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
Unboxing: Gear & Install Kit Package
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
Choosing A Differential Repair Shop
So you don’t have the time to work on your own differential? Who can you trust to do a good job? Whenever I take my truck to someone for repairs, I always cross my fingers, even if I know them. The automotive repair industry has a bad reputation for a reason, mostly because there are many unqualified or corrupt people in the industry. Now don’t send me a bunch of letters defending the trade. I have made my living by doing repairs and selling parts for more than twenty years now, and I know that there are a lot of good people involved in auto and truck repair. However, identifying them can be difficult.Finding a good diff repair shop can be harder than just finding someone who is honest and who truly cares about doing the job right. They must also be competent. When it comes to differentials, most mechanics, dealerships included, do not like to work on them. There are not many good manuals available, there are no really good training programs that I am aware of, and I have found differentials to be more of an art than a science. Unfortunately, this also leaves repair shops feeling frustrated in their search for a good diff mechanic. When it comes to differential repair, I recommend trying to find someone at, or through, a four wheel drive shop. Four wheelers typically have more experience with diffs than speed shops or machine shops, although there are exceptions. Even if they do not do the work themselves, they can probably recommend someone who does. Before having any work done, I always like to see the mechanic’s work area. If the shop is clean, organized, and the personnel are proud to show it off, then I am somewhat more at ease. I also like to ask a lot of questions before I turn over my keys. Where do they get their parts from? Do they have them in stock? What kind of warranty comes with the parts and labor? How long will it take to do the job? How many diffs do they do each week? One thing I always do is insist on getting an estimate for tear-down, inspection, and reassemble, in case I decide not to have the repairs done after receiving the estimate. Also, I always insist on an exact estimate for the repairs needed prior to them starting any actual repair work. Some states have excellent laws that protect the customer by requiring all repair facilities to provide these estimates, while some states provide no protection for the consumer at all. Finally, I recommend paying with a credit card. This not only insures that you have some recourse in the event of a problem with the shop, it also weeds out the shops that credit card companies will not do business with. One other thing I want to mention is that although I do not like to drive long distances just to have my truck worked on, I have found that the drive to a reputable shop is usually easier than the hassle of a bad repair experience. Do I sound more than a little paranoid? Over the years, there have been many times that I have chosen not to work on my own trucks for one reason or another, and it has always made me uneasy to leave them with someone new. Fortunately, there are a lot of honest, competent repair facilities out there. Be aware though, they want your money as much as you do, and it never hurts to be cautious and ask a lot of questions. Simply taking time to investigate potential repair shops before any work is done will lower your chances of receiving a poor repair and increase your chances of receiving a fair deal. Popular Resources: New Gear Break-In Properly Setting Preload with Side Adjusters Size Matters
Differential Install: Small Details Make a Big Difference (Part 2)
When working on any rearend, always pay very close attention to the axle shafts and axle bearings. Sealed ball bearing type axle bearings are usually very easy to diagnose and any roughness makes replacement the obvious choice. Flat roller bearing style axles are not as obvious to diagnose, and many times people dismiss wear that soon after leads to larger problems. Any pits, rust, grooves, or odd wear on the bearing surface of the axle shaft will lead to more wear. Just the same as pot-holes in the road always get larger with traffic, axle shaft wear always gets worse. Large tires and towing heavy loads accelerates axle wear and makes inspection and replacement extremely important. Axle splines are another area that can easily be overlooked. The axle splines in most differential designs hold up well and seldom wear. There are a few designs, however, that tend to wear out the splines quickly. Nine-inch Ford rearends are notorious for wearing out the axle spline wear, especially when they use a Trac-Loc. The Track-Loc uses a two-piece side gear and clutch hub on the left side, which tend to spread the load to the splines less evenly and accelerate wear. Swapping the axles from left to right can sometimes work as a fix if the wear is not to extreme, but we usually recommend installing a new axle shaft. Bent axle housings are another problem seldom noticed and rarely fixed. A bent housing causes the axle splines to be worked harder than normal due to the angular contact with the side gear and the sliding action that happens to the splines each time the axle rotates. Bent housings can sometimes be spotted by sighting down the axle tubes after the axles and carrier case have been removed. This takes some practice, but once the technique is mastered it is easy to determine if the housing is bent. Even though it may not be the best way to straighten a housing, an axle truss is definitely a good idea for any situation where the vehicle is being overloaded or abused, and it will help keep the housing straight. Although we have seen people use an axle truss to pull the housing straight, we recommend removing the housing from your vehicle and taking it to a competent welder or machine shop. Carrier bearing adjusters are another detail that will affect the life of the differential if the worn parts are not noticed and fixed or replaced. Often the carrier bearings will spin in the housing and wear a groove into the adjuster. If the wear is not too extreme, the adjuster can be saved by filing the contact surface flat again. Just make sure that the surface is filed flat and square, and not at an angle. Clutch plates and clutch plate guides are also important to differential life. Clutch guides are the small, half round, hard metal plates that keep the clutches from eating into the carrier case on many limited slip designs. These guides can wear to the point of breaking, and once they are broken they can get between the ring and pinion gears and wreak havoc. Popular Resources: New Gear Break-In Properly Setting Preload with Side Adjusters Size Matters