mph. I'm focusing in on the driveshaft. I'll make one more change to further reduce u-joint angles. And then get the shaft The Driveshaft Shop up in Salisbury, NC --- ask them to spin it up with yokes/reluctors/etc and see what they see.

 

Measuring stuff with precision and accuracy is.....in a word....hard.

I keep coming up with discrepancies of .3, .4, 1.0 degree when I take the same measurement 2 different ways. Began to dig into that.

Had a spare slip yoke --- zero'd the angle finder on the shaft and measured the machined surface where the u-joint cap goes. They should be parallel. .3 difference - pics below. Making me question whether I can trust measurements from the slip yoke on the car - without doing a complete "map" of each end with the differences that show up so I can adjust with math. What a pain in the ***.....but necessary I suppose if you're trying to find 1/2 a degree difference somewhere. Realized that the outer surface of my pinion yoke (where the bearing caps are pushed through and clipped) are cast, not machined. Kept getting different readings from one side to the other -- they're not parallel, so I can't use them. Which means to measure the rear u-joint angle, I have to remove the driveshaft and use the pinion flange for my zero, then re-install the shaft and measure it's angle relative. And that's a different approach than what's needed for the front angle -- where I have a machined surface on the slip yoke. Making myself crazy....

Also made a tool so that the angle finder would sit longitudinally on the driveshaft -- a challenge when you're placing a flat magnetic surface on a round surface. Added some magnets to the tool -- so I can stick the "open" end of the U on the driveshaft and then have a flat surface to place the magnet on. And I adjusted the tool so that there's less than a tenth difference between the two sides.

Lowered back of tranny, raised the pinion -- about an 1/8" on each end. Angle finder shows I'm still parallel between pinion and tranny output shaft to about .2 of a degree. That should mean my front and rear angles are the same --- but in opposite directions (pinion lower than engine). The front u-joint angle dropped from 2.6 or so to 2.1. However, try as I might, the rear angle I'm measuring at 2.9. And based on the .2 within parallel measurement of pinion/tranny, the rear angle should either be 1.9 or 2.3. Can't figure out where .5-1.0 degree showed up.....head scratching. Realized that the outer surface of my pinion yoke (where the bearing caps are pushed through and clipped) are cast, not machined. Kept getting different readings from one side to the other -- they're not parallel, don't know if either is perpendicular to the flange face, so I can't use them. Which means to measure the rear u-joint angle, I have to remove the driveshaft and use the pinion flange for my zero, then re-install the shaft and measure it's angle relative to the pinion flange -- that's what nets me a 2.9 degree measurement. And that's a different approach than what's needed for the front angle -- where I have a machined surface on the slip yoke. Making myself crazy....

Pulled a string from centerline of pinion to centerline of bell housing (there's a convenient notch for that purpose) and then hung a plumb bob from centerline of tranny output shaft. Almost dead on for 0 horizontal angle -- maybe 1/32" between the strings. So that appears to be a non-issue and confirms I did my homework when I put the tranny back where it was before the swap AND had the center of the pinion moved 5/16" towards the driver's side when I put the 8.8" rearend in the car 6-7 years ago.

Oh - one more piece of the mystery. Kicking myself for not realizing it sooner. Amazing how you can look at something 20 times and not 'get it' - and then on time #21 a freaking floodlight comes on. When I thought I would add my VSS reluctor at the FRONT of the driveshaft, I added 17 small teeth to the slip yoke. Duh. Now, they're very small, and the size of each as well as the size of the gaps between them are within a couple of tenths of a millimeter -- so I concluded, not a balance issue. But -- I need to let that assumption go. Driveshaft to the DS shop next week to check out yokes, balance, runout, etc. By the time they've checked it out, it may be economically advantageous to just have them build me a new one. I've wanted to go aluminum anyway - maybe this is the time to do it, if I have the room....

 

I would not consider the outer face of that UJ yoke to be a surface suitable for referencing against the shaft of the yoke.

As long as the axis of the holes down through it are at 90deg to the main yoke, that is what matters. Outer surfaces arent relevant

 

Actually, the measurement of that surface relative to the shaft is relevant -- so with a bit of math you can use that surface as a proxy for the shaft. The mistake is to assume it's parallel to the shaft.

 

Have you checked your mounts(engine) ?

 

Vibration is independent of engine rpm; dependent on road speed - not a mount or engine issue.

 

True enough in that sensor, I thought you were showing it maybe suggesting the yoke itself wasnt true.

Again, get the driven wheels in the air and run it up to speed and see if anything is amiss. It's a lot cheaper and easier than pulling it apart and taking it to a shop to test...in a test that may not be relevant to the installed vehicle.

 

Initially I thought it was possible two of em might've flat spotted -- but I've already run that down and it's not the case. Besides, the frequency of the vibration is wrong for a wheel/tire problem - I should've recognized that earlier on during my attempts at diagnosis. At this point the evidence points to some sort of issue with the rotating assembly between tranny and rearend, so that's the next line of discovery.

stevieturbo - I appreciate your perspective. You've suggested the jack test several times. When I was a teenager a neighbor had a really bad accident at home when a car run up to speed on jack stands came off the stands. It left a lasting impression on me (and on the neighbor!) and I simply won't do it. It may take a bit more time/money to figure it out, but I'm willing to invest it. Others may make a different choice, and I'm ok with that -- so it's good that it's ventilated here in the thread.

 

That's fair do. But it can be done easily with pretty much zero risk.

Point is, it's all well and good testing things off the car...but the reality is it is on the car that matters.

 

I've made an alignment jig using laser pointers from cat toys that measures the angle run out in both dimensions. I've never like the angle finders. If the laser lines are the same distance apart everywhere than they two shafts are parallel.

http://forums.hybridz.org/topic/4399...lignment-tool/

But having said that you are wasting your time chasing fractions of an angle in the driveline. Things move around way too much under torque for that to be an issue.

I guess there could be a run out issue on the shaft, rotating slightly off centerline. I've read posts from guys who fixed the issue with a better seated yoke or new U joints. Maybe you just changed the resonant frequency of the vehicle so minor existing vibrations are starting to harmonize.

I'm still betting on tires. At 100K miles my minivan is doing just what you describe. It is getting a new set tires Monday morning.

Good luck.

 

Never a waste of time to take the time to understand why things are showing up the way they are - at least for me. Well aware that as the rear axle and body/chassis move around while in motion that the driveline angles change. And as I've said before, I believe the frequency of the vibration is all wrong for it to be a tire issue. But have fun with new tires on the minivan!

 

One thing you can try is this...

 

Thanks for posting that - may help others following along. Me and apps = no thanks.

Measured the pinion yoke and slip yoke on my driveshaft this morning -- compared the mating surface to the face of the yokes I'd been using to measure angles. Both were off - the pinion yoke by .7 of a degree and the slip yoke by .5 degree. So all of my u-joint angle measurements were thrown off by that. 10 minutes work with a hand file and now I have surfaces on both ends that are accurate proxies for the pinion flange and tranny output shaft. So, I'll re-install, measure again and go drive the car. I'd like to have decent data for the driveshaft shop.

Yup - I wanted to move from "pretty much" zero risk to absolute zero risk of the car coming off the stands. As for testing - that's why it's been make a change, drive the car, make a change, drive the car....

 

That app is a great idea, shame they wanted $400 for it :-O

 

Why thank you, I will.

And hope you enjoy your vibration.

 

Try the hose clamp trick to check shaft balance?