bad vibration

[philo_beddoe]

If you listen carefully, you can hear it, "it" being whatever is causing the vibration. There is no noise like tapping or knocking, engine overall runs smooth. Someone else mentioned fan cluth, but i dont have one. The tranny shifts great up and down. The h-balancer is tight hasnt changed.

I can remember a month or two ago, it was just a pulsating vibration i would feel at about 40-50 mph.

Tomorrow a tranny shop is going to take a look. Hopefully some good news in 24 hours from this post.

[philo_beddoe]

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.

Mine is very similiar zieg, i also have a th400, and even a slight whirl or whine is present, very slight.

[Greybeard]

The balancer/damper may be tight but that does not mean it's good. Use a timing light and see if it is still showing the correct timing. If the mark on the balancer/damper can't be seen at idle with the vacuum advance removed it has slipped on it's axis, very common on those older dampers. It's just two heavy pieces of metal with a rubber elastomer connection between the two. It cannot come apart (at least I've never heard of one coming apart) but it can slip rotationally and possibly make a very slight noise.   

[egleaves]

I think you can likely rule out the u-joints.

I just had to have mine replaced (both ends of one piece shaft).  The truck would shake pretty bad under acceleration, but at no other time.  Speed or RPM made no difference.

[Rattler12]

May have already been mentioned but water pump heading south can cause a vibration

[philo_beddoe]

The tranny guy said it really sounds and feels like the flywheel. If its not the engine thats what it most likely is. Will know soon.

[Greybeard]

Terminology lesson, flex plate for automatic, flywheel for manual. A flex plate technically does not flex (to my knowledge), and a flywheel does not fly. That is irrelevant however, one is called a flex plate and the other is a flywheel. 

[philo_beddoe]

Ok, flexplate it is. Breaking news!! The tranny guy who is an old timer, which is good, is near 100% that i have a crack in flexplate, which is also causing my trans fluid leak... bad bushings. Stay tuned!

[zieg85]

Ok, flexplate it is. Breaking news!! The tranny guy who is an old timer, which is good, is near 100% that i have a crack in flexplate, which is also causing my trans fluid leak... bad bushings. Stay tuned!

Hope he's right,  pictures please if it is.  I am very interested.  "Usually" a crack in the flexplate will sound like an engine knock under certain conditions and if bad enough the starter will sound funny when it is cranking...

[philo_beddoe]

If indeed it is the flexplate, i'm going to frame it and display. Yes i will post detailed pictures and anything else. Stay tuned!

I'm trying not to get exited, but i cant help it.

[zieg85]

If indeed it is the flexplate, i'm going to frame it and display. Yes i will post detailed pictures and anything else. Stay tuned!

I'm trying not to get exited, but i cant help it.

I would too!!!  It gives me hope of a fairly inexpensive fix or at least a bandage for my truck to get it mobile...

[Captain Swampy]

I hope you got it fixed. If that isn't it, I'd try a new damper.

[philo_beddoe]

Me too swampy! I'm getting exited and terrified!

[philo_beddoe]

Havnt had truck in three days, starting to feel light headed.

[zieg85]

Truck withdrawals are awful and they don't make a methadone sort of drug that helps any.  I just buy another truck which does help...