so i cant recall when this started to happen but i do know at one point in time there was no vibration at all. so starting with whats done to the drive line... i have a stage 5b T56 (top of the line build from sixspeedsinc) transmission which has maybe 30k on it now and never any issues at all. linked to that is a PST 3.5" aluminum driveshaft then to a moser 9" rear with a detroit locker 4.11s and 35 spline axles. i am running the big 1350 series u joint and yoke also. suspensions is all adjustable tubular CM with delsphere rod ends and all suspension components are tight nothing loose or with more than normal play.

the problem: over some harsh bumps i get an odd noise from the rear which almost sounds like something is loose suspension wise or like loose wheels or something along those lines...NOTHING is loose!

at cruising speeds of 40-70mph i get a weird knocking noise/feeling that isnt constant it comes and goes frequently though. to me it feels like maybe a loose torque arm or something loose that is mounted to the chassis or maybe even a loose driveshaft? NOTHING is loose!!!

at speeds of 110mph+ i begin to get a very harsh vibration that gets faster and more harsh as i increase speed and i can feel it through the shifter **** and all along the centerline of the car like it feels to be driveshaft related. again nothing is loose and ive checked and adjusted my pinion angle a million times! ive tried various different angles and still nothing seems to fix this vibration. ive had my DS balanced, pulled my axles to make sure they were straight and true and they are even made sure my wheels were properly balanced....still cant seem to figure this out...

i tried jacking up the rear to see if i can duplicate this vibration with the tires in the are and i can get it to vibrate but no where near as bad as when driving. ive also put it in neutral and reved it up and there will not be any vibration through the RPMS so it is not RPM related nor engine/input shaft related....

now ive been wondering if maybe it was something wrong with locker as its so harsh on the drivetrain if you dont baby the car when shifting normally it will buck like hell and all you can hear and feel is banging of the driveshaft and it seriously feels brutal on parts.... BUT i dont think the locker is the actual problem maybe it is what had damaged something to cause this problem?

im REALLY hoping nothing is damaged on the output shaft side of my tranny and also REALLY hoping nothing in my rear end as all that **** is costly and a pain in the *** to fix.

anyone have any suggestions? maybe have dealt with the same issues?? today i have off from work so im going to try removing my driveshaft and check a few things with it out

 

Short torque arm or at least chassis mounted long arm I presume? What sway bar? What end links? Clunking and knocking are normal once you get your suspension to this level. As for vibrations, have you centered the rear end, also have you set pinion angle to zero, by zero I mean identical angles for the front and rear u joint. Where are you measuring pinion angle from? I'd measure directly from the u joint caps if it was me.

 

does still sound like a pinion angle issue. What method are you using to set it? Where are you measuring from? Does it seem to go away if you accelerate from a cruise or does it get worse?

 

im using a full length tq arm that is mounted to the trans cross member rather than the trans. im using the UMI tq arm relocation cross member and the front of the tq arm can be adjusted up and down im all the way at the top setting simply because my kooks y pipe will not allow the tq arm to be adjusted down in front. i have a 1" solid rear drag sway bar with the included endlinks and poly bushings from spohn. im also running a Fays2 Watts link instead of a panhard rod and my rear seems to be visually centered as im on 315s and the spacing on each side compared to my wheel arches look to be identical.
as for the clunking i specifically bought the delsphere ends to help with that as i did have rod ends before and they just got to be too noisy... when i first installed the delspheres i had no unusual road noises.

im using your method of measuring angle! the harsh vibration seems to come at 85mph+ and it will get more severe as speed increases but once i get to 150mph it seems to slightly settle off? it comes with speed... i can let off the gas and it will continue until ive slowed down to 90ish also if i let out the clutch it will remain until i drop some speed...

i didnt remove the DS just yet as i was playing around with pinion angles with the rear jacked in the air and the front lifted on cinder blocks (so car is near perfectly level) ALSO my car is lowered maybe 2" so im wondering if that has anything to do with it? what should my pinion angle be when im lowered?? im wondering if the fact that i cant adjust the front end of the tq arm downwards if that may be what is throwing things off?? ive tried a lot of different angles the BMR way and currently am at -.5 as it seems to be the least violent... problem here is my rear pinion is at a positive angle +1 while my DS is negative -1.5 and i didnt think a positive pinion angle was a good thing?? i also tried 0* pinion and -.5* DS whichis the same -.5* relation...

 

All the confusion aside, make your joint angles even, like dead nuts the same. I had the same vibe with a BMR torque arm cross member. Turns out my pinion angle was fucked as soon as I put it on. My trans was down 3 degrees, so I matched my rear by aiming it up 3 degrees and everything is smooth. My vibes came in at about 80-90 just like yours. Simplest way to explain it is whatever your trans tail angle (measure from the front u joint) is, make the rear end match by adjusting the torque arm. Make them the exact same, if the angle gauge says 6 on one, make the other read identical.

 

Search driveline angles on YouTube and see what's up, great info there where you can see live spinning driveshafts as demonstrations.

 

how are you measuring from the front u joint? im using a magnetic angle finder and dont really see a spot i can mount it on flush??

also something i just noticed.... i have my tq arm mounted to my Moser 9" using the inward set of bolt hole not the outer set like you can see in all of UMI and Spohns pictures where theirs are attached using the outward bolt locations??? theres actually no way i can mount it to this rear end using the outers because the floor boards will not allow it and id be scraping/banging on them with every rear movement. im assuming these inward mounting holes are there for a reason such as when used with a Moser rear end??? but thats just me assuming can anyone confirm this? i need someone running an aftermarket tq arm either spohn or UMI with a moser 9" to compare...

