csxfbird

iTrader: (5)

So over the last six months, I've gone through and upgraded several suspension and drivetrain bits on my car, and in addition to the enhanced appearance and handling prowress, I've also been subject to noticeable (but not violent) vibrations at freeway speeds, 70-90 mph felt throughout the entire car (particularly through the seats). I've read through the forums, checked most of the items that could cause such vibrations, and still have issues. It appears to be speed-dependent and not RPM-dependent. The car has 59k miles on it. Here's a quick list of mods:

-Koni 4/4s with Strano springs
-UMI adjustable torque arm with relocation kit (reused factory rubber tranny mount)
-UMI adjustable poly/rod LCAs
-UMI adjustable panhard bar with relocation kit

Here's a few common problems/fixes I've tried:

-Adjusted pinion angle to -2 (driveshaft angle of -1, sloping downward to rear of car, and rearend angle of -1, sloping downward to front of car)
-Originally installed poly transmission mount with torque arm relocation kit, suspected it may cause vibration, so replaced original rubber mount, no effect on vibrations
-Had factory aluminum driveshaft balanced. Shop claimed runout was somewhat high, so after replacing one of the u-joints and balancing, no appreciable affect on the vibrations
-Had tires/wheels rebalanced, no effect on vibrations

Frankly, I'm out of ideas at this point. Suspension and Flowmaster catback aside, the car is stock, and these problems began after the suspension/drivetrain install. I know that an increase in NVH is expected, particularly with the poly/rod ends used on some of the components, but I don't think such a noticeable, speed-related vibration is normal. Any chance at all this could be related to my potential need for a new clutch? The factory unit seems to be on its way out, but wasn't sure if it could cause vibrations such as the ones I'm experiencing.

Thoughts?

*UPDATE*

Solved my vibrations by measuring and setting my pinion angle precisely using a digital angle finder. See Post #13 for great info on proper u-joint angles and Post #50 for my update

SSRed2k2

iTrader: (6)

Just a couple ideas for you...
Alot of these cars experience a "vibration" at 70mph. It has been explained to me that it could be the harmonics of the car and that 70ish is the sweet spot for this feeling.
Road Force Tire Balance?
4 Wheel Alignment with thrust line checked.
I would go for the alignment first as the road force since you have already had a spin balance.

csxfbird

iTrader: (5)

Thanks for the reply - I was unaware that these cars had a harmonic sweet spot.

I had a 4-wheel alignment performed after the Koni/spring install, so I think we can rule that out.

I've never heard of a road force tire balance, but after a quick Google, seems like it could be worthwhile endeavor. I'll see if any of the local Discount Tires have one of those machines.

Sam Strano

iTrader: (41)

I think your pinion angle is off. Adjust it one way or the other a little bit and see if it gets better or worse. If it changes either way you know you culprit and just have to find the happy place where it doesn't shake.

csxfbird

iTrader: (5)

Thanks Sam - that's a distinct possibility. I tried re-balancing the wheels and tires (spin balance only), and they were all off by less than an ounce according to Discount Tire. This didn't help with the vibrations.

I did a 300 miles of freeway driving this past weekend, and made an observation. The vibration comes and goes, as I noticed if I maintain a constant speed long enough. It never goes away fully, but definitely dwindles down to tolerable levels, but eventually returns.

I have the car in the air, and upon doing a little reading on the UMI torque arm relocation kit, realized that I have the front bracket/bushing holder in the incorrect place - the instructions calls for using the second set of holes from the top, but this is for a stock height car - they recommend the third set for lowered cars. I don't know how much of an impact this instant center adjustment would make, but I figure it's worth doing this and re-adjusting the pinion angle accordingly.

Will update with results when I adjust.

Sam Strano

iTrader: (41)

If it comes and goes.... and it gets worse and worse as it comes and then goes away that's DEFINITELY a pinion angle issue.

MasterV8

iTrader: (7)

+1 for road force balance! find someone with a GSP9700 machine.

