[Michael G]

Converted my muncie to a th-400 last year and am now plaged with a harmonic vibration when cruising at 65 mph and 3000 rpm. I've ran two driveshafts,the second being balanced twice and I also witnessed for straightness. Had it rebalanced because I transfered the yoke from the original shaft and thought I carried the problem over.
The engine assembly was fully balanced with the flywheel. The counterweights were drilled in the back and filled toward the front of the motor so I can't believe the flywheel was used to correct crank balance even thou it also had a drill mark on it.
The engine and trans are currently out of the car for other changes, and I need some advice on where else to check before it goes back in.
Could the problem be in my new torque converter? Where in the phila/nj area can I have it checked?
If nothing else I plan on rotating the converter to the next hole on the flexplate. And also removing the pilot bearing that I didn't feel like taking out during the convertion.
Any comments greatly appreciated. Thanks, Mike

[Michael G]

Converted my muncie to a th-400 last year and am now plaged with a harmonic vibration when cruising at 65 mph and 3000 rpm. I've ran two driveshafts,the second being balanced twice and I also witnessed for straightness. Had it rebalanced because I transfered the yoke from the original shaft and thought I carried the problem over.
The engine assembly was fully balanced with the flywheel. The counterweights were drilled in the back and filled toward the front of the motor so I can't believe the flywheel was used to correct crank balance even thou it also had a drill mark on it.
The engine and trans are currently out of the car for other changes, and I need some advice on where else to check before it goes back in.
Could the problem be in my new torque converter? Where in the phila/nj area can I have it checked?
If nothing else I plan on rotating the converter to the next hole on the flexplate. And also removing the pilot bearing that I didn't feel like taking out during the convertion.
Any comments greatly appreciated. Thanks, Mike

[mike nixon]

is the output shaft bushing in the trans tight? if the driveshaft yoke is loose in the trans when installed you will get the vibration you discribed. mike

[Half-Inch Stud]

Hmmm, yea even the TH400 may have several wiped brass bushings. If the vibrations occur at speed, rather in neutral, with smooth engine rev-ups for vibe-sensing, then the whole TH400 rotating assy may have too much bushing slop and allow "off-center" clutch-pack engagements to occur.

Converter hub neck into Front Pump..that's another bushing to check. Front pump shaft to front pump wear patterns. Center-Support bushing is long and large [for good reason] and usually shows either smooth wear or erosion wear. Last of the internals; the 1-2 rear Planetary bushing to case. Then, the driveshaft yoke bushing in the Tail extension..but that is not usually the problem.

A highway evaluation I do to my TH400 is get up to cruise speed, no other cars around [noise], observe nominal vibration. Put TH400 into neutral, while keeping motor near equaly rev. Re-engage into Drive and see if nominal vibrations get better, worse or stay the same. Repeat.

Loose TH400 Bushings; lets clutch packs function as crankshaft counterweights.

Another possibility: I had solid motor and Tranny mounts in the 69Streetbird for 5 years that caused a cyclic vibration at highway speed. vibe would come and go at a 10 second rate. May have had something to do with the solid-mounted exhaust system too.
Well, replaed the TH400 mount and the passenger mount with rubber, and all evidence of the vibe syndrom went away.
Still have the steel motor mount in the driver side.


H.I. Stud

[This message has been edited by Half-Inch Stud (edited 01-06-2001).]

[Michael G]

Thanks for the replies. 1/2" you always give a good rundown of many possibilies. It was really hard to tell from placing in neutral and holding to 3000 rpm because the vibs did go away but the speed also droped off.
I'm going to inspect the output shaft area, replace my modified trans mount and go with
it. Was more concerned with a negative impact on the engine then anything else. The trans is fresh so I do not suspect any internal bushing wear.

[Half-Inch Stud]

Well, good to hear the TH400 is fresh...tough to make a rebuilt TH400 vibrate.

[Scott Misus]

Unless the brass bushings weren't inspected and replaced.

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"Do you have any auburn wigs to go with this dress and this pickup truck?" --Jerry Bull

[pontiacjim]

Does it have a clutch fan ? The clutch could be bad.

[PROBRD]

Michael- My first thought was U-joints but it looks like those have been replaced. My second thought was the torque converter. Did it vibrate in park at 3000 rpm's? If so it is probably a torque converter balance problem. If you have a converter company around take it to them and have them check to see if it has a balance problem. Cheap converters are notorious for this. By rotating the converter on the flexplate you will probably change the rpm at which the vibration occurs but it might get out of the range of normal operation. Keep us posted to what you find out.

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1/8th mile 6.56 @ 104
1/4 mile 10.43 @ 127

[Half-Inch Stud]

SURE, a locked fan clutch, if applicable, would be a certain source of vibes, and unseasonable wind gusts at idle. Certain other effects too;

I locked 3 of those, and cracked an iron water pump open on the highway during a 2-3 upshift with the A/C on, on 4 Aug 1989. [still made it to the wedding on time] Went back to the flex fans, and have been using aluminum water pumps since. Have not had any cooling issues for over 11 years.

[Michael G]

Checked the output shaft bearing clearance and came up with about .006"
Reinstalled the motor and trans this weekend.
Probrd I'm with you on this one. If I had to bet my last dollar I would have said it was driveshaft related. The clutch fan was a carry over from the 4 speed. The torque converter is not an off the shelf setup and should be ok, but I would not have minded to pay for a balance check to rule it out. For now I'll just rebolt the converter in a different hole and see what happens.
I did find a bent pushrod during the cam change, so who knows maybe that was the culprit.

[PROBRD]

Michael- Rev the engine in park or nuetral. If you still have the vibration unbolt the converter and try it again. Go slow it will rev a lot quicker. If it is then gone it has to be the converter. Good luck.

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1/8th mile 6.56 @ 104
1/4 mile 10.43 @ 127