Driveline Whirring Worsens

[swebster]

I was hoping to get some opinions on this as I have a little more information about the whirring noise in my driveline.

I originally posted (See Previous Post ) about a whirring sound and vibration at speed when the engine and driveline where in "sync". That is to say I had no positive load (accelerating) or negative load (decelerating) between the engine and driveline. So basically I could "coast" at 70mph and hold the engine speed up with the throttle and get this noise. The noise/vibration was also noticeable for only a second as I transitioned from a downhill coast to an uphill climb.

First thoughts and replies on the earlier post were realted to failing carrier bearings and/or u joints. I still have to replace these so they may still be the issue...however on the advice of an RV mechanic I tried something on the last trip that adds a little more information to this noise.

His opinion was that this could actually be in the torque converter or the parking brake...based on my description and the fact that most of the noise and vibration inside the coach seems to be up near the doghouse rather than back by the door (where the first carrier bearing is located).

He suggested that I get up to speed, coast on a downhill and CAREFULLY put the transmission in Neutral. His thought was by "disconnecting" the engine from the driveline and checking for the same noise it would point toward the converter, transmission, parking brake area. Sure enough on my last trip I tried this procedure and the noise and vibration were there and consistent.

So...even though I'm still replacing the bearings and u-joints. Does anyone else think based on this additional "test" that I have an issue in the converter/transmission/parking brake area?

[59toaster]

Cracked flex plates are not uncommon.

There is a inspection cover on the bottom of the transmission bell housing. Take a peak up inthere. Check that all the bolts are tight to the torque converter. Look for a lot of metal dust or grindings. If you see that the flex plate is probably cracked. The metal dust will be the two sides of the crack rubbing together. As it gets worse it will sound like a rod knocking.

[74Argosy24MH]

The flex plate and torque converter are driven by the engine. When you put the trans in neutral (I am assuming you let the engine go to idle) you removed these from the equation. With the noise still there I would look further back. As long as it sounds like it is coming from the trans area when you start on the u joints and carrier bearing check the bushing in the tail shaft housing of the trans.

John

[59toaster]

Originally posted by 74Argosy24MH
The flex plate and torque converter are driven by the engine. When you put the trans in neutral (I am assuming you let the engine go to idle) you removed these from the equation. With the noise still there I would look further back. As long as it sounds like it is coming from the trans area when you start on the u joints and carrier bearing check the bushing in the tail shaft housing of the trans.

John

\

Good point.

Isn't the TH400 straight cut gears? My Burb seems to make just a little noise if I get the gass just right. Never has changed in 8K that I put on it. I wrote it off and gear noise.

[mcneon]

Have you checked your rear transmission mount? Mine got old and settled, allowing metal-to-metal contact between mount and crossmember. Lots of pump whirring entered the structure, and it was very load-dependent.

That was the easy, cheap problem. I also recently developed a new, very loud whirring in my tranny. The noise was so loud my neighbors came over to see what was the matter. It kind of came and went at random, sometimes disappearing completely when I stopped and restarted the engine.

Within a very short time it got much worse. Turned out to be a failed torque converter, which unfortunately ground itself to a fine powder and welded itself to the input shaft, ruining the transmission. One core charge, transmission rebuild, and heavy-duty torque converter later, all seems to be well. Check your fluid for evidence of finely powdered metal.

Last year my carrier bearing went bad, and the sound then was much more of a roar at various engine speeds. That noise, too, would come and go. It was much lower in frequency than the converter noise, which made it that much more difficult to localize.

Bob McKeown
Nashville

[swebster]

Thanks for all of the suggestions. I hope to get under there this weekend and look at everything mentioned. The vibration is getting worse so its time to pay the piper and spend some quality time under my AS.

(Maybe it will climb into the 60's this weekend?)

[George]

While you are checking things, check your diff. yoke.
I had one "spread" so the "U" joint was not in the center and the rear part of the driveshaft was very off center
causing vibration/unbalance.
with the retaing straps loose, check to see if the joint can be moved side to side.
The little retaing tabs should allow little or NO movement.
Luck!!
ol'George

[jim8860]

Originally posted by swebster@myrvadvanta
His thought was by "disconnecting" the engine from the driveline and checking for the same noise it would point toward the converter, transmission, parking brake area.

Drive line nosies are the worst to find.I work on off-road trucks all day long and it seems that every truck has a unique noise.As for you problem even though you put your camper in "neutral" every thing is still turning. Is the noise getting louder over time? If you parking brake was sticking you will most likely not hear a peep out of it unless the shoes are worn out. Try to apply the e-brake when you are rolling down a hill at a slow speed and listen closely.As for the flexplate the only way to check it is to pull the cover off the fly wheel area and unbolt the converter (all you need is a few simple tools to do this job) and get a good light and look for cracks.If that all looks good it just may be the nature of the beast and you have to deal with it ,my camper has a bit of a tranny noise I am just to lazy to look around.Good luck Jim