I just swapped a rebuilt 305 into my car behind a 700R4. I am having an issue with vibration @ 2K+ RPM. It happens while driving or when revving the motor in park or neutral but it is much less noticable when its under load and especially bad when I let off the gas and coast. I have read that maybe the torque converter needs to be turned... any other ideas? Thanks.

 

engine mount could be busted

 

There wasnt anything noticable when I put the new motor in....Any particular area to check?

 

Was your new engine balanced?

 

If you have the stock mounts check the rubber inserts for tears or cracks. But Ill pose the same question was your engine ever balanced

 

The motor is just a replacement from an old pickup truck. It was fine in the truck, I have no idea if it was ever balanced but I know its not common practice for any backyard engine builder I know.

 

which balancer and flywheel did you use?your old ones or ones w/new motor?

 

I used the flywheel from the car because the truck had a manual and I used the balancer from the truck. The balancer that was in the truck was much bigger than the one originally in the car. I guessing that I cant mix and match....

 

You can mix and match balancers from anything except a 400.

 

So how can I tell if Ive got an issue there? I will try rotating the TC and check the motor mounts and see if the helps.

 

i have this same exact issue 2k+rpm's only with a 400 and a 350 and two different trransmission with different torque converters and i just got the flexplate replaced and the motor mounts were brand new when i put the 350 in? i've been struggling with mine for over a year now. please any help would be great.

 

I have the same problem. Rev anytime to 2K RPM and it vibrates.

 

I still have the same problem. I havnt driven the car at all since I first posted but I adjusted the timing and that got rid of some of it but its still there at 2100-2600 then clears up. I dont know what else to do....

 

Did you guys ever figure out the vibration problem? I'm going through the same thing right now. My motor mounts are fine, torque converter bolts and bell housing bolts are tight. This past week I pulled my driveshaft and the u-joints were perfect. Tranny mount is 2 months old and is poly. I changed the bearing in my tailshaft because it was pretty worn but that was'nt the problem. Any help is greatly appreciated!

 

Do you have a mechanical clutch fan on it? Try running it for a little bit without it on to see if anything changes. That's what it ended up being for me.

 

Mine has an electric fan. I found out the hard way what my problem was…I spun a rod bearing. Boy does it have a knock!