1997 80-series Vibration while Stopped in Gear (1 Viewer)

[JTinNM]

Hello, I am seeking advice about a vibration that has emerged while my 80-series LC is stopped with the engine running and in gear. At a cold strat with the vehicle in park or in gear there is no noticeable vibration. As the vehicle reaches operating temps an evident vibration develops when I come to a stop with the vehicle in gear. When I put the vehicle in park the vibration goes away, similarly if I put the center diff in neutral the vibration stops. I have crawled under the vehicle looking for broken exhaust or engine mounts but don't see that to be the problem. Because the vehicle is not moving I have elimiated the driveline as the source of the vibrations. While I was under the vehicle with a friend putting in and taking it out of gear I have noticed what seems to be a vibration through the transmission bell housing. I don't known much about automatic transmissions but it seems to shifting and operating fine while driving. When the transmission oil was last replaced it may have been over filled. When the vibration developed I checked the tranny fluid, which appeared to be high and I drained ~1-quart but that did not resolve the vibration. Any thoughts are appreciated.

 

[devo]

My ‘97 has been vibrating in Drive while holding the brake for the 15 years I’ve owned it. Smooth in Park and Neutral.
I remember doing a search on the subject and I do believe it has all to do with how the computers lean it out and do some other adjustment? It’s not unique.
Used to bug the sh^t out of me and now 15 years later it is what it is!

 

[LC4LIFE]

Yep, not unique. I personally believe it’s from the torque converter and nothing can be done and it’s not worth worrying about.

 

[ATXnative]

I replaced engine mounts and it reduced it by about 90%. I suspect the rest would be resolved by trans mounts, exhaust mounts maybe but that’s a lot of work for something minor. doesn’t bother me anymore

 

[BlackRifle]

What is your RPM while in gear and not moving? My 96 is doing something similar and I’ve noticed my idle go up to 750+/- RPM. It used to sit at around 650+/-.

 

[COYS]

I replaced engine mounts and it reduced it by about 90%. I suspect the rest would be resolved by trans mounts, exhaust mounts maybe but that’s a lot of work for something minor. doesn’t bother me anymore

I replaced all the same mounts with oem new. No vibes before and after. Ever. Not normal.

 

[flintknapper]

Its a very common 'harmonics' issue. I'd wager as soon as you increase engine rpm a couple hundred it quits, right?

Replacing motor and transmission mounts can help in some cases. Also....be sure your engine is in good 'tune' and that it runs and idles smoothly (no missing or erratic idle).

If the motor mounts have never been replaced.....odds are good they have cracks. The rubber dries out and loses its dampening capability.

Here is what mine looked like:

 

[JTinNM]

What is your RPM while in gear and not moving? My 96 is doing something similar and I’ve noticed my idle go up to 750+/- RPM. It used to sit at around 650+/-.

My RPMs while idling in park are ~700 RPMs and oddly the idle drops when placed in gear to just above 600 RPMs.

 

[JTinNM]

Its a very common 'harmonics' issue. I'd wager as soon as you increase engine rpm a couple hundred it quits, right?

Replacing motor and transmission mounts can help in some cases. Also....be sure your engine is in good 'tune' and that it runs and idles smoothly (no missing or erratic idle).

If the motor mounts have never been replaced.....odds are good they have cracks. The rubber dries out and loses its dampening capability.

Here is what mine looked like:

View attachment 3513513View attachment 3513514

Thanks for suggestion, I will look at this more closely. I don't know if my logic is correct, but one reason I eliminated the motor and and exhaust mounts is by pressing on the accelerator while the tranny was in park to see if a vibration developed and none did it, the engine went smoothly up RPMs with no vibration. Can engine mounts be replaced without pulling the engine?

 

[JTinNM]

I replaced all the same mounts with oem new. No vibes before and after. Ever. Not normal.

How bad was yours, mine vibrates the dash when stopped in gear. It annoys the hell out of me!

 

[COYS]

How bad was yours, mine vibrates the dash when stopped in gear. It annoys the hell out of me!

? Mine never vibrated before and after.

