Highway speed vibration from rear end

Awesome video - sorry the pinion wasn't the cause but I don't feel totally guilty for suggesting it as you did find it was out of spec.

... that looks like some scary ride you went for. did it damage the floor or anything else ?

Hopefully the "experts" will be just that, experts and find the root cause. If you re-read my original post, I mention how I had a new shaft made and then later (like a year or more ..) took it to another shop to have it checked because while discussing the problem at Cruise nite with some friends, one said "who made the driveshaft, XXX ? None of their stuff comes out correct.

Of course, XXX was highly recommended to me by some other car friends ou:

Good Luck .. keep us updated, and never give up !!

 

I'll definitely keep you posted. They had to order parts to reassemble the driveshaft so I'm still a few days away from an answer with it sitting at the shop. Sure wish I would have checked it before I went out on a 100mph test drive! ou:

The underside of the body took a beating but it didn't add any vent holes. My exhaust is completely beat into submission and just about laying on the ground.

I asked the shop if the geometry looked ok and they said it looks "fine". I Wish they gave me the angle measurements but I can do that at home when I get it back I guess.

The control arms look like an awesome way to customize the rear end angle. I'm still hoping I can get it close with a quick cross member shim if its out of tolerance though.

 

I am with Jacob on this. I too had to shim my 2004r up almost to where the knuckle of the u joint touched the tunnel. This gave the tailshaft of the trans a 2 degree down. This brought my driveline angle correct with my rear end which is 2 degrees up, thus removing any driveline vibration.

 

Not sure if I am buying any of it...First a guy sells you a "balanced" driveshaft that you say wobbles clearly in your sight. Then you have someone do another driveshaft that looks like you just put 800hp to it.....I wish the car were here,I would almost bet a straight junkyard driveshaft would solve the problem. I have seen a lot of tire guys balance bent rims too....junk is junk. I think you need a true driveshaft. Dan

 

Perhaps he's right around the corner, Dan, but without your location in your profile - we'll never know

 

I have a junkyard driveshaft in my car. Have no clue what car it even came out of. All I knew was the length I needed. The rest I made work. Held up for the past 30,000 miles so I guess it's good. Don't think I'll trust it behind the new motor though

 

looks like your driveshaft has been to long for a while, bet you had very little fore or aft movement on install, then when setting car down and driving under accelleration total bind up,( no fore or aft slack) to compensate for suspension travel, good luck,

 

I have never bought a new driveshaft. I think the last post may be a little closer to the truth also. If that driveshaft cannot slide in and out at least an inch or more with the car sitting on the ground,it will definitely bind. It could literally jolt you out of the seat and never break in two pieces like the last pic. I live north of Flint,Michigan and every bone yard around here has school buses full of used driveshafts. Unless you are putting 800 hp to the ground,you should have no problem. My 396 nova has an aluminum Ford Ranger driveshaft in it. I did not even have to change the u-joints. There are only a few manufacturers of the driveline pieces,so if you measure length and caliper the size of the u - joint,it should be fine. It is one of the MANY areas that spending more is not necessarily getting more. If you want to see air under the front tires on your launch,then buy an aftermarket shaft,other than that,just put in a correct length straight one. Dan

 

Dan, I'm not trying to be argumentative but - it only took me 550hp to do this, which these days is a mild to moderate BBB Build. And, a lot of the stock Buick original driveshafts were 2 piece slip joint units with a rubber coupler connecting the two. I don't trust that 45+ year old rubber .. and I twisted a stock shaft years ago with less power. Heavy car ? Yes ..

 

I don't have junkyard drive shaft in my car. And after looking at the pictures of that poor mangled one I am really glad. A top notch custom drive shaft is just not that expensive. I have a little less than $300 in one from here: http://www.dynotechengineering.com/ delivered to my door in less than a week.

 

New drive shaft is in and the angles are much closer after a 1/2 inch spacer was installed under the trans mount. The angle meter I used to test didn't quite fit between the cross member and the trans yoke, but I was able to use a straightedge to get close. By my measurements the transmission is up 3 and the rear is at down 2.5. The broken drive line took out the transmission tail shaft bushing and seal so I'm not driving it much until that gets replaced. What little I've driven it seems pretty smooth.

Now talking tailshaft bushings... I have a 1/16th inch slop with the yoke in that's way excessive right? Since the housing doesn't come off I'll have to find a transmission shop that has a puller to keep from having to tear down the whole transmission?

 

I think the angle of the 2004r is too severe when installed in an A-body car without a shim or spacer. I have heard of several people having to do this to correct driveline angle, myself being one of them

 

I never measured the driveline angle but I went off of what Ken (techg8) had said when he did the 2004r swap. He had to shim the Trans up to where it almost hit the floor in order to get the angle correct. I never shimmed my transmission the first time and used the th350 transmission mount. I would get a horrible shake coasting from highway speeds. Everywhere else it felt fine. The next time I removed and reinstalled the transmission I shimmed it up about 1/2" and the shudder wasn't so bad. The car is apart now so once I put it back together I'll check the driveline angle to get an accurate gauge of where I am at.

 

The issue is the location of the mount on the 2004r as compared to the th400 or th350. The way the casing design is......the mount sits up much too high thus making the tailshaft way to low once it is sitting on the crossmember. So its not that I had to tilt the tailshaft pointing up, it just needs to be shimmed higher for it is, in my case, now pointing down 2 degrees rather than the 8 degrees or so prior to being shimmed

 

Thanks for putting numbers to the scenario Jay. I never measured so I couldn't put exact numbers on the difference. I do know it points down way too far using a stock transmission mount and raising the tail of the transmission up (to -2 degrees like you mentioned) solves the driveline angle issues. Adjusting the pinion angle to match the transmission otherwise would be too severe of an angle. At least that's how I understand it.