Hey guys I wanted to create a new thread because I'm having such issues with a vibration that comes on at about 55-60 and I CANNOT get it to go away.


Heres the symtoms
Car drives well around town and vibration starts to become noticible around 40-45 and then peaks in violence at about 60-65. At this speed the vibration is what I would call low frequency vibration (my fuel cell which I unbolted and is hanging off a single bolt visible bounces up and down at this speed) that obviously increases in frequency as the car goes faster. The vibration is worse when I accelerate at all even ever so slightly. When I'm off the gas it does get better though. The vibration originates clearly from the rear of the car and you can feel it through the seat then as you move faster the vibration starts to be a higher frequency and moves through the floor boards and then throughout the car (even shakes the rearview mirror to the point you cant see whats behind you, like haveing a big subwoofer in the car for you audio guys) Car has delrin differential and rear subframe mounts which do transmit noticible gear whine noise into the car but I dont think its possible that a vibration like this could be transmitted just by the bushings.

So the vibration is deff speed related but is also tied to whether you accelerate or coast/decelerate.

What I've done so far
-Thought it was a bad U-joint so I pulled the driveshaft and brought it to get it checked out and balanced. They said the ujoints were fine but they rebalanced the driveshaft. Put the driveshaft back in, and made zero difference.

-Changed the tires just in case and had them balanced, No difference

-Swapped the halfshafts as excess play in the inner CVs can cause a vibration like a bad u joint. Made zero difference.

- Got an alignment made no difference but did make the car more stable obviously.

- Checked driveline angle today of tranny and rear diff in relation to the driveshaft.

Got my angle finder got the angle of the driveshaft, then zeroed it out and took the angle of the tranny (and verified it using the top of the intake manifold. The tranny was sloping down towards the back of the car 3 degrees in relation to the driveshaft. Then measured the angle of the rear end and what do you know its sloping up 4.5 degrees in relation to the driveshaft. So I felt better figuring alright they arent equal I know this can create driveline vibrations. Problem is the rear end is already as low as I can put it. I even put spacers between the rear subframe mount and the body to space the rear subframe down a bit and pull the nose of the differential down a bit, and I've already spaced the tranny down to the point where you can barely thread the nuts onto the bolts of the tranny mounts. So basically the tranny is already as low as it can go without modifying grannys trranny mount and the front of the rear diff is already as low as it can go. So I said well lets try something.

I couldent bring the car on the road today, because its been snowing like crazy. So I jacked the back end of the car and put it on jack stands with the wheels off the ground. I then unbolted the tranny mount all together and literally let the engine/tranny hang by the motor mounts. That gave me 4 degrees of downward slope (not an ideal situation by any meens and still doesnt equal the 4.5 degrees of upward slope of the rear end but closer) well I started up the car and got the wheels up to speed and the car vibrated like usual. Shut it down and then I jacked the tranny back up into place and re-bolted it to the tranny mounts (back where I had it originally) turned the car back on and brought it up to speed and again same ****. Vibration clearly coming from the rear. And the 1 degree difference in tranny angle didnt make **** difference.

Took the wheels off and did it again just to be sure it wasnt the wheels and it wasnt.

I know when the wheels are hanging the halfshafts are at odd angles and may cause a vibration in its self but like I said I couldent even get the car a foot down my driveway so I couldent bring it on the highway but the vibration on the jackstands happened at the same speed and in the same fashion as the original vibration.

So now I know the angles of the drivetrain arent perfect and I should fix them but I dont know how its physically possible, but even more interesting is the fact that I dont think the lion share of this vibration is because of the inequalities of the driveline angles. I think its something more rearward in the rear end/ half shafts wheels, In that area.

I know the rear end is offset a 3/4 of an inch or something to one side of the car (thats what grannys says anyway) so is there a left and right halfshafts because I havent checked them but they all look the same length to me.. Maybe if there was a right/left and I had em backwards or something... who knows I am just trying to come up with new ideas cause I'm fresh out.

Now that I'm done writing my college thesis here I think I'm gonna go drink till I get smarter.

Car btw is an 89 GTU with ls1/t56 swap and delrin bushings for the rear diff and rear subframe. I can hear extra gear whine but this vibration is like a massage chair. I dont think bushings could create a vibration like this but I could be wrong

 

check on your driveshaft near the yokes for missing weights,

 

Thats the first thing I did. I bought the driveshaft second hand so I pulled it and had the u joints checked as well as getting it rebalanced. It made no diference

 

have them recheck the driveshaft, if you swapped wheels and tires or rebalanced them with no difference i think the driveshaft shop duped you and did a half *** friday afternoon job. it's most definitely bad u-joints or tires out of balance. the only other thing would be internal engine balancing, has the motor been rebuilt recently? if so, it would be engine RPM dependent anyways and easy to verify by just pushing in the clutch.

 

Deff not engine/rpm related. Deff speed related and load related though. Doesnt matter if I put the clutch in or I just get off the gas when I reduce the load the vibration greatly decreases, under even the slightest load though it gets much worse.

 

might have missed it but did you check the differential pinion mount?

 

I havent and that was brought up on v8rx7forum too. I can get the car back up on the jack stands and get the wheels up to speed and then climb under there and see. I could also rig up a restraining strap that goes around the pinion and ties it down to the subframe to see if that helps in case he pinion mount is slipping.

