UPDATE for those who wanted to know, I solved the vibration!! I could not be more happy right now, turns out my brand new moser housing was bent, had the rear end straightened and all is good


Alright, I made a thread on this before, but decided its time for a new one. Basically I was completely stock except for a textralia clutch lid/cutout and konis. I added the following mods:

Poly motor mounts
UMI Adjustable Torque Arm
UMI Torque Arm Relocation Bracket
UMI Adjustable LCA's
Moser 9", 4.11s, truetrac
New Stock Rubber trans mount

Ever since I installed these items I've had a horrible vibration above 60. I bought a new PST 3.5" aluminum driveshaft and shortened the length of the LCA's to move the rear end forward to put the slip yoke into the transmission more, so the driveshaft is not too short. The vibration was drastically reduced and was at least bearable. The pinion seal on my 9" went bad, so I was going to replace it. I pulled the driveshaft out and after seeing my exhaust was in the way and going to make things difficult to replace the pinion seal, I put the driveshaft back in and didnt replace the seal. The next time I drove it the vibration was back in full force. WTF All I did was pull the driveshaft out and put it back in. So i put the car in the air again, unbolted the driveshaft and rotated it 180* and put it back in and it didnt help at all. Played with the pinion angle basically from +5* to -5* and the vibration didnt change at all.

There was quite a bit of play where the driveshaft went into the transmission and my trans was getting stuck in 4th gear, so I sent the trans off to get it rebuilt. Stage 3 viper output shaft, machined tailshaft with new bushing from Tick Performance with new bigger slip yoke, new front U-joint. Put the driveshaft back in, seemed nice and tight, no play, go for the first drive and the vibration is just as bad as it was before the trans went in to get rebuilt . Checked my pinion angle and it was at around +3* which was off, because I think I gave up on pinion angle when I was messing with it and thats what it ended up at. Reset it to around -2*. While I was under there I noticed there was play where the driveshaft goes into the transmission AGAIN. I guess what I am getting at here, since I'm basically completely out of ideas, is could running +3* of pinion angle for around 100 highway miles of vibration ruin the trans tailshaft bushing to the point where when I get the pinion angle set at what its supposed to be, that its too late?

I've already gone through everything else, new tires and wheels. New rear rotors etc. The vibration feels like its coming through the floorboard right underneath the seat, but I cant really feel it in the shifter. The vibration is reduced when I've got my foot on the gas at 75, but when I let off to coast it gets horrible. Then above 80 its just horrible all around. If its not the tailshaft bushing, could something in the 9" be causing the vibration?

 

I have the same symptoms with basically the same setup as you, except with a poly trans mount (made no difference with stock mount). I figured it was just the nature of the beast with the torque arm bolted directly to the body.

 

It feels like something is going to explode underneath my car when I go over 90, it seriously cant be that bad.

 

Yeah ~120mph I can't even see out my side mirrors. I got the car aligned at a dealership when I lowered it, and it helped out a little bit. Hopefully someone can help shed some light on the situation.

 

A lot of us have gone through the vibration nightmare and survived to tell about it. The first thing is to set your pinion at zero to minus 1/2 degree--mine had to be that close to stop vibration. It's important how you measure it too. Measure (with the driveshaft out) at the rear of the trans and match the pinion yoke to the same angle (these are nearly vertical surfaces you are matching). That gives you zero. Move the pinion down from there if you want negative. Check the run-out of your pinion yoke. Mine was excessive and needed to be replaced. Check your rear to make sure it's lined up properly side to side, front to back and square. If you've run your u-joints with an extreme pinion angle for even a short time, chances are they are toast. They don't have to feel sloppy either. Replace them. Finally, I run a body mount torque arm and I put rubber spacers between the body and the mount. Each of the items I've talked about contributed to my vibration. I'm running smooth now. Hope this helps. It sucks to have a high performace car that you can't drive over 60!

 

I guess I'm just confused as to why pulling the driveshaft out and then putting it back in would cause the vibration to get bad again. I'll set the pinion angle to -1/2* and get a new rear ujoint so we'll see.

 

K went under the car to put the stock torque arm mount and trans crossmember in and noticed that my brand new trans is leaking from the rear. What would cause my car to eat up the tailshaft bushing?

