DESCRIPTION & OPERATION
| CAUTION | THIS INFORMATION COVERS MOST GENERAL MOTORS VEHICLES, HOWEVER, SOME SYSTEMS MAY VARY IN DESIGN FROM INFORMATION PROVIDED. |
Note. This covers GENERAL MOTORS vehicles only. Other manufacturers offer generic information & procedure.
Front Driveshaft Description
The front driveshaft transmits rotating force from the transfer case to the front differential when the transfer case is engaged. The front driveshaft connects to the transfer case using a splined slip joint.
One Piece Driveshaft Description
A one piece driveshaft uses a splined slip joint to connect the driveline to the transmission or transfer case.
Two Piece Driveshaft Description
There are 3 universal joints used on the 2 piece driveshaft, A center bearing assembly is used to support the driveshaft connection point, and help isolate the vehicle from vibration.
Driveshaft Phasing Description
The driveshaft is designed and built with the yoke lugs (ears) in line with each other. This produces the smoothest running shaft possible. A driveshaft designed with built in yoke lugs in line is known as in-phase. An out of phase driveshaft often causes vibration. The driveshaft generates vibration from speeding up and slowing down each time the universal joint goes around. The vibration is the same as a person snapping a rope and watching the wave reaction flow to the end. An in phase driveshaft is similar to 2 persons snapping a rope at the same time and watching the waves meet and cancel each other out. A total cancellation of vibration produces a smooth flow of power in the drive line. All splined shaft slip yokes are keyed in order to ensure proper phasing.
Universal Joint Description
The universal joint is connected to the driveshaft. The universal consist of 4 caps with needle bearings and grease seals mounted on the trunnions of a cross or spider. These bearings and caps are greased at the factory and no periodic maintenance is required. There are 2 universal joints used in a one piece driveshaft and 3 used in 2 piece driveshaft. The bearings and caps are pressed into the yokes and held in place with snap rings, except for 2 bearings on some models witch are strapped onto the pinion flange of the differential. Universal joints are designed to handle the effects of various loads and rear axle windup conditions during acceleration and braking. The universal joint operates efficiently and safely within the designed angle variations. When the design angles are exceeded, the operational life of the joint decreases.
Center Bearing Description
Center bearings support the driveline when using 2 or more driveshafts. The center bearing is a ball bearing mounted in a rubber cushion that attaches to a frame crossmember. The manufacturer pre-lubricates and seals the bearing. The cushion allows vertical motion at the driveline and helps isolate the vehicle from vibration.
The Vibrate Software (J-38792-VS), is a computer software program which is designed to be used in support of the Vibration Analysis diagnostic tables, along with the Electronic Vibration Analyzer (EVA) (J-38792-A), and a scan tool, to help in determining the source of a vibration concern. The vibrate software is designed to provide quick calculations and produce a chart of the rotational speeds and frequency ranges for specific vehicle systems and components, based upon vehicle data parameters inputted by the user.
The vibrate software uses the vehicle data parameters, such as axle ratio, number of engine cylinders, etc. to create the base chart, depicting the relationships of the various vehicle systems and/or components. The chart view can be modified to show data related to vehicle speed only, engine speed only, or both vehicle speed and engine speed. The user can then plot the dominant frequency reading obtained on the EVA which correlates with the vibration concern, and the engine RPM obtained on a scan tool which correlates with the concern. Once these pieces of data are correctly plotted, the chart will point to the source of the vibration concern, which should confirm the results obtained through the following the Vibration Analysis diagnostic tables.
Description
- The reed tachometer consists of 2 rows of reeds arranged side-by-side. Each reed is tuned to vibrate or resonate when it is excited by a specific frequency. The reeds are arranged by their specific resonant frequency, increasing from left to right, ranging from 10-80 Hz. This arrangement allows for a visual display of the most dominate frequencies which fall within this range.
- The reed tachometer can be a helpful diagnostic tool, however it is extremely sensitive to external inputs that are not related to the vibration concern, such as rough road surfaces, etc., and it is difficult to master its use. Due to these conditions, the reed tachometer has limited diagnostic capability.
- Due to the limited diagnostic capability, limited availability and increasing costs of the reed tachometer, it is not recommended as the primary tool to use in diagnosing a vibration concern.
- When diagnosing a vibration concern, use the Electronic Vibration Analyzer (EVA) 2 (J-38792-A). The EVA has been designed to overcome the shortcomings to the reed tachometer. See «ELECTRONIC VIBRATION ANALYZER (EVA)»(ref-166336-S37061621232004092000000) under DESCRIPTION & OPERATION.