randys blog
Grinding Gears
Many people would rather have their children genetically altered before they would grind gear teeth. Gears are not handed to us by God. They are designed by people who have figured out how to form steel into shapes that can be used to multiply torque and change power-shaft directions. Although some of us hold gears in very high esteem, they are not sacred. They can be ground on a surprising amount with little or no loss of strength. As long as the gears do not become hot (over 600 degrees) from the grinding, the molecular structure will remain the same and the hardness of the gear-set will not change. There are many situations where grinding gear teeth is not only OK, but can be helpful. Some of these include, but are not limited to: grinding to clear the cross-pin shaft, removing nicks from shipping with poor packing, rounding the corners on chips from a brittle surface, trimming the ring gear toe to clear 9″ Ford pilot bearing, chamfering the toe of the pinion teeth to clear the carrier case, smoothing high spots due to machining, or back-cutting race gears to allow for tooth bending. The drive side of the gear-set takes much more load than the coast side does and therefore it is a good idea to have a little restraint and think ahead before getting carried away on the drive side of a gear tooth. On the other hand, the coast side of the tooth gets loaded very little and not very often so it can take a huge amount of grinding with no negative side effects. Although I have seen vehicle run with half of a ring gear or pinion tooth missing, I do NOT recommend pushing your luck that far. However, I have no problem running a gear-set in my own vehicle with 1/4 of tooth ground off of the toe of one or two ring gear or pinion teeth. If the same 1/4 of the tooth was removed from the heel, I would be wary. I would not recommend removing more than about a 1/5 of the tooth from the heel of ring gear, because most of the load is from the center of the tooth to the heel when under load. And, it is the heel of the tooth that receives the hardest load. The pinion is another thing entirely. The last 1/4″ to 3/8″ of the pinion gear teeth do not even come close to touching the ring gear teeth on the drive side and therefore the tip can be removed entirely if the tooth or teeth are chipped, dinged, or damaged in any way. This heel portion of the pinion teeth often gets damaged in production or shipping and bothers people who are unfamiliar with rear end gears. If any part of the tooth does not contact other teeth, it can be removed without strength problems. In order to improve my confidence when attacking a new gear set, I often practice on an old gear set right before I approach the new set. This helps me pick the right cutting tool, set the angle of attack, and find the best cutter speed before I begin. The main thing to remember when grinding gears is to make sure that all corners are chamfered and there are no sharp edges to cut into the other teeth.
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