Differential Fixin’s

Update by Per Schroeder to the Berkeley Sports project car
Nov 3, 2008

We're sticking with our current gearbox, as we think the design is sound.
We need Denny Crabill to fix our differential, but unfortunately, he doesn't live in our garage. So, we've got to use the second-best tool ever, UPS, to get our differential to Pennsylvania.

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.

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View comments on the GRM forums
Javelin GRM+ Memberand MegaDork
11/3/08 6:41 p.m.

Why not just use the factory bike trans and make a single-gear reverse-rotation diff? It seems like you are over-complicating this part of the build.

Spinout007 GRM+ Memberand UltraDork
11/5/08 9:04 a.m.

What about the 90's goldwing setup? Not quite sure of how it worked but might be something to look at.

avendlerdp New Reader
3/4/09 9:56 p.m.

Hey guys. Not sure if you have heard of the Geo Metro Gnome. It's a motorcycle powered Geo Metro that we race out here at west coast LeMons races. Here is a link to some coverage:


We are using a bit of a different setup but the two cars have a lot in common. The #1 issue was getting enough links into the chain. Your setup looks great but that super short chain might have some trouble overheating and thus stretching very fast. We solved the problem on ours by running twin chains with a smaller pitch. If you would like to get the contact info on the guy who made the rig for us on a budget, feel free to email.



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