ThoR294

iTrader: (6)

I've posted a few threads about this, but all lead to a dead end. I am about to drive my damn car off of a cliff at this point.

I have this driveline vibration over 70MPH. I managed to tone it down, but it is still there.

It is completely non-existent when I am in gear driving. If I let my foot off the gas, you can KIND OF feel it, but not really.

If I SHIFT INTO NEUTRAL or PUSH THE CLUTCH PEDAL IN, you can feel it bad. It is in your butt and it feels like the driveshaft is going to fly out of the car. Again, over 70MPH.

What I have done:
Tried 2 different T56 transmissions
Tried 2 rear ends (first one was fully rebuilt minus axles)
I replaced my torque arm, but I CANNOT REMEMBER if the vibration was present with the stock torque arm. Stock one was cracked, so I dont have it anymore.
Tried an LS1 alum driveshaft, and I had my stock steel one balanced with new U joints.


My trans angle is -3.1 degrees (pointing down)... so I had my rear set to +2.65 and -3.2. Both angles were about the same, but at -3.2 it fixed it while in gear. Now it is only there with the clutch engaged/trans in neutral.

Engine off/on doesn't change a thing.

I am at such a god damn loss... help

MTN_Z

iTrader: (7)

I have some vibes in mine too, but I have my suspicions regarding the relocation crossmember. I have one as well. Try going back to the stock trans crossmember and trans mounted TA. If I can't get mine dialed in, I might try going back to stock location as well to see if that's the issue.

ThoR294

iTrader: (6)

I am wondering if it is the relocation Xmember as well. I might go to a junkyard and grab the stock t/a

MTN_Z

iTrader: (7)

Keep us updated. I don't know when I will be able to get around to swapping mine, so I'm curious to see if it improves anything. I've always heard that the TA being more or less directly mounted to the body through the crossmember will increase NVH, but it seems excessive.

ThoR294

iTrader: (6)

yeah its bad. I don't feel safe in the car at all at those speeds.

Might try to go to a junkyard Friday and see if I can snag one

guppymech

iTrader: (7)

Does it vibrate during a normal shift from 5th to 6th at 70? or only when you set the car up in some unusual condition that you would not normally operate it in? ie. coasting in neutral at 70 mph.

Do both of you guys have TA relocation crossmembers? I installed a UMI relocation xmbr and I did a 'before and after' measurement of the trans height. The relo xmbr positioned the trans .375 lower than the stock xmbr, I shimmed up the trans mount to position the trans at the same height as stock.

ThoR294

iTrader: (6)

It does vibrate while shifting (because I have to push the pedal in).

Doesn't matter what Im doing at 70mph, as long as its in neutral or clutch pedal is in... its vibrating.

Yes, I do have a TA relocation xmember.. I did not do a before measurement though.

guppymech

iTrader: (7)

I measured from the front edge of the shifter cutout in the floor down to the top of the trans. The dimension is 1.259 with the stock trans crossmember and trans mount. The UMI relo xmbr dropped the trans to 1.635. I was doing a clutch at the same time so I had the dreaded #6 boot out. If your trans is too low it could contribute to the vibrations.
Side note: I also picked up some vibes that weren't there before the relo xmbr, braking from high speed in neutral like at the strip. They're not as bad as your's sound though.

ThoR294

iTrader: (6)

I have a spacer that will raise the transmission....

MTN_Z

iTrader: (7)

I didn't get a chance to measure mine before I put my UMI relocation crossmember in, but that makes sense. I might have to shim it because the trans and pinion angles I'm getting with my angle finder are much higher than I was expecting. Like 4+ degrees tailshaft pointing down. Might have to shim that. It doesn't feel dangerously bad like Thor294 is saying, but it's pretty annoying.

ThoR294

iTrader: (6)

I should take a video lol

cardo0

Just a couple of suggestions.

Have your driveshaft balanced.

Differential angle and trans tailshaft angles should be parallel and not cross. Driveshaft should make all the bends at the u-joints. Lines extending out the differential and out the tailshaft should not cross.

Hope this helps,
cardo

ThoR294

iTrader: (6)

My steel driveshaft was balanced already.

By parallel do you mean if my trans is down 3 degrees my rear should be up 3 degrees?

Shownomercy

iTrader: (1)

That is what he said, but I disagree.

You should shoot for a couple degrees of negative pinion angle.

ThoR294

iTrader: (6)

I felt like ive had my rear end at every angle possible and it doesnt kill it. I was thinking maybe -3 on my trans is too much?

Shownomercy

iTrader: (1)

For a stock car, yes.

Honestly, if you are never really launching the car, stick with the 0 degree pinion. That will give you the best noise avoidance I would think.

ThoR294

iTrader: (6)

so put shims in my trans mount so the transmission has as close to 0 degrees as possible?

Shownomercy

iTrader: (1)

IDK what kinda torque arm you have but I would use the TA adjustment to make up pinion angle vs dicking with shims at the trans.

moehorsepower

iTrader: (3)

Ok basically you are feeling it when the motor is free spooling correct? You've checked everything in the drive line, did you ever check the clutch assy when you had the tranny off?

ThoR294

iTrader: (6)

i feel it when I am doing over 70mph. doesnt matter what engine the RPM is at. The engine can be off and the vibration doesn't change. I've had the clutch replaced, new flywheel, new everything. didn't change it at all. It is MPH related, not RPM related.

I have a UMI torque arm with the relocation x member. I was just thinking maybe the trans is pointing down too far.. *shrug*