Differential Diagnostics Oct 8, 2008
After the $2008 Challenge, we knew something wasn't right with our Berzerkeley's driveline. During our first run in the autocross competition, the car lost the ability to drive. We had spent quite a bit of time on testing for the car, so suffering a component failure was especially frustrating. However, now that the milk had been spilled, we could only hope to learn from the situation by analyzing what went wrong.
We could immediately see that our primary drive chain from the bike gearbox to the custom differential had stretched, but the real trouble seemed to be inside the aluminum differential housing. We could hear some pretty terrible noises from that area when rolling the car on the ground, so we were sure that something inside had likely come apart. Once we had returned to GRM headquarters, we were able to remove the differential carrier and inspect it.
Once we'd removed the carrier from the chassis, we removed the screws holding the top access plate and looked inside. Our fears were confirmed as we saw that not one, not two, but three of the gears in our special gearbox had failed. This sucked on an epic level, since it wrecked the gears completely and made it hard to determine what broke first. After looking at the damage closely, we are facing a few hypotheses:
a) The aluminum carrier flexed enough to spoil the precise gear mesh, destroying the teeth.
b) The gearset at the upper end of the carrier--the one that switches between reverse and forward--wasn't lubricated sufficiently.
c) The gearbox had somehow gotten halfway between forward and reverse, which created too much strain on one side of the gears and sheared them.
Regardless of the root cause, the failure made us rethink our need for a reverse gear. The additional complexity and expense simply aren't worth the trouble at this stage of the project. We could add these features down the road if necessary. By simplifying the differential assembly, we should lose a little weight and a lot of complexity. Plus, we might even recover some of our budget. We've also considered leaving out the Torsen differential and replacing it with a solid spool for some of the same reasons.
The simplest solution would be to weld a sprocket on a solid intermediate shaft; this shaft would run to the two drive axles. Unfortunately, the reversed mounting orientation of our GSX-R 750 engine prevents that simple solution. We might be forced to rebuild or recreate the existing differential carrier after determining the true root cause of this failure. We're also going to keep our eyes open for a small, strong and inexpensive gearset stout enough to handle the load and reverse rotation of the drive force.
Differential Fixin’s Nov 3, 2008
After an extended powwow with Denny, we have figured how to get our Berzerkeley back on track. The plan involves retaining the front gearbox, as we think the design is quite sound; the gears are rather large and the case itself is quite thick—much thicker than it needs to be.
We also need to make sure that the gear box will remain capable of reversing the rotation of the shafts. That way, our motorcycle engine and transmission will feature five gears that move the car forward, not backward.
Speaking of moving backward, we will be removing the actual reversing mechanism to prevent the gearbox from getting caught between gears. If this problem were to occur, it would place way too much strain on the gears--in fact, it was the most likely cause of our first failure.
So, what are we going to do about reverse? Typically, an autocross doesn't require a car to move backward. There are actually plenty of classes--A Mod, B Mod, F Mod, etc.--that feature cars that aren't equipped with reversing mechanisms. Autocross starting lines, finish lines and grid layouts all typically accommodate forward-only cars.
Differential Do-Over May 4, 2009
After a less-than-stellar public debut at the GRM $2008 Challenge, our Berzerkeley was relegated to a dark corner of the garage. Our struggles with sorting the car had been frustrating, and the embarrassing on-course driveline failure put us over the top. Rather than do something rash or reactionary, we parked the car, removed the gearbox for analysis, and moved on with other projects.
Now that we've cooled off a bit and reflected on the problems we've encountered, we've gained a fresh outlook on how to go about resolving them. Since the reversing mechanism is now eliminated, the new arrangement promises to be more durable and undoubtedly simpler. It may require us to get out and push the car once in a while, but we're willing to live with that compromise for now. Once the car is sorted, we can always reinstall the reversing parts.
Reinstalling the gearbox was easier than the removal; this time, gravity was working for us. We also took this opportunity to rework the tabs that are used to tension the drive chain. Once everything was in place, we decided that it would also be a good time to install a new chain, since ours had stretched beyond our tensioner's range of adjustment.
With all of the parts in place, we're ready to continue sorting the car. We'll try to reduce the ride height as much as possible to lower the center of gravity. We'll also perform a fresh alignment to make sure everything is pointing in the right direction. Look for more updates as we make progress.
Sorta Sorted Jun 2, 2009
Tom and Per spent an evening sorting out some issues with our Berzerkeley project. The car runs well, but it still exhibits erratic handling at higher speeds.
We checked the alignment and dialed in more caster, but to no effect. We also set the toe at zero—it was about 1/2-inch toed out. Next we focused on camber; our tire wear indicated we weren't using the whole front tire, so an extra degree of negative camber was added.
We had recently installed a new chain with the fixed differential. Now that it had undergone its initial stretch, it was time to adjust it. The chain is now tight and ready to put the power down.
From here, we'll be working on making our Berzerkeley a little more drivable at the limit. It's a handful now.
Bye-Bye, Berzerkeley Sep 11, 2009
Thanks to some intense testing and sorting, our Berkeley's handling issues were mostly cured. Even our gearbox woes were finally resolved. So we turned our attention to the Berkeley's paint--or lack of it.
Be sure to check out the November 2009 issue of GRM for more details, but here's the short version:
For months the Berzerkeley had been nearly naked, wearing nothing but gelcoat over its heavily modified 1958 fiberglass. We figured it was time to freshen it up a bit, so we removed the body from the frame--again.
Removing the body would allow us to do a nice job on the prep and paint. Whether you’re dealing with fiberglass, metal or body filler, you can’t lay down a smooth coat of paint over a rough surface.
After smoothing and filling some pinholes, we were ready to go. We decided to stick with white because it looked sleek and the red wheels popped against it. We shot the paint outside, and our patience was rewarded with a nice, smooth finish.
We finished off the look with red stripes from Hawkeye Graphics--the perfect complement to the vintage race car look.
After that, we realized there wasn't much left for us to do with the Berzkerkeley. So we're calling this one finished. Luckily, a friend offered to take on the project and continue developing it, so future updates are entirely possible.