4th gear vibration

olddog · #1 (**permalink**) 09-18-2008, 06:10 PM

I have a TKO 600 that only had about 3K miles on it when I bought the car. It has alway had a vibration in the shifter. I replaced a bad U-joint and had drive shaft ballanced right after a got it. That got rid of most of the vibration, but not all. I had kind of assumed that the short drive shaft and angles were causing the vibration.

Anyway I got to paying attention to this. If I lightly push the shifter, as if to pull it out of gear, I can feel the vibration real bad. However the vibration is only there when pulling. If I decellerate, it is smooth as silk. Ok that makes sense as the gears are meshing on the other side of the teeth, so I must have a chip on one side of a tooth.

I can do this in any other gear and the tranny is smooth as glass. Now for the kicker. I have noticed that sometimes it is worse than others. Tonight I shifted into 4th and it was smooth as glass, no matter what the speed or power level. After testing this from 1500 rpm to 3500 rpm and flat to the floor the darn thing was perfect. So I pulled it out of 4th and stuck it back in and the vibration was back. I tried it several times and the vibration changes from better to worse. So it appears that it depends on which tooth happens to match up as to how bad the vibration is and that there actually is a set of teeth that are perfectly mated and run well together with no vibration. I'm guessing that these teeth were running together when what ever damage happened to occure.

Also the trany has the .63 ratio 5th gear, which I do not like.

So if I pull this appart, what is the likely hood that I can stone out what ever ding is causing the vibration or will the gear need replaced?

Assuming I do all the labor my self and only purchase parts:

What would it likely cost to replace 4th gear like for like?

What would it likely cost to replace 5th gear with the .82 ratio?

vector1 · #2 (**permalink**) 09-18-2008, 08:27 PM

i checked on replacing a 63 with a 82 not too long ago, and the cost indicates they don't want you to do this, something like $500 or so, maybe more, can't remember for sure but i remember saying something unprintable.

Barnsnake · #3 (**permalink**) 09-18-2008, 08:33 PM

The gears are in constant mesh, so you're not changing tooth combinations when you go in and out of gear. You might have a problem with a shift collar, shifter fork, or bearing.

olddog · #4 (**permalink**) 09-19-2008, 03:00 PM

Quote:

Originally Posted by Barnsnake

The gears are in constant mesh, so you're not changing tooth combinations when you go in and out of gear. You might have a problem with a shift collar, shifter fork, or bearing.

Are you positive? If the teeth of every gear is alway in mesh, then they must be locking and unlocking down at the shaft as they slide in and out. I thought the shifting forks slide the gears up and down the shaft and take the teeth in or out of mesh. In nuetral no teeth would be meshed. If I am wrong, please explaing this to me. It's been 28 years since I saw a manual appart.

I was playing with it today. I can go to neutral and back into 4th and feel a different intensity of the vibration most times. I have also found that majic no vibration spot at will many times. It may take 4 or 5 attempts, but I can find it every time I try.

With 4th being the only 1:1 ratio (having the same number of teeth on both gears), it would be the only gear that, once meshed, the same teeth would alway touch each other.

Danr55 · #5 (**permalink**) 09-19-2008, 03:24 PM

Are you sure it's in the Xmission? I had a similar problem with my car. 428 with a TKO 600. Everytime I jumped on it, it shook like hell and when I accelerated smoothly, it only shook a little bit, but you could definitely feel it. Checked Ujoints, drive shaft, engine mounts, rear end.......finally because I had nowhere else to go, I replaced the harmonic balancer. Everything went away and it now runs smooth as silk.. Just one more thing to consider.

Barnsnake · #6 (**permalink**) 09-19-2008, 07:01 PM

The shift collars lock the selected gear to its respective shaft.

If it absolutely never happens in any gear but 4th that's a clue. 4th is the "straight through" gear. The power takes a different path through the transmission in 4th. It may be a bearing. I would contact a transmission expert.

CobraV8 · #7 (**permalink**) 09-20-2008, 03:01 AM

In a transmission for a standard rwd setup, the input shaft is locked to the output shaft when 4th gear is engaged. Because of this dyno runs are made with the transmission in "straight through" gear, when there is no load on any of the gears and therefore no gear meshing losses.

This also means that 4th is the only gear with no load on the countershaft cluster gear.

Maybe there's a problem with the countershaft or its bearings? Anyway it's hard to guess what causes the vibrations without disassembling the transmission.

Simon