727 Trans or Torque Converter Sound

[AR67GTX]

No help but I would be a little suspicious of a rebuild of a high mileage transmission and the only problem part found was the tail shaft bushing. I sort of suspect it's not transmission caused due to the unsteady harmonics - but just guessing.

If the rear bushing was worn did you look at the yoke for wear also? U-joints replaced? Driveshaft angles as mentioned above?

 

[khryslerkid]

Check driveshaft angle,(?) sometimes these videos don’t help us at all; i kept thinking u-joint till I saw this is another d-shaft.Kinda sounds like binding(?).

Angle is good. We tried a different driveshaft today just to eliminate it. The one I had in the car, I totally rebuilt but you never know. Changing to another one didn't make any difference.

I know a video isn't like being there. The sound that I'm hearing is noticeable in the video. There's also some harmonics or slight vibration that's felt with it.

What inside of a trans would sound like two gears, running together and not running smoothly? Reminds me of a cheap gearbox on a piece of farm equipment.

 

[khryslerkid]

No help but I would be a little suspicious of a rebuild of a high mileage transmission and the only problem part found was the tail shaft bushing. I sort of suspect it's not transmission caused due to the unsteady harmonics - but just guessing.

If the rear bushing was worn did you look at the yoke for wear also? U-joints replaced? Driveshaft angles as mentioned above?

This is a '62 pushbutton trans, front and rear pump. No yoke, has a flange for a trunion driveshaft. No play in the flange or joints, all new. I'm wondering how worn something else would be inside of the trans. The builder said everything looked ok. I trust him, 60 years in business and he knows these transmissions. I'm just trying to find out what component inside the trans would make this sound/vibration. Pump, planetary gears, torque converter, ect.

 

[Paul_G]

I had a torque converter vibrating badly once, the symptom was a bad vibration over 3000 RPM. It would do it at that rpm regardless of being in any gear or in neutral, and it had no stahl, it wanted to pull right off idle. I dont think your experiencing any of that. But I would check the flywheel to converter mounting bolts.

Idling in the garage, run the engine RPM up to the point you experience the issue, and above. What happens?

It sounds more like wind buffeting, or something rubbing. I would look closely at the front of the engine too for a loose alternator, or pulley, stuff like that.

 

[miller]

Just a thought, and easy to check. Pull the inspection plate off the trans, and watch the converter/flexplate, looking to see if they run true. If not, flexplate is probably warped.

 

[khryslerkid]

I had a torque converter vibrating badly once, the symptom was a bad vibration over 3000 RPM. It would do it at that rpm regardless of being in any gear or in neutral, and it had no stahl, it wanted to pull right off idle. I dont think your experiencing any of that. But I would check the flywheel to converter mounting bolts.

Idling in the garage, run the engine RPM up to the point you experience the issue, and above. What happens?

It sounds more like wind buffeting, or something rubbing. I would look closely at the front of the engine too for a loose alternator, or pulley, stuff like that.

I do kind of have the vibration in neutral but ever so slightly. In gear it feels like it could be the converter. It's a very tight converter, like you stated, it has almost no slippage. Coming to a stop while driving it, I'm waiting for the trans to downshift so I'll get it stopped. The converter was supposed to have been reworked for a higher than stock stall. I haven't found any stall rpm yet. It's a 19 spline and they can't get much stall out of them when modifying. Im leaning in this direction but I can't be definite.

The sound I'm hearing from inside the car is just like wind buffeting. Then there's a harmonic sound resonating from the hump area and a sound like a badly meshed gear. When this is all taking place I can place it in neutral and it instantly stops.

 

[khryslerkid]

Just a thought, and easy to check. Pull the inspection plate off the trans, and watch the converter/flexplate, looking to see if they run true. If not, flexplate is probably warped.

You know, last week I had the front up on stands, removed the inspection cover to check crankshaft endplay. That was good. Then I checked for any loose converter bolts or interference and all was good.