Sam Strano

iTrader: (41)

I'm sure as I can be given the description I've seen here, that this is NOT a balance issue.

sscamaroburn02

iTrader: (14)

please post your results when you find the problem. thanks.

silversrtman

iTrader: (20)

both my friend and I have had vibration issues with these cars for years and years with different setups. I think there is no helping it with these cars, once you get rid of that stamped steel torque arm and lower the car it all goes to hell. Please if you find a cure post it up. I have adjusted my pinion angle a million times using all sorts of methods and angle finders. I really think its just the nature of the f-body

Sam, obviously your car is setup correctly. Do you have any driveline vibrations at speed? I will hold out hope if you say no, but aside from that I have been trying to just live with it.

HoLLo

iTrader: (17)

My car is the same way. Seemed to REALLY amplify when I installed my Moser 9". I have tried a lot of different things. Mine is infinitely worse when I just let off the gas at highway speeds. Cruising with my foot on the gas (even lightly just maintaining speed), it's not too bad, but if I need to slow down because of a hill and I just let off the gas, it feels like something back there is about to explode..

sscamaroburn02

iTrader: (14)

wow now I'm not looking forward to my near rear end later this year. LOL. What is yalls pinion angle set at? This seems to be the common occurence that causes these vibrations.

lees02WS6

iTrader: (5)

I changed my drive line angle completely. I put shims under my tailshaft to push it up to 0°. I then set my pinion to the same. You don't have to do this.

For a stick axle car, driven on the street, I'm a firm believer in the equal opposite angle at either end of the drive line. Most likely your tailshaft is sloping down between 2° and 3°, therefore your pinion should be sloping up an equal amount. There is flex in the torque arm, in the bushing or the arm itself, and in the tailshaft, some change in the angles is to be expected.



Equal angles as this video points out, cancels vibration.


Remember too, you have angles in plan view and top view. Top view usually isn't an issue unless you've got one control arm much different in length than the other, or your engine and trans are skewed in such a way that the center line of them is not parallel with the center line of the pinion.

_JB_

iTrader: (33)

Put the rear of the car in the air and load the suspension. Run the car up to 70MPH and look for any rim wobble.

HoLLo

iTrader: (17)

I've tried several different angles with my UMI adjustable torque arm myself, but have not tried anything on the transmission. What you are describing makes sense, I've seen similar problems in the 4x4 world. What are you using to shim your transmission, just some grade 8 washers under the bolts or something?

lees02WS6

iTrader: (5)

Just pieces of flat stock. I'm going to weld them to the cross member shortly. Some people will compensate for pinion climb during acceleration. They'll set their pinion a degree lower to account for that change in angle under power.

In the 4x4 world the angle of the driveshaft comes into play more so because they can exceed the maximum operating angle of the joint. The end of the shaft can bind up against the bearing cap. This less angle you have on the joint on either end the better it will work, and the more power it will transfer.

blk383z

iTrader: (1)

I've been battling highway speed vibrations since the day I put my moser 9" in. It has only gotten worse and amplified as I upgraded my suspension. I have been through 3 different driveshafts which my current one 1" longer which helped but didn't cure the vibration. Also have tried countless different pinion angles, different wheels, even have a different tranny. It's definitely a driveline vibration, comes on at about 75-85 goes away at 90 and gets horrible over 100 to the point I can't see out my rearview. I don't even want to drive on the highway anymore.

nascarnate326

iTrader: (1)

Is this vibration just something that is accepted?

Is it mechanically safe to drive the car at high speeds?

thechef

iTrader: (13)

so did this fix the vibrations??????

lees02WS6

iTrader: (5)

I've driven my car over 100mph now without experiencing driveline vibration. It's something I've talked with Denny's, PST, and Tom Wood's about. You have to measure the whole drive line, not just the pinion to know whether what you've got is correct. In a solid axle car your pinion is going to climb in acceleration, so compensating for this maybe necessary depending what kind of driving you are doing.