Technical 3 days later and vibration still there.

Ok for 3 days I have been fighting to get this vibration out of the car. Vibration in 3rd gear, automatic trans and vibration comes in at 65 mph, only under acceleration or foot on gas. Take foot off gas and let it coast it goes away, Starts vibrating a bit easy you can feel it lightly in steering wheel and more in accelerator pedal and hardly anything in shifter that's mounted directly to transmission, then if you lay the power down to try to climb out of it, it doesn't all the way to 90... So at 62mph I'm at 2100 rpm on a 2500 stall. 90 its rolling about 2900 give or take. So the rear end has some slop when you go from reverse to forward gears. turns driveshaft about 1/8 of a turn from lock to lock. Could this be spider gears causing weird issues? With the vibration not really feeling like a frequency generator and increasing with speed really its got me stumped... Just gains intensity for higher speeds... Rear is a parallel 4 link with coil overs and panhard bar.

So day one. looked at u-joints and grabbed driveshaft, had a small bit of walk so replaced rear u joint, well now that's 100% and it still vibrates.
Checked all driveline angles and they were within .25% of a degree.

Day 2 went through and was irritated and decided to lay the pinion angle out, since the axle is higher than tailshaft I angled the axle at 4 degrees when trans is at 6 degrees... wanted to try to make this issue worse to see if there was something I am missing. and to my surprise...... NO change.

Day 3 tore it all apart again, checked tolerances on suspension components everything is tight and running true.

So here it is day 4 back to my day job and scratching my head, so I am here asking the best place with great information for a bit of help.

Thinking of pulling rear tires off and run it on stands to see how that reacts.... If it was a pinion angle issue shouldn't it start in about 30 mph roughly? Been fighting this issue for a while now, finally got fed up of driving 60 mph everywhere.

 

New build or did it just start?

 

..check to see if there is any slop at the tail end of the trans,....in my case I had a worn bushing at the tail housing of the trans,...Miller

 

Its been here and there, sometimes its hardly there then you make some turns etc and it it gets worse. but has been there for a while, just ready to drive this thing out of town frequently and cant do that right now.

 

Pull wheels and check balances--- I know you said it was only under throttle, but it's a good idea (and easy) to verify balance (and runout and overall tire condition) to eliminate it from the equation. My wife's OT had a 70+mph wobble under throttle that was just that.

Also check tailshaft yoke and bushing for wobble.

 

Been fighting the same thing. I had a driveshaft out of line .045 Retubed and balanced and still had a vibration but less and no longer cyclical. I think I have gut it figured out to the rear tires. They balance good, have less than 1500 miles on them but are 15 years old. If I drive it from being parked for a week I have vibration. If I drive it the second time the same day the vibration is much less. I think the tires soften up. These are modern radials.

 

Did you have the drive shaft balanced? HRP

 

Driveshaft is 2 yrs old... was fully done with new stuff.. But sometimes new stuff aint as good as the good ole stuff.

Going to dip into my inner hulk if those rear tires are the issue all along... May even do it like the old discount tire commercial and throw it through their window. I know a front has a small bit of runout, and can feel that at 90 kick in but its not bad, I at least know what that one is.

 

What happens if you jack the rear tires off the ground and run it up in gear?
If it doesn't have a posi or otherwise locked rear end you can raise one tire at a time and run it up and see if and where you get the vibration.

I'd check the front yoke and bushing for movement too as Miller suggested in post 3. A tiny wiggle there might translate into a serious vibration at higher speeds.

If I hadn't had the driveshaft balanced or didn't know that it had been balanced I'd have that checked too. I went for years cutting driveshafts down and running them without a problem and then ran through a couple in one truck that would shake you out of it.

 

Had similar thing happen with a 'tight' U-joint once. Might be worth a look. Re-check phase while you're at it.

 

Is the front u-joint smooth when it is moved by hand? it may have brinneling (grooves from the rollers)
3x^ check the trans output bushing for any play.
tires should not be used if they are over 6 years old....no matter what.....
I have looked at many cars that had vibrations, most turned out to be from internal tire problems, cord shift, plugged holes breaking cords, flat spots from sitting and tread separation.

 

Ok, I might be beating a dead horse here...

Years back I had a similar issue, same thing... Tried everything, the driveshaft was newly made from a reputable shop.

Still vibration!

I spoke to an old race car guy and this is what he had me do.

At the rear of your driveshaft, about 1 inch from the yoke weld. Mark your driveshaft with a grease pen or white out... Mark it into 4 quarters radially. Put a hose clamp large enough to go around the driveshaft, align the screw at your first mark and tighten it.
Go for a ride, if it still vibrates, loosen and rotate the clamp.... It took me 2 times to eliminate the vibration using this method, I used a stainless clamp.... Sold the car with the clamp still attached.

I know it sounds crazy but just because your driveshaft is balanced doesn't mean all the little rotating parts jive when spinning.

Pete-

 

I'd look at those u joints and drive shaft for sure. JC

 

Ill check the output bushing again, front u joint was in perfect condition and felt smooth and no free play...

Tires are only 2 yrs old, BFG radial TA... Keep yall posted on what pulling tires does for sure.