The only thing is when I had the back end of the car on jack stands and brought it up to speed it obviously vibrated with increasing frequency starting at about 50-55 like usual but the wheels were off the car and just the hubs/rotors were spinning thus there was almost zero load on the drivetrain at all. Not enough anyway to lift the front of the differential.

 

I had a similar issue.
ended up repacking the front wheel bearings and setting the spindle nut to 20-30 ft-lbs. Problem solved

 

could be time for new struts?

 

maybe its your hubs, i tightened mine and i lost alot of vibration

 

Spindle nut at 20-30 lbs arent those supposed to be like 150- 200lbs? As far as I know those are the only thing I had to tighten with the breaker bar to get it within torque spec.

My vibration comes from the rear

 

I'm not sure.. I have half a mind to disconnect the halfshafts from the differential and do the same test and get the car up to speed again on the jack stands. Then if it still vibrates I replace the rear end with the spare I have laying around. If it still vibrates I know its the driveshaft/driveline angles.

If it goes away when I pull the half shafts off then I know its the halfshafts hubs/rotors bearings (cause I know its not the wheels)

Thanks for giving me that idea.

 

Check your pinion shaft and make sure it spins true with no wobble. Mine had two bent studs on the shaft where the driveshaft bolts up to and caused me vibration problems like you describe.

 

Thats a good idea.

I'm gonna tear into it tomorrow. I am gonna disconnect the half shafts first see where that gets me. Then if that doesnt make any difference I'll disconnect the driveshaft from the rear end and pull it. Hell I didnt think I was gonna be pulling the rear end/suspension again but while its out I also might as well do the DTSS eliminator bushings.

Anyway before I drop the rear end you guys know any way to spin the rear end with the driveshaft disconnected. Trying to think of a way to spin the pinion shaft with a drill or something, that would be a good test.

EDIT: Ahh looks like theres a nut on the flange I wonder if I can spin the pinion shaft with it

 

Sounds like a driveline boom. check to see if your driveline is bent and make sure it is in phase (u-joints line up)
here is the proper way to check and verify driveline angle.\

Place transmission in netural.
Raise and support the vehicle at the axles as level as possible.
Remove any external bearing snap rings from universal joint so protractor base(or socket and angle finder) sits flat.
Rotate the shaft until transmission/transfer case output yoke bearing is facing downward.
NOTE: Always make measurements from front to rear and from the same side of the vehicle.

Place Inclinometer on yoke bearing (A) parallel to the shaft (OUTPUT YOKE ANGLE (A)). Center bubble in sight glass and record measurement.
NOTE: This measurement will give you the Output Yoke Angle (A).

Rotate propeller shaft 90 degrees and place Inclinometer on yoke bearing parallel to the shaft (PROPELLER SHAFT ANGLE (C)). Center bubble in sight glass and record measurement. This measurement can also be taken at the rear end of the shaft.
NOTE: This measurement will give you the Propeller Shaft Angle (C).

Subtract smaller figure from larger (C minus A) to obtain Transmission Output Operating Angle.
Rotate propeller shaft 90 degrees and place Inclinometer on pinion yoke bearing parallel to the shaft (INPUT YOKE ANGLE (B)). Center bubble in sight glass and record measurement.
NOTE: This measurement will give you the pinion shaft or Input Yoke Angle (B).

Subtract smaller figure from larger (C minus B) to obtain axle Input Operating Angle.
Refer to rules given below and the example in (UNIVERSAL JOINT ANGLE EXAMPLE) for additional information.

Good cancellation of U-joint operating angles (within 1°).
Operating angles less than 3°.
At least 1/2 of one degree continuous operating (propeller shaft) angle.

 

i seriously doubt it is anywhere in the diff, halfshafts or hubs. i still suspect the driveshaft shop just felt the u-joints and shipped the shaft back to you without even checking the balance. i have one driveshaft right now that twisted under a hard load and had to be re-balanced even though it was rebuilt that same day.

 

They could have screwed up but they deff did something there. I brought it to a local place that does 5" or 6" (something crazy like that) driveshafts for truck pulling competitions. They were also the only local guys who do aluminum driveshafts. Anyway when I dropped it off there was a ton of weight on it like 6 or 7 weights. You can see on the driveshaft where they ground off all the weights and started fresh. now theres only 2 or 3 weights. That being said if I put the new diff in and it still vibrates without the halfshafts connected you can be damn sure I am bringing that thing back ASAP. I'de be bullshit if it just turned out someone didnt do what I paid them to do and put me through this horseshit because of it

That being said today I disconnected the half shafts and ran the car up to speed and it still vibrated but not as bad (so I may have more than one source of vibration) Still too much vibration for anyones liking though. So I am pulling the rear subframe and putting my spare diff in just to be sure. Also the driveshaft I am using is from a corvette c4 and is popular with the Ls1/T56 FC guys but it is about a 1/4 in too short, not usually a big deal but sometimes too short a driveshaft can cause wobbling of the slip yolk in the tranny and vibrations as well as excess wear and tear.

Anyway today I spent the whole day just pulling **** off to get to the rear subframe I also pulled appart both rear hubs and I'm gonna do the DTSS eliminators as well as trying to free up the frozen toe adjusters.

Pics from today
Pulling the car appart



Driveshaft did have what looked like it might be some wear on the very tip of of the slip yolk

Not a very good pic and I dont think its anything, but I figured I'de show you you guys just in case.



And finally my sentiments about the car and project cars in general



Tomorrow I gotta get another jack and hopefully be able to get the spare diff in there. I'll report back