Major vibration thru coupe when it's revved!! Arrrg!

Topsterguy · April 17, 2005, 11:25:06 PM

Okay, so here's one for you! With the car running at idle everything seems fine, but rev it up and there's major vibration through the car and it doesn't go away! Nothing touching anywhere. I'm figuring unbalanced flex plate, unbalanced torque converter, flex plate mounted out of faze??? Talked to the machinist from the shop where the engine machining was done and he says to pull the trans and check the flexplate etc It's a 383 SBC so it was "supposedly" balanced externally and he doesn't think it's in the engine. Ideas?

Pep · April 17, 2005, 11:30:50 PM

I'd be inclined to undo the bolts on the flex plate/converter via the inspection cover and start the engine. That will either prove the converter or engine.

enjenjo · April 18, 2005, 12:43:58 AM

It's my guess that if it's a 383, it was balanced internally, and you have an external balance 400 flex plate, or it's not balanced internally, and you have a 350 neutral balance flex plate. One other possibility, it you have a 454 external balance flex plate, it won't be right for the 383 no matter if it's balanced internally or externally.

Bruce Dorsi · April 18, 2005, 01:45:20 AM

Does it have the correct balancer/dampener?

......I believe most of the 383's require a 400sbc balancer.

Topsterguy · April 18, 2005, 01:46:32 AM

Thanks guys! Well, I know it's an externally balanced 400 flexplate, and "supposedly" they're sure it was balanced for that, but didthey? I like the idea of checking for obvious things first, like the flexplate Pep, but would it be obvious? Going over the bills for the work it mentions all the numbers etc for the balancing, but it doesn't say anything anywhere about the flexplate (ie whether it was balanced or not). I'm talking to the guy I bought the converter from tomorrow about that, but it's hard to imagine someone that does performance converters not balancing them............right!!???

Jimbob · April 18, 2005, 02:29:23 AM

Check for a busted motor mount, that'll do it.

Leon · April 18, 2005, 03:57:42 AM

I'd be inclined to think it's the wrong flexplate. Like mentioned earlier, disconnect the converter (wire it back out of the way so it doesn't vibrate forward) and try the engine. If the vibration is still there, I'd try a neutral balance 350 flexplate.

Poida · April 18, 2005, 06:34:32 AM

Pull the tranny inspection cover, then, using a marking pen or similar, number the flex plate and converter where the 3 bolts bolt the converter to the flex plate. Remove the 3 nuts & bolts, slide the converter back (and wire it out of the way as has been suggested) and start the motor.

If the vibration disappears then the problem is behind the flex plate, and probably an out of balance torque converter. As for the marks on the flex plate & converter - I almost eliminated a bad vibration in my A by rotating the converter 120 degrees (the next bolt hole) when I bolted it back up.

p
___________
Health nuts are going to feel stupid someday, lying in hospitals and dying of nothing.

Dolly · April 18, 2005, 08:38:14 AM

Sounds just like Carp's car. I always had it down as the driver being out of balance.

Dave · April 18, 2005, 07:10:47 PM

Quote from: "Poida"Pull the tranny inspection cover, then, using a marking pen or similar, number the flex plate and converter where the 3 bolts bolt the converter to the flex plate. Remove the 3 nuts & bolts, slide the converter back (and wire it out of the way as has been suggested) and start the motor.

If the vibration disappears then the problem is behind the flex plate, and probably an out of balance torque converter. As for the marks on the flex plate & converter - I almost eliminated a bad vibration in my A by rotating the converter 120 degrees (the next bolt hole) when I bolted it back up.

p
___________
Health nuts are going to feel stupid someday, lying in hospitals and dying of nothing.

Humn thats interesting ill keep that in mind about rotating the converter but it sure sounds logical specially with a crate motor as everything in mass produced now and there could be a little out of balance condition on the engine as well .
Dave

32coupe · April 18, 2005, 07:25:07 PM

I had the same problem when i first fired up my coupe, I put in a new flex plate, and hey presto, no more vibration.

Topsterguy · April 18, 2005, 11:21:22 PM

Again, thanks BIGTIME all - much appreciated!!!

I'll let you know what we find! Larry

Pep · April 18, 2005, 11:39:06 PM

I've seen flex plates break around the crank mounting bolts cause the alignment was just out a smidgen.. Can be caused by the locating dowel(s) in the block that locate into the bell housing are missing. It is common on recoed engines that they don't fit them back in when they re-assemble them....worth a look.

reborn55 · April 19, 2005, 01:40:33 PM

Just out of curiousity--did you remove the belts and see if the vibration goes away. Have seen water pumps cause vibration, pulleys etc.

Topsterguy · April 21, 2005, 01:30:42 AM

Okeedokee then, we pulled the converter back and ran the engine - still vibrated. So we dropped the trans and sure enough the flex plate was 180 out of faze, so we remounted it lining the dowel hole up with the right hole in the flex plate, put it all back together again and flashed it up. Runs perfect - no vibration at all! Yeehaw! Life is good! Thanks again everyone!