86t/a383

iTrader: (1)

02' WS6 M6 402 LS2 W/L92 heads Textralia clutch n Moser 12 bolt w/ 4.10s. Mid 90s Grand Sport wheels (GM, Not repops) 17x9.5 w275/40 front 17x11 w315/35 rear.

Substantial vibration 70-75mph in gear, 5th n 6th, light load. Feels like driveshaft. More throttle = less vibration and gone once passed 77 or so. Let off throttle n it gets worse till below 69~70. I neglected to check the conditions in 4th.

Driveshaft has been balanced. Rear tires have been replaced and balanced. Rear end was found with pinion play n leak n a poor pattern on ring gear. New ring n pinion installed. Vibration has gone unchanged.

Ideas?

Darth_V8r

iTrader: (4)

Dude, I just went through the ringer on this. Feel for you.

Here are the things that worked for me. First, ask yourself "is the vibration audible?". At 70mph, the tire rotates 15-16 times per second, which is out of range of human hearing. This would be more of a vibration you feel in your gut or through the steering wheel.

The driveshaft rotates at 4.1 times that on your gears, which is 60-65 Hz. Would present as a bassy hum through the floor of the car. If it has that hum, check the first three on the list before you start spending serious dollars. A good way to test this is to raise the rear, put jack stands as close to the wheels as you can, and run the car through all the gears. Don't support the pumpkin, as it throws off your angle measurements and your angle settings, so it'll be good in the air and bad on the ground. This way, you can try things without road testing all the time.

1. U-joints. My u-joints were worn, but not like how they are normally bad. In the car, they felt solid. When I took the drive shaft off, I found that they "clicked" into place at the center, which meant a flat needle bearing. Also, they were very limp in that they could not support the weight of the yoke. Vibrations got much better after that

2. Transmission mount. I had put a poly in. Ripped it back our and put a stocker in.

3. Pinon angles. I played around with angles and set the overall pinion angle very close to zero. I still have the stock torque arm, stock transmission mount. I ended up putting 1/2" of rubber shims under the trans mount to simultaneously raise the transmission tail shaft and the pinion yoke. Angles went from 6 at trans and 3 at rear to 4.2 down at trans rear and 3.7 up at rear pinion yoke. Made a huge difference.

4. After doing all that, I noticed the humming vibration had completely gone away, and now I only had a front end vibration, but it was definitely slower than the driveline vibrations I had. I exchanged rims and tires thinking I'd get rid of it, but it was still the same. Turns out, a road force balancing fixed this. it's not the same as spin balancing. They find the soft spots in the tire and compensate for them. it's particularly helpful with low profile tires, which I see you have.

Having done all of the above, my wife will now ride in the car again

Darth_V8r

iTrader: (4)

Here is a diagram showing my pinion angles and what worked for me. My advise is to set the rear pinon and transmission parallel. Then, make adjustments from there. Once you make one adjustment, it'll either get worse or better, so you'll know what to do after that:


This is an attempt to depict the angles that worked for me. The angles are all relative to level with the earth. Remember, if your U joints aren't supporting the driveshaft, setting angles is a wild goose chase, so check them first.

Darth_V8r

iTrader: (4)

Here is an alternate arrangement that I've heard people say works. For me, it was not possible to achieve these angles. Again, all angles are stated relative to level with the earth, not to other parts on the car:


Again, all angles are relative to level with the earth. In this arrangement, you want both interior angles of the U-joints to match.

maroonls1z

Probably pinion angle. Mine likes between -1 and -2

86t/a383

iTrader: (1)

Good info. Ill go back to the shop this weekend. Tech played with pinion angle. Car hooks better but vibration is unchanged. I will see if he knows someone with a road force balancer that will actually use it. I would watch so many techs blow off the advice from that machine when I was at the dealer before all the GM consolidation and before my career change. I wanted to buy it when they closed but was outbid. I have a receipt from previous owner for new ujoints and a driveshaft balance but it couldnt hurt to recheck it. Tranny mount is stock. Rear has LCA relocation brackets and non adj LCAs. Torque arm is adjustable. Stock springs.

