Hey, I've got a 97 1500 5.2. Starting a few days ago, the transmission has been shaking pretty bad. It's at its worst going 50 and above in OD. If I switch it off, the vibration ceases completely. It also vibrates (I think) in third going slower (around 25 to 30 mph). If I stick her into 1st or 2nd, there's no shaking at all. There's also cylinder 1 and 8 misfiring. The misfiring has been around for a month or so, coming and going as it pleases, regardless of what I do. But it went away, and then came back about 3 days later exactly when this Transmission starting acting up on me. (And of course the engine light flashes like it's mad at me on acceleration) So, I'm no genius, but reading around has told me that it could either be the torque converter or maybe related to this misfire... Maybe. Or maybe my transmission is toast. Any thoughts?

 

I had a similar issue with my '95. I was lucky enough to trace it to the fan clutch. Went bad and vibrated over 35 mph.

Couldn't hurt to go out n try to spin it.

 

The fan itself spins fine by hand if that's what you mean...

 

Overdrive amplifies the sensation of misfires. Fix that and you'll probably be in fine shape.

 

I agree that this would be the initial condition to rectify and then proceed if necessary.

Check that #8 has been re-routed as outlined in the TSB.

Check them while it's running at night (dark) to see if there's any visible arcing. Check the injectors on both cylinders with a noid, and check/clean and gap the plugs. It may help to switch them with a different cylinder and check to see if the miss follows from a p301/p308 to where you put them.

 

Awesome, so it turns out it was just the spark plugs. I popped out 1 and 8 and both were covered in corosion. Got a small valve cover leak right there in the back. I went ahead put in all new plugs and it's running smoother than butter. I had absolutely no idea something as big as transmission problems could be affected by engine misfires. Thanks so much for the help! That's a load of stress off my mind.

 

Gotta love an easy fix, huh? Glad you got it, and thanks for following up so the next guy to search the forum gets some useful information.

It's not really a transmission problem. The same energy that you felt during the misfire in overdrive was there every other time the engine misfired at that RPM, but you didn't feel it. Being in overdrive strips away the mechanical advantage the wheels would otherwise have so their flywheel effect (to push the engine through the dead spot) is minimal, and locking the torque converter takes away its ability to damp the mechanical shock. So you feel it more, that's all. It's just a kick in the pants saying hey, buddy, we could use a tuneup here.

Glad ya got it fixed!

 

Bad plugs or wires WILL cause a transmission to malfunction even without any misfiring.

Sounds odd, I know, but have seen it more than once. Has something to do with torque output levels.

 

In what ways can an automatic transmission malfunction as a result of a spark plug or wire that is failing in some way that's not a misfire? Or even as a result of actual misfire?

 

I don't know why changing spark plug wires fixed my transmission but it did. Have also seen it on another car. Both GM V6. As I mentioned, I think it may have something to do with engine output or possibly vacuum out of spec. Not interested in debating with you as I have no way to prove that a weakened spark due to bad wire or plug can still fire on time but not put out enough spark to burn efficiently or completely.