Went from an SM420 to a T5, now have a question about pinion angle - The 1947 - Present Chevrolet & GMC Truck Message Board Network

mark '87 930 · 06-04-2013, 10:27 PM

So as most of you know, the T5 is almost 12"s longer than the SM420.. so my driveshaft had to be cut for installation of the T5. That said, I'm no geometry teacher, but there's no way the pinion angle is good anymore. I get increasing vibrations. I am pretty certain it's because my angles changed. Would hat make sense? Or am i barking up the wrong tree?

That said, I never went 65-70mph with the old sm420.. so I don't knwo if the vibrations were there beforehand. Could maybe also be my rear diff.

NEWFISHER · 06-04-2013, 11:47 PM

Check the angle of the transat the yoke and same with rear diff. If they are both within 1 degree +- then check driveshaft ujoint phase, if good then have driveshaft rebalenced. Have all tires checked for balence. Those are the most common causes I have experienced. If rear diff was that bad, something would be leaking.
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mknittle · 06-05-2013, 10:36 AM

The length won't change the vertical angle. all that it will change is how steep the driveline is. If the pinion/transmission yoke weren't parallel the problem may not have been noticeable at low speeds as you said. Do as NEWKINGFISHER said but first I would check the universal joints. even if they are new they may have a tight spot.

OrrieG · 06-05-2013, 01:44 PM

When I went to 4wd the transfer case shortened the drive line and the pinon and trans/transfer ended up not parallel. I had a very good shop shorten and balance the driveline and did not have any problems with vibration for 80K miles, may at highway speeds (75-80 for me). Mine is a short wheelbase truck. I would suspect a bad universal or driveline balance, there are lots of trucks like mine that do not have problems. Check to make sure you got the right universals, there are some that will fit but are narrower than the seat and can move off center. Did you drive the truck the T5 came out of to make sure the output shaft did not have issues? Like was said if you were having issues with the pinion shaft/bearing or back of the tranny there would be fluid leaking because it would hog out the seals.

mark '87 930 · 06-06-2013, 11:37 PM

no leaks in the diff. i'll check universals and maybe see if i can get the driveshaft verified for balance. Whats the best way to check u-joints?

06-04-2013, 10:27 PM	#1
mark '87 930 Registered User Join Date: Nov 2011 Location: Toronto, Ontario Posts: 222	Went from an SM420 to a T5, now have a question about pinion angle So as most of you know, the T5 is almost 12"s longer than the SM420.. so my driveshaft had to be cut for installation of the T5. That said, I'm no geometry teacher, but there's no way the pinion angle is good anymore. I get increasing vibrations. I am pretty certain it's because my angles changed. Would hat make sense? Or am i barking up the wrong tree? That said, I never went 65-70mph with the old sm420.. so I don't knwo if the vibrations were there beforehand. Could maybe also be my rear diff.

06-04-2013, 11:47 PM	#2
NEWFISHER Registered User Join Date: Sep 2012 Location: Oregon Posts: 3,303	Re: Went from an SM420 to a T5, now have a question about pinion angle Check the angle of the transat the yoke and same with rear diff. If they are both within 1 degree +- then check driveshaft ujoint phase, if good then have driveshaft rebalenced. Have all tires checked for balence. Those are the most common causes I have experienced. If rear diff was that bad, something would be leaking. Posted via Mobile Device

06-05-2013, 10:36 AM	#3
mknittle Registered User Join Date: Jul 2011 Location: Auburn ca. Posts: 2,886	Re: Went from an SM420 to a T5, now have a question about pinion angle The length won't change the vertical angle. all that it will change is how steep the driveline is. If the pinion/transmission yoke weren't parallel the problem may not have been noticeable at low speeds as you said. Do as NEWKINGFISHER said but first I would check the universal joints. even if they are new they may have a tight spot. __________________ Mark My GMC build. http://67-72chevytrucks.com/vboard/s...d.php?t=536602

06-05-2013, 01:44 PM	#4
OrrieG Registered User Join Date: Jun 2006 Location: Idaho Posts: 8,800	Re: Went from an SM420 to a T5, now have a question about pinion angle When I went to 4wd the transfer case shortened the drive line and the pinon and trans/transfer ended up not parallel. I had a very good shop shorten and balance the driveline and did not have any problems with vibration for 80K miles, may at highway speeds (75-80 for me). Mine is a short wheelbase truck. I would suspect a bad universal or driveline balance, there are lots of trucks like mine that do not have problems. Check to make sure you got the right universals, there are some that will fit but are narrower than the seat and can move off center. Did you drive the truck the T5 came out of to make sure the output shaft did not have issues? Like was said if you were having issues with the pinion shaft/bearing or back of the tranny there would be fluid leaking because it would hog out the seals. __________________ 1959 Chevy Short Fleetside w/ 74 4WD drive train (current project) OrrieG Build Thread 1964 Chevelle Malibu w/ 355-350TH (daily driver) Helpful AD and TF Manual Site Old Car Manual Project

06-06-2013, 11:37 PM	#5
mark '87 930 Registered User Join Date: Nov 2011 Location: Toronto, Ontario Posts: 222	Re: Went from an SM420 to a T5, now have a question about pinion angle no leaks in the diff. i'll check universals and maybe see if i can get the driveshaft verified for balance. Whats the best way to check u-joints?



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