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iTrader: (6)

Ok my car is 95 formula ,6 speed,lt1.

When i hit 70mph and up the car begin to vibrate a little and it vibes a lot more as the speed goes up.The sound is clearly audible in 6th gear on the higway.Its a kind of cyclical vibration thats sound like this:

(sound/vibration).......(sound vibration)......(sound vibration).......

The dot are for silence moment.As the speed goes up the vibration/sound is more loud and the silence mark begin to be shorter and shorter.

Since im a little crazy i ve changed a lot of new parts and do a little tune up to find or help find the trouble:

-Strange 12 bolts,hd posi,33 splines,3.73 gear,LPW cover
-Spohn chromoly hd drivehaft properly balance
-Spohn ajustable torque arm,safety loop
-UMI adjustable lower control arm and panhard rod
-Koni adjustable shock set on stock spring
-Stranos 35mm front sway bar/22mm rear sway bar with poly bushing and end link
-Subframe connector welded
-Strut bar
-UMI C5 brake conversion kit with stop tech braided lines,**** pad
-Magnaflow cat back
-Short stick,160 thermostat,lt4 km, hpp3
-Moroso cai with trick flow elbow
-Accel extreme 9000 wire with 8 tr55 gap .050
-Msd blaster coil
-Msd cap and rotor kit
-Power steering pump
-New belt
-ABS/TCS delete ,line lock,proportion valve
-FLUSH of all fluid :rad, power steering,engine,transmission,brake
-18"x9.5" all black ZR1,285/35zr18 fk-451 tire properly balance
-Verification of the alignement twice and chassis lubrification

I know thats some of this parts where not related to the problem but i just want to be sure that you all know what i ve changed and what are the mods on the car.

Since i install a Sphon adjustable torque arm i tried all the pinion angle possible from -10degree to +10degree just in case and it didnt fix the problem.Now the pinion is set at -1degree.

Now im lost A lot of f-body owners experience this problem but i never hear about someone that actually fix it.

Could it be the tranny mount,the transmission output shaft transmission bearing,name it because I DONT KNOW

I got this trouble for a year and a half now and im really desperate to solve it.I put a lot of money/hours on it and still cant drive it like it should be drive


So could someone help me...please

ChocoTaco369

i'm gonna guess it's the driveshaft? i remember with stock LT1 cars they would vibrate badly at highway speeds if memory serves correctly back from my V6 f-body days. the fix at the dealership was to put in an alumium one - vibration cured.

i would get your driveshaft checked for balance. FWIW, i put an alumium one on my V6 firebird and it was 100% vibration free afterwards - it came stock with a 2 piece steel driveshaft .

i see you have an aftermarket one up top but it's still a possibility. have it double checked

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iTrader: (6)

The problem was there with my stock steel driveshaft.But just like i wrote i install a brand new sphon HD chromoly driveshaft properly balanced.

Thanks for the try

ChocoTaco369

yea i missed that mod the first read so i tried to edit my original post to the best of my ability. you may have a cracked transmission mount then. since your torque is transferred to the rear from the tranny (i assume the torque arm is mounted to the tranny in LT1's too?), if a mount is cracked and the tranny is vibrating, so will your rear at high speeds. i'd check both the tranny and motor mounts, you may have a broken one.

sorry about the confusion, i totally missed that line about your new driveshaft

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iTrader: (6)

No problem The spohn torque arm front mounting point is relocated to the tunnel brace,so no more load on the transmission tail shaft.

But i will check for bad motor and tranny mount.

ChocoTaco369

even so the driveshaft will still channel that vibration from the motor and tranny to the rear. i'd say mounts have to be the problem since your suspension has thousands dumped into it. isn't that like life though? you'll spend thousands trying to fix the problem and after all the work it was a $50 part?

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iTrader: (6)

I hope that you are right Im just beginning to be a little tired and irritate by this stupide problem

ChocoTaco369

yea i don't blame you. just get them checked before you buy anything. i hear they're a bitch and a half to install.

DONAIMIAN

iTrader: (18)

Pinion angle, also when was the last time you had the wheels balanced?

