I've been chasing a vibration for a long time from the rear forward. New tires, axles, bearings, ujoints, balanced four different ways.... etc, and have made my way towards the tranny. The shake follows engine rpm and not travel speed... worst around 2500, Drop it into neutral at cruising speed and it goes away. Get on the gas at highway speed and it shakes like a wet dog. A fellow at the drive-shop thought it may have the wrong flex-plate. It a 350/350 combo, with center-bolt valve covers. Hencho in Mexico. I've been having a tough time getting any readable numbers off it. I see the flexplate has a weight, does that tell me anything... What else may tell me if this is the right or wrong one?
350s dont take the weight on the flexplate..its a 400 thing. Its not a 383 which uses a 400 crank is it? If it's truly a 350, I'd say the weight on your flexplate would give you a shake or vibration..
When you drop it to neutral,,,do you keep the rpm up or let go to idle? On the flex plate,,,,late model one piece rear seal,,,,does take a weight like that on the flex . Tommy
NOPE. They make a couple 350 crate motors that requires a externally balanced flywheel or flexplate. Here for example. https://www.jegs.com/i/Chevrolet-Performance/809/19210007/10002/-1 {Flywheel / Flexplate: Like all small block V-8 engines produced since 1986, the 350 HO engine has a 3.00” diameter flywheel flange bolt pattern. Small block V-8 engines produced from 1958 through 1985 had a 3.58” diameter flywheel flange bolt pattern. This change in bolt circle diameter was made to accommodate a leak-resistant one-piece rear main seal. Due to revisions in the crankshaft design, a 350 HO engine must have a counterweighted flywheel (or flexplate) for proper balance.}
if I let rpm drop the shake goes away at sub 900 rpm... keep drifting at 60mph in neutral; and rev to 2500, and it comes back.
This is a crate engine from Mexico. Did you install it,,,,and has it always had the vibration? How long have you had it,,,,about how many miles on it since install? How is the oil pressure holding up? Tommy
If it's in the flywheel/ rotating assy, it should vibrate with the car sitting still shouldn't it? If you bring it up to 2500 sitting there. I had one that had a similar issue and it was the redi-sleeve (bushing) in the tailshaft housing. When you was accelerating it was smooth, if you was cruising it vibrated, and when you lifted it smoothed out.
Lloyd,,,you are absolutely correct. I was also thinking about the converter. since it goes away below 900 rpm. Tommy
I may have found the culprit... but my video skills aren't what they could be. If you use the settings in the youtube screen and move it to the lowest speed setting your may catch that the flexplate has a 'movement' in it.
With the car just sitting there, you in the driver's seat, and bringing the car up to 2500rpm, can you feel the vibration? Or is it only when you're driving it?
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