The hunt for bad vibrations
Thread Starter
Racer
Joined: Oct 2001
Posts: 279
Likes: 1
From: Stonewall N.C.
The hunt for bad vibrations
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
Melting Slicks
Joined: Feb 2002
Posts: 2,298
Likes: 1
From: Sodertalje/Sweden
Re: The hunt for bad vibrations (vettedreams)
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:
Thread Starter
Racer
Joined: Oct 2001
Posts: 279
Likes: 1
From: Stonewall N.C.
Re: The hunt for bad vibrations (GDaina)
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!
Racer
Joined: Nov 2001
Posts: 251
Likes: 0
From: Lake Hughes CA
Re: The hunt for bad vibrations (vettedreams)
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.
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.
Thread Starter
Racer
Joined: Oct 2001
Posts: 279
Likes: 1
From: Stonewall N.C.
Re: The hunt for bad vibrations (gerry c)
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.
Drifting
Joined: Feb 2002
Posts: 1,987
Likes: 3
From: Manchester, Dead Center in the Middle of TN 25 miles to Jack Daniels,10 miles to Geo Dickle, and .8 mile from the Liquor Store at I-24 Exit 114
St. Jude Donor '05
Re: The hunt for bad vibrations (vettedreams)
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
Thread Starter
Racer
Joined: Oct 2001
Posts: 279
Likes: 1
From: Stonewall N.C.
Re: The hunt for bad vibrations (PROSOUTH)
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?
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Le Mans Master
Joined: Jan 2000
Posts: 8,918
Likes: 27
From: New Hill NC
Re: The hunt for bad vibrations (vettedreams)
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]
[Modified by wombvette, 6:47 PM 1/1/2003]
Thread Starter
Racer
Joined: Oct 2001
Posts: 279
Likes: 1
From: Stonewall N.C.
Re: The hunt for bad vibrations (wombvette)
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
Drifting
Joined: Feb 2002
Posts: 1,987
Likes: 3
From: Manchester, Dead Center in the Middle of TN 25 miles to Jack Daniels,10 miles to Geo Dickle, and .8 mile from the Liquor Store at I-24 Exit 114
St. Jude Donor '05
Re: The hunt for bad vibrations (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.
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
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
Thread Starter
Racer
Joined: Oct 2001
Posts: 279
Likes: 1
From: Stonewall N.C.
Re: The hunt for bad vibrations (PROSOUTH)
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 .
Melting Slicks
Joined: Jun 2002
Posts: 2,844
Likes: 99
From: Orrtanna Pa.
Re: The hunt for bad vibrations (vettedreams)
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.
Thread Starter
Racer
Joined: Oct 2001
Posts: 279
Likes: 1
From: Stonewall N.C.
Re: The hunt for bad vibrations (The Money Pit)
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
