BOTTLEDZ28

iTrader: (9)

I have been trying to track down a vibration problem in my car and I am 99% sure I have tracked it down to the NEW Spohn T56 crossmember I have. Once the crossmember is bolted up to the car and I start it up and rev it, the car will vibrate. the dash and steering wheel shake real bad and so does the console. the cossmember I have is part of a built in safety loop and torque arm. If I loosen the bolts on the crossmember and tranny mount and leave the tranny where it should be with a jack, the car will not shake at all I cant figure it out at all. I have checked to see if the crossmember is touching anywhere and it is not. What can be causing this. I did remove the tranny and put a new flywheel in and then started the car and it revved nice and smooth. I then put a new SPEC clutch in and started it and I picked up a slight vibration for a few hundred RPMS around 2000 but thats it. I then put the tranny in and here I am now with this problem. It is NOT the input shaft ( I dont think), when the car shakes I push the clutch pedal in and the shake is still there so that is how I dont think it is the input shaft. someone please shed some light on this please.

onebinky

iTrader: (1)

I'd think the only way the crossmember would cause a viberation is if it changes the drivetrain geometry to where you have a more extreme pinion angle then before. But even then you would only have the viberation while rolling. If you have a viberation in neutral, my guess is that it would be an imbalance with either the inputshaft, clutch, or flywheel. If it does do it while in gear, it could be anything from the crank on back to the tires.

Good luck, and keep us updated. I'm curious to see what it ends up being.

EDIT: The viberation probably goes away with the crossmember loose because it's transmitting the majority of the viberation thru the jack instead of thru the car.

BOTTLEDZ28

iTrader: (9)

well I am 99% sure it is not the flywheel and clutch because I have changed both out. I first changd out just the clutch and it was still there. I then changed out the flywheel to a stock LT1 and it got 1000 times worse. I found out later that I cannot use a stock T56 flywheel with a bob weight on it on my internally balanced 383 setup. So I then put the SLP neatral balanced flywheel back in. The thing is is that the vibration is ONLY there after I put the trans back in.With that said, I can only look at a few things, first being the input shaft, BUT if I push the clutch pedal in and rev it, the vibration is STILL there. Pushing the clutch in will disingage the input shaft and it should stop spinning correct?????. And I cant see how it can be the input shaft, it was fine last all last year up until I pulled the trans for the engine rebuild. This really has me stumped.

RB83L69

It's not caused by the crossmember. So don't thin it's the crossmember's "fault" somehow.

It's something about the engine or flywheel or clutch being out of balance. The crossmember merely transfers the vibration to the car.

Are you using actual real clutch bolts, purchased specifically as "clutch bolts"? Not just some random bolts from wherever that are about the right size? Clutch bolts are special; they have short threads and a larger section behind the threads, and the flywheel has a larger section of the hole before the bolt reaches the threads; the "shoulder" behind the threads of the bolt acts as a dowel pin to positively locate the clutch centered on the flywheel.

BOTTLEDZ28

iTrader: (9)

yes, I am using the real GM bolts for the clutch and flywheel. I had this same trans in the car before I did the 383 setup and eveything worked great. All I chaged is the the displacment(interanlly balanced), SPEC clutch, SLP billet flywheel(neatral balanced), 8" balancer(neatral balanced) and a Spohn T56 crossmember. The vitration starts about 2000RPMs. It will not go away if I push the clutch in either. Can someone explain the details to how and when the input spins on the t56. I am under the assumtion that it will spin only when the trans is in gear and the pedal is up. If the pedal is pushed in then the input shaft should STOP spinning correct. I am asking because this should rule out a bad pilot bushing or input shaft right?

RB83L69

The clutch gear in a T-56 spins under the same circumstances as any other manual transmission: clutch engaged, engine running.

If you push in the clutch and put the car in gear with the car sitting still, the clutch disc and the clutch gear will be held stationary, by being splined to the (stationary) drive shaft. Under those conditions, the engine, flywheel, and clutch are spinning; but not the clutch disc, or any part of the transmission including the clutch gear.

If you have a motor-RPM vibe with the clutch released, the car sitting still, and the trans in gear, you have an out-of-balance motor, out-of-balance flywheel, or an out-of-balance or off-center clutch.

Sounds to me like you have the wrong flywheel to go with your motor.

If you have an "internally balanced" 1-piece rear main seal motor, then "neutral balance" should include the little bat-wing weight on the flywheel, which substitutes for the rearmost crank counterweight (which is the odd-shaped flywheel flange on a 2-piece RMS motor). Obviously it's mighty tough to make a round seal fit over an irregularyl-shaped object; so they had to move that portion of the "internal" balance weight from the crank to the flywheel.

So if you have a flywheel with the weight removed, and a stock-balanced crank, then that's your vibe right there.

BOTTLEDZ28

iTrader: (9)

well with that said, my SLP flywheel does not have any weights on it at all. SLP told me that it was neatral balanced. it also doesnt have any drill marks in it. the thing that has me stumped is that there is no vibration in the car if i rev it up with just the flywheel in it. do you think that the problem is still there but i can only feel it after i put the trans and crossmember back on

Jonathan Dyer

iTrader: (5)

Dredging up an old thread...but I'm looking through all old threads on vibrations and this one describes my situation exactly. Did a quick search and see that your still posting on here.

Were you able to solve the vibration issue?
Did it have anything to do with the crossmember in the end?

I've revved the engine by itself, with just the flywheel, with the flywheel and clutch etc.. Getting frustrated driving a fast looking car that can't get safely over 45 mph!!

Thanks,
Jon

BOTTLEDZ28

iTrader: (9)

I did fix the problem. It was the rotating assembly
In my newly built engine. I had to strip it all down and have all the parts balanced as a complete assembly. Each part was balanced from the manufacturer and within it specs but when all the parts were assembled together, it created a slight off balance that I just didn't like. So, I had a shop balance everything from the crank pulley to the pressure plate on a machine and then had all the parts scribed so I would know the orientation on how they went back together.

I called each manufacturer of my parts and all of them told me that their product was within their specs. It came down to a little off here and a little off there being a big off when all bolted together. That cost me $1,000 after it was all said and done

Jonathan Dyer

iTrader: (5)

Wow, that bites. Not the answer I wanted to hear either! My engine is a GMPP crate that I've had in the car for two years. I've always wondered if I should have it balanced since I first installed it.

That being said, my vibration seems to be speed related. At 35 mph or so and geared such that the engine is spinning at 3000rpm I can feel a vibration from the exhaust through the whole car. By 60mph the vibration is extreme although I'm only turning 2000rpm. There is a bit of a difference while maintaining speed but shifting between 5th and 6th gear (a little better in 6th). It feels though that the difference has more to do with the load placed on the drive line than engine speed.

I'd pretty much given up on it being a pinion angle problem to focus more on the differential. Had it checked at a very reputable shop that specializes in tranny and rear end repair. They found one axle to have a slight wobble to it but they didn't think it was my problem. I had them change it anyway but no real change.

So now I'm back to scratching my head over tail shaft to pinion relationships. Also wondering about buying a used rear and just to see if it makes any difference rather than changing the other axle and all the bearings.

Anyways, thanks for posting back so quickly.
Jon

BOTTLEDZ28

iTrader: (9)

Have you looked into the possibility that the driveshaft may be slightly out of balance? I would swap that out along with the wheels before you go and swap the rear out.

Jonathan Dyer

iTrader: (5)

Have had my steel DS balanced twice as well as my aluminum one. Vibration is a constant with both my TT2s and my stock Iroc wheels.