Matt has an issue with his GTC where he's getting drivetrain vibration at 50-60 miles per hour. I suggested that maybe his driveshafts were out of phase.

Anyone have this problem or dealt with it in the past? I'm going to crawl under mine and see how the u-joints are aligned. I haven't had mine on the highway that much but don't remember a specific vibration like this.

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Nick Taylor - Green & White 1974 Hall GTC.
www.NicksGarage.com == www.HallGTC.com == www.NicksTeardrop.com

Matt here to confirm what Nick said. I have 2 out of 3 new U joints, a new support bearing and mounting assembly, but I still get hairy vibes @ > 50 and < 60, but ONLY when accelerating. The 3d, old U joint feels solid and looks fine.....

Any ideas will be most welcome!

Were you able to check out the phasing of your driveshafts?

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Nick Taylor - Green & White 1974 Hall GTC.
www.NicksGarage.com == www.HallGTC.com == www.NicksTeardrop.com

I don't have that issue on mine.. We had ours up over 70 and went up a big hill.. (Funny to see people turn and look when getting passed on the freeway)

I'll try to snap pictures of mine this weekend. I had the one off when they towed my van home a year ago.

Check out this web site.

http://www.vibratesoftware.com/html_hel ... Angles.htm

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Nick Taylor - Green & White 1974 Hall GTC.
www.NicksGarage.com == www.HallGTC.com == www.NicksTeardrop.com

I checked the driveline software page as suggested by Nick and then crawled underneath to see what 's what. Unfortunately, everything appears to be just as described, so now I'm really at a loss! Could be the aft U-joint, but it feels very solid. ??????????

Eric,

Do you have a tach that shows you how many RPM's there are when going 70? Do you know what the OD of the rear tires is? Our rides have 4:10 rear-ends, so I'm curious what's going on at high speed. I know that mine sounds nice and smooth up in that range, but I think it might gobble fuel while doing so. Another question for the collective: What is the safe top end in 2d, especially when down-shifting? The automatic downshift on mine isn't adjusted quite right, I think, since it doesn't like doing it at higher speeds (above 25 MPH or so).

Matt, did you have this vibration before the engine/transmission swap? Did you check your driveshafts for any damage such as dents?

Even though that one u-joint feels tight, it might stil have a binding issue.

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Nick Taylor - Green & White 1974 Hall GTC.
www.NicksGarage.com == www.HallGTC.com == www.NicksTeardrop.com

Not to this extent, though there was some. It definitely is way more noticeable now - no load and it goes away.

I posted the question on a mopar forum and someone suggested checking for a cracked flex plate.

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Nick Taylor - Green & White 1974 Hall GTC.
www.NicksGarage.com == www.HallGTC.com == www.NicksTeardrop.com

That would suck. The flex plate is brand new and made for high HP truck and hotrod applications, as is the torque converter. Also, it only happens @ between 50 and 60 under load, not in lower gears.

This morning I replaced the rear U joint, which appeared to be perfect, but it wasn't! I'm only too happy to report that it is now fully driveable at all speeds. Knock on wood. Thanks for the suggestions!

At least it was something cheap,,, for once!

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Nick Taylor - Green & White 1974 Hall GTC.
www.NicksGarage.com == www.HallGTC.com == www.NicksTeardrop.com

No lie. $12.00 for the joint and $40.00 to have it pressed in. And it was only $4.00 for a new castelated nut to fix the wander all over the road when least expected problem with the steering. Even better!