1979 360 flex plate

[440sixpack]

The flex plate on my 79 360 was like new so I reused it when I rebuild the engine. I had never run the engine before the rebuild. it's the type with cut outs but they say that style is for internal balance engines and I did not have in balanced. it seems to vibrate a bit but not bad.

1979 was external balance correct? so should I have the solid flex plate wit the weight?

[HeavyMetalThunder_81]

The solid flexplate are for the TC727 transmission. The cutout ones are for the TH400. Depending if it was for an inline 6, 304, 360, or 401 determines the balance.

[440sixpack]

I see. it's a TH400 so maybe it's correct.

It doesn't vibrate bad at all but it's not glass smooth. I wish I had just internally balanced it like I do everything else.

[HeavyMetalThunder_81]

Might be a slight misfire.

Or

Did you reinstall the bushing in the end of the crank for the torque converter snout?

[4bz]

Try removing your driveshafts, one at a time, and driving the vehicle with only one driveshaft. If the vibration goes away or is significantly reduced, you may have a driveshaft issue and not an engine balance problem. You can also try running in low range (if you have a low range) to see if that affects the vibration. If it is truly an engine vibration, it will show up at a lower speed than where you usually start to feel it. A driveshaft vibration may not show up at all, because the driveshaft will be rotating at a much slower speed in low range.

I had to replace my rear driveshaft at 88K miles, because it was causing an annoying vibration that started at about 1600 rpms in high range. The front driveshaft was also causing a vibration, but hardly noticeable. My vehicle is part time 4wd, so it will be a while before I replace the front driveshaft. The rear driveshaft failure was caused by normal wear in the spline (slip) joint.