89mulletbird

iTrader: (4)

I've been chasing the vibration issue down for 2yrs with limited success. The vibration starts happening around 70MPH and just gets worse with speed. It makes no difference if I'm accelerating or coasting, if it's in gear or in neutral, if the clutch is in or out - all the same.

Here is what I've already tried:

- Put rear axle on stands and brought the car up to 100MPH with wheels removed, no difference (its not the rims/tires)

- Tried a 4th gen aluminum driveshaft, seemed to help slightly

- Bought new Strange S60 rear end, no difference

- Bought new Strange steel driveshaft, no difference

- Installed new T56 tailshaft bushing, no difference

- Set different pinion angles with my adustable torque arm, no difference

My question is: Is there anything else inside the T56 transmission that could be causing this vibration? The only thing that made a difference at all was a 4th gen aluminum driveshaft, but the vibration was mostly still there. I'm wondering if I should get the T56 rebuilt? I'd hate to do this for no reason though, it will be a bit pricey.

big gear head

It's probably in the drive shaft. Get a larger diameter drive shaft and the problem should go away. I've seen this several times before.

dragsta

i too vote; drive shaft. get a nice aluminum shaft made. before you do though, make absolutely certain it's not a rim or wheel balance issue.

89mulletbird

iTrader: (4)

Yeah, I ran the car on jack stands with wheels/tires removed and still had the vibrations. I'll take the DS in for balance check.

lunati397

If you have replaced the rear the wheels and the DS have you thought about it might be the flywheel although that would make it a RPM related

it still does it on stands

You may be missing a chunk of one of the gears in the trans or the main shaft in the trans could be bent slightly there is no way to tell without pulling the trans apart

lunati397

long shot but maybe a bad or missing pilot bushing

big gear head

Most drive shaft shops will not be able to test for a high speed vibration. Most drive shaft ballance machines are low speed. The drive shaft may be perfectly ballanced, but at high speeds it starts to bend in the middle. This is where the vibration comes in, and why you need a larger diameter shaft.

skirkland1980

iTrader: (2)

You can check driveshaft runout with a dial indicator.

dragsta

when you disengage the clutch does it still vibrate?

did you install a hard rubber trans mount? they're cheap at autozone.

does it vibrate at a specific RPM or just at high speed?

89mulletbird

iTrader: (4)

Clutch or gear selection makes no difference, it's strictly related to MPH (70+ with 4.10 gears). I can run it to redline in low gears and there is no vibrations.

The trans mount appears to be an OEM style rubber mount.

dragsta

don't rule out a loose, plastic body panel vibrating in the wind. also; check the bellhousing bolts to make sure that they aren't loose. i had a MORON install a trans for me and he had it bolted to the engine with only one tight bolt. the others were totally loose.

did you drive 70mph in a lower gear to see if it still vibrates?

is the vibration coming through the shifter ****?

cmichael

iTrader: (2)

X2 on the bellhousing bolts. also check the motor mounts that bolt to the block.

89mulletbird

iTrader: (4)

Bellhousing and motor mounts should be fine, but thanks. I had the vibration before and after I rebuilt the engine so both sets of bolts have been removed and torqued down.

jmd

iTrader: (4)

sounds like driveline (too-tall trans. mount-like)
or the T56 rear section (press-fit worn on certain parts)

shinzon1

iTrader: (1)

Just swapped my old steel driveshaft with an aluminum one out of an 02 SS. Got rid of my vibration at 70. I had swapped several steel shafts and made no difference.

dragsta

i had this problem after a T5 transplant in my 62 Chev truck. it turned out to be a combo platter of screw-ups by a moron mechanic. the driveshaft he built was visibly out of phase, too short and unbalanced. i had a nice, fat aluminum shaft made and corrected some other problems and now it runs smooth.

check the phase of your shaft. no, not the one in your pants. that one is meant to vibrate.

89mulletbird

iTrader: (4)

I'm going to check the driveshaft phase next.

I also read on LS1TECH that a guy removed his DS, stuck a yoke in the back of the trans, and revved it up to 100MPH to see if the isssue was his DS or his T56. It was his T56.

jmd

iTrader: (4)

If you can use a yoke with a hole in it, the mainshaft is tapped M12x1.75 at the end.

Ed1LE

iTrader: (39)

Did you have determine the vibration culprit?

89mulletbird

iTrader: (4)

I removed the DS and shoved a yoke into the trans, revved up to 3k RPM in 6th gear and no vibration so this pointed to something to the rear of the trans.

I sent my Strange driveshaft into Denny's shop. He confirmed the yoke was not true. He replaced the yoke on the DS and rebalanced it. 90% of the vibration is gone now.

I think because I have a Spohn torque arm with poly bushings this is the best I can get. The vibrations are barely noticeable anymore.

I highly recommend Denny's Driveshaft, it's certainly worth the extra $$ to get it right the first time!

Aares1982

I had the same problem a while back only it started at about 80, I replaced the spark plugs and that fixed it