raven3

Realize the forum is all about GM truck but made a comparison of drive shafts of 2015 Silverado vs 2015 F150. The drive shafts are completely different in design and material. Silverado uses a single section aluminum drive shaft for all configurations, except crew cab with standard box, which incorporates a two section steel drive shaft with an intermediate support bearing and the Z71 crew cab with short box, which has a single section steel material drive shaft. All the drive line tubes are welded to the yoke. F150 uses a two section steel material drive shaft on all configurations with intermediate support bearing, except the regular cab regular box, which has a single section aluminum material drive shaft. The tubes are press fit and heat shrunk to the yoke with pressed fit compression ring over the tube for steel and aluminum drive shafts. There are NO welds. The drive shaft must have have maximum .005" runout tolerance on the ends and a maximum .010" run out tolerance in the middle of the tube. The drive shaft must also be dynamically balanced. Note that the drive shaft maybe balanced, but still have excessive run out. Excessive run out will cause excessive forces can create vibration in adjacent structures. Run out can be reduced by straightening the drive tube by applying torch heat on the high side then quenching with water to shrink the metal. It is much easier to straighten a steel tube compared to an aluminum tube because the two metals behave much differently when heated and cooled. Drive line shops are more experienced with steel drive shafts than aluminum drive shafts.

On a quality drive shaft the run out tolerance measured at each end should be no greater than .005". The centripetal force caused by Excessive run out of the drive line tube will excite vibration, even if the drive line is perfectly dynamically balanced. The drive shaft can be heated with a gas torch and water cooled to reduce the run out using a drive line machine similar in appearance to bench type lathe and a dial indicator. Noticed all the aluminum drive shafts have welded tube to yoke joint with a circumferential bead weld. Welding will distort the tube. Have an aluminum drive shaft removed from a 1989 ,non GM light duty truck, where is there no circumferential weld, as typically used on steel drive shafts. The aluminum yoke is pressed into the tube with an external collar sleeve over the yoke to tube joint. A pin is inserted through the joint connection. The aluminum pin has only a small tack weld on each end the collar to secure it in place. Aluminum welds are sensitive to fatigue cracking caused from vibration. A quality drive line is bench balanced using specialized drive line machine with counter weights tack welded on both ends of the drive line tube. The bench method uses a dial indicator. The tolerance is only .002" run out for a quality drive shaft. Of all the dozen 2015 Silverados I crawled under at the dealership , found no counter weights on any aluminum drive shafts. Balancing the drive shaft installed on the vehicle has advantages. The mass of the differential pinion shaft , housing, pinion gear are integrated into the balance as opposed to a bench method balance. Stainless steel worm screw hose clamps secured the drive shaft tube maybe used. The worm screw and cap weight approximately 1/2 ounce. A small hand held vibration analyzer, strobe light and vibration sensor maybe used to balance the drive shaft. The analyzer will indicate the frequency of maximum vibration amplitude and the level of amplitude. In addition, the tubes are not perfectly straight and some are bowed more than others. The straighter the tube the smoother it will run. A quality drive shaft will have a .010" maximum run out tolerance at center of the shaft compared to .005" run out tolerance at the ends.

Visited a Chevrolet dealer today with a magnet in hand. Crawled under every Silverado 1500. The models having a one piece aluminum material drive shaft are double cab with 6.5' box, crew cab with 5.5' box. The model having the two piece steel material drive shaft is the crew cab with 6.5' box. The model having the one piece steel material drive shaft is the Z71 off road crew cab with 5.5' box. Regular cab both 6.5 ft and 8 ft boxes have one piece aluminum material drive shafts. Those models were the only models the dealer had on the lot. Impacting my fingers on the 5" diameter aluminum drive shaft , the thickness of the tube seemed quite thin.

Acknowledge that your double cab has an aluminum material drive shaft. Maybe the V8 have aluminum, while the V6 has steel drive shaft. Ran across a 14 double cab recently that had a steel drive shaft shaft made in Canada. Believe first year for 17" rims is 2008 and first year for 16" rims is 1999 when Chevrolet PU truck was renamed Silverado. Prior to 1999, 15" rims where used. Some research indicates 15" rims used 235/75/15 tires with 28.9" OD resulting in 7.0" wall height. 16" rims used 235/75/16 tires with 29.8" OD resulting in 6.9" wall height 17" rims uses 245/70/17 tires with 30.6" OD resulting in 6.8" wall height The 15" rim tire has slightly higher wall than current 17" rim tire, resulting in slightly more compliant ride.

What happened to 15" steel rims? 17", 18", 20" rims use lower profile tires with more rigid side walls. Always thought the purpose of rubber tires was to absorb the impact energy from the road deformation. Lower profile tires deform less than higher profile tires. It appears the crew cab configuration, assembled in Mexico incorporates the large 5" diameter aluminum material drive shaft, while the double cab configuration assembled in Fort Wayne, IN ,incorporates a smaller diameter steel material drive shaft.

