Chasing a vibration

[lime73]

I have a automatic transmission/drive line vibration that I am having a hell of a time tracking down.  Engine is mild 440 with purple shaft.  Transmission is a 727 fresh rebuild with a Turbo Action converter #17850ST. I had car completely apart and did ALOT of changes before reassembly and noticing vibration.

Symptoms are as follows:

Pulsing vibration in what feels like transmission area while cruising around at consistent speed.  RPM range of vibration changes with gear changes.  Seems to get worse as it warms up ( maybe that part is in my head and I am just paying attention more as I drive more).  Vibration goes away during acceleration.

Thing changed prior to vibration appearing:

 Transmission rebuild, new rear springs shocks and bushings all around. Also included are New POLY motor and transmission mounts, march pulley setup and headers swap from manifolds. 

Things i have eliminated as problems so far.

Pinion angle,  shimmed rear end and had NO change at all in vibration.  Took the drive shaft to shop that built it and had the recheck balance, they said it was fine but installed new U-joints just to be sure (very reputable local shop).  Rear tire balance and wheel straightness are not an issue as i ran it on stands without the wheels on with no change.  Also ran it without drums on it, NO change.  I installed a "scalloped" flex plate from B&M and there was NO change.   

Next thing I am going to try is going back into the valve body as it never shifted as hard as i expected when i used the B&M shift kit during build.  Shifts real smooth but not as firm as i expected.  Also installing a Trans cooler and new lines as the lines on the car now run real close to the headers. 

Any help would be greatly appreciated as I would love to get this ironed out for a full summer of enjoyment.

Thanks all

[Chryco Psycho]

Did you retune the carb with the headers , could be an engine miss , more noticable with Poly mounts .
 What make of tires , BFG are not round even when balanced !

[barracuda7199]

What kind crank is in the engine?  Did it need the b&m flexplate for the engine balance to be right?

[lime73]

Tires are BF Goodies but not the problem as the vibration is present without the back tires even being on the car.  i dont think it is a carb problem as it does not vibrate when run up in neutral.  I have installed a b&m flexplate correct for the later cast crank.

[lime73]

Stupid question.....  Is there a way to run it up on jack stands without the drive shaft in to possibly eliminate a transmission problem?

[Chryco Psycho]

Stupid question.....  Is there a way to run it up on jack stands without the drive shaft in to possibly eliminate a transmission problem?

Yes , you need a spare slip yolk , drop the shaft , slide in a slip yolk & go

[lime73]

Has anyone ever actually done that.  That sounds like it could go bad really fast

[Haddixj]

Yea I would see that yoke coming out of there pretty quick and violently. Sounds like its a trans problem. Some shops can run the trans on a dyno. Does it do it in park? Is the converter a neutral balance?

[Chryco Psycho]

Yes I have done that

[BS CUDA]

Yes I have done that

 I also have seen this done - but I wouldn't even worry about useing a slip yoke, you will not lose much oil if any at all. If you are concerned about oil loss I would just use a chunk of cardboard tube roughly the size of the OD of the tailshaft housing and duct tape it on over the output shaft and tape the end of the tube. I actually use a plastic plug that slips tightly inside the seal but over the output shaft. A plastic cup could also be used if you can find one the right size. Just some ideas - all of which I am 100% are safe and will not drain your transmission. "Adapt and Overcome" "If you don't figure it out - someone will"  - just a couple of terms I use in my own garage as well as use to motivate my employees.

[lime73]

Doesn't the slip yolk need to be in place to keep the output shaft centered.  I could see more vibration if it isn't in place as that is what keeps the whole back half of the output shaft centered.  In my mind all i can see is that yolk coming out somewhere about 3000RPM in 3rd wiping out floor board and then dancing across the garage floor.

[azmoparboy]

Hi, I really feel for you buddy. I went through the same thing myself with a motor that I got out of an RV. I even heard it run before I bought it, thought I was getting a very good engine. It had a vibration, just like yours. I did all of the things that are mentioned here. I picked up that engine for a small price, thinking that it would get me started down the road.

It was a cast crank engine and everyone that I had chatted with said that the next thing to do was to get the engine out of the car, and get it balanced. I didn't want to put more $ into an engine that would not return any of my $ so I went looking for a steel crank engine. Found a good engine to do a full rebuild on, got it all balanced, assembled it and installed it. Also I changed out the neutral torque converter for a internal balanced engine converter. Now no vibration felt. Wished I'd have just made a new engine in the first place. Good Luck this hobbie is so much fun.

Steve

[lime73]

I am very certain it is not the motor as it was not vibrating like this before i made these changes.  there are just soooo many changes i made at once and i am going to have to go through them 1 at a time and eliminate the possibilities.   Gonna be a long summer, but worth it

[Moparal]

What degree shims did you install in the differential perches?   If it was the engine, it would do it in neutral to.  Dowel pins at the end of the block for trans alignment could be off a bit to?  But back to the rear.  2 degrees 4 degrees install wedge in front then try in back.  Certain syptoms apply for cruising and under acceleration and cruising and under  deceleration.  And 2 degrees is a lot of change. Also see if you need to raise or lower your tail shaft housing now. And check the tail shaft brass bushing for wear.

[cudabob496]

out of balance converter