ChopperDoc

First off, I know that this topic has been addressed multiple times, since I have read probably 20 threads on this, however, there is always something missing in ALL of these threads - definitive answers.

I have a 4L80e with 12 bolt Moser, 1350 everything, PST steel driveshaft (2nd one), and a BMR adjustable torque arm.

Car likes to vibrate pretty bad above 60 and worse above 80. This is speed related and not rpm, as I put it in neutral to confirm this several times. Pinion angle has been adjusted multiple times to no avail. First time I installed the PST aluminum driveshaft (1st one), I set the angle to -2 degrees @ the pinion. I never even thought to check the transmission angle since the instructions never mentioned it. Later I saw the flaw in this, as the trans was angled down -4.5 degrees, meaning that BOTH ends were pointed down.

So I adjusted the pinion up to + 2 degrees to account for load. Same vibration. Then I tried -4.5 and +4.5. Same result. Then I tried an new driveshaft. No change. Then I did a 1/4" drop on my K member, and shimmed the trans mount up 1/2". This changed the trans angle to just -2.1 degrees. I was happy with that, so I set the pinion to 0, again to account for load. Same vibe. Then I set it to +2.0, and +1, and 0.5, etc. Same deal. Only changes were the speeds the vibration occurred were up or down a bit. Still enough to rattle the car though.

So then I start looking at the tailshaft bushing. It's got some play in it with the yoke installed. Probably around .005-.010" range of "slop" in it. This made me happy to have "found the issue" until my replacement tailshaft with new bushings arrived. It has even MORE play in it. Nearest I can tell this is normal, according to all the other threads I have read.

I have also changed the trans mount out several times. No avail. Got the AC Delco stocker in there now. It's tougher than the prophane ones that I tried before. One of them actually broke on install because I "over-torqued" it. Last time I buy that crap.

I'm just looking for any ideas here, and to see if perhaps a carbon fiber driveshaft is in my future. What are the thoughts on this? I know for a fact that others have dealt with this, but what ended up being the solution? That seems to be a secret for some reason. At this point though, I don't blame you for what you have been though. Perhaps those that have dealt with this want others to feel their pain. Could use some pointers here gents.

The transmission has barley 1000 miles on it. It's a stage 2 from Jakes Performance.

ss.slp.ls1

iTrader: (36)

Since you say you changed driveshafts and angles multiple times to no avail, that leads me to believe the problem lies within your transmission or your rear end. I'm leaning towards your rear end. I don't know of a way to check the clearances or amount of play in the rear end. Any chance your wheel bearings are shot or your tires are unbalanced? Not much help I know...

RockinWs6

I had a bad vibration above 60 and it was the carrier in the rear. Lets make a list of what could be causing a vibration @60mph ANYTHING THAT MOVES! Rotors axles wheels tires yokes carrier transmission. Sometimes its really hard to find. Last thing I would have though was causing my vibration was the carrier BUT luckily I knew right away because it was the only part changed in the rear when the vibration started. Inspecting the carrier sure enough it was NEVER balanced! from the manufacturer. That carrier weighs in at over 30lbs! Yes over 30lbs and was not balanced. It was so far out of balance if you drove on a smooth quiet road you could feel it start around 30mph until by 60 it was terrible. I've been involved in a few vibration in drive line on new cars and trucks right off the car carrier and its not fun. End up changing and effin around usually what we did was get another vehicle of the same then start swapping everything starting with the DS, be surprised what we found. Axles wheels tires rotors drive shafts bent axle housings

ChopperDoc

You are very correct sir as far as anything that rotates has potential for vibes. I'm just trying to figure out the cheapest option first, and to hear other ideas that I haven't thought of yet, if you know what I mean. I already made the mistake in replacing the driveshaft, which turned into even more money because I had to buy the wife a set of $500 louvers for her stang to ease her mind off the fact I smoked $600 on the first shaft which fixed nothing. Yeah, that's how it is at my house. Rivals in the driveway together.

