Slick 60's

I just replaced the drive shaft in my truck for a 4" aluminum one to chase out a drive line vibration at 75-85. It's slightly better but now shakes like hell if I coast at those speeds but the vibration drops a bit if I decelerate with the engine.

this is totally new, I am thinking my pinion bearings are toast. Any ideas?

could you have pinion angle out as well? mabye your pinion brg is worn, mabye its in trans itself, wheels, axels etc etc could be many things, need to eliminate them one by one, I used to use an electronic device for diagnosing vibrations, but an assometer works too as long as you have good reference to go with, hertzometers can work as wel las long as you know what the hz is relating to for each type of vibration

Not a chance of a drive line missalignment. Ruled that stuff out long ago.

The drive shaft is 60" joint to joint and was a 3" steel tube. Max recomended RPM for that shaft was 3800 and with my overdrive TKO 80 MPH put me right in that range. That is the reason why I went with the larger aluminum shaft. I know I am getting less or no driveline buzz because my spedo now has a steady needle where before it would bounce around pretty good at those speeds.

I'm gonna pull it apart tomorrow and check it out. This Sucks!

I once installed a new u-joint that was bad and had the same problem you describe. Thanks, Lyman.

the transmission yoke & the differential yoke should be lined up not 180 out. if your pinion brg's are toast you should be able to here it, also you will have metal in the gear lube, the silver look.

Dave should be able to tell you what a pinion bearing going out feels like. Might also be the transmission end going sloppy, although a TKO should be pretty tough.... Probably the lower mass of the alum driveshaft accentuates whatever was there before, would be my guess. Pinion brg would be a good place to start.

I went out and hammered on it last night. Diff sounds like a jet engine at about 45-60 MPH, that's new too and no way in hell it's a bad U-joint. The new shaft is defineatley unmasking problems that the old one was hiding.

My '84 Mustang has a worn transmission tailshaft bushing & has the vibrations you're describing. I can put it in neutral & wiggle the front yoke around in the tailshaft housing. It's also worn the yoke, which I replaced...that took away about half the vibration. I haven't replaced the bushing as of yet.

Maybe the yoke on the new driveline is a titch smaller diameter than your old one, therefore slopping around in the bushing?
The noisy rear end you describe doesn't sound good, though.

same yoke, excelent condition. No slop in the trans, fits real nice.

Geezus, I am suprised no one has brought this up. Its probably the rest of the truck finally revolting against the chevy heart transplant.

O.K.
The easy way to find out.........
It only takes a few minutes to remove 4 nuts on the U-joint and 5 (I think) bolts and the pinion pops right out.
Easy way to tell if the bearing is shot.
Shouldn't even lose any grease. That is what I would do.
Just a thought from a lazy, fat, old white boy from Texas.......
U@ss

Jarrod wrote:Geezus, I am suprised no one has brought this up. Its probably the rest of the truck finally revolting against the chevy heart transplant.

Agreed, it is trying to cough up that hairball under the hood.

Har Har Har, thought about taking your act on the road?

My hair ball will still kick your blue blood square in the teeth!

Dropping the pinion carrier was suggested. With everything out it appears to be in good shape.

Tearing apart the tail shaft to measure the output bushing right now.

ELpolacko wrote:Har Har Har, thought about taking your act on the road?

My hair ball will still kick your blue blood square in the teeth!

We can sure find that out sometime.

Now that we got that out of the way Tim, Got any REAL suggestions as to the problem?

Short of dropping a fresh 3rd member into the rearend housing, I can't think of a thing that has not been mentioned.

Edit: Is your rearend housing straight from end to end?

I just went through the rear axle. I ended up fabricating girdles across the back. I have evidence that the third member has been deflecting back in excess of .75" (diff coverplate had wear marks from the panhard bar that is almost .75" of space behind the rear) under acceleration and had a bow backwards of .188" static.

After welding I checked every dimension with my digital level and fixturing. Toe in is dead nuts straight camber dimensions are about a half degree positive unloaded and slightly positive but nearly straight up loaded.

Axles are 31 spline Strange Extra heavy duty, bearings are new Green bearings and the diff itself is a torque biasing Detroit Tru-Trac.

The girdle has made a huge improvement in launch charicteristics. Just judging by my calibrated ass dyno I should be able to drop my 60 footer on or under the 2 second mark.

Hmm what trans do yo have?

Early fords had a vibration damper that hung from the tranny. Later models had a flywheel affair as part of the yoke, is it possible u have the wrong flywheel and its outa balance?

O and the best yet - we have found output yokes on the diff and tranny yokes that were not centred, out as much as 1/4" and that really plays havock. Some so badly out of centre it was visible to the naked eye

So put it up on jack stands, and set up a piece of wire with a white grease pencil in it likea dial indicator and run the truck, slowly move the grease pencil into the drive sahft - front yoke, then rear yoke - I bet you will be very surprised - and pissed. One or the other is likely to be the culprit.

I am leanin towrds this cuz you said with the aluminum driveshaft it got better - and that would be because of less inertial wieght to toss around on the outa centre yoke(s) - both could be bad by the way

Most people dont know this but ford considers up to an 3/16" outa centre to be acceptable unless someone comes in for warranty. My biddies 2006 just had both yokes replaced

;o)

ELpolacko wrote:...my calibrated ass dyno...

Nice...