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TSB 18-49-98

Driveline Induced Vehicle Surge/Vibration Diagnosis

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Date: December 30, 1998

Models: 1996-1999 BR/BE Ram 1500 series 4X4 with automatic AND 3.55 rear end (sales code DMD).

Discussion:

The TSB discusses engine miss/ buck/ surge/ vibration and driveline diagnosis.
NOTE: TSB 18-48-98 SHOULD BE PERFORMED PRIOR TO THIS DRIVELINE DIAGNOSIS.

Three driveline areas of concern that might induce an incorrect diagnosis of a vehicle surge/vibration are:

Driveline Angle

When two shafts come together at a common joint, the angel that is formed is called the operating angle. Universal joints produce system speed variations when operating at an angle. This characteristic causes the propeller shaft to speed up and slow down twice each rotation due to the working angle at the front of the propeller shaft. The speed vibration is canceled at the rear axle when the rear universal joint is operating at exactly the same angle as the front u-joint. Whenever there is a difference in the front and rear u-joint angles on the driveline, driveline roughness will result and if great enough, a vehicle surge or vibration may be felt. The larger the angle, the larger the amount of angular acceleration and deceleration at the joint and the greater the roughness.

Because of their relatively high working angles, four wheel drive and short wheel base vehicles are more sensitive to angular differences. To help minimize the amount of acceleration and deceleration at the joint, the operating angle of the driveline must be kept to a minimum.

Tire Force Variation

A tire may normally appear to be a true circle with a uniform internal structure. However, due to the construction characteristics of a tire, the tires weight, its internal rigidity, and its' dimensions, tires may have a small amount of variation.

Force variation should not be confused with out-of-round tires or tire imbalance. In fact, tire force variation cannot be determined by the naked eye or most types of balancing equipment. Tire force variation can only be determined by setting a tire on a drum, applying a load to the tire, and then rotating it while the drum axis-to-tire distance is kept constant. While the tire is rotating, the various reaction force that cyclically develop on the ground contact is measured (Fig 1). High force variation can contribute to a vehicle surge or vibration.

NOTE: Penstar tire balancer H-9702-DD-R (Hunter GSP 9700) has the capability to measure tire force variation.

Differential Ring Gear Pitch Line Runout

The differential enters into the differential housing perpendicular to the ring gear and just below the centerline of the ring gear. The point where the center line of the pinion meshes into the ring gear is called the pitch line. If either the pinion gear or the ring gear have irregularities that can cause either gear to have runout, the angles between the ring gear and the pinion gear will change. Similar to the working angles of the propeller shaft, changing angles in the ring and pinion gears can cause the ring gear to accelerate and decelerate resulting in vehicle surge or vibration.

The following information is an aid to diagnosis of driveline induced vehicle surge/vibration on 4X4 Ram 1500 Trucks equipped with a 5.2L or 5.9L gas engine, automatic transmission, and the 9 1/4" axle with a 3.55 ratio.

Even though this diagnosis is for a specific vehicle, similar diagnosis can be performed on other vehicles. The speed at which another vehicle will exhibit driveline surge/vibration may be higher or lower than the speeds for this vehicle. Different options, body configurations, tire sizes, etc will all affect the diagnosis speeds.

Diagnosis:  

  1.  Locate a road that fairly smooth and is safe to drive at  a speed in which the customer indicates that surge/vibration occurs. Note when the surge/vibration occurs. Things to be aware of include:
  1. Use the following chart (Fig 2) to help identify driveline components that may cause surge/vibration.
  2. If the surge/vibration starts to occur at approximately 20 mph (32 kph) and starts to disappear at aprox 60 mph (97 kph) and is torque sensitive, perform the Driveline Angle Diagnosis.   If the surge/vibration starts at approx 22 mph (35 kph) and goes away at approx 32 mph (51 kph) and/or starts at approx 48 mph (77 kph) and goes away at approx 78 mph (126 kph), perform the Wheel/Tire Diagnosis.   If the surge/vibration starts at approx 45 mph (77 kph) when the torque converter engages ( torque converter clutch MUST be engaged ) and then goes away at approx 62 mph (100 kph), perform the Rear Axle Diagnosis.
DRIVELINE ANGLE DIAGNOSIS

Driveline Angle surge/vibration starts to occur at approximately 20 mph (32 kph) and starts to disappear at approx 60 mph (97 kph) and is torque sensitive. If using the EVA, driveline surge/vibration will have a vibration frequency of approx 24 - 84 Hz. Refer to the 1999 Ram Truck Service Manual page 3-3 for propeller shaft and u-joint driveline vibration diagnosis.  The driveline angle must be measured. Follow the service procedures from pages 3-4 through 3-6. All measurements must be taken at curb weight with the vehicle supported by its wheels/tires. Normal joint angles for the Ram Truck 4X4 are 1-5 deg with a maximum of 1 deg difference between joints in a series. Driveline angles that exceed the 1 deg maximum difference must have the axle shimmed.

CAUTION: It is extremely important to have at least three threads of the spring U-Bolt showing when the nut is torqued to specification. To ensure that the U-Bolt has the proper clamping force, there should be no more than two shims used per side.

WHEEL/TIRE DIAGNOSIS

  1. Wheel/Tire surge/vibration starts at approx 22 mph (35 kph) and goes away at approx 32 mph (51 kph) and/or starts at approx 48 mph (77 kph) and goes away at approx 78 mph (126 kph). THe EVA will indicate a vibration frequency of 4 - 6 HZ and 10 - 16 Hz. Tires and wheels must first be properly balanced.
  2. If the tires/wheels are properly balanced and the surge/vibration still occurs at the above speed range, perform the match mounting service procedures in the 1999 service manual page 22-5.
  3. If all tires are properly mounted to the wheel and the surge/vibration still occurs, perform the Tire And Wheel Runout diagnosis in the 1999 service manual pages 22-8 and 22-9.
  4. If the tires and wheels are within the specifications listed in the service manual and the surge vibration outlined above is still present, the tires and wheels could have a force variation that causes the surge/vibration. If tire balancer such as the H-9702-DD-R is not available to determine tire force variation, the tires should be exchanged with a Ram Truck that does not exhibit the surge/vibration condition. If the exchanged tires correct the condition, replace the original tires. If the exchanged tires have no effect on the surge/vibration, re-evaluate the surge/vibration to verify whether or not the surge/vibration starts to occur just as the torque converter clutch engages. If the surge/vibration is sensitive to torque converter clutch engagement, perform the Rear Axle Diagnosis.
NOTE: Return the exchanged tires to the original vehicle.

REAR AXLE DIAGNOSIS

Rear axle pitch line runout on the 4X4 Ram 1500 Truck with a 9 1/4" axle and 3.55 axle ratio can cause a Surge/vibration to start at approx 45 mph (77 kph) when the torque converter engages ( torque converter clutch MUST be engaged ) and then goes away at approx 62 mph (100 kph). The condition is most noticeable when the vehicle is under a light load (e.g driving up a small hill). The EVA will measure the surge/vibration frequency at approximately 8 - 12 Hz. If your diagnosis has determined that the root cause of the surge/vibration is pitch line runout, replace the rear axle and pinion gear set.

notes: TSB 18-48-98 SHOULD BE PERFORMED PRIOR TO THIS DRIVELINE DIAGNOSIS. Do not replace a ring and pinion gear set until 18-48-98 has been done without satisfaction.


Thanks to Bob Bergevin for providing this TSB information

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This page was edited on: May 3, 2004