randys blog
Diagnosing Noise (Part 1)
Many things can go wrong inside a differential. Although the hints are often subtle, most impending failures give fair warning in the form of noise. Several situations can create ring-and-pinion noise. If the gears have been quiet and begin to howl, they are probably worn or wearing. If the gears howl during deceleration only, it’s possible that the pinion-bearing preload has loosened. Howling under acceleration at all speeds indicates that something in the differential — gears, pinion or carrier bearings — has worn or no longer keeps the gear alignment correct. If the gears howl while accelerating over a certain speed range, but not all speeds, it’s likely that the gears are worn due to lubrication failure or overloading. When a newly installed gear set howls, suspect the design or setup. A common problem is worn carrier bearings, as indicated by a low-pitch rumble above 20 mph. On vehicles with C-clip axles, the noise may vary while negotiating turns. Worn pinion bearings can cause whirring noises at all speeds, under deceleration and/or acceleration. Pinion bearings tend to whir, rather than rumble, because the pinion is turning several times faster (depending on gear ratio) than the carrier. Badly worn bearings can also cause howl if they do not support the gears correctly. Worn wheel bearings can be difficult to determine. A very bad wheel bearing typically makes itself heard with great clarity; it’s the bearing that is going bad, but not destroyed, that is hard to find. Turning back and forth from hard right to hard left can identify the culprit; however, I’ve been fooled by right-front wheel bearings that make noise when turning right (which heavily loads the inside-left-front wheel bearing, but also loads the outside-right-front bearing). One common situation that may not make any noise: The pinion spins, but the tires don’t rotate. Broken spider gears can render the differential immobile, and usually make a loud, crunching sound as they make their final departure. A broken ring gear will allow the differential to propel the vehicle for about eight feet at a time, then bang or grind as the section with broken teeth tries to engage the pinion. Depending on ratio, a broken pinion tooth (or teeth) will clunk about every two or three feet. A broken axle is easily determined. After it breaks, a C-clip design axle can be pulled out of the housing without unbolting anything — or may even find its own way out. On many bolt-in-design axles, the wheel will give the broken axle shaft away by cambering in at an angle. A high spot on a gear tooth may sound similar to a broken gear, but will only make noise while accelerating or decelerating, since the spot appears on just one side of the offending tooth. A high spot on the ring gear will make a heavy clicking sound about every eight feet; a high spot on the pinion makes noise every two or three feet and is much more pronounced due to its higher frequency. Whether large or small, differential noise is telling you something. Listen carefully! If in doubt, pull off the cover or remove the third member for a closer look. Catching a bad part before is ruins others is definitely worth the effort. Popular Resources: New Gear Break-In Properly Setting Preload with Side Adjusters Size Matters
Before You Call For Rearend Parts
It may sound silly, but there are many things to consider and lots of data to collect prior to picking up the phone to find rearend parts. Unlike engine or suspension parts, rearend parts are not easy to look up, and can vary greatly on any vehicle make/model. Just because it has a specific engine size or transmission type does not mean that the vehicle uses one specific gear ratio. Vehicle manufacturers will usually offer at least two gear ratios for any given vehicle model. The gear ratio can vary with little or no correlation to its intended use or market area. I have seen many models released that offer four different ratios with little or no other variations in the vehicle. Another thing that complicates matters is there does not appear to be a standard or good book that a salesperson can use to look up the right parts for a vehicle by year, make, and model. And, for whatever reason, the VIN number is not helpful. For most vehicles, the VIN does not provide gear ratio or limited slip information. One way to get the right parts to the end user is by process of elimination. In this scenario, the vendor sells parts that they think may be right until they find the right combination. This is often referred to as the “we got your credit card number and that’s all that is important” method. But don’t count on your friends to identify the differential for you, as they may not be accurate. If the diff is not the model they say it is, there may be restock charges for sending back parts. The only sure-fire way to determine the right parts for a rearend is to find someone who really knows rearends and be prepared to answer a lot of questions. Here’s some questions to answer BEFORE calling: How do you use or plan on using the vehicle? Year, make (Chevy, Jeep, Ford, Dodge, etc.), model (1/2 ton, Cherokee, etc.) Tire size Old gear ratio New ratio you think you want Axle spline count Number of cover