 

[CJK]

Mine does this but I don't know why either soooo hopefully we figure it out. It feels almost like a "lean idle stumble" but I have a wideband O2 sensor so I know the engine isn't lean (lambda @ 1.00 at the time)

I have new motor + transmission mounts on the shelf to install at some point as that was my next guess.

 

[Whitetail]

I replaced the motor and tranny mount and that helped a lot. I replaced the crank pulley and the vibes went away. ymmv.

 

[JTinNM]

I replaced the motor and tranny mount and that helped a lot. I replaced the crank pulley and the vibes went away. ymmv.

The crank pulley, that's something I haven't considered, thank you.

 

[devo]

Sounds like yours really vibrates a lot? When I spoke of my vibration it is mostly kind of a buzz at the H/L shifter but not up into the dash.

PS: I’m in Santa Fe

 

[flintknapper]

Thanks for suggestion, I will look at this more closely. I don't know if my logic is correct, but one reason I eliminated the motor and and exhaust mounts is by pressing on the accelerator while the tranny was in park to see if a vibration developed and none did it, the engine went smoothly up RPMs with no vibration. Can engine mounts be replaced without pulling the engine?

Pressing the accelerator increased the engine RPM (creating a new harmonic), I would expect the vibration to go away. Typically between 800 and 1000 rpm it will smooth out. Lower than that is usually where the engine harmonics are enough out of balance that you feel it. When the mounts are cracked or the rubber has hardened too much.....it transfers to the body of the vehicle.

Anytime you feel the vibration....increase engine rpm just a few hundred rpm and see if it goes away. I'd wager it does.

IF it does....consider replacing the mounts and making sure your engine is in good tune (good plug wires, spark plugs, distributor cap and rotor, clean the intake, be sure there are no vacuum leaks, etc).

Yes, you can change out motor mounts (and trans mount) without removing the engine. Its not fun, not fun at all.....but doable.

 

[JTinNM]

Pressing the accelerator increased the engine RPM (creating a new harmonic), I would expect the vibration to go away. Typically between 800 and 1000 rpm it will smooth out. Lower than that is usually where the engine harmonics are enough out of balance that you feel it. When the mounts are cracked or the rubber has hardened too much.....it transfers to the body of the vehicle.

Anytime you feel the vibration....increase engine rpm just a few hundred rpm and see if it goes away. I'd wager it does.

IF it does....consider replacing the mounts and making sure your engine is in good tune (good plug wires, spark plugs, distributor cap and rotor, clean the intake, be sure there are no vacuum leaks, etc).

Yes, you can change out motor mounts (and trans mount) without removing the engine. Its not fun, not fun at all.....but doable.

Thanks Flintknapper, I appreciate your thoughts.

 

[JTinNM]

Pressing the accelerator increased the engine RPM (creating a new harmonic), I would expect the vibration to go away. Typically between 800 and 1000 rpm it will smooth out. Lower than that is usually where the engine harmonics are enough out of balance that you feel it. When the mounts are cracked or the rubber has hardened too much.....it transfers to the body of the vehicle.

Anytime you feel the vibration....increase engine rpm just a few hundred rpm and see if it goes away. I'd wager it does.

IF it does....consider replacing the mounts and making sure your engine is in good tune (good plug wires, spark plugs, distributor cap and rotor, clean the intake, be sure there are no vacuum leaks, etc).

Yes, you can change out motor mounts (and trans mount) without removing the engine. Its not fun, not fun at all.....but doable.

After reading your reply, I started the truck drove it around for a few minutes to warm it up enough for the vibration to develop, when stopped with the vehicle in gear, I put my foot simultaneously on the brake and accelerator and slowly began increasing the rpms. Your are correct, the vibration went away as the rpm's increased past ~1000 rpms. This is encouraging because I now know the vibration is not present at driving rpms/speeds. It was not previously clear if the vibration was being masked by the vehicle's movement. I will look more closely at the condition of the engine and tranny mounts. Thank you.

 

[CJK]

Yes, you can change out motor mounts (and trans mount) without removing the engine. Its not fun, not fun at all.....but doable.

So I've read...and hence why my replacements are still on the shelf

 

[joxeale]

Had the same issue. Went away after replacing engine mounts, all 3, go OEM.