Pinion angle - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Jake Wade · 08-21-2013, 10:33 PM

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

Keith Seymore · 08-21-2013, 11:01 PM

Quote:

Originally Posted by Jake Wade

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

Yes.

Keith Seymore · 08-21-2013, 11:03 PM

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

naphtali5725 · 08-22-2013, 04:40 AM

thanks Keith!

Jake Wade · 08-22-2013, 06:41 AM

Thank you very much!

8lugnutz · 08-22-2013, 11:25 PM

Keith, once again, your knowledge amazes me.
Posted via Mobile Device

Ski-me · 08-23-2013, 10:56 AM

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?

wraprail · 08-23-2013, 05:00 PM

How are the motor and trans mounts? The stock rubber clamshell motor mounts can slip causing mis-alignment and vibration.
Posted via Mobile Device

Ski-me · 08-23-2013, 05:10 PM

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

08-21-2013, 10:33 PM	#1
Jake Wade Registered User Join Date: Aug 2005 Location: Louisiana Posts: 711	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

08-21-2013, 11:03 PM	#3
Keith Seymore Registered User Join Date: May 2009 Location: Motor City Posts: 9,490	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 __________________ Chevrolet Flint Assembly 1979-1986 GM Full Size Truck Engineering 1986 - 2019 Intro from an Old Assembly Guy: http://67-72chevytrucks.com/vboard/s...d.php?t=342926 My Pontiac story: http://forums.maxperformanceinc.com/...d.php?t=560524 Chevelle intro: http://www.superchevy.com/features/s...hevy-chevelle/

08-22-2013, 04:40 AM	#4
naphtali5725 Registered User Join Date: Mar 2012 Location: NC Posts: 1,103	Re: Pinion angle thanks Keith! __________________ My build thread... http://67-72chevytrucks.com/vboard/s...d.php?t=515829 Disabled Veteran 82nd Airborne Division Operations: Desert Shield, Desert Storm, and Uphold Democracy

08-22-2013, 06:41 AM	#5
Jake Wade Registered User Join Date: Aug 2005 Location: Louisiana Posts: 711	Re: Pinion angle Thank you very much!

08-22-2013, 11:25 PM	#6
8lugnutz Registered User Join Date: Jul 2013 Location: Canton, TX Posts: 245	Re: Pinion angle Keith, once again, your knowledge amazes me. Posted via Mobile Device __________________ 1980 Chevy K10 Silverado --> Build Page My wife told me I spent too much time on Facebook. So I bought an old truck. Now she wishes I was on Facebook, it was cheaper.

08-23-2013, 10:56 AM	#7
Ski-me Registered User Join Date: May 2012 Location: Colo Springs, CO Posts: 870	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? __________________ - Jeff 89' K5 Blazer, 2.5" lift, 35" tires 04' GMC Yukon XL, 3/4 ton, 8.1L

08-23-2013, 05:00 PM	#8
wraprail Registered User Join Date: Sep 2010 Location: Lake Havasu City Arizona Posts: 863	Re: Pinion angle How are the motor and trans mounts? The stock rubber clamshell motor mounts can slip causing mis-alignment and vibration. Posted via Mobile Device __________________

08-23-2013, 05:10 PM	#9
Ski-me Registered User Join Date: May 2012 Location: Colo Springs, CO Posts: 870	Re: Pinion angle The motor mounts are brand new, energy suspension ones. The tranny mount seems solid.... __________________ - Jeff 89' K5 Blazer, 2.5" lift, 35" tires 04' GMC Yukon XL, 3/4 ton, 8.1L



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