Pinion angle
 

School me on correct pinion angle. I just recently bought a 85 GMC 2wd 1/2 ton with a TH350,305,10bolt with 2.73 axle ratio. I have a slight driveline vibration that I thought was the driveshaft. I had it balanced and installed new joints, no change. New tires and rims, no change.

The truck has a McGaughtys 2.5/4 drop.

What is the proper pinion angle in relation to transmission angle?

The pinion was pointing way up, like 7º. I installed 6º shims and now it is pointing up about 1º. This seemed to help slightly.

If transmission is angled down say, 3º should pinion be angled up 3º?

Thanks

Re: Pinion angle
 

Yes.

Re: Pinion angle
 

Here's a link to a flow chart for vibration diagnosis.

If you can follow this logic tree then you can fix any vibration problem.

http://67-72chevytrucks.com/vboard/s...d.php?t=522180

K

Re: Pinion angle
 

thanks Keith!

Re: Pinion angle
 

Thank you very much!

Re: Pinion angle
 

Keith, once again, your knowledge amazes me.
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Re: Pinion angle
 

Well, since we are on pinion angles and vibration, I'll ask.

Just installed a new 14SF and a brand new driveline (with new ujoints). My t-case and pinion angles are within 1 degree of one another, but I now get a vibration around 65 and it almost, pulsates every 3-5 seconds. I have also felt it at lower speeds as well....not JUST 65.

When I installed the new driveline, I also installed a new t-case seal and sleeve. The t case has a drop kit to allow for the 2.5" lift. Is it possible that the vibration is coming from the t-case sleeve that I just installed? The old one I pulled out was worn pretty good on the bottom side of the sleeve.

On a different issue, I did swap back in the old 10 bolt and old driveline (new tcase seal and sleeve).....and the vibration was still there.

Possible t-case?

Re: Pinion angle
 

How are the motor and trans mounts? The stock rubber clamshell motor mounts can slip causing mis-alignment and vibration.
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Re: Pinion angle
 

The motor mounts are brand new, energy suspension ones. The tranny mount seems solid....