Shakey 6th gear?!?

**natews6** · 04-06-2010, 08:23 PM

Hello to everyone since I'm new to this site!
I bought a 1999 WS6 about 2 weeks ago and it has a violent vibration in 6th gear. The motor and trans have been rebuilt. Motor has about 7k and trans has about the same with a new SPEC 3 clutch. The guy I bought it from told be that the new aluminum drive shaft was the problem because it was knocked over when it was leaning against a wall and someone knocked it over when they were about to install it. In my opinion I think the car shakes way to hard for it to be the drive shaft and I think if its the drive shaft it should do it in all gears? The guy swears that its not the trans because he says "it didn't shake a bit before the rebuild". He also said a family friend did the rebuild. It goes into 6th easily, but when i give it a little gas its like an earthquake. I think the 6th gear may have a tooth missing. Anyone have any input on what the problem could be? Thank you-Nate

**JohnnyBs98WS6Rag** · 04-08-2010, 09:18 AM

If the vibration occurs just at a certain vehicle speed, then it could be the driveshaft. But then it'd do it regardless if it was in 5th or 6th. From the sounds of it you have either a messed up 6th gear in the trans like you described, or a serious missfire that for some reason occurs in 6th but not 5th.

**justinmc978** · 04-08-2010, 12:42 PM

its only in 6th gear? even down low? try going the same speed in 5th and see if it shakes the same, if not, its not your driveshaft, just my 2cents,

welcome to the site btw, lots of good info here

**Knight** · 04-08-2010, 02:10 PM

I had a Jeep that did the same thing when I put it in fifth - it was an m5. It's the tranny - as long as what Justin said isn't the case.

**natews6** · 04-08-2010, 05:11 PM

5th gear is perfect, just when i shift into 6th it's an earthquake. I took my driveshaft out earlier today and it's straight as an arrow. Defiantly not the driveshaft. I think it's either the 6th gear itself or the flywheel.

**Zinergy** · 04-09-2010, 11:56 AM

Originally Posted by natews6

5th gear is perfect, just when i shift into 6th it's an earthquake. I took my driveshaft out earlier today and it's straight as an arrow. Defiantly not the driveshaft. I think it's either the 6th gear itself or the flywheel.

What difference would the fly wheel make. If it only happens in 6th its probably 6th. Get a t-56 service manual and open that bitch up.

Go 50mph, put it in 5th floor it, it should feel smooth but slow accel because of obvious low speed. Then put it in 6th at the same speed and push the gas down. Does it shake like an earthquake, if so i would say its the tranny, either the gear or the shift fork isn't moving things into place properly.

**natews6** · 04-10-2010, 08:37 AM

A service manual will defiantly come in handy.

**MrMasterCraft** · 04-10-2010, 08:54 PM

Bought an M6/LS1, 40k miles, would shake in 6th gear as violent as you described. Could never figure it out. Changed the plugs/wires on all cylinders (yes even the back 2 on the passenger side), and didn't have that problem.

Thought it was odd that a misfire like that could have such a violent impact on the car. Especially at 40k miles it already needed a plug change? Perhaps the car was sprayed beforehand

Start with the cheapest/easiest troubleshooting first, that's what I would do

**MrMasterCraft** · 04-10-2010, 08:56 PM

Originally Posted by Zinergy

Go 50mph, put it in 5th floor it, it should feel smooth but slow accel because of obvious low speed. Then put it in 6th at the same speed and push the gas down. Does it shake like an earthquake, if so i would say its the tranny, either the gear or the shift fork isn't moving things into place properly.

This is what I did, and a tune-up fixed it completely...

**natews6** · 04-11-2010, 05:31 PM

Did your plugs look bad when you pulled them out?

**natews6** · 04-20-2010, 11:17 AM

Originally Posted by MrMasterCraft

Bought an M6/LS1, 40k miles, would shake in 6th gear as violent as you described. Could never figure it out. Changed the plugs/wires on all cylinders (yes even the back 2 on the passenger side), and didn't have that problem.

Thought it was odd that a misfire like that could have such a violent impact on the car. Especially at 40k miles it already needed a plug change? Perhaps the car was sprayed beforehand

Start with the cheapest/easiest troubleshooting first, that's what I would do

I went to a tranny shop and rode a guy around with me for about 15 minutes and this is what he told me the problem was.... never would have thought about that.

**LSCyaL8R** · 04-20-2010, 12:53 PM

While It seems that we all agree that his car needs a tune I would just like to chime in on driveshafts for a moment.

Looks can be quite deceiving. All a DS needs to cause great vibration is poor body structure and a slight balance imperfection. This was the case with the Lincoln Mark VIII which would exhibit terrible vibrations at speeds in excess of 70mph if you were unlucky enough to have a driveline with these imperfections. A former Ford transmission engineer made an EXCELLENT writeup on the vibrations their cause and the remedies. He used to be a member of one of the Lincoln boards I used to frequent. It's a long read but since driveshaft vibes were brought up here I think it appropriate to share for all to learn.

http://www.tccoa.com/articles/tranny...n/page17.shtml

It's part of a larger article on how to build a high horsepower auto trans but this is the relevant page to driveshaft discussion.