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iTrader: (6)

I ve tried every pinion angle and done a test drive after every change from -10degree(-10,-9,-8,-6 etc) to +10degree and he vibration never quit.

I ve also tried my 16inch wheel with my stock brakes and the vibe was there.I then changed to c5 brakes and put some new 18inch wheel properly balanced (check more then 3 times to be sure) and still the vibe is there.

Thanks

SLO98Z

iTrader: (10)

Since it looks like you've checked everything else pretty much, you might want to make sure the bushing in the tailshaft housing isn't worn out. This would cause some vibration and possibly noise. You would usually notice a leak from the tailshaft rear seal if the bushing is worn out, but not always. I would check the tailshaft housing completely and also your driveshaft/pinion angles. If you still have the stock trans mount, now is the time to change it. Go with stock unless you have poly motor mounts. Make sure the trans is centered just right, before torquing it all down. This would also cause a vibration under a big load. I'm reinstalling my tailshaft housing today. I took it off last night to get a new bushing and seal pressed in. We wore that sucker out on the dyno and mine was leaking a bit when I ran the hell out of it. My torque arm bushing was beat and I think it was ultimately the culprit. Are we having fun yet? Good luck man!

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iTrader: (6)

Yep i got a slight leak from the rear seal.Yep i still got the stock trans mount.

Now could you explain me how to check the housing.Can this part be taking of the trans or i got to take the hole trans out(dont wanna do that).

I dont have really good knowledge when it comes to transmission.I didnt know that there was a bushing in there.I always thaught that there was a rear seal and a bearing behind

Thank you

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iTrader: (6)

Dont be shy i will not bite you

SLO98Z

iTrader: (10)

Just get under there and look all around the housing for any cracks....just a good visual inspection.There is a bronze bushing behind the seal that has to be pressed in. I'm not sure, but I think the whole trans has to come out to change it if it's a manual trans. On the autos, you can just pull off the extension housing. If I were you, I'd get a new stock trans mount as soon as possible. Poly would be good if you had poly motor mounts. Are you sure the torque arm mount & bushing is still good?

I stayed up late and finished mine last night. New torque arm bushing, u-joints, trans seal and bushing seems to have tightened things back up.

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iTrader: (6)

Well my sphon torque arm has less then 2000miles on it so it should be good but i will check.

Also when i ve checked it seems that the tail shaft housing can be seperate from the tranny with i think 6 bolts so i will check this to.

Since evryone is thinking this way i will change my tranny mount and check for crack or something on the housing.

Whats the torque of the trans mount bolts?

Thanks

always faster

iTrader: (6)

My new DS come with 2 new u-joint.

CW00BlackTA

iTrader: (31)

Some things to consider--been through this myself. If you adjusted your pinion angle as much as you say, it's possible you killed your rear u-joint in the process. They are designed to live within +- 2.5 degress if I remember. From my own experience with this problem, I know you can kill them in a matter of days or weeks--I did it. Another thing is to check the run-out on your rear yoke. My brand new one had about 0.006 inch run-out which caused vibration. A new billet yoke fixed that. Last, pinion angle is important. There are at least 3 ways that I've seen and some don't work so well. I measure the angle on the face of the crank pulley. Then I make the angle of the yoke match that. Then I move the yoke down 1 degree for a -1 setting. This setting works well for my daily driver. Larger angles caused more vibration in my car with the Spohn torque arm.

Good luck with it.

BlackHawk T/A

iTrader: (3)

I have the same type of vibration and I have a new built tranny and prothane transmission mount. Stock torque arm. I am going to switch back to a rubber mount and see if it helps. It got much worse with this mount.

The faster you go the faster it "bumps', and it has those short pauses in-between. It starts to become apparent around 65mph.

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iTrader: (6)

Yep you got the same trouble that i got.

BlackHawk T/A

iTrader: (3)

Yeah I am also running new wheels/tires, and those didn't change anything. They are computer balanced also.

It is 100% drivetrain related and there is no arguing that. The car is smooth as soon as you put it into N...