bolts, or is it a drop out Number of ring gear bolts Bill of material number or tag numbers Transmission type Engine size (I hope you know this one, surprisingly a lot of people do not) Engine rpm that you are comfortable cruising down the highway at. This will only work if you have a tach, and it may require driving in a lower gear to experience higher RPMs. Number of wheel lugs Trailer Weight (For those of you who pull trailers or other vehicles) Standard or reverse rotation front ring & pinion This can be determined by whether the pinion enters above or below the axle housing centerline. Reverse rotation gears have the pinion shaft entering above the axle centerline and standard rotation gears enter the housing below the axle centerline. Independent Front Suspension or solid straight axle in front Outer diameter axle bearings It may seem ridiculous to have to answer so many questions, but in the end, it is far easier to order parts once correctly, than to order and return the wrong parts several times. If you take the time to find out the answers to a lot of questions, and find a salesman who knows what questions to ask. It will save a whole lot of frustration for everyone involved, especially you. If a parts representative asks about the condition of other parts, they are usually trying to help you with a better price on all of the parts you will need for a complete repair, and save you from having to run to the local parts store after you get the differential apart. Popular Resources: Diagnosing Noise (Part 1) Ford 9 Inch Differential Information Four Critical Ring & Pinion Settings
Unboxing: Gear & Install Kit Package
Part of our Yukon Gear & Axle product unboxing series.
Driveline Angles & Vibration
I have had more than a few customers come back to our service shop after a gear ratio change to complain that we caused a new vibration in their vehicle. In actuality, we inadvertently caused the vibration by increasing the driveline speed. When changing to a lower gear ratio (numerically higher) the driveline speed increases proportionally to the change in the ratio. For example, when changing the ratio from 3.08 to 4.56 there is a 48% change in the ratio and a 48% increase in driveline speed. This means that a vibration that would have been noticeable at about 90 mph is now noticeable at 60 mph. This higher driveline speed makes the vibration more noticeable because while it previously existed at 90 mph, it may have gone unnoticed due to the amount of vehicle vibrations it had to overcome in order to be noticed. If the customer installed taller tires and raised the vehicle before changing the gear ratio, the vibration is probably caused by the lift. This vibration caused by the lift and wrong driveline angles would not be noticeable until the new ratio was installed, since the tall tires and stock ratio kept the driveline speeds too slow for the vibrations to be felt. Vibrations due to wrong angles are usually easy to identify because they are harmonic or cyclic. This means that the vibration varies in pitch or intensity even when traveling at a steady speed. The results is a “whir … whir … whir” type of noise. The solution to wrong angles is easy in theory, but not always easy in practice. There have been many good technical papers written on this subject, so I won’t go into detail now. I will however cover a few of the basics. In order for a two U-joint driveline to be free of vibration it must be in balance, and the angle of the front U-joint must be the same as, or very close to, the angle of the rear U-joint. If there is a noticeable difference in the angles, there will be a vibration. If it is not possible to match the front and rear angles, a constant-velocity joint can be used at the transfer case end with no angle in the U-joint on the differential end. Although it is expensive, and only works if the pinion is not offset side-to-side from the output shaft, this is the only cure in many lift situations. I have seen vehicles use a constant-velocity joint at each end of the driveline. This is more expensive but will fix any angle problem. Another solution is to rotate the differential pinion angle up or down to match the front angle. This is usually not easy and can be accomplished with wedges, by moving the spring pads, or by rotating the axles tubes in relation to the differential center section. For some vehicles there are aftermarket kits available for lowering the transfer case or installing adjustable length control arms. Although these may seem like extreme measures, they are sometimes the only way to eliminate or lessen vibrations. Note: If the vehicle has a differential pinion offset to the side from the center of the output shaft on the transmission or transfer case, the angles due to this offset will not cause vibration. This is because the pinion shaft and the output shaft are still parallel with respect to these side-to-side angles. I have seen some lifted vehicles that vibrate no matter how much care is taken to balance the driveline and match the angles. It is one of the things that we sometimes have to live with in order to have a lifted vehicle. Popular Resources: Diagnosing Noise (Part 1) Ford 9 Inch Differential Information Four Critical Ring & Pinion Settings