 

Uh have you checked the motor mounts? Bad mounts and a poorly balance motor (think stock here) will give you some shake especially under acceleration. Just a thought.

 

I've heard of the hose clamp method, but never had occasion to try it. Good to know that it's worked in some cases.

 

Beaner... I had fought motor balance.. pulled the motor and swapped torque converters, I can sit there in neutral or park up to 5k and nothing. could put a glass of water on top of the motor from 2000 to 5k

 

I'd check that which changes when you are under load vs. coasting. Ie: does the axle rotate significantly under load vs. not under load. Too, does the engine rotate while under load?? Check the things that would change driveshaft angle while under load. Check for binding as well.

Good Luck,
Cosmo

 

Put bfg t/a's on my T when first built , took 5 tires to get 2 ROUND frts& 3 rears to get 2 ROUND ones , ran 'em for a year , sold 'em at a swap meet , went to cooper , no more problems ..dave

 

When they built the drive shaft did they get the joints in plane?

 

Is this some sort of race car?Does the converter ever lock up at normal highway speeds? Not suggesting that is part of the problem but I don't see it doing anything good for the performance....

 

I used it on stock cars, only we put a 1 oz wheel weight under the clamp. The idea was to re-weld the OG balance slug on, but on my Nova, we just left it that way.

 

The operating angle of the universal joints is way too big and causing the vibration.

Spicer recommends no more than a 3* operating angle to avoid vibration.

With the trans output at 6* down and the pinion at 6* up, you would have a 6* operating angle if the driveshaft was level.

But you said the trans output is lower than the pinion, so that would indicate the driveshaft is running uphill from front to rear. With that situation, you have to add the measured driveshaft angle to the trans output angle to get the total operating angle of the u joints. That angle is going to be more than 6* and more than twice what's recommended to avoid vibration..

Spicer also gives a table of absolute max operating angles based on driveshaft rpm, and for 3000 rpm the max is 5.8 degrees. At 90 mph you're above the absolute max angle as well as being at more than twice the max recommended angle.

Spicer driveline installation manual at http://www.waterousco.com/media/wysiwyg/pdfs/content/J3311-1-DSSP.pdf

No simple fix for this short of raising the rear of the trans and rotating the pinion down to match such that the operating angle of the joints is within the normal range.

 

Metalmumcher types faster when I get called away.

Your Trans is 6* down
Your rear axle pinion is higher than tail shaft. soooo Your drive shaft goes up hill to the rear. What's the angle of the drive shaft?

If your drive shaft were at 0.00* you'd have a 6* working angle in the front u joint. Since its running up hill to the rear, you'd add that angle of the drive shaft to the angle of the Trans and this would be your working angle. The max is 3.5* as published by many sources.

Now the ujoint working angles between front and rear should be close to each other.

 

It's this one right?
I can see with xray vision the drastic driveline angles.

 

cant see the pic... I think Im at about 12 degrees up angle on driveshaft. Hell Ive had 4wd with 15 degree angles with no real issues ever. always kept pinion angles set to each other and never had vibration issues. but I do see how 6 degrees on both ends now has a negative effect on everything. Just perplexed how many people have their stuff low and don't have the same issues, or maybe Im thinking that those people actually drive on freeway for hours at a time and am wrong. The offset carrier probably doubles the issues being the u joints are doing 2 angles at the same time. so compounding the issues at hand. hmmm... A lot of stuff to check and think about here.

 

Justperplexed how many people have their stuff low and don't have the sameissues,

So far there's been no way to cheat physics. How do you know these other super low rides don't have problems?
I don't know, but the drive shaft rules and physics, and keeping the oil pan out of the pavement while having room for your feet says that it "should" cause issue.

Riding low, with the pinion above the driveshaft, is best done with the engine closer to zero and huge tunnel as far as layout of driveline angles go.

 

In this situation would a Constant velocity joint fix the problem with the angle? Pete

 

Good catch Pete.

A double cardan type CV joint at the trans might help enough to avoid a major rework.

With the CV joint at the front, you would rotate the pinion down to the point where the driveshaft is running approximately straight into the pinion rather than using the
parallel angles used with a normal driveshaft. The net effect of rotating the pinion down is that you'd decrease the current upward angle of the driveshaft. Decreasing this angle decreases the operating angle at the rear of the trans. A double cardan joint operates more smoothly due to the fact that the two joints largely cancel the variation in angular velocity that's present in a normal single cardan joint.

By taking some measurements and doing a layout, the OP should be able to get a good idea of what he'd end up with as an operating angle at the CV joint.

Picture here along with some info on drivelines made up with CV joints. Note that most of the info there relates to off-road stuff where they commonly put up with the downsides of big driveline angles since most of their stuff is done at low speeds. IOW, don't make the mistake of assuming the angles he mentions would be workable on your hotrod.

http://www.4xshaft.com/driveline101.asp

 

Ok. So tonight's project. Correcting driveline angles. Best I can get without a full rebuild of the floor.

Pinion angle 4
Tail shaft 4.5
And a 6 degree driveshaft.

I think this is more in the right direction. 1" shim under trans mount. What y'all think?

Glad I gave myself extra room in the tunnel when I built it is all I will say for this