4L60E Vibration at Higher RPM's

I had my 4L60E rebuilt in January when the reverse cone splines stripped--which I've heard is a common problem with this year. Car is a '95 RMW.

Now the transmission shifts very well through all four speeds and the lockup works on the highway. However, if I accelerate fast enough to get the rpms above 4000, there is a severe vibration in the drivetrain. The vibration occurs in all four gears above about 4000 rpm. I did not have this problem before the transmission rebuild. When revving the engine in neutral, there is no vibration.

If you drive the car normally--no downshifts or fast acceleration--you'd never know there was a problem.

I suspect the torque converter is the problem, as it was changed with the rebuild and it makes sense to me that it would cause a problem like this.

Any suggestions?

 

Did you have the driveline rebuilt? Other than a possible problem with the flexplate or the T/C (not impossible, even if new), I'd think the driveline's wear is the problem.

 

The transmission was rebuilt and the torque converter replaced with a rebuilt unit. Nothing was done with the drivetrain.

Before the trans rebuild, there was no vibration, but immediately after, it vibrates in all gears--not vehicle speed related, but rpm related. Vibration begins to be noticeable at about 4,000 rpm and gets worse as rpm's go up. Shakes the body, floorboards badly. No vibration in neutral at all.

 

One other thing: was the driveline disconnected at the diff, even if it was marked? Sometimes, just because, it gets put back on 180* out (90* if it has a flange instead of a yoke), and it causes vibrations, because drivelines and differentials DO break-in and wear to each other, and changing their relation to each other causes vibrations. So if it was removed, change the installation and road-test to see if it makes any difference.

 

Think about what you said about the driveshaft.

At 4000 rpm in first gear, the car is traveling about 45 mph and I feel the vibration. At 45 mph vehicle speed, the driveshaft turns the same speed whichever gear the transmission is in, first, second, third, or fourth.

If the problem was driveshaft balance, the car would vibrate in fourth gear at 45 mph as badly as it does in first gear.

In neutral, the engine is extremely smooth up to 5000 rpm +.

My problem is transmission-related, not the rest of the drivetrain. The most likely suspect is the torque converter. I don't think there is a way to troubleshoot except by replacement.

 

There is considerably different amount of difference in the torque applied by those gears.
I'd be checking the u-joints before pulling the torque converter.
Maybe it just wasn't put back together very well.

 

I am an ASE-certified Master Tech, so I'm spitballing on ideas here; based on what you've already told me, either the torque convertor is bad, the pump is bad, the driveshaft is bad, or something was not reassembled correctly. As for the driveshaft itself, I wasn't referring to balance, but to wear-in or break-in. Taking a driveshaft off, then putting it back on out of position causes harmonic vibration, which means it won't necessarily appear when the car is traveling in First or Second, but it will in third or Fourth, because the rotational speed in the first two gears has not reached the first harmonic; that only occurs when you get enough rotational speed in third, at least. When you disassemble an engine, do you just toss the parts in a pile if you intend on reassembling it? No. You keep them in order so they go back together exactly where they came from. If you don't, you cause all kinds of problems and eventually, the engine is scrapworthy.

 

I'm just a back yard mechanic and even before I read the last 2 posts, u-joints and/or the drive shaft may be out of balance. I had a beater Impala way back and once while up on jack stands I smucked the drive shaft and a balancing weight poped off. city driving was normal but HYW driving it vibrated bad, had the shaft rebalanced and problem solved.

 

It vibrates in first, second, & third. Vibration is as bad at 4000 rpm in first as it is at 4000 rpm in third. How can this be a driveshaft problem? There is no vibration if rpm's are kept below 3000.

 

Just going by what the others wrote, experience feeling similar unbalance, and the fact my son recently changed to a heavey duty two piece drive shaft and heavy duty 5-speed, he had the same sort of problems.
He removed the rear drive shaft and rotated it 1/2. Problem seems to be solved. At least rotating the drive shaft maybe 90% then another 90% is way easier and cheaper than removing the tranny for another torque converter..... Yes that could also be the problem. Or even a flex plate out of balance.
Always go for the easy cheap fix first.

 

That was lesson number one in car repair. You haven't said if the driveline was removed or not when the trans was pulled, but if it was, try taking it off and putting it back on 180*, then driving it. It may change the vibration, it may eliminate it, but try that first. Costs nothing but effort.

 

In my experience U-joints tent to cause vibrations at certain RPM's, not MPH of the car, but RPM of the driveshaft. I would check the U-joints for wear by pulling the shaft, and just to eliminate the possibility I would reinstall the driveshaft 180 degrees from how it was removed. Just to see if it affect the issue.
Remember to check both for worn, and stiff U-joints. To me it sounds like a U-joint that is stiff or ceized in one direction, and free moving in the other.

That way you can eliminate 2 of our sugestions, and maybe prove we are idiots. It could still be Transmission or TC related. I just start with the easy thins 1st. Or just drive it back to the trans shop and see what they say?

 

and maybe prove we are idiots.
Jeff R you can't prove nuthin!

 

I believe the OP's diagnosis is good. The drive shaft is rotating at different speeds at 4K RPM is each gear, so it is not common to the problem. The only thing common to the problem is the transmission, and it has to be connected to the engine directly, because it only occurs at the same RPM in all gears. It could be a broken flex plate, as they are notorious for that to some degree. The flex plate is not under stress with the trans out of gear, so could possibly not show up under that condition.

 

Have you brought the car back to the transmission shop and mentioned the problem you are having?

I would agree that it is not driveshaft related because drive shaft vibrations are proportionate to road speed. Since the vibration is proportionate to engine speed it does sound like it could be torque convertor or flexplate. But, either of those would qualify as a mechanical vibration and be present regardless of selected gear or road speed. Since it doesn't exhibit the vibration in neutral, it sounds like it's not an out of balance issue. You can try this: remove the inspection cover from the front of the trans, start the engine, take a look underneath to see if your flexplate is wobbling at all. It should run pretty strait. The pilot of the torque convertor engages into the back of the crank. It's possible during trans installation that the pilot gets hung-up as it goes into the hole. What happens is as the convertor bolts are tightened the flexplate will bend towards the conv. This can usually be fixed by loosening the 3 convertor bolts and then using a prybar to push the convertor kinda firmly (not super hard) against the flexplate as you tighten each bolt. This would really cause a mechanical vibration that would occur at the same engine speed whether driving or parked. However, pressures in the torque convertor change with load. So, it's a possibility. The flexplate does just as the name states. The has the ability to flex as pressures change. If it were tightened in a manner where it bends against the convertor, then it wasn't installed in a relaxed position and won't work as it should.


Here are more things I would look towards: engine misfire, fuel delivery like a weak injector or weak fuel pump or restricted fuel filter. Induction, like a restricted air filter---but that would surprise me as that symptom is usually smooth. Or, perhaps a collapsed engine mount that will transfer vibration under load.
Misfire seems to be pretty likely. Get a scanner on it that can display data. I believe the GM's from that time do display individual cylinder misfire data.

Let us know what you find. It's a somewhat obscure problem and I'm curious on the outcome.

Mark
Berkshire Transmissions
North Adams, Massachusetts