vettedreams

There is a very bad vib. around 3500 & 2500 rpm."s I can shift the 4 speed into neutral at those rpm"s and the vibration goes away, I"ve tried to turn the drive shaft 180 deg. with no avail. Well I finally removed the M20 to look at the clutch assembly, looks pretty good. Where should I look now for possible solutions? :confused: :mad :cry

BB wowbagger

Have you looked at your pilotbearing?It sits at the end of the crank.When they go bad they usuallt creates some vibrations.. :smash: :smash: :cheers:

GDaina

check your motor mounts and the tranny mount. Vulcanized rubber tends to seperate from the metal.

What about your tires?

vettedreams

The mounts look new, some time ago a crate 454ci. was fitted into this "71 which originaly housed a 350ci. As for the tire balance, I"ve experienced that in a truck before and it resembles the vib. not in my vette!

gerry c

If it goes away in nuetral, the driveshaft could not be it anyway.

What happens if you leave it in gear and depress the clucth?

If it is still there, it would be trans or mounts. If it goes away it would be engine, engine accesories or mounts.

vettedreams

I hate to sound needy, but what in the engine could cause such a violent vibration? Also how do I know if the right damper is on this 454 crate motor? Thanks,I"ll try the depress clutch next.

PROSOUTH

I had this problem on my '70 454 car some years ago. I know you 180'd the driveshaft, but did you check the front yoke on it? The front yoke will wear and have ridges,grooves, etc on the input shaft. If it shows excess wear you will need to replace it and make sure you check the rear bushing in the transmission also. When it wasn't under power it didn't vibrate.JIM

vettedreams

The input shaft does have some ridges on it, the end .25" is not as thick as the rest of the shaft, sort of ground down, could this cause the problem?

wombvette

Has it ever run without vibrating? 454s are externally balanced while 327-427-350 are internally balanced. So if you used the 350 flywheel it would be a problem. If the wrong balance or flywheel is used, it will cause a big problem. You can tell the difference by looking at them. The 454s have a large heavy weighted area on them. Another thing to check is the fan for balance.


[Modified by wombvette, 6:47 PM 1/1/2003]

vettedreams

The vibs have been with the car as long as I"ve owned the car. As for the flywheel, I"m not sure about this one. There are three places on the engine side of the flywheel that are cast into the fly. one longer than the others. As for the fan it"s plastic

PROSOUTH

There is a very bad vib. around 3500 & 2500 rpm."s I can shift the 4 speed into neutral at those rpm"s and the vibration goes away, I"ve tried to turn the drive shaft 180 deg. with no avail.

OK, Let's assume it's going down the road. You say it goes away after shifting into neutral. Does it also go away with the clutch in and it still in gear?

There are ridges and wear on the front yoke input shaft?

Good possibility this is your problem. A lot of times the front yoke will only do this under load. When under load it will also increase with speed (MPH)

This may be only one of many causes and several other good causes have been given.

From GM Shop Manual

With Tachometer installed in car, determine whether Propeller Shaft is the cause of complaint by driving through speed range and note the engine RPM at which vibration is most pronounced. Then Shift transmission to a different gear range and drive the car at the same engine speed (rpm) at which vibration was noted before. Note the effect on the vibration.

If vibration occurs at the same engine speed (rpm) regardless of transmission gear range selected, drive shaft assembly is NOT at fault, since the speed (rpm) varies'

If vibration decreased, or is eliminated in a different gear range but at the same engine speed (rpm) check for possibles causes.[/B]

Try this, If your results match we'll look elsewhere. I will post the other possible causes list from the manual if needed. JIM

vettedreams

I"m going to put the trans. back in and try the push in clutch check. I"m going to take a pic of the frt. yoke input shaft , I just need to figure out how to post the pic. I"ve tried the checks mentioned in the manual, at least the one that you posted, that is the only check that I know of .

The Money Pit

Did you mean you shift into neutral with the car running on the highway,or standing still for the vibrations to stop. If you can rev it OK standing still,then the engine and clutch assembly are balanced OK. The problem would be transmission back.(Bearings,U-joints,tire balance/wear.)If you're still on the highway and shift into neutral and the vibration stops with the engine rpm the same as when the clutch was engaged and in gear,maybe your clutch is slipping a bit. Try goosing the gas while you watch the tach when in gear. You may notice the tach climbs quite a bit more than the speedometer,indicating slippage.

vettedreams

When I"m running at 3500 RPM let off the gas, shift to neutral the vibs go away shift into fourth it"s back again :cry :cry :cry :cry :cry :cry