 

hey going through the same thing here with the same setup as you cant drive over 55 without car feeling like its gonna fall apart...just wondering if you solved your vibrations yet. I just figured it was something in the rearend...Also noticed my tranny leaking in the rear which never happened before

 

Tranny leaking in the rear most likely means that your tailshaft bushing went bad and took the seal out with it. Mine just did the same thing, so the vibration is eating up the rear bushing. I havent solved the vibration yet, I'm pulling the 9" out to have it looked at in a couple weeks.

 

I stopped driving my car in early November so I never got around to adjust it like CW00BlackTA said.

 

i guess im just gonna switch back to the tranny mount for the torque arm and see if the relocation bracket is causing it...i also think these rod end control arms just make matters worse

 

I just posted to your other post and had forgot about this one. Anyways, if you drove with that pinion angle for 100 miles, I'd be your rear and maybe front u-joints are shot. I ate several of them sorting my problems out. Getting the pinion angle right the first time saves lots of woes later. And it has to be really close sometimes (0 to - 1/2 degree for mine). Also, make sure you measure and set the angle correctly. The relationship of the trans main shaft and pinion shaft is what's important.

Just jack the car up by the suspension. Pull the drive shaft. Measure the angle at flat by the trans tail shaft. Make the pinion yoke face match that angle. That puts you at zero. For a street car I'd try it there, again at minus 1/2, and again at minus 1 to see where it works best. To get negative angle, just adjust your torque arm so the from of the pinion yoke moves downward.

 

There seems to be a major argument on how to set pinion angle. That's how I did it the first time, however, BMR suspension has a video on their website telling you that you measure the pinion angle based on the relation of the driveshaft angle to the pinion on the rear. I actually mentioned it in a thread that BMR posted in about pinion angle and they told me that they do it their way because thats what works. So now I dunno WTF is going on with pinion angle as there are 2 different ways to set it. When I set it how you describe, then measure according to BMR's instructions the pinion angle is +3*. If I set it according to BMRs instructions and measure it based on how you tell me to set it, then my pinion angle would be more like -5*. So, who knows what the correct way is?

Here's the thread: https://ls1tech.com/forums/suspensio...orque-arm.html

Why does this have to be so complicated?!

 

I'll give you a bit more explanation and you can decide for yourself. The crankshaft and trans main shaft are parallel--because they were designed that way. To transmit max power to your rearend, you want the pinion shaft to be parallel to the trans mainshaft under load. There is a relationship between the transmission and the rearend and they are connected by the driveshaft. To get everything right, you have to understand the relationship. Doing things like lowering your car or swapping trans mounts can change that relationship. Therefore, you need to understand how it all ties together rather that just working the angle between the driveshaft and the pinion shaft. Make sense?

When you set the pinion shaft parallel to the trans mainshaft, you establish the relationship you want under power--but you aren't under power yet. The next step is to compensate for load on the system--which will tend to raise the front of the pinion. Drag racing loads are higher than daily driver loads so they may choose a minus 3 angle for example. Most daily drivers are between zero and minus 1. The idea is to put the front of the pinion lower without load so it raises up under load to give the best power transmission through the driveshaft. Also, by setting it up this way, you ensure your u-joint angles are equal and minimized. Note that if they run over 1.5 degrees it will shorten their life. Larger anges can kill them very quickly.

Do a web search, you can find all of this out yourself. Regarding the BMR site, that method probably works for a lot of cars--but once you start modifying things, you need to know more than just the angle between the pinion shaft and driveshaft. BTW, I used that method when I first set up my 9 inch and Spohn TA. Vibrated like a bitch! I finally learned how to do it right and solved the problem.

 

I understand your method and was under the impression that that is the correct way until BMR told me otherwise. Your method is the way I set it up the first time. I've tried both methods without any result and thus am beginning to believe that there is something more serious going on with my setup than pinion angle. Rear end is coming out and going to a shop, its the last thing I can think of.

 

Any updates? I feel like I might be suffering from the same thing. I replaced the tail shaft seal and since then it vibrates above 65. Not leaking fluid though...

 

i installed a moser 9 inch into my car with a bmr adj ta amd the umi ta relocation crossmember and i could not get the pinion angle right for the life of me! if would vibrate really bad around 40 mph and up. i took off the ta and the umi crossmember and but the stock ta and crossmember back on. NOT A SINGLE vibration. i came to the concluesion that i totally suck at setting pinion angles. the thing is that i had the ta relocation and the adj ta with my 10 bolt and didn't have and vibrations until 120 mph. i installed a small peice of rubber between the crossmember and the body and didn't have any vibrations.

 

update at beginning of first post