Probably should have posted here.

I have a 1968 f250 2wd with a 300 6cyl, automatic c4/c5? long story short version. lol i bought truck from previous owner who owned since 1982. I traded it off to my stepdad and recently got it back.

So, truck had a slight vibration in the motor at certain rpm. Drivable wasn't that bad but you can feel. fast forward my stepdad pulled a empty car trailer with it about 600+ miles and pulled some steep hills near Shasta California. well transmission failed and got rebuilt. and now vibration is worse to the point it well noticeable. I guess my question is? can a new converter require or should be balanced? engine does not knock just a big vibration. I don't want to keep running it if it might end engines life?? could be harmonic dampener Failing?


Tim C,
68' f250 2wd.
69' f150 4wd shortbed
71 f250 4wd crewcab/shortbed
69 Bronco 4wd

 

I can't imagine it would be the torque converter if this problem followed the rebuilt transmission (unless the converter was reused). My money would be on the harmonic balancer, unless you are getting a consistent misfire or something in the engine.

 

Ok do you know if the flex plate was also change4d when the transmission was rebuilt?
I ask because the 300 flex does not use balance weights like the other small block (SB) motors do but they will bolt up.
It could have been changed because the teeth were not looking good and being there lets do it.

Now we are also finding that when parts will bolt up to different motor sizes a bean counter says lets put all of them under 1 part number.
So the 300 / 302 that has 2 different weights / 351 will all fall under 1 part number and not 4 part numbers.

Now I dont know what side the weight is welded on but I think you can pop the cover off for the converter and turn the motor over by hand to check for a weight and if you find one remove it.
I dont know if you can unbolt the converter from the flex plate and push it back from the flex and run the motor so only the flex spins?
The balancer and converter can be bad too but if it started with the transmission rebuild I would go with flex plate / transmission.
Dave ----

 

as for converter and /or flexplate been changed/ not sure? I will check flex plate for weights. I plan to change harmonic balancer just for giggles. thanks guy's