Update: Driveshaft looks fine. Smooth movement in all directions at U Joints, no play that i can feel, and i sat there for 10 minutes trying to find some.

Because.... all i can think at this point is the transmission. I've since noticed that while it seems to vibrate at 70mph+ in any gear, it will also start to vibrate at 40mph in 4th and 6th gear specifically. Nowhere near the intensity that it does at 70mph+, but it's definitely there. 5th gear at 40mph is silky smooth.

Busticated transmission seem likely to anyone else?

I have to get under the car again after work to put the driveshaft and midpipe back up, i'll check the PPF angle for the 37th time.

 

Take a look at drive shaft angle side to side as well as up and down

 

Will do.

Do my symptoms point to transmission like my pea brain thinks it does, otherwise?

Trans had a fairly major leak from neutral sensor, likely for awhile. I have no doubts it was run quite low on fluid. Shifts good though and doesn't seem excessively noisy, which is why I didn't originally go straight to that.

 

I had a very similar problem; although, mine was not dependent at all on gearing. Nearing 70 MPH I would get an increasing vibration that seemed to come from the rear of the vehicle, and it would increase dramatically as I increased in speed beyond 70. After trying numerous solutions, I took my driveshaft in to be re-balanced and that solved it. I'm not sure how my driveshaft became out of balance but there were no obvious signs of damage to it. It was only about a 3-year old driveshaft with probably 15K miles on it, but I have taken it out of the vehicle several times and may have knocked out of balance in the process.

Bryan

 

I would consider taking it up to speed while up on jack stands and isolate what may be moving.

 

Nothing moves or appears out of place. We've had it up to 70mph in the air.

 

I got nothing

 

Me neither. Just ordered RMS and more trans fluid. Guess i'll swap the trans this weekend yayyyyyyyyyyyyyyy.

At this point i may as well put together a new motor, too. It's the only mechanical thing i haven't replaced now.

 

You're certainly bold for tempting fate like this.

 

Did you ever solve this? Deviett is having a similar problem. Blackbird drop mounts, poly diff, 6-speed, new driveshaft, 70mph and gets worse with speed. I’ll do a ppf alignment, but I’m wondering what your solution was.

 

I messed with the PPF alignment this morning, didn’t seem to make any difference. No guarantee I did everything right though.

Tested by jacking the rear of the car up, removing the wheels, and running the car up to speed in the air. Noticeable vibration by 60mph, gets really bad once I hit 80.

 

I wonder if the drop mounts require a different alignment. You might tru loosening all three front ppf bolts and letting it drop all the way and trying again. Or let AR do it, I hate having you waste time on this. We still have another driveshaft to try as well.

 

I’m going to drop it back by on Tuesday. I’ll let you have fun!

 

subscribed. Similar vibration. Interested in the diagnosis.

 

Nope. I've had 3 sets of motor mounts in the car, currently on AWR 70 not-drop mounts. I've swapped trans, diff, driveshaft, and i've aligned the PPF a dozen or so times. It's as perfect as it gets. It's a bit mind-boggling in general. The car, mechanically-speaking, is one of the most perfect things i've ever owned.

I have another set of motor mounts and a complete set of loaded uprights with SadFAB sphericals in the rear uprights to slam into it when i get a chance, but cars aren't real important to me at the moment. If the uprights don't fix it, i have to move on to checking stupid crap like brake rotors and wheels. I do have one wheel/tire set that we couldn't get under 12lbs of road force , the other three got down to 7lbs. Unfortunately i didn't mark which one that was, nor am i sure if the car is THAT sensitive, 12lbs isn't much. (I'll be pretty salty if my brand new Hypergrams are the cause of this entire thing, though.)

 

Well that isn't encouraging. Sounds like you had a lot more variables going on though, only changes in my setup were the driveshaft and potentially PPF alignment. Other than all the turbo bits, but I wouldn't think that would cause this since it is unrelated to engine speed.

 

Well.... all those things were changed in search of a solution to the vibration. It was present prior. It's a bit frustrating, there's cubic dollars in this car, and not a single knockoff/cheap part on it, anywhere. I easily took the crown away from you for "most expensive 140hp car."

 

I keep telling myself that it isn't a competition, but I don't think my wife believes me.

Prior to the most recent work I only had vibration approaching 100mph. What I'm feeling at 60 now is worse than what I had at 100 before, so if I could just get back to the way things were that would be a major improvement.

 

I doubt this car will ever see 100mph, so if i could just push the ceiling up to that, that would be fine with me.

 

Both of you have verified that the diff balancing guibo is not loose?

Also, one of you should try jumping on the rocker panels, and I'll let Ben guess who that should be