Vibration starting @ 58 mph

[geezer#99]

String line between the frame rails with a plumbob down to the pinion is the easy way.
A washer on a string makes a good plumbob.

[diggerbob]

Originally Posted by geezer#99

String line between the frame rails with a plumbob down to the pinion is the easy way.
A washer on a string makes a good plumbob.

19.25" from each frame rail to center line of pinion. She looks to be squared up good from the top view with no offset front or back.

[geezer#99]

Well!
You have a rarity. A motor, tranny and rear that are all dead centre in your frame.
Would you have a pic of your rear from the side showing your pinion angle? As the truck sits in the driveway of course.

[diggerbob]

Originally Posted by geezer#99

Well!
You have a rarity. A motor, tranny and rear that are all dead centre in your frame.
Would you have a pic of your rear from the side showing your pinion angle? As the truck sits in the driveway of course.

here ya go....

[geezer#99]

Thanks for the pic.
I'm tapped. Got no more clues.
Good luck finding it.

[diggerbob]

Originally Posted by geezer#99

Thanks for the pic.
I'm tapped. Got no more clues.
Good luck finding it.

I am gonna put a new rubber transmission mount on and add an extra 1/2 degree shim to the rear end.

[diggerbob]

I noticed that my driver side rear shock is in a bit of a bind on the lower mount. Instead of the bolt fitting straight through the shock and lower mount like on the passenger side, it is at a bit of an angle.I replace this shock mount several years ago. Probably grabbing at straws ...but I wonder....

[diggerbob]

Originally Posted by 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.

I have zeroed in on my vibration issue ( quick summary-it started at around 55 mph and subsided around 62 mph.) Today, I replaced my rubber transmission mount with a new rubber mount. My old one looked good but it was sort of collapsed. Comparing the new mount with the one that was in my truck, I could not see a difference in the height of the two mounts, but my vibration got even worse when I put the new one in. I could also tell that my launch was suffering like I had a bind or something. I was thinkin' "WTH?"

Back on the garage floor, measuring angles, it turned out that the new rubber mount, as installed, gave me several tenths of degrees more angle than my prior one. I measured everything again, taking special care. HINT- using a 5/8" or 11/16" socket on the top or bottom of the bearing caps to put your level on helps a lot in making accurate measurements in cramped spaces without having to take the driveshaft off. Take these measurements several times to make sure that you are getting accurate measurements. Don't move the truck when you are taking these measurements. If you do-start over!

My short bad truck used to have a 2 piece drive shaft and a 3-speed manual. I now have a 700R with a custom made aluminum driveshaft. I had to shim up my differential by 4 degrees (it was originally running 8 degrees at the pinion).

After my mods, I was running an operating angle of 2.9 degrees on my output shaft and 2.5 degrees on my pinion. This gave me a difference of around 0.4 degrees. Conventional wisdom says that you are ok as long as they are within 1/2 degree. I was in this range. Conventional wisdom also says that you should keep your operating angle under 3 degrees as vibration gets worse as you approach the 3 degree threshold. I was still getting this shake from the rear end. Dammit!

I decided to dial it in closer so I shimmed my tranny mount until I got the same angle angle for my tranny and my rear end within 1/10th degree. I test drove it and viola! No more vibes. My lesson learned: For a one piece drive shaft, get your output and pinion angles within 1/10th degree of each other. A $30 digital level can help you a lot. as long as you measure carefully.

[austinstocker]

Good job, glad to hear you got it figured out!