I heard you can get a gearset with a bigger pinion, which is stronger. Should I do that?
We do sell both the standard and large pinions. The big pinion gearsets are made from 9310 material, and they are called Pro Gears. But they are designed for drag racing, so they are actually made of a softer material designed to handle really high horsepower, combined with the shock of launching off the trans brake. For circle track applications, usually the 8620 standard gearsets are ideal.
What is the difference between a mini spool and a full spool? Is the mini spool smaller and lighter?
A lot of people asked me about mini spools versus full spools. The mini spool is designed to be a budget, entry-level unit. Basically, what you do is take out the standard open carrier, pull the internal pieces like the spider gears out, and replace them with the mini spool. Then you put the carrier back into the rearend. Those units are very cheap, but compared to a lightweight spool they are not as durable and they are also quite a bit heavier too because you are still running the cast iron carrier.
If you can run a full spool there definitely is a difference. The full spool gets rid of the carrier because the ring gear bolts right to it, so you are saving another 4 to 6 pounds of rotating weight. We sell the mini spool for about $15 and the lightweight full spool goes for $68. But even though it is more expensive there definitely is an advantage to the full spool because you are getting rid of that heavy carrier. We do have both, by the way, available in 28- and 31-spline.
What type of gear oil is best?
The mineral-based oils tend to work a lot better with the 9-inch for a couple of reasons. One of the bigger reasons is the hypoid angle the 9-inch gears are cut at. They are cut at a pretty extreme angle, which helps with strength. That’s one of the reasons the 9-inch gear is so strong because they typically have more teeth in contact at all times than other styles of rearends, but that also generates a lot of heat. The mineral-based oil does tend to impregnate the metal better and actually does a better job of pulling the heat out of the ring-and-pinion and helping it run cool.
Now, a lot of guys will argue that and say “Well, when I run synthetic my rearend doesn’t feel hot.” But that’s because the synthetic oil is not as good a job pulling the heat out of the ring-and-pinion metal and dissipating it through the rearend. It is actually acting as an insulator instead of helping dissipate the heat.
Just keep it simple and use the silicone, that usually works out best
For a circle track application we do recommend four quarts (a full gallon) of a non-synthetic, high-quality 80 to 90 weight gear oil. We also recommend that it be GL-5 rated. The reason that we recommend so much is because we don’t run inner tube seals in our rearends.
I do get asked quite a bit about the inner tube seals, and we don’t really recommend them. I have seen multiple occasions where the seals will wear a little bit and actually let oil sneak past it. Then the oil gets trapped out in the tube behind the seals and you run the risk of starving your ring-and-pinion of oil. When there is too little lubrication around the gears it winds up getting a hot, which ultimately leads to failure.
On the other hand, if you do not run the seals you allow the oil to run out into the tube, which helps it cool down. And by running a full gallon you have a sufficient amount to where you are not running dry at any point. It does also get some of that oil to the outer bearings, but I still recommend that you keep an eye on them and repack your bearings as necessary, but it doesn’t hurt them.
Do I need to break in a new rearend?
The short answer is yes. For a new ring-and-pinion set and bearings, those things definitely need to be properly broken in. I understand that a lot of guys want to just put a new rearend or center section in the car and take off and go, but that’s really detrimental to the life of the ring-and-pinion. There are a couple different ways we recommend to properly break in a ring-and-pinion. The guy could put the car up on stands and let it run in gear without putting a heavy load on it until the gears get up to temperature. Once it is at operating temperature, shut the car off and let it cool down naturally and then repeat that heat cycle four times. Or if you have access to a track or private roads or something that you could run some laps at half speed, that is acceptable too -- as long as they are not driving aggressively. And you need four heat cycles with this method as well. After that you should be good to go. Just make sure everything looks good and you don’t have any leaks. You don’t necessarily have to change your gear oil after the break in. Some guys do and some guys don’t; I don’t think that’s a major concern. But if you do look at the oil and there is a lot of shavings in it, you may have something else going on. Anytime you see metal in your oil, it’s probably a good idea to stop and take a good look around to see what might be causing that.
How often should the gear oil be changed?
That’s a good question. About every eight nights of racing or so should be reasonable. Whenever you do change your gear oil, that’s also a good time to make a quick check on your gears. The first check is with your nose. Mineral-based oil has a very distinct smell. We can actually tell pretty easily by just smelling a gearset if it is then ran with synthetic or mineral-based oil. And if the gear has seen too much heat the mineral-based oil will smell burnt too. If it does smell really burned, chances are you may need to pay some more attention to the rearend. You can have a ring-and-pinion that is not set up properly, you can have too much preload on your bearing, you can have a bearing that’s going bad. I always suggest you use all of your senses and don’t limit it to just the way it looks. Shine a light through the oil fill hole and take a look at your gears. Run the oil between your fingers and feel for metal. If you find anything that seems out of place, definitely do some more investigating to make sure that if there is an issue you find the root cause of it. Catching a potential problem early will almost always save you time and money because you can avoid having to fix bigger problems down the line.
Any other maintenance tips?
The heavy-duty tapered bearings on the floating 9-inch rearends have a seal built into them that can be another fairly common issue. Guys are always in a hurry at the track. They are pulling their axles out, and when they go in just jamming things together. If that seal gets pinched or mangled, it obviously won’t seal up as good as it used to, and that can lead to issues. I try to tell people to slow down and take a minute when they are putting things back together and try to make sure that seal doesn’t get pinched.
If you notice the seal is gritty, the bearing makes a grinding sound or the wheel has more resistance when turning it by hand, that would be a good sign that your bearing may have sand or grit in it and needs attention. Repacking your wheel bearings should be a part of every race team’s regular maintenance routine, and depending on your conditions you may have to do it quite often.
You have to take care with your wheel studs. A lot of guys will take an impact gun and just spin those lug nuts home. And that’s not good. We recommend 75 foot-pounds of torque. If you go much past that spec, it will stretch the wheel studs, which will significantly weaken them. That could lead to other bigger issues such as a failure of the stud.
As far as sealing up the third member to the housing. We recommend using a high-quality, oil-resistant RTV silicone gasket maker. That will seal up and work a lot better than a gasket. There are a lot of really thick reusable gaskets on the market, but we really don’t like those because it actually shims the third member out away from the housing. That will throw the centerline of your spool off from the centerline of the axles, which will cause extra wear and tear on your splines and other parts. Just keep it simple and use the silicone, that usually works out best.