The force of the accident...
The force of the accident twisted off one of the axle shafts (left) where the splines connect with the carrier.
This upgrade can be done in your shop, but low labor costs make it worth going to an expert.The crash was downright nasty. There was fire, a car climbing the wall, and mud flying everywhere. In other words, a real crowd pleaser. Thankfully, good construction practices paid off and the driver walked away. The old Monte Carlo, though, wasn't as lucky. Among the many items on the repair list was a busted rearend.
Instead of simply throwing the same parts back at the rearend, we decided an upgrade was in order. Granted, there is no guarantee that anything short of a Sherman tank would have survived this mishap without some serious damage, but that's not the point. Because gear ratios multiply torque, it is possible to inflict over three times the torque your engine produces on the rear axles. Combine that with the fact that, depending on conditions, a dirt racetrack can be as slippery as glass or provide a tremendous amount of traction. And let's face it, most of us aren't like Winston Cup teams that replace an entire rearend after a set number of laps. Most racers run 'em until they break, then fix them as best they can and keep on going. Knowing your rearend is capable of handling a season's worth of abuse without letting you down can save us all a few headaches.
A thorough inspection showed the damage to the rearend was not as substantial as first thought. The left-side axle had sheared off at the splines from twisting forces. Obviously, a new set of axles was in order, but to find out what else we needed, we took the center chunk to a professional. Richard Mellentine is a former Winston Cup gear specialist who has recently set up shop on his own-RM Gear and Harness-building transmissions, rearends, and wiring harnesses for racers on all levels. A complete inspection produced no more damaged parts, but Mellentine did recommend several steps we could take to beef up the rearend without increasing rotating weight.
Dig In The first step is a complete disassembly of the rearend's center section. Every piece is meticulously inspected-except for the bolts, which are immediately thrown in the trash. "There's probably nothing wrong with any of them," Mellentine explains, "but it's cheap insurance. Bolts are subjected to a certain amount of stretch if they are properly torqued into place. It's a good idea to replace them after every couple of teardowns. Since I don't know the history of this rearend, I'll go ahead and replace them now."
To reduce the chance of tearing...
To reduce the chance of tearing up another set of axles, we went with 31-spline units from Quick Performance. Here, the broken piece of our old axle is sitting on top of the new one to give you an idea of the size difference we are talking about. A little goes a long way.
Another piece headed for the junk bin is our cast-iron carrier. It's bulky, heavy at 13.4 pounds, and prone to cracking. Most racers will upgrade this piece with an aluminum spool, but we turned to Quick Performance to try its new ultra-lightweight steel spool. This spool uses just five finger-shaped flanges for bolting up the ring gear and is actually lighter than most aluminum spools at only 5.6 pounds. Because we are reducing rotating weight in the spool by a jaw-dropping 7.8 pounds, it allows us to beef up the axles to make them stronger without hurting performance. The axles that were damaged were 28-spline units, so we are switching to thicker 31-spline axles (1.195 inches in diameter for the 28-spline versus 1.325 for the 31). And of course, the new spool had to be ordered to accept 31-spline axles.
Spit Shined If the ring-and-pinion is damaged in an accident such as ours, it is usually in the form of broken or cracked gear teeth. This ring-and-pinion turned out to be fine, but since Mellentine had it out on the table anyway, he recommended cutting and polishing the gears to reduce friction and heat buildup. Mellentine is one of the rare gear specialists who does not depend on an REM machine when it comes to polishing gears. Instead, believing he can do a better job himself, he does all the work by hand. His setup is surprisingly simple and effective-something most racers can do themselves.
This is the cause of all our...
This is the cause of all our troubles. Luckily, the driver walked away.