Numerous drive axle problems can result in a vibration which is propshaft speed or tire speed related.
If the vehicle has a vibration that is equal to any order propshaft or tire rotation, and it is not present when testing the vehicle in the stall, then it is possible that the vibration is being generated by internal front or rear axle components. This may also be true if the vibration was correctable in the stall, but returned when the vehicle was driven on the road. These vibrations tend to be aggravated by the load of the vehicle working against the ring and pinion gear set.
Heel and Toe identify the ends of the gear tooth. Imagine you and 12 other people are standing in a circle facing each other, your toes are pointing inside of the circle and your heels are pointing outside of the circle.
The Pitch Line is an imaginary line that divides the upper and lower halves of the gear tooth contact area.
The Pitch Point is the theoretical point where the pitch lines of both meshing gear teeth meet while rotating relative to one another.
The Root Line is an imaginary line that indicated the bottom of the meshing gear tooth contact area.
Face and Flank identify the area in the contact area of the gear tooth.
The Drive Side and Coast Side of the gear tooth identify the sides of the gear tooth used under acceleration and deceleration.
Backlash is the endplay between the gear teeth as the gear sets rotate relative to one another.
Clearance is the distance between the top of one gear tooth and the bottom of the area between two gear teeth it is meshing with.
In-Stall Loaded Testing
This test is designed to load the pinion so it will produce the vibration on the hoist, then allow the technician to identify and isolate the source.
Example: if the vibration was originally noted at 55 mph, accelerate and decelerate from 45 mph to 65 mph, back to 45 mph and so on. Repeat this while taking note as to whether or not the pinion nose vibrates under load during the acceleration and/or deceleration.
IMPORTANT- Make sure that both axle shafts are rotating at the same speed. The action of a differential when one tire is spinning faster than the other may mask the vibration. Adjusting the rear brakes equally will usually correct this condition.
Improperly loaded, specifically under loaded, pinion bearings and side bearings will allow excessive gear movement resulting in noise and vibration.
Theoretically, every tooth of a gear set should have the same backlash when setup properly. In the real world this is rarely the case. Backlash variation is a difference in the backlash from one gear tooth to another gear tooth. Gear tooth backlash may be within specifications on one tooth and out of specifications on the next tooth. Backlash variation should be checked on EVERY tooth of a gear set.
Heat induced gear tooth expansion can decrease backlash and worsen the vibration as the gears warm up. If any of the following conditions occur, the heat induced gear tooth expansion will occur more quickly.
If the ring gear was machined incorrectly:
If the pinion gear was machined incorrectly:
Maximum differential case radial runout = 0.002" (0.0508mm)
Maximum differential case lateral runout = 0.002" (0.0508mm)
A variation in gear tooth depth and width consistency of the ring gear or pinion gear teeth which can cause gear tooth binding. Click here to diagnose Pitch-Line Runout.
Possibly resulting from a rear-end collision where the rear axle was forced into the propshaft and transmission with excessive force.
Possibly resulting from improper installation of the bearings or from the bearings being installed into a dirty or contaminated surface. Click here to download the TIMKEN Bearing Diagnosis Guide
Anything that can affect the pinion gear and how it contacts the ring gear as it rotates can contribute to any order, torque sensitive propshaft vibration. The only way to correct these conditions is to replace the affected components. In most cases this means the ring and pinion gear set and related bearings, but in some cases, it may include the axle housing. Presently, there is no way to effectively measure or identify the exact component at fault, except close visual inspection for unusual wear marks that may or may not be present.
Sometimes the installation of a "known good" axle assembly from a stock unit is the best way to quickly isolate an internal axle problem as the cause. Always qualify or evaluate the "known good" stock unit to ensure that it does not have a vibration problem.
Once an internal axle problem has been corrected, perform a road test. Determine if the vibration has been eliminated. It may be necessary to 'line tune" the vehicle by performing a system balance of the propshaft
A two-speed or double reduction MD/HD truck axle has additional components which can also cause a vibration. These components can rotate at speeds that do not match the speed of the propshaft or the tires. For example: A two speed axle might have a gear ratio set of 6.14 in high, and 8.38 in low. The gear reduction ratio = 8.38 / 6.14 = 1.36:1. (This reduction is typically accomplished with a planetary gear set). This means that in low range, there is an additional 1.36: gear reduction taking place.
A vibration caused by any of the reduction components may cause a vibration that is 1.36 times faster than the speed of the propshaft. The vibration frequency of this type of component will not match any on the lines on the vibration graph. Shifting the axle from high to low may assist in isolating the source of the vibration.
This page was last modified Tuesday, November 19, 2013 10:02:34 PM
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