Darth_V8r

iTrader: (4)

If you lift the rear and run it, you might be able to help narrow it down. If it runs smooth lifted and rough on the ground, that would almost certainly tell you tires or wheels.

Good luck. I'm no expert, I can only tell you what worked for me. FWIW, Discount Tire near me has a road force balancer - $16 per tire

1 FMF

iTrader: (1)

i have a 2002 camaro with around 75k miles, i put a strange s60 rear in 1 or 2 years ago.
i've been chasing a vibe that i don't care for, before i do anything else i will live with it till i replace my tires which are continental 275/40-17 on the oem 10-spoke rim. i've had one set of aftermarket wheels that i ran for a while and had the original 10-spoke rims with the original goodyear tires and swapping to them ALWAYS seemed to make the car run very smooth like it was new. after replacing those with the continentals, i'm skeptical and considering tire balance and the tire itself, i did buy them online and over the years i've noticed tires bought online seem to be not as good as from a local brand name place. when i got my continentals, from DTD, they had some funk on the sidewalls that took a year to clean off and i don't know how long ago they were manufactured.

And I would label Darth-V8 an expert based on his drawing, that makes it very simple to understand. it's simple physics and you want the opposite angles of the parallelogram equal, that is what cancels out the ujoint vibration. it's called phase angle. when the difference between those angles, the phase angle, is zero there is no vibe caused by the two ujoints. in real world there is deflection so you set the rear angle lower by some little amount to account for that. i have a umi adjustable torque arm and i've played around seeing how much deflection i can cause, and i can't induce more than 0.2° before lifting the car. so in my opinion setting rear pinion angle lower more than 1° may be causing more harm than good. guys use the -2° to -3° setting based on dragstrip environment when you're running 100% power the whole time, so yeah deflection will be greatest and maybe that is the best setting. but when on the highway cruising you are using less than 50hp to maintain speed, so is there really any force there causing a deflection to begin with? and don't forget action reaction, when foot on the gas under power the rear wheels rotate in the forward direction meaning it's the torque arm keeping the rear axle from rotating the opposite (upward) direction. this is all that anyone thinks about. BUT when you're off the gas and slowing down coasting from a high speed, the axle will then want to rotate downward. if you set your pinion angle under static no load condition to a significant negative angle to begin with, it will only get worse during coasting down and engine braking if the torque arm and rear lower control arms allow any significant deflection. i can adjust my umi tq arm easily at will and have done so making more of a downward or upward angle to where i can feel vibes on highway driving to work at 60+ mph. i'm now set at 0.5° downward and that seems to be the best spot for normal driving, anywhere between 1.5° up or down has little affect... provided my $30 harbor freight inclinometer is accurate. i have to really turn the adjusters on the umi tq arm and get greater than a 2° phase angle before i can tell it driving.

Darth_V8r

iTrader: (4)

I appreciate that, but I would say 01SSRedA4 is the real expert. His posts helped me figure the pinion angles out. For an angle finder, I used an iPhone app that can measure 0.1 degrees.

I laughing a bit at your tire story. Mine, I replaced all four tires and wheels, only to get the same vibration, only to discover I had a soft spot on both the tires that ended up on the same corner of the vehicle. That's where the road force balance helped, because they canceled out the soft spot somehow. not just balanced by rotational mass.

Something else I read on an older thread when I was searching like crazy - someone with a S60 had some vibes and added hub-centric wheel spacers between their wheels and axles, and it completely fixed their vibrations. Then, an argument ensued over whether our cars are lug-centric or hub-centric. i don't know what the answer was, but that spacer trick might be worth a shot for you.

OP, since your torque arm is adjustable, you can probably get this resolved pretty quickly. Just start with zero (both angles match perfectly) and go from there. I ended up with the rear 0.5 degrees lower than the trans, but you might end up differently. It's a lot of trial and error. Just double check the vibes with the tires off the ground. Nothing sucks worse than going through your pinon angles a dozen times only to realize it was tire-related.