bad vibration

[philo_beddoe]

I will certainly consider that capt. Thanks for the heads up.

[Captain Swampy]

Pinion is in the axle. It's what drives the ring gear. He must have missed when you said it vibrates while not moving.

[philo_beddoe]

Oh, ok. I get it. Yes in neutral or park still vibes.

[zieg85]

Take the torque converter bolts out of the flex plate and slide it back some for clearance.  Check it again.

[philo_beddoe]

Its gotta be that flywheel!  (Or flexplate as some call it)

Does it really flex?

[Greybeard]

Good question...I don't know and I'm not sticking my head in there to find out. 
I don't mean any offense here but you said you are going to take out the tranny but you don't know what a pinion is? There is a disconnect here. Taking out an automatic tranny is not a job for the un-initiated. It's not all that hard as I will assume you know, but it does take doing things in a very careful manner. Most auto tranny's weigh as much if not more than a sm465 manual and that tranny is a beast! At least when a NP205 t-case is still attached and a young fool expects to remove it all by himself...only forgets to remove the tranny shifter.    So this young fool lays there on his back with 300lbs of metal sitting on his chest while his younger brother sits in a lawn chair drinking a beer and laughing his arse off. Yup, true story. To say I learned at the university of hard knocks is an understatement.

[philo_beddoe]

I understand, my cousin is my mechanic. He does the tough stuff for me. Has an ultimate shop.  He was a tranny guy at a dealer shop. I wouldnt dare drop a tranny. I'm still reading manuals on how to change air filter!

Anyway, got to work this morning. Went slow took back roads. If all roads were downhill i'd be fine.

[Captain Swampy]

At this point....I think it's in your radio    A new stereo, amp, speakers, and a couple 12" subwoofers would surely cover up (I mean fix) this problem! Maybe a layer of Dynomat on the firewall and floor also. 

[Jim_Hensley]

just because the u joints are tight doesnt mean they are not bad,  alot of times they dry out and gall the cross ,  Id replace both for insurance , its cheap.

[philo_beddoe]

I know jim, but it vibrates bad in park/neutral. I wish it were the ujoints.

[philo_beddoe]

I have a bad feeling it aint the the motor mounts though. Gonna change anyway. This vibration has become top priority.  I do not enjoying driving my squarebody this way.

[zieg85]

I have a bad feeling it aint the the motor mounts though. Gonna change anyway.

Please do my suggestion, your transmission may be the culprit

[philo_beddoe]

Seriously, that may be the case zeig.

[zieg85]

Seriously, that may be the case zeig.

The TH400 in my truck is about to grenade and vibrates like how you are talking.  It is rpm related rather than a certain speed.  Mine vibrates worse roughly 45 mph, toss it in neutral and the engine goes to idle and it is fine.  I have yet to take loose the transmission torque converter to try my theory but mine whines bad and makes a whirling noise that comes to a stop after I put it in park.

[Greybeard]

It;s two wheel drive, it has an auto trans, that narrows it down. It makes no noise that sounds like a helicopter    but it vibrates in park as well while moving...that also narrows it down, It vibrates while accelerating in park but idles nice and smooth and not like a helicopter does not sound. OK, if there is no obvious sound that can narrow the vibration down source down some I cannot help but to think it is a bad damper or fan clutch. As we all probably know, a damper can slip easy enough since the best among them are about 30 years old now. If it is the damper (some call it a dampener, mine was only damp when I was running underwater), anyway, I had a fan clutch go bad after hitting deep water too many times and it made a hellacious vibration, but not much noise. If yours has a clutch fan shake it from front to back, should have NO movement on axis. Try to spin it, it should not spin too easily.

From front to back it has to be in the rotating mass right? Forward most part is the fan, then the sheaves, then the damper, crank, cam, cam chain (not necessarily in that order), the piston rods and pistons, the flex plate, the trans input shaft, the converter, and the trans oil pump and associated gears. Did I miss anything, working on four hours sleep each for past three days. Only one of those items is vibrating when in park. That means something is out of balance, if there is no discernible noise that goes along with the vibrations and no engine misses, it has to be something outside the engine. Something that won't/doesn't make noise. That leaves two possibilities, the damper and fan clutch. Maybe a third, a bad oil pump in the tranny. I've never heard of that but I seldom drove a truck with an automatic tranny in it. So as Zeig says- isolation is key. Come to think of it, the flex plate is not a balanced unit but is universal for all small blocks I believe, a big block has external balancing however. Regardless, pull the inspection cover, unbolt the converter bolts, pry/slide the converter back about 1/2" and start the truck. Just be easy with the throttle it's a free turning beast now and revs much easier. It will show you in a moment just how much power is wasted by an automatic trans.   

And on a different tack..

If it turns out to be a faulty plug or loose plug wire I'll laugh all day! BTW- If the plugs in it are new and they happen to be Champions, check each one (outside the engine) for spark and/or change them to another brand. Check the gap too, to wide and it will run fine at low rpm's but the big gap has too much resistance to let the spark jump at higher rpms (causing a miss and vibration). To small of gap and again it will run fine at low rpms (idle) but as the fuel ramps up the spark is too quick to ignite it (not enough duration, or dwell as it's called, the resistance is so low it goes pop and it's over or it gets quenched by the incoming turbulence). If only one spark plug is bad it can drive you crazy.