Tranny/Torque Converter ?

[5.0Flareside]

ok so a few weeks ago i felt a vibration in what i thought was the tranny or rear end. well i had figured out to me i felt it from the tranny. well i took it to the transmission shop that i whole heartily trust and neither me or my family have had any problems with and have always been great. well they told me it was not in the drive line (tranny, U-joints, driveshaft, or rear end). so i took that and drove since then with it. but the whole time the vibration was still there after rotating and balancing my tires and new pads and rotors. well i was noticing it was very strong just as the tranny was in between shifts and at the end right before it shifted. but it wasnt to bad even the times i had it on the interstate running her sometimes out to 90+ with no problems.

Well the interstate portion all changed tonight. Me and Ann were going into Murfreesboro (bout 10 miles Via Interstate 24) and i was cruising along at 70 until i needed to pass someone so i wound the ole 351 up to around 80 and as it went between 73ish and 80 ish there was a VERY VERY bad vibration when i was in the throttle. but when i would let out the vibration would completely go away.

This to me seems almost like its not the actual transmission but Torque Converter. no im not real sure on how the TC functions but i know it locks/unlocks but im not sure when and why and at what speeds etc.
can someone diagnose this for me?



and huge thanks to any help at all.

 

[d-kuzmen]

Are you getting any unusual noises? How about if you brake stand it (one foot on brake and other on gas) do you get any vibraitions?

 

[5.0Flareside]

Are you getting any unusual noises? How about if you brake stand it (one foot on brake and other on gas) do you get any vibraitions?

i havent done that. but ive got it possibly narrowed down to either the harmonic balancer or Flexplate. but im gonna go everything like mounts and u-joints again tomorrow. just to be sure.

i might go and do a brake stand in it and see if i get any vibrations.

 

[blacksnapon]

The converter should unlock when the brake is depressed.

 

[5.0Flareside]

ok i did a brake stand and unintentionally did a burnout at a stop light. ahhaahah at least i know the truck can still do it. but the vibration was somewhat there just not a lot.

 

[d-kuzmen]

ok i did a brake stand and unintentionally did a burnout at a stop light. ahhaahah at least i know the truck can still do it. but the vibration was somewhat there just not a lot.

You may have a cracked flexplate or the converter is on it's way out, because when you have your foot on the brake and gas it nothing else is (should) be turning except the flexplate and converter.