Rpm specific vibration above 2600 rpm

[berserk]

I hijacked my own thread that was of a different topic to try and get some help with this issue. But some new symptoms appeared and I figured this deserved its own specific post.

I have had this issue for a year now, above 2600 RPM a vibration starts in the floor board and cause my T case shifter to vibrate loudly.

It is 100% rpm related as I can replicate it at any speed as long as the gear I am in is above 2600 RPM. The vibration intensifies the higher in the rpm band I am in
 

I checked/ fixed, pinion angle, complete rear drive line rebuild and balance, T case mount, T case output yoke and bearing and the issue stayed.

But tonight on the way to work I tried something new, I put the truck in neutral at a stop light and revved the engine to 3000+ rpm and held it there and....the vibration started badly. Shook the T case shifter and floor board significantly, and I was sitting completely still.

Obvious things to check would be balancer, clutch fan, flex plate. But I'm kind of worried it may be the torque converter or in the transmission.

Anyone have ideas of other possibilities, signs to check for these issue Or similar experiences?

[zieg85]

I had a similar situation.  Vibrated at a certain engine rpm.  Ended up being my transmission/torque convertor.  I changed both and that fixed it.  Mine was a TH400 2 wheel drive

[berserk]

Ok I think I may have read your old post on that topic recent months. I REALLY hoped it wasn't my transmission, I have a ridiculous amount of money in this ol greasy rust truck after 2 years of building /dumping money into it. I just want to drive it and use it for what I built it for 😆

I'll check everything else and then consider the possibility. Thanks

[zieg85]

I took all the belts off to rule out anything on front of engine. 

[JohnnyPopper]

Taking the belts off is a good gauge, still leaved the vibration damper suspect.

Internal trans components are too restricted to cause such a wobble, IMHO. Seems that much slop would quickly grenade.

That leaves the TC, odd of that happening in itself. Having said that, if the internal stater decomposed (never heard of) and deposited material toward an imbalance, that might be feasible. 

Last suspect is the spring plate. Do you hear noise from that area?

I've had cracked SP's but never a severed one. I imagine that the offset from a bad crack or severance could cause some trouble. Like excess wear on the TC carrier bearing, leading to a wobble and surely followed by a leaking seal.

Sorry Cra-cray (berserk), only one way to find out. 

[bd]

Unbolt the torque converter from the flexplate.  Slide the converter rearward toward the transmission as far as it will go.  Fabricate a metal strap to hold the converter away from the flexplate.  Inspect the flexplate for cracks using a bright flashlight and mirror as you bar the engine over one full revolution.  If there are no cracks, start the engine and run it up to the offending RPM range to see whether the vibration persists.  This will indicate whether the vibration is emanating from the engine or further rearward.

[berserk]

Thanks for all the great suggestions, I have to drive a truck at the moment but we'll put it back in the garage and get to checking it out soon. I'll give a progress update as I go