 

Use a socket of the correct size to act as a spacer to get to the u joint cap itself. So the socket goes inbetween the u joint and your angle finder so you can get a true reading.

 

Alright thanks ill try that when i get home...hopefully this works because next suspect is output shaft bearings and i really dont want to pull out my transmission...

 

This video may help explain a little better how to measure and relate the angles. The driveshaft measurement is irrelevant honestly. Many people try to do it and use math to figure the angles but that just over complicates things. Just measure your crank pulley and your torque arm mount flange or the pinion yoke

 

ok the video did help a little better... so i measured from the crank pulley got 3.5* down towards the rear and it matched exactly at the transmission yoke 3.5* down....i first tried to match the rear pinion making it 3.5* up towards the front... it did help a little bit now the vibration starts around 100-105mph and gets increasingly harsh all the way up to 150mph or so and then it begins to smooth out BUT it will have intermittent bursts of vibration if i hold it at that speed??? i also toyed around with the pinion angle a little more just to see if i could find a sweet spot and nothing seemed to really improve it just would get worse or stay the same...

i cant feel any play in the u joints while its attached except for some front end play but i really cant tell if thats normal and cant tell if its the output shaft side or the actual u joint??? if i grab the front end of the shaft with both hands and try to force it up and down it will mover ever so slightly... not a lot but enough to notice where as if i try the same thing on the rear side its is SOLID no movement at all! is this minimal amount of movement in the front normal??? can you do this with a stock DS and transmission? so just to try and ease my mind with the DS removed i went through the gears all the way up to max speed and there were no irregular noises or ANY AT ALL vibrations....(yes some tranny fluid leaked out the rear seal but i was prepared for that)

at this point im kind of stumped and am now thinking maybe something might be wrong with my DS maybe it wasnt properly balanced before or maybe a joint is bad and i just cant tell or who knows maybe its still the rear output shaft???

 

Yes that very slight play is normal.

 

You are not supposed to match the angles, there should be 2" of difference between them. If you are measuring the engine/trans at 3.5 then you need to set the rear end to read 1.5. This will allow for preload under acceleration. What is happening is the rear end is rotating upwards while you are under hard acceleration and the angle is changing from 0* to +2* which will cause a harsh fast vibration at those speeds

 

He is chasing a vibration under coast/maintain. Setting pinion to negative 2° not 2" is not the optimal setting for anti-vibration. It is the strongest setting for launch/accel under power because it sets the joints as close to perfect as possible under power, meaning at coast the angles are not optimum. I believe in eliminating variables, and if you're chasing a vibe, set your pinion angle at 0. This -2° is perfect for everything is ridiculous.

 

That was supposed to be 2* not 2". From what I understand, he is having vibrations at high speed, which would not be considered a "maintain" vibration. That is under load/acceleration where any and all bushing slack will be preloaded in the loaded position. This is why we recommend the -2* because it allows for load of the bushings rotating the rear end back to equalize the angles. If he is starting at zero, then the angle will climb to roughly 2* positive and cause vibrations at speed as he is describing. Here is a good video we found explaining how and why this causes the issues it does

https://www.facebook.com/photo.php?v...716400&fref=nf

 

I dunno what they teach in suspension school, and don't care. But I've had identical vibrations to him. The A number one thing that got me to a vibe free starting point was getting my pinion to a zero, THEN going from there. When it doubt, you take it back to square one. Square one for this guy is being able to drive 80+ with no vibes. From my experience, getting a 100% neutral driveline angle is the appropriate first step.

 

ok back in here... i tried replacing my drive shaft to see if maybe that was contributing but no luck still the same problems...

and to clarify my problem.... this vibration happens under all conditions! at this current point of testing my car is sitting on blocks under the front wheels and jack stands on the rear end perfectly level in my garage. i will slowly accelerate to 100mph and from there my vibration will start... no matter how slowly or quickly i accell from there it will get extremely harsh and i will feel it along the center of my car and through my shifter ****... once i reach around 150mph it will smooth out. also i have to state my suspension is all aftermarket so no OEM rubber bushings i have a poly on the front end of the TQ arm and everything else are delshpere bushings from Spohn.

now for the weird thing.... when i am actually placing a load on the driveline and driving the car on pavement if im simply just cruising at highway speeds i feel something loose and again its coming from the center of the car. a weird wobbling feeling to me feels like a loose drive shaft (but its not loose and its NEW) i thought maybe its my exhaust??? but no signs at all of it hitting anywhere and that noise is different from this wobbling loose sounding noise...???

man THIS is why i want a corvette!!! better design less headaches!

EDIT: oh and ive tried zeroing out my pinion angle matching it with the crank pulley and tailshaft even tried taking a few degrees out of it to make it - when compared to the rest... just doesnt seem to go away!!! i love my car and could never get rid of it, have so many more plans that i want to get working on BUT i refuse to put any major money into the car until ive found out what this vibration is!

 

Whar transmission mount are you running?

 

i have the UMI tq arm relocation tranny mount with a poly bushing that the bushing has never given me any problems even when it was on the OEM cross member

 

so ive tried everything and am coming back to this... to better describe the "play" or movement if the yoke inside the trans i took a video. the movement/play im talking about is in an up/down side/side motion (not rotational side to side) and in the video i will grab the DS and move it around and you can see the yoke itself moving insde of the tailshaft of the transmission... can you or anyone reassure me that this type of movement is normal on a car that is not experiencing any vibrations? being that i can feel this harsh vibration come in through the shifter know it makes me wonder that this slight play could be whats throwing the DS off when rotating at speed just enough to cause the vibration that i am feeling? im picturing rather than the DS rotate on its own axis it will rotate out of axis because of this movement and therefore cause the specific vibration i am feeling?