Hey everybody, so I just finished up a Chevy 63 swap on my 91 pickup. And on the first test drive I immediately noticed it has a really bad shake / shudder at low speeds from around 5-15 mph. It goes away completely after 30 mph, and I noticed it’s the worst when starting from a stop or when I go to downshift to another gear and release the clutch.

At first I thought it could be the play between the front leaf spring bushing and the bolt on the Chevy springs, cause the sky’s kit included a small bolt for the front hanger that had about 1/8” or more of play in the bushing. So I got a bigger bolt and bored out the hangers so now there is no slop between the bolt and the springs, but it didn’t change the shaking at all.

However during the 63 swap my driveshaft slipped apart and I didn’t have marks on it so I put it back as close to how I thought it was as possible, but it may still be off. Could it be as simple as that? Or is it possible it could be an issue somewhere with the spring install? Everything looks lined up well and there is no play/movement in any of the components that I can find. This feels different from other drive shaft wobbles I’ve felt but I’ve only experienced that a couple other times so wondering if this could be a symptom of the D/S splines being misaligned

 

Another note I should add, I pulled the rear driveshaft and drove it around the block in front wheel drive and the shaking was gone. I know it may seem dumb even asking having ruled that out, but I’m not sure if that could have made it go away just because the torque wasn’t going to the rear end anymore and just from the front. Just hoping to see if anybody has had similar symptoms like this. Thanks guys!

 

It could well be that the driveshaft yokes being put back together out of phase, after coming apart, is the issue.

 

In addition to phasing (mentioned by Millball) https://www.drivelinesnw.com/part-tr...lysis/phasing/ , the drive shaft is balanced. With only two universal joints, there are two engagements with correct phasing. But one of them is probably out of balance.

At least check the phasing.

 

It's most likely phasing as Millball mentions, driveshaft balance will normally only be an issue at higher speeds rather than lower speeds and sometimes will have a sweet spot where they vibrate a lot then smooth out as you go faster. but that also is not a likely scenario.
check your pinion angle and maybe take your driveshaft to have it balanced/inspected.

 

Awesome thanks guys! Driveshaft phasing is news to me. Just checked and the u joint ears on the driveshaft are perpendicular to eachother. I’ll be pulling it apart and trying to correct it when I get home from work. Hopefully that fixes it and if not I’ll bring it to a driveline shop to get it checked out. Thanks guys!

 

That is absolutely out of phase, now as scope mentioned, you have a 50/50 chance of getting it back in line where it was originally balanced.
your vibration is guaranteed to be better, but the right thing to do is take it to a driveshaft shop and have it balanced if you have the moolah.

 

That was it! Pulled the driveshaft apart the other day and lined up the u joint ears parallel, and after that the shaking was completely gone. Thank you guys! Still a slight vibration at about 40 mph but I’m guessing that I’m a just spline or two off after putting it back together. Gonna bring the ds to a driveline shop to get it balanced before the build is done but at least for now there’s no more bad shaking for the test runs as I make more progress. Thanks again guys!!

 

Hopefully getting your drive shaft back in phase and balanced fixes your vibration.

I had to go with a double cardan shaft after lift and going with 63's even though the drive shaft angle was within tolerance. I would get a vibration and noise that sounded like it was in my transmission mainly at highway speeds and especially while slowing down or coasting. You have to rotate your pinion up and set pinion angle to do this. So I cut off spring perches and replaced with new to re set my pinion angle. All good after that. Just giving you a heads up in case you still have vibration or noise.