You think I would have fired it up and watched the flywheel/converter? I'm slipping in my golden years! I'll try to do this tomorrow.

 

[493 Mike]

Kid,
Have you spoken to the converter people about this?
Mike

 

[khryslerkid]

Kid,
Have you spoken to the converter people about this?
Mike

Not yet. My trans shop did the ordering of the tc. It's who they use so I'll have to call my trans guy.

 

[oldbee]

Where’s Doug when we need him? If you go to neutral with a rear oil pump is everything still kinda being driven by it? Throwing out ideas.

 

[khryslerkid]

I finally got around to checking out the flex plate and TC. I lined up the inspection bolt flange to the edge of the flex plate so I would have a reference. You can see the flywheel starter ring on the left side. Ran it up to 2,000 rpm, then backed it off to 1,800 rpm. That's the range I experience the sound. Then I revved it up a couple of times to try and flex the plate. Looks pretty true to me.

 

[Fran Blacker]

Wonder if a strobe light would help you see better?

 

[AR67GTX]

I may be disagreed with but my small bit of experience with a stock-type flex plates seems to indicate that as long as they are close they are OK. I tried out the original and about 3 new replacements when I rebuilt my transmission and all of them had ears that were out. The original was the worst and it was also the thickest metal. But I worked with a dial indicator to try to true a couple of them up, which were bolted to the crank and it took almost no force to bend an ear a little bit. I guess that's why they call them flex plates. Any small amount of run out on an ear is easily self-adjusted when bolted down to the stiff torque converter. And I can't see the small stresses in that thin flex plate creating any issues with the pump or bushing. Now, a heavy duty, race-unit flex plate might be another story.

Could be something internal to the toque converter but I don't think the flex plate could be at issue unless it's cracked - which is worth checking for.

 

[oldbee]

THAT is one great video. No problem I can see either( that’s why it’s a “flexplate”. The journey continues- planetary gear going bad? Trying to think what’s kinda not locked up solid. May have to get out FSM & really scrutinize.

 

[khryslerkid]

Wonder if a strobe light would help you see better?

I'm thinking a strobe would freeze it. Just as useing the timing light. It would appear to be sitting still. I can see that it's running true in both directions.

Could be something internal to the toque converter but I don't think the flex plate could be at issue unless it's cracked - which is worth checking for.

I checked for cracks. Bolts are tight and nothing is scraping. I really think it's in that TC but I don't want to pull the trans, replace the TC just to find out its in the trans. The trans was just gone over and all was good but you never know. I'm hoping for someone to say "that's the same thing that I had once."

THAT is one great video. No problem I can see either( that’s why it’s a “flexplate”. The journey continues- planetary gear going bad? Trying to think what’s kinda not locked up solid. May have to get out FSM & really scrutinize.

The FMS only pertains to diagnosing a new trans, not one with milage on it. Out of adjustment problems, low on fluid problems, that is what they give information to. I haven't talked to the rebuilder yet. I might even take it to him so he can hear what it's doing. He's 25 miles away and I'm not really keen on driving it that far not knowing what the problem might be. My trailer hasn't moved for six years and I'm not wild about useing it. Oh the drama! Lol

 

[Fran Blacker]

Was thinking of an adjustable strobe where you could set the flash rate. Probably need to set it very fast to make so it would flash every quarter turn of engine. Curious what your answer would be.

 

[khryslerkid]

Was thinking of an adjustable strobe where you could set the flash rate. Probably need to set it very fast to make so it would flash every quarter turn of engine. Curious what your answer would be.

An adjustable strobe would slow it down. Too bad I don't have one.

 

[Fran Blacker]

An adjustable strobe would slow it down. Too bad I don't have one.

$20 amazon. Maybe your trans could come to your place or some where in between.

 

[khryslerkid]

$20 amazon. Maybe your trans could come to your place or some where in between.

I'll find out when I contact him, maybe one of his techs lives close to me. His techs are up on these trans also. If I can't get ahold of him tomorrow, it will be Monday.