M-20 vibration
Thread Starter
Instructor
Joined: Apr 2005
Posts: 104
Likes: 0
From: Salem Oregon
M-20 vibration
Not to run this latest drivetrain vibration issue into the ground, but I've got a problem. In 4th gear at 2900 through 3200 rpm's I've got a medium vibration. I can feel it in the shifter and in the floor of the car. If you push in the clutch and leave the gas on, you can feel it. I can feel it at stop with the rpm's at 3000 (although somewhat less). No other gear seems to be affected. Over 3200 rpm's, no problems. I run the car to 3000 rpm's to shift as a rule and need to do the same rpm's to do 60 mph on the freeway, so the problem is driving me nuts. A couple of guys think the problem is in the clutch/pressure plate area. Any ideas on how to fix? The clutch is a Centerforce II. Clutch and flywheel are three years old (12,000 miles) the 406 is the same age. Car runs strong and spends weekends dusting 'stangs and V-tech whatevers. Linkage is Hurst. Thanks
Burning Brakes
Joined: May 2007
Posts: 945
Likes: 0
From: Ventura California
If you're getting the vibes when you have 4th selected, clutch in, car stopped, at 3000 rpm, the prob isn't the trans per se. Clutch / Flywheel assembly would be suspect. Time to drop the trans and check that all your flywheel bolts are there and tight as well as those on the pressure plate. If that all looks good, I'd next check to be sure all the friction material is on the clutch plate. That's where I would do my detective work. JMHO.
Thread Starter
Instructor
Joined: Apr 2005
Posts: 104
Likes: 0
From: Salem Oregon
Thank you weimer20, I'm going to fire it up this evening and double check all the scenarios to make sure I've covered them all. Pulling the tranny for a "maybe" is not my idea of fun. I'll be sure to check closely where the vibe comes on and in what gear, if any, when in neutral. Then I'll pull the trans and nut and bolt check.
Burning Brakes
Joined: May 2007
Posts: 945
Likes: 0
From: Ventura California
Thank you weimer20, I'm going to fire it up this evening and double check all the scenarios to make sure I've covered them all. Pulling the tranny for a "maybe" is not my idea of fun. I'll be sure to check closely where the vibe comes on and in what gear, if any, when in neutral. Then I'll pull the trans and nut and bolt check.
Melting Slicks
Joined: Mar 2006
Posts: 3,342
Likes: 7
From: Connecticut
I had the same problem with my '73 last year
2700 -3200 RPM or so in 4th at around 70-90 MPH and the vibration was there. Push the clutch in and it would pretty much disappear.
I was almost ready to pull the driveshafts and then the trans but Im glad I didn't, I fine tuned it first.
Problem was the engine running a bit rough at higher rpm.
It was a combination of timing and jetting not being right on.
I believe I also needed the tires balanced which helped as well.
120 + MPH now and no vibration at all.
Just sharing my experience.
2700 -3200 RPM or so in 4th at around 70-90 MPH and the vibration was there. Push the clutch in and it would pretty much disappear.
I was almost ready to pull the driveshafts and then the trans but Im glad I didn't, I fine tuned it first.
Problem was the engine running a bit rough at higher rpm.
It was a combination of timing and jetting not being right on.
I believe I also needed the tires balanced which helped as well.
120 + MPH now and no vibration at all.
Just sharing my experience.
Race Director
Joined: Feb 1999
Posts: 19,659
Likes: 34
From: Lenoir City Tennessee
Ci 6, 8 & 10 Veteran
St. Jude Donor '05-'06-'07-'08-'09-'10-'11-'12-'13-'14-'15
I think you can remove the inspection cover on the tranny and stick a wrench up there on the bolts for pressure plate. That would be another base covered before having to pull the tranny.
Thread Starter
Instructor
Joined: Apr 2005
Posts: 104
Likes: 0
From: Salem Oregon
Thank you guys for the feed back. weimer20- no work on the car I can think of. However, both my sons (20 and 25) have been home in the last month for a week each. They like to run their moms Vette hard when in town. Hmm, I'm seeing a pattern here.
Bob Oint-I'm going to replace plugs, wires, and cap this week just in case. I trust my Holley 750 DP is working fine.
Eddie 70-I had not thought about the insp. plate. I'll pull it tomorrow after work and see if I can see or feel up there.
I did take the car out on I-5 and ran up and down the rpm range. Vibes in all but first gear. Vibes a little more with clutch pushed in and trans in gear while rolling down the road at 60 mph. Going to start with the easy stuff first. Thanks again.
Bob Oint-I'm going to replace plugs, wires, and cap this week just in case. I trust my Holley 750 DP is working fine.
Eddie 70-I had not thought about the insp. plate. I'll pull it tomorrow after work and see if I can see or feel up there.
I did take the car out on I-5 and ran up and down the rpm range. Vibes in all but first gear. Vibes a little more with clutch pushed in and trans in gear while rolling down the road at 60 mph. Going to start with the easy stuff first. Thanks again.
Melting Slicks
Joined: Mar 2006
Posts: 3,342
Likes: 7
From: Connecticut
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Pro
Joined: Dec 2006
Posts: 582
Likes: 3
From: Glen Allen (Richmond) Virginia
I had a vibration that was driving me nuts then I started thinking about how many years it had been since the driveshaft was balenced (38 years) I had it balenced and no more vibration. 
Racer
Joined: Mar 2006
Posts: 454
Likes: 0
From: SAN CLEMENTE CALIFORNIA
Same thing
Not to run this latest drivetrain vibration issue into the ground, but I've got a problem. In 4th gear at 2900 through 3200 rpm's I've got a medium vibration. I can feel it in the shifter and in the floor of the car. If you push in the clutch and leave the gas on, you can feel it. I can feel it at stop with the rpm's at 3000 (although somewhat less). No other gear seems to be affected. Over 3200 rpm's, no problems. I run the car to 3000 rpm's to shift as a rule and need to do the same rpm's to do 60 mph on the freeway, so the problem is driving me nuts. A couple of guys think the problem is in the clutch/pressure plate area. Any ideas on how to fix? The clutch is a Centerforce II. Clutch and flywheel are three years old (12,000 miles) the 406 is the same age. Car runs strong and spends weekends dusting 'stangs and V-tech whatevers. Linkage is Hurst. Thanks
Thread Starter
Instructor
Joined: Apr 2005
Posts: 104
Likes: 0
From: Salem Oregon
Have not gotten the prob fixed yet. The drive line is still at the shop not done (balanced). I'm going to replace the harmonic balancer, and remove all the belts to see if that makes the vibration go away when the car is sitting (some vibration at 3000rpm's). I bought a new set of Taylor wires and spark plugs to eliminate any kind of tune-up problems. I'll install the drive line Mon. evening and see if cured. If not, I guess I'm down to removing the tranny. One thing I'm not sure of is, once I've got the trans out, and if the disk, pressure plate and throw out look OK, then what? I don't think on a 400 sb you can remove the fly wheel and check it and the clutch for balance. The guy that built motor is absolutely sure the engine is fine. I have to agree with him. Above 3200 rpm's, and below 2900 rpm's the motor sings the rants and ravings of a well heeled 406.