Guys / gals,

What the most likely place to start looking for a vibration from my freshly rebuilt 727?

The shop is taking it back for a look-see tomorrow AM and I'm interested in the "talking points". I figure most likely a poorly balanced converter? Otherwise I figure there ain't much that gets balanced.

BACKGROUND:
Local shop, very reputable and reliable Mopar-lovers. I gave them my car with 727 for a rebuild, new converter, seals, bands, etc. They pulled the tranny, opened it up, found busted flanges in the case at the pump. I went over there and they showed me everything. So we bought a used 727 and swapped all my stuff into the unbroken case.

The 'new' tranny shifts and drives 200% better than my old one - nice and tight - except it vibrates in "waves" when accelerating - around 25mph, 45mph and not so much above that. How much does it vibrate? - Enough to make the car feel "rough".

It doesn't do it off-throttle. I feel it in my butt. Plus a little vibration in the steering wheel. I think it's the tranny and the shake is transmitted to the chassis at the mounts.

Opinions?


Thanks!
- Art

Unbolt the rear of the driveshaft and rotate it 180 degrees, bolt it back in and test. Sometimes it is as simple as that.

Does it vibrate at speed in neutral?

Thanks - I'll test the vibration in N at road speed. I don't know if they disconnected the rear of the shaft, but trying to rotate it 180 is reasonable (and easy). Because the "feel" of the vibration is kinda like that. Not as strong as an unbalanced tire.

I'll go try that right now.
- Art

I'd also check the converter part number to confirm it's the right balance as in internal balance forged motor or cast external. Not sure whether you're running a SB or BB from the post.

Check the tail shaft bushing. If the yoke is sloppy in the bushing it will go into convulsions like that.

Kevin

Thanks 80fbody - It's a '67 Satellite with original 383 2bbl engine. I don't know which it has, but I'll find out online.

And - I eliminated the yoke/driveshaft/u-joints as possible culprits:

Just sitting in the driveway with the engine running, in Park or Neutral, I can bring on the vibration just by throttling up to the "right" RPM**.

It's going back to the shop tomorrow and I'll have them check the part number.

I think we're done here.
- Art

**PS - At roadspeed, putting it in Neutral and dropping the engine down to idle, the vibration goes away completely.

They didn't put in a cast crank converter by mistake did they? You can see the balance weight or the lack of thru the inspection cover when you turn the engine over.

Kevin

HOLY SMOKES!!!

This is exactly the problem I have...and this is on a freshly rebuilt 360 motor, factory crank, offset weight crank damper, B&M offset flexplate and neutrally blanced converter. Brand new driveshaft, new U-joints, new Yokes (trans and rear end, that's billet piece). The motor was balanced at a machine shop.

I ruled out all drivetrain motion culprits since the 'wave' goes in Neutral/Park as the car sits and the RPMs are raised.

Best I can tell is that the shop either completely screwed up the balance job, or the converter itself is off-balance. The unknown in my case is whether having the converer sitting in a box for several years (like 10 actually...lol) while I worked on the car has caused some kind of damage to it.

I'm saying ....wrong converter.

I would think that if it was a TC/eng balance issue that once the RPM got high enough for the imbalance amount to be enough for it to be felt that that amount of vibration would either stay the same or get more pronounced as the RPM increased rather than come and go as the RPM increases. It wouldn't be going back into balance as the RPM's went up

True...not sure about OP's details, but in my case the vibration comes and goes in 'waves'...so at any particular RPM, it's this wave like pattern that is felt...at some RPMs the pulse is higher in amplitude, ie it is stronger, at other RPMs it's much less intense.

With the trans in park and neutral there isn't much of anything inside the trans that is spinning , the input shaft , the rear clutch retainer and the maybe the front clutch via parasitic drag, which would spin the sun shell, everything that is splined to the output shaft is not moving if the car is not moving .

Anything bolted to the the crankshaft is spinning when the engine is running and it becomes part of the engine imbalance equation.

Someone said something naughty ???

You're too sharp for me bro , I gotta have the coffee 1st

Yep - the new torque converter was not balanced correctly from the M'fr. The shop owns up to it and says it happens about 1% of the time.

For diagnosis - with the car parked and the engine running in Park or Neutral the only parts that rotate are the (pistons, crank, cam(s), flex plate and t.converter. I could find the shake at certain harmonic RPM's. An added diagnosis was to drive the car down a moderate hill, find the vibration, then shift to Neutral and turn the engine off - and the shake disappears, which eliminates yoke/driveshaft/ujoint imbalance.

The engine is not a factor because it was smooth before the tranny rebuild.

The shop mechanic sat in the car, revved it a couple times in Park and knew it was the TC.

According to the mechanic, there are two types of TC's, one for 360 and one for the 383/440 BB's. They ordered the correct part number, but they simply got an incorrectly balanced TC right out of the box.

They'll get me in the shop next week.
- Art

I guess the shop doesn't dyno their transmissions after a rebuild? If they do, they should have found the vibration then.

if your old convertor had no wights and new one does you can just knock them off