Rear axle angle of elevation - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Cyco Path · 10-15-2002, 02:20 PM

When you drop a truck more than 4" in the rear aren't you suppose to decrease the angle of elevation on the rear axle? If so, by how much?

**MikeB** · 10-15-2002, 04:05 PM

Yeah, ideally you'd want to tip the entire rear axle forward a little, but I'm not sure how much. Maybe it doesn't even matter with just a 4" drop so far back from the trans. Check out some 4-wheeler sites to see what maximum angles should be.

Mike C · 10-15-2002, 07:29 PM

It depends. You want the overall pinion angle (between the back of the trans and the rear axle) to remain the same. Ideally they should be ~1 degree each or so, and no more than 2 degrees of misalignment to each other. On a drag car, pinion angle is set to be slightly negative relative to the trans angle, then under WOT operation, the axle rotates to the point the angles are equal. If it over rotates, this actually reduces the contact patch on the ground which in turn reduces traction. Depending on your method of lowering, pinion angle may need to be adjusted. With leaves, raising the rear of the spring to lower the truck rotates the pinion downward, which increases pinion angle and the housing should be shimmed up to restore. Blocks on a coil spring should not change the angle. There are two angles you are talking about so its hard not to confuse them. Their is the relationship of the back of the trans to the yoke and then their is the angle the driveshaft is at. Completely different. I forget the max angle that a single u-joint can function in but it's about 30 degrees before excessive wear occurs I believe. It is possible to switch to a CV driveshaft in which case you want the top angle to be a degreed number while the single joint at the axle should be a zero angle. (pinion centerline and driveshaft centerline are same)

10-15-2002, 02:20 PM	#1
Cyco Path Registered User Join Date: May 2002 Location: Robertsdale, AL, USA Posts: 77	Rear axle angle of elevation When you drop a truck more than 4" in the rear aren't you suppose to decrease the angle of elevation on the rear axle? If so, by how much? __________________ Looking for '67 to replace the '68 I sold. Robertsdale, AL

10-15-2002, 04:05 PM	#2
MikeB Senior Member Join Date: Jul 2000 Location: North Texas Posts: 3,599	Yeah, ideally you'd want to tip the entire rear axle forward a little, but I'm not sure how much. Maybe it doesn't even matter with just a 4" drop so far back from the trans. Check out some 4-wheeler sites to see what maximum angles should be. __________________ Mike 1969 C10 LWB -- owned for 35 years. 350/TH350, 3.08 posi, 1st Gen Vintage Air, recent AAW wiring harness, 5-lug conversion, 1985 spindles and brakes. 1982 C10 SWB -- sold 1981 C10 Silverado LWB -- sold, but wish I still had it! 1969 C10 (not the current one) that I bought in the early 1980s. Paid $1200; sold for $1500 a few years later. Just a hint at the appreciation that was coming. Retired as a factory automation products salesman. Worked part-time over the years for an engine builder and a classic car repair shop. Member here for 24 years! This is the very first car/truck Internet forum I joined. I still used a dial-up modem back then!

10-15-2002, 07:29 PM	#3
Mike C Registered User Join Date: Dec 1999 Location: Austin, TX, USA Posts: 7,728	It depends. You want the overall pinion angle (between the back of the trans and the rear axle) to remain the same. Ideally they should be ~1 degree each or so, and no more than 2 degrees of misalignment to each other. On a drag car, pinion angle is set to be slightly negative relative to the trans angle, then under WOT operation, the axle rotates to the point the angles are equal. If it over rotates, this actually reduces the contact patch on the ground which in turn reduces traction. Depending on your method of lowering, pinion angle may need to be adjusted. With leaves, raising the rear of the spring to lower the truck rotates the pinion downward, which increases pinion angle and the housing should be shimmed up to restore. Blocks on a coil spring should not change the angle. There are two angles you are talking about so its hard not to confuse them. Their is the relationship of the back of the trans to the yoke and then their is the angle the driveshaft is at. Completely different. I forget the max angle that a single u-joint can function in but it's about 30 degrees before excessive wear occurs I believe. It is possible to switch to a CV driveshaft in which case you want the top angle to be a degreed number while the single joint at the axle should be a zero angle. (pinion centerline and driveshaft centerline are same) __________________ 44 Willys MB 52 M38A1 64 Corvette Coupe 68 Camaro 'vert LT1 & TH700 69 Z/28 355 12.6's @110 69 Chevy Short Step 4 1/2"/7" drop 72 Jimmy 4WD 4spd 4" & 35's 02 GMC 2500HD 4x4 Duramax



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