Measured rear driveline angles

FL335i · February 21, 2016

Ok, I have a bone stock truck. Look at my signature for more details. I have 38,xxx miles on my truck. I have been wanting to measure the angles since I bought it, but never got around to and kept forgetting. Well for the past 2k miles or so at speeds above 77 I am getting some rear end vibration as if a tire is out of balance. I have the OEM SRA's with about 50% tread on them. So I I got out my angle finder and here is what I have:

Tcase is is pointing down 6*.

Driveshaft is pointing up 5*.

Pinion is pointing up 7*.

Our trucks have leafs in the rear. When I built my rock crawler and was into custom drive lines, I always set my pinion down 1-2* relative to the Tcase so under acceleration and torque the pinion would rotate UPWARD 1-2* and angles would be zeroed out in the system making everything vibration free. So for my truck with the above figures, the pinion shouuld be pointing upward 4 or 5 degrees, not 7. I manged to build a straight axle 4runner conversion in my driveway and that truck would do 100 mph vibration free on 35" MTR's. Yet my '14 truck vibes at 77+ with SRA's. I'm very surprised that the stock rear pinion angle is pointed higher than the tcase. That goes against everything I've learned and done in drive lines. Under highway speeds and torque applications the pinion is going to be pushing upward and making the angles even more goofy; pinion is probably 8-9* upward at 80mph. This is probably why I have a vibration in my truck. Being the Tcase is down 6* and the pinion is up 7*.... We're already starting off wrong. I need to bring the pinion down 2* so it's upward 5*. Giving it 1* of preload In the correct direction! I'm going to look at getting GM shims or talk to a local drive line shop to see what they have. I'd like to get it on their rack and work with them under the truck to get it right. It's like the drive line engineers got the concept of drive line angles completely backwards. If I'm driving in reverse at 80 MPH it will probably be perfect.... After going through my drive line angles, makes me wonder if this is the culprit for all the viber-a-dos. And let's be honest, most dealership techs are not drive line experts, nor are they building rock buggies after work. I will update the post when I get the rear axle re-shimmed and my angles are proper.

07Softail · February 21, 2016

I agree the drive lines on these trucks are all over the place like said pinion angles to axle offset and driveshaft lengths. Very poor workman ship IMO.

RT

FL335i · February 21, 2016

^Yes. I quickly checked the drive line angles today on my stock '89 K5 GMC Jimmy (AKA Blazer) and the angles are correct. Need to send these drive line guys back to 1989. I'm pretty confident the drive line angles being goofed up is the issue. Feels like a drive shaft out of balance or more so... out of whack on angles so the vibes are not getting canceled out. I checked my rear axle... all I have are some aluminum blocks in there. They do not seem to have any angle to them. Just aluminum blocks; 0*. I need to get with a dealership parts dept and get the correct GM shims. I want to do this right.

chadder1313 · February 22, 2016

Very interesting. In for info.

southern_sierra · February 22, 2016

Wonder if some of the axle housing spring mounts are welded in the wrong place since some vibrate and some don't. This would change the angle. My vib I had between 75 and 85 went away after I tightened the hell out of my axle u-bolts. I carry about 400 lbs all the time in the bed so my drive line angle is different from a truck with no weight in the bed. Just my 2 cents worth.

FL335i · February 22, 2016

Southern_sierra: what is the torque spec on the u-bolts?

southern_sierra · February 22, 2016

Southern_sierra: what is the torque spec on the u-bolts?

Not sure some people here have said 110lbft. I tightened each nut on mine until you could feel a slight twist. If you have fooled with u-blots before you will know what I mean. Have them about as tight as you can get them.

FL335i · February 23, 2016

^ Understood. I'd still like to know the GM spec on them for grins. I'll search and see what I come up with.

FL335i · February 24, 2016

14mm bolts = 59 Lb/Ft.

16mm bolts = 89 Lb/Ft.

Found another bit of info for our '14's +. first pass 59 ft.lbs, second pass 130 degrees

So seems like we can agree that if you have the 14mm bolts, you can throw the torque wrench on them at 59 # to verify they're not loose. I'm betting my truck has 14mm bolts.

Towerhog · February 24, 2016

U bolt torque per 2014 Chevy manual says: 80 NM or 59 ft-lb first pass then 130 degrees on the second pass while using a criss-cross pattern.

FL335i · February 25, 2016

Thanks towerhog.

BuyAmericanIron · February 25, 2016

FL335i, I am curious to know what you find. Make sure to post up new information.

BO TIE 1 · March 20, 2016

FL335i, I think your on the right track.

Check out post #20 in this thread

http://www.gm-trucks.com/forums/topic/184400-shakevibration-fix/page-2

I`ll be checking my angles when I get a chance.

FL335i · March 20, 2016

Well I've been slammed with work and I've been doing some big jobs on my '89 K5 Jimmy on the weekends. I just wrapped up restoring the heater/AC box. Still have the dash off.... And I completed the coolant filter on my Silverado. So my weekends have been chalk full of truck work. Ok, update. I called a Chevy dealer near me and their parts people told me GM does not make axle shims for correcting the drive line angles. How the hell is that even possible? Have not called a 2nd dealer yet.

FL335i · June 4, 2016

Ok, revisiting this. Last night I had the time to pull the truck into the garage and measure the drive line angles. Driveshaft was angled 5*. Rear pinion was up around 4*, so a 1* operating angle. Tcase was down around 3 or 4*, making a 1-2* operating angle. They are fine.... These are very small operating angles. I must of goofed up measuring my angles on the driveway originally. Sorry guys... no dice here. angles are fine.