[leeklm]

So... I continue to struggle with a vibration felt through the car that starts about 65mph, and gets VERY noticeable and irritating by the time you hit 75-80. I went through each tire/wheel with the tech on the RoadForce, so we are in good shape there. Up to 60mph, the car is perfectly smooth.

I have been again focusing on driveline angles, and went out and purchased a digital angle gauge, and have been reading up on the topic.

The attached pic shows my current angles.

I am a little confused however... most would say to run a -2 or so on the pinion, but that would really throw off the working angle. From what I have here, it would appear that I should either move my pinion up to +1.5, or reduce my trans angle a little in order to have a perfect offsetting/cancellation angle.

Am I looking at this right? The challenge is that I am about out of adjustment on my upper control arms, I could maybe go another turn and still be safe. Also, I am about to the limit on my trans height, maybe can go another 1/8" shim.

Anyway, it seems to me that these angles should be within "spec" that would not cause the high speed vibrations I have. A difference of 1 degree on the working angle should be good, right?

Any thoughts from those have been down this road? Frustrating...

[Blued and Painted]

Please refresh our memory about the drive shaft.

[leeklm]

Originally Posted by Blued and Painted

Please refresh our memory about the drive shaft.

Driveshaft was recently balanced. Yoke is in good shape, new ujoints. I rotated it 180 on the pinion, but no noticeable difference.

Also, I have been through the Muncie, replaced the tailshaft bushing. I upgraded the muncie with AG case, midplate & front bearing. Shifts like a dream and does not miss a beat.

Vibration is not connected to engine speed, only road speed. I can push in the clutch at 80mph, and no change in vibration.

[Blued and Painted]

have you checked the lateral run-out on the axle flanges?

[leeklm]

yep. Had the same issue with my old 8.2" rear, as with the current 12-bolt. Upgraded the current axles to aftermarket forged.

[Bill Eveland]

Most or just about all the first order vibrations I've dealt with (one per revolution) occur at lower speeds, usually 45-55 mph. I would say at higher speeds you could have other issues. If you can get a sirometer and hold it againt something solid on the car you can get the frequency and find the rpm of the vibration . First order driveline vibrations are 25-35 HZ or up to 45 hz which is a driveshaft speed of 1500-2100 rpm depending on wheel speed and ring gear ratio for driveline speed. Here is a chart from a Ford tsb that has a little info that may be usefull.

[Blued and Painted]

Sounds like not your average vibration so I'll throw some things against the wall and see if anything sticks.

Hub centric wheel balance on a lug centric or uni-lug wheel. Lug centric balancing adapters are available.

Drive shaft to long. With the weight on the wheels, you should have enough clearance to flip the rear joint out of the pinion yoke.

Some have observed the factory drive shafts may look like a jump rope going down the road. Check installed run-out at front, rear, and middle.

[leeklm]

Originally Posted by Blued and Painted

Sounds like not your average vibration so I'll throw some things against the wall and see if anything sticks.

Hub centric wheel balance on a lug centric or uni-lug wheel. Lug centric balancing adapters are available.

Drive shaft to long. With the weight on the wheels, you should have enough clearance to flip the rear joint out of the pinion yoke.

Some have observed the factory drive shafts may look like a jump rope going down the road. Check installed run-out at front, rear, and middle.

Good info, thx. These are the replacement steel rally 1 wheels, so all lug centric, at least they have the self-centering lug holes, so I THINK they are lug centric. On edit... I just thought of something. While mounting wheels yesterday I was looking at the chrome aftermarket lugs, and while the wheel appears to be centered after installing a couple of lugs, it almost looks like the shoulder of the lug (the non-tapered part) comes in contact with the rim earlier than it should. Theses are the lugs that come with the replacement wheel kits from the Pontiac suppliers. A long shot, but worth a look.

Driveshaft length looks good. Took it out yesterday by the method you mentioned.

I need to take a closer look at potential run-out on the driveshaft. The shaft seems pretty robust, so I do not think it is factory. I have a chassis dyno session setup for Wednesday, so might be a good chance to have someone look at the shaft. The dyno shop specializes in performance & muscle cars, so may have one of their guys take a ride with me for another opinion.

[pggto]

Check to make sure your U joint fits properly in the rear end yoke. I have this problem at the moment. The u joint has .015 of side to side movement, this caused a bad vibration. I shimmed to to test my findings and sure enough the car is not vibrating as bad with a couple of .007 shims centering the joint in the yoke. A new yoke will be installed shortly on my car.

[FrankieT/A]

If the vibration is in the driveshaft you would certainly feel it in the shifter, resting your hand on it. If you don't feel it when you push the clutch in that would lead me to believe it is tire related, possible rear axle. If it's your driveshaft angle is off you either feel it while you bear on the gas lightly or letting off. As for tires, You can balance an egg but you can't make it round. Tire runout needs to less than .045 of and inch according to GoodYear. Most tires exceed this. Better Goodyear stores actually have a micrometer on a stand to measure run out. Any Goodyear tire can be adjusted if not within this tolerance. I was tired of ride disturbance myself, so my procedure was this: the first thing I did was get together about 10 rally II wheels with no tires on them. I brought them to my friends shop and put them on the tire balancer, spun them by hand and picked the four straightest wheels. Next went to the tire store, bought four tires and had them mounted. Had them spin them by hand looking for straightness and concentricity on their balancer. It took 6 tires to get four good ones. Then I took them to a place that did road force balancing and had them balanced there. It was all a pain in the neck but my car is smooth as glass up to a buck twenty. Sorry to be long winded. Just trying to help.