I actually checked with Jakes today and had a long conversation with one of the builders. He seems to think it might be an axle. That I will look into further, but I really, really don't think it's the carrier. It's a Moser 12 bolt. It's still nice and tight, and when I initially rebuilt the car, vibrations were not too substantial. That, or I didn't notice them due to the tune being so far off for all the upgrades.

Another thing I read today that got me thinking was center line for the housing. I took lot's of measurements, etc when installing. I have a BMR watts link, and adjustable LCR's. The car has been aligned with these installed and it checked out perfect. Apparently I got it just right as far as the tires go, but I never thought to check to see if the housing is centered on the shaft. That could also cause problems. I will be looking at that too.

And fwiw, I've worked on, flown, and crewed helicopters for over 16 years. I owe most of my back problems to vibrations, and possibly some of my hearing loss. I just wish I had a vibration analyzer that worked on cars like we use to balance the blades on an H-1 or H-60. Then it's more in my realm of expertise.

Ron

ChopperDoc

Too few miles to tell if the bearings are shot. They are still new, as in less than 1500 miles. Transmission is a stage 2 from Jakes, rear is a 12 bolt Moser. I did however smoke 2 housing seals on the left side, but I attributed that to FOD in the tube from relocating the vent hole for installing the watts link. I assumed, at least the first one must have been from a stray metal shaving I didn't get out with the air or the swap and magnet I ran through there. Could be an axle issue. I plan on checking those, but not before messing around with re-centering the housing. Bearings were totally fine in both cases too. Tires are all also pretty new, and no weights have came off. I will be having them checked, again, though, just to be sure. I will definitely post any progress I make on this. Seems to be a problem many have had, especially when doing 80 swaps.

Ron

RockinWs6

I can tell you this when the carrier was unbalanced the vibration had a very heavy feel to it. Carrier being worn or new has nothing to do with it. If its out of balance weighs 30+ lbs and is spinning its going to cause vibration. If you checked everything else I'd pull the carrier and have it check. Its nothing to compared to chasing your tail. One other thing is how much offset is there in the housing compared to transmission and how much thrust angle. These may be things you want to look at.

ChopperDoc

Thank you for your insight. I am definitely taking a look at any possible "angle" here, har har, and I would have never thought of the carrier. The carrier I think would cause low speed vibrations too. The vibe at 60 isn't particularly bad, or audible. When it hits 80, then it starts getting pretty noisy, and I can feel it right through the center of the car, especially on decel, which leads me to think it's an angle problem.

In my last post I was actually referring to checking the offset/thrust angle when I said "centering the housing". When I installed the rear, I did check on all of this initially. I also had it aligned, but I doubt they went that far with it beyond checking the front and rear wheel alignment. 1 degree at the center isn't going to be much of a difference at the wheel, but could cause this.

All of these things are on my list for this weekend. I am also doing another, even nastier cam while I have the car off the ground. I am also fabricating a new stereo panel to accommodate my WB, fuel press, and trans press gauges. So I may or may not have the car back up and running for a while. Plus household 06 doesn't like it when I stick her with our small kids and spend all day out in the garage, which limits my time most days.

I really appreciate your attention to this. So far this is the first time something has got me stumped and frustrated bad enough to start a thread on it. I am usually pretty good about solving all my own problems. Building a 427 stroker LS3 and stuffing it in a 4th gen is proof of that I think... Just wish I could finish this damn thing and call it good.

RockinWs6

Maybe have someone drive the car while you follow and see if anything is vibrating like a tire or wheel or the entire rear is shaking. Try putting 4 people in the car and drive it. Try lowering or raising the tire pressures too. Buy a remote camera and mount it under the car so you can see what might be the cause. Hell strap your wife under there!< just kidding

ChopperDoc

Lol. If I stuck her under there all I would get back as a report would be "the big black thing, shinny thing, red tube thing, etc..." I like the idea of the camera. I have also considered that. Might give it a shot. Plus it would be cool to see the watts link in action.