Vibration starting @ 58 mph

[diggerbob]

I have tried almost everything to try to cure a vibration problem in my 70 SWB that starts at 58 mph and seems to smooth back out @ 67 mph. I installed a new 4" aluminum driveshaft made by Denny's; checked my pinion angle/xmission output angles to make sure they are in the proper range; installed ECE disc brakes on front and changed the rear drums to new Raybestos drums; and balanced the wheels. Yet I still get a vibration shaking my seat that comes on @ 58 mph. Could it be my torque converter or flex plate? I am running out of things to try (and I'm getting a little frustrated!)

[70STOVEBOLT]

Does it only occur while while going down the road? It may be RPM related rather than speed related. Is the vibration damper original rubber type?

[TBONE1964]

Like 70STOVEBOLT says, you need to try and isolate your problem. The next time you are driving between 58 and 67 MPH, pop it in neutral and let you foot of the gas and let it coast and see what happens.

If there is no change then you most likely have a drive line vibration. If it goes away then you have a power train vibration due to an unbalance in the rotating assembly of your engine or a out of balance torque converter, etc.

[Tinkermc]

try aligning the rear and balance same. don't ask how I know.

[diggerbob]

Originally Posted by Tinkermc

try aligning the rear and balance same. don't ask how I know.

How do you align the rear end? ...and please tell me how you know...

[theredmeadow]

all my vibration went away when I took out the 1 piece shaft the PO installed. Even though the 1 piece was balanced at fast speeds it was turning into a jump rope and vibrating like crazy. original 2 piece has been smooth cruisin.

[In The Ten Ring]

Could it be the tires themselves? I had that happen once with a set of Dunlops. They'd begin to vibrate badly around 60 mph and quit at 70+. I hate to admit it, but that was my first car and I never knew what "tire rotation" was!

[austinstocker]

The working angles of the one piece driveline were probably what was causing the vibration then. The two piece driveline allows a less severe working angle throughout the driveline.

[diggerbob]

its definitely speed, not rpm. I installed shims between my trailing arms and rear end to get acceptable operating angles (<3 degrees) on front and rear u-joints per Spicer recommendations. The front and rear operating angles are within 1/2 degree of being equal. My axle bearings have been replaced as well. I also have new trailing arm bushings.

[frank69]

did u replace the bushing in the extension housing on the trans. I had a similar problem on my 67 gto and a 77 c-10 with a th 350. the gto was a Muncie 4spd

[diggerbob]

Originally Posted by frank69

did u replace the bushing in the extension housing on the trans. I had a similar problem on my 67 gto and a 77 c-10 with a th 350. the gto was a Muncie 4spd

Yep. I replaced that when I installed the high $$$ aluminum driveshaft.

[geezer#99]

What exactly is the pinion angle and the angle at the tranny?
And how did you measure it?

[diggerbob]

Originally Posted by geezer#99

What exactly is the pinion angle and the angle at the tranny?
And how did you measure it?

The pinion angle is 4 degrees, driveshaft is 6.1 degrees and output shaft is 3.6 degrees. This gives me an operating angle of 2.1 degrees at the pinion and 2.5 degrees at the output shaft. I measured angles using a digital level.

[geezer#99]

Suspension loaded or unloaded?
Loaded means full weight of the truck sitting on a flat surface just like you'd drive it down the road.

[67 chevelle]

one more thing to check is , pinion bearing , when it goes bad it does exactly what you are describing , hard to tell where the noise is coming fryour pinon yoke will move slightly up and down if it is bad , they all rotate slightly and that is normal but up and down movement is no good

[diggerbob]

Originally Posted by geezer#99

Suspension loaded or unloaded?
Loaded means full weight of the truck sitting on a flat surface just like you'd drive it down the road.

Measurements were taken with the truck parked in my garage. I checked the pinion bearing for play too. There was none.

I can't hear any noise - just vibration.

[geezer#99]

So your tranny is at 3.6 and your pinion is at 4.
Your pinion has a tendency to climb up at speed increasing your pinion angle.
Drop the pinion down one degree.

[diggerbob]

Originally Posted by geezer#99

So your tranny is at 3.6 and your pinion is at 4.
Your pinion has a tendency to climb up at speed increasing your pinion angle.
Drop the pinion down one degree.

I am already using 4 degree shims on the trailing arms...I can't find a bigger one. (I had 8 degrees on the pinion before I did that). I have coil springs so I wouldn't think that my pinion angle should change that much at speed.

My truck used to have a two piece shaft and three speed tranny which I changed over to a one piece shaft and a 700R.

[geezer#99]

Bear with me.
Just trying to get my head wrapped around this!
Did you put in 4 degree shims to bring the pinion angle down?

[geezer#99]

One more thought!!
When you installed the 700R did you maintain the centreline of your motor/tranny to be the same as the centreline of your pinion. Your pinion is offset to the passenger side. The output shaft of the tranny should be offset too. They should be parallel as viewed from the top.
If you centered it in the frame you could be causing a compound angle vibration.

[diggerbob]

Originally Posted by geezer#99

One more thought!!
When you installed the 700R did you maintain the centreline of your motor/tranny to be the same as the centreline of your pinion. Your pinion is offset to the passenger side. The output shaft of the tranny should be offset too. They should be parallel as viewed from the top.
If you centered it in the frame you could be causing a compound angle vibration.

Yes. I brought the angle down 4 degrees so that the centerline of the pinion was closer to horizontal.

As for offset, a jerk who I hired years ago installed my crossmember in the new location to accommodate the different length of the 700 tranny vs the 350. The engine was in place so I believe that he just slid the crossmember back on the frame so that it would line up with the transmission mounts and made new holes to attached the crossmember to the frame. I have been thinking about getting a new crossmember from Bow Tie overdrives since they are made to bolt up in the original bolt holes on the frame.

[boostedc10]

Originally Posted by diggerbob

Yes. I brought the angle down 4 degrees so that the centerline of the pinion was closer to horizontal.

As for offset, a jerk who I hired years ago installed my crossmember in the new location to accommodate the different length of the 700 tranny vs the 350. The engine was in place so I believe that he just slid the crossmember back on the frame so that it would line up with the transmission mounts and made new holes to attached the crossmember to the frame. I have been thinking about getting a new crossmember from Bow Tie overdrives since they are made to bolt up in the original bolt holes on the frame.

Digger, what size wheels/tires are on the truck? Not to send you another direction but when you had the tires balanced did they also do road force? I have seen a ton of new tires with excessive road force cause this issue. Its a cheap thing to have done to ensure you aren't chasing a ghost.

[diggerbob]

Originally Posted by boostedc10

Digger, what size wheels/tires are on the truck? Not to send you another direction but when you had the tires balanced did they also do road force? I have seen a ton of new tires with excessive road force cause this issue. Its a cheap thing to have done to ensure you aren't chasing a ghost.

Tires are 255/70R15. I never heard of a "road force" balance. Is that when they spin balance it on the vehicle?

[geezer#99]

http://www.gsp9700.com/

Road force balance is usually done at a simulated 65 mph compared to a normal spin balance at 35 mph. The road force will show if you have a bent rim or out of round tire.

[boostedc10]

Actually road force has nothing to do with a speed it has to do with loading a tire to ensure uniformity. The balancer applies about 1200 lbs of force to contact surface of the tire with a drum to simulate how it would react on the road. This can detect issues in a tire that normal balancing cant detect.