[Bill Eveland]

I would set the angles so they are the same or a little lower on the rear end , it will kick up some at slower speeds under heavier acceleration. But by the time your at highway speeds when your vibration occurs most or all of that kick up on the pinion should be gone.

Did all the wheels road force under 25 lbs?

[leeklm]

Originally Posted by Bill Eveland

I would set the angles so they are the same or a little lower on the rear end , it will kick up some at slower speeds under heavier acceleration. But by the time your at highway speeds when your vibration occurs most or all of that kick up on the pinion should be gone.

Did all the wheels road force under 25 lbs?

Bill, I am not 100% clear on what you mean about "same or lower" on rear end. Do you mean in comparison to the trans?

I did not get the exact readout from the road force, but only one was out of "spec". We spun the tire 180 on rim and then was fine. The guy running the balancer was the shop's key tech, and seemed to have quite a bit of experience. One rim has a little run out, but I ran a test drive replacing that tire/rim with my true & round spare, and no difference in feel.

Regarding vibration on the shifter, you can feel it, but its not like it shakes out of your hand either. Feels about the same as it does through the rest of the car. Running on the chassis dyno Wednesday night so hopefully can diagnose something spinning the driveline while standing still...

[leeklm]

Running on the dyno, the vibration comes on at 65-70 as expected, gets worse up through 100-110 or so, and then actually gets better at 115-120mph! I assume it is moving through its harmonic at that point.

Was under the car today moving wiggling the driveshaft looking for play.

How much side-side- up-down movement should i be able to get at the trans yoke/ujoint? To me, it seems like there is plenty of movement. New bushing in the tailshaft, and the yoke shaft measures a consistent 1.5" OD. I assume 1.5" OD is correct, as I am not experiencing any leaks, maybe just a small drop at times.

[Bill Eveland]

I meant whatever angle the trans was pointing down, the same angle pointing up at the rear or 1/2 degree lower to help compensate for torque kick up. Those HZ readings on the tsb I posted per rpm and speed were based on vehicles with a 3:55-3:73 ish gear ratio.

I helped someone on here years ago with a driveline vibration and it was caused by too much backlash variance in the ring and pinion. Usually over .004 to .005 variance will cause a driveline vibration. The only way to check is measuring backlash about every 3rd or 4th tooth around one revolution.

A small engine repair shop would have the sirometer I talked about, it's used to tune 1 cylinder engines. Too bad you couldn't borrow one for your dyno time to measure the frequency to find the rpm of what's vibrating. The 65-110 mph would be referred to the point of resonance for the vibration. Just adding weight to the driveshaft like a couple hose clamps could change the point of resonance to the point where you won't feel it. Have them opposing each other at the back end of the shaft. This is if everything else like angles are correct.

http://www.treysit.com/16.html


On the drive shaft I would say an 1/8" total is acceptable?

[Blued and Painted]

If it's a posi unit you might try jacking up the rear, remove the tires, bolt on the drums, then spin it up.

[grandville455]

what did it make on dyno??

[leeklm]

Originally Posted by grandville455

what did it make on dyno??

Here are the dyno sheets at the rear wheels. No tuning, just 3 pulls. The leaner A/F line you see is when i removed the air cleaner lid.

Overall numbers are not quite as high as I would have expected, but I assume there is room for some tuning.

As a seat-of-the-pants comparison, this engine feels much stronger than my last 455 build. that engine turned about 410/500 at the crank.

As I think about it, these factors would likely equal a fair amount of HP loss compared to engine dyno...

--Power steering & Alternator (which will slow the engine down at idle about 150rpm when the electric fans kick in
--mechanical water pump
--mechanical fuel pump
--Drive train
--iron (ram air) manifolds, 2.5" exhaust with street mufflers
--warn/humid shop air instead of cool outside air directly to the carb that we had on the engine dyno

[428GTO70]

Originally Posted by leeklm

Was under the car today moving wiggling the driveshaft looking for play.

How much side-side- up-down movement should i be able to get at the trans yoke/ujoint? To me, it seems like there is plenty of movement. New bushing in the tailshaft, and the yoke shaft measures a consistent 1.5" OD. I assume 1.5" OD is correct, as I am not experiencing any leaks, maybe just a small drop at times.

Hmm I don't know. The tail shaft of my th400 moves plenty without the yoke slipped in obviously but with the driveshaft/slip yoke installed I have very little movement, its pretty much solid.

So to me if you are saying it moves around what you feel is "Plenty of movement" that sounds wrong to me? And there shouldn't be any drips at all imo.

I hope you figure this out. It was one thing I was worried about with my car but thankfully so far mine is good. I've had it up to about 90 so far and it seems to only get smoother the faster I get, smooth as glass. You will get there too.

[FrankieT/A]

The rear bushing in the tranny is the shaft support, so with no yoke you will have a lot of play. It must be checked with the yoke installed.

[GOLDOHC]

The first thing I would try, if you haven't already is to put on a different set of known to be good set of rims and tires. Hopefully you or a buddy has a set.