Light duty truck OEMs brag about the hydro formed high strength street frames. High strength steel has greater yield strength than mild or even low strength steel, which means the material can be loaded with greater stress levels before yielding the material to cause permanent deformation. Though the frames have be optimized for minimum weight, the fully boxed section results in a stiffer frame. A stiffer frame will flex less that previous generations with open section frame rails in both bending and torsion modes. Since the high strength frame has less flex, then less road generated vibration energy is absorbed by the frame in the form of strain energy, compared to a more compliant mild steel frame with open section side rails and cross members. The non absorbed road generated vibration is then transmitted to the cabin structure through the elastomer body mounts. More compliant body mounts would absorb a percentage of the energy in the form of heat. Just finished a project of replacing flattened out rubber body mounts on a vintage light truck with urethane mounts. The process is quite time consuming. Doubt if GM would replace the cabin body mounts to reduce the amount of vibration felt in the cabin. Semi truck tractors with steel leaf spring suspension transmit a large amount of vibration energy to the cabin structure. Knew a long haul truck driver that had to take pain medication for neck pain resulting from years of cabin low frequency vibration. Understand why an individual who purchases a so called "luxury" light duty truck has the expectation of a comfortable ride quality. When this ride quality is compromised from excessive cabin vibration, the complaints are launched. One source of vibration that can be reduced would be to replace the steel drive shaft with an aluminum drive shaft. The tube between the two U-Joints accelerates and deaccelebrates twice with each rotation, even if the drive shaft is perfectly aligned, balanced & phased. Acceleration creates a force. This force is transmitted to the frame from the drive shaft tube through the rear axle to the leaf springs and to the frame. The drive shaft vibration energy is also transmitted through the transmission or transfer case to the transmission mount and then the cross member to the frame rails. An alumnium material drive shaft will reduce the amount of generated vibration enuergy. This assembly is not horribly expensive, but being aluminum would be more sensitive to fatigue cracking than a steel drive shaft. GM may have considered this trade off with the 100K mile power train warranty. If had an issue with excessive vibration this custom modication would be first on the list. The labor to replace the drive shaft is minimal. Noticed some folks solved their excessive vibration issue with "Just Tires". Could purchase an aluminum drive shaft for much < $ than a set of LT tires.

Have taken a keen interest to the vibration issue topic, since spent my 40+ year career in the field of applied mechanics dynamics and vibration. Read lots of replies and inputs, because planning on purchasing a new light duty truck. The light duty PU truck is designed to carry a nominal 2000# load in the box. Leaf spring and coil spring suspension and frame are also designed to handle this load traveling on rough road conditions. The steel frame is now lighter and more rigid than the open channel frames of past truck generations. Leaf springs have not changed much since previous generations were still rated at nominal 1/2 capacity. The cabin structure is now lighter weight to improve MPG ratings. Dynamic energy stem from several sources to produce vibration in structures and sub structures. The cabin box is a structure. The cabin roof and floor are substructures. 1. Wheels are a random source of dynamic energy from road pertibations. 2. Drive shaft is a source of sinusoidal dynamic vibration energy. 3. Engine is a source of sinusoidal dynamic vibration energy. 4. Torque converter is a source of sinusoidal dynamic vibration energy. The trucks are mass produced. There is a wide manufacturing tolerance on parts and assemblies. The engine pistons are pulled from bin. All the pistons are not of equal weight. In a performance engine all pistons are machined to have equal weight. It is common knowledge that a V8 engine runs smoother and with less vibration than a V6 engine. It is the luck of the draw. Some engines come off the assembly more balanced than others. Some are in left field and some are in right field depending on what side of the bell curve the stack up tolerances add. Very few engines are at the center of the bell curve that are perfectly balanced. Same thing goes for the drive shaft, torque converter , tires & wheels. The vibration energy from the major sources are all transmitted to the frame. The elastomer body mounts help isolate some of the vibration energy from the frame to the cabin structure. The lighter weight cabin structure is more sensitive to vibration than the more heavy weight cabins of previous generations. The cabin floor will vibrate more. The cabin will vibrate more. The vibrating steering column is supported from the cabin structure. Decreasing the durometer hardness of the rubber cabin vibration isolators and increasing the thickness of vibration isolators would decrease the vibration energy transmitted to the cabin structure. In the past aluminum drive shafts were used to decrease the vibration energy generated by drive shafts. Some drive shaft assemblies are balanced better than others. It is all important to have the pinion shaft parallel to transmission output shaft in the operating condition. Typically, the pinion shaft is set 1 to 2 degrees lower than the transmission shaft to allow for rotation of the rear axle from applied drive line torque. Incorporating an oil filled engine mount to the steel frame would decrease the engine vibration energy transmitted to the frame. Tire cupping can be a major source of vibration caused where the weight distribution between the front wheels and rear wheels is not equal and rough concrete road surfaces. The rear leaf springs and shocks absorb energy in the form of strain energy for springs and heat for the shocks. A characteristic of the truck is stiff suspension. So much of the energy generated where the tire impacts the road will be transmitted to the frame. My take on the vibration issue is GM should use more compliant elastomer body mounts and more compliant engine mounts to compensate for the lighter weight cabin.