AHHHHHH help please

[crewcab higgy]

I need help please

I have a pulsating vibration that gets noticeable around 60 or 2800 rpm. but hardly noticeable in neutral and vibrates right before the shift and is holding on to second for a long time. I have replaced the u joints and carrier bearing. I rebuild the 454 about 600 miles ago and when i got it running the vibration got much worse than before. My fuel economy was good though 10-12 ish I unbolted the torque converter and turned it then bolted back together the vibration got better for a little bit. after about 100 mile the vibration came back and is getting worse. i have brought it to 2 transmission and both have told be its one of three things 1. harmonic balancer 2 fly wheel or 3 torque converter. I marked the balancer and cant see that its moved but i can see a vertical black line on it. i unbolted the tc and started it up and the vibration became very noticeable. on top of all this as the vibration has getting worse so has my gas mileage which is why i was leaning towards the tc but now that i unbolted it and the vibration got worse. Maybe my fuel economy is unrelated but I'm lost as **** right now and moving 1200 miles in 2 weeks and need my truck bad. now im down to 6mpg.

 

[MadOgre]

I need help please

I have a pulsating vibration that gets noticeable around 60 or 2800 rpm. but hardly noticeable in neutral and vibrates right before the shift and is holding on to second for a long time. I have replaced the u joints and carrier bearing. I rebuild the 454 about 600 miles ago and when i got it running the vibration got much worse than before. My fuel economy was good though 10-12 ish I unbolted the torque converter and turned it then bolted back together the vibration got better for a little bit. after about 100 mile the vibration came back and is getting worse. i have brought it to 2 transmission and both have told be its one of three things 1. harmonic balancer 2 fly wheel or 3 torque converter. I marked the balancer and cant see that its moved but i can see a vertical black line on it. i unbolted the tc and started it up and the vibration became very noticeable. on top of all this as the vibration has getting worse so has my gas mileage which is why i was leaning towards the tc but now that i unbolted it and the vibration got worse. Maybe my fuel economy is unrelated but I'm lost as **** right now and moving 1200 miles in 2 weeks and need my truck bad. now im down to 6mpg.

Well its a process of elimination. You seemed to have eliminated the torque converter. I would check the flex plate very carefully for cracks with a very bright light. Un bolt the torque converter so you can get as good a look as possible.

Did you mark the slip yoke and replace it in the same position relative to the drive shaft when you changed U joints ? If you put a string down the drive shafts are they straight ? How does the balancer look ?

 

[bucket]

Did the flexplate maybe lose it's balance weights?

 

[crewcab higgy]

Well its a process of elimination. You seemed to have eliminated the torque converter. I would check the flex plate very carefully for cracks with a very bright light. Un bolt the torque converter so you can get as good a look as possible.

Did you mark the slip yoke and replace it in the same position relative to the drive shaft when you changed U joints ? If you put a string down the drive shafts are they straight ? How does the balancer look ?

Man your a welth of knowledge I think you've replied to every question I've had.
I marked the shafts when I pulled them and I had the problem prior to pulling it. The shafts are straight all wright's on and I can replicate the vibration with the tc disconnected in my drive way. I marked the harmonic ballencer as nd I think that's where my problem lies but I can't see how that would cause such a change in mpg. Unless I have more then one problem. Here's what I'm concerned with with the harmonic ballencer

 

[350runner]

x3 flywheel

Sent from the dust in front of you!

 

[MadOgre]

Ya I don't see no issues with the balancer at least from that picture.

Check that flex plate for cracks I think @HotRodPC had the same issue once if I remember correctly.

 

[77 K20]

My wife's full size Blazer had a 400 with a cracked flexplate years ago. Like you said in neutral it was nice and quiet, but near shifts it would get louder. I had no idea what it was.

Finally I pulled the inspection cover and had someone listen while lying along the side of the Blazer while I power braked it. The sound was then very noticeable. He could tell the sound was coming from the flexplate. Turns out there were little cracks coming out from each bolt that held it onto the crank. I'm amazed it hadn't blown apart.

 

[MadOgre]

If it does turn out to be the flex plate for Gods sake! do not strip the bolts that bolt it to the crankshaft. I had a buddy "help me" and he took the air gun and at an angle decided he was gonna spin them off. well he spun all the corners off and left me with a giant sized mess.

Just a heads up LOL

 

[HotRodPC]

Ya I don't see no issues with the balancer at least from that picture.

Check that flex plate for cracks I think @HotRodPC had the same issue once if I remember correctly.

My problem was both. I never could time my engine, the mark was WAYYYY off. I finally determined it was a slipped balancer. IIRC, it was about 45 degrees out. Swapped the balancer and was much better. Also had a cracked flexplate, but it wasn't enough to cause a problem. I replaced it though when I did the trans swap due to some shredded teeth on the outer ring. And replaced with a dual bolt pattern SFI plate so now I can use Th350, Th400 or 700r4 Converters.