The VW transmission, or any modern transmission for that matter, relies on brass synchronizer rings to allow matching of gear speed to transmission input shaft or pinion shaft speed to allow grind-free shifting. It helps to picture in your mind that this brass synchronizer ring is a kind of circular brake pad pressing against the gear itself which would be analogous to a brake rotor. Now each "brake pad" synchronizer has to stop its gear from turning every time a different gear is selected. (All forward VW gears have their own synchronizer. Reverse does not have a synchronizer.) Now, when a car's driver moves the shift lever faster from gear to gear, the synchronizer ring has to stop its gear from turning in less time than if the shift was made slower. Sometimes a gear change is made faster than what the brass synchronizer can physically handle and the gears grind together before they mesh, often causing only very slight damage to the gear teeth as the gears are extremely hard (Reverse gears are the exception here, they are not as hard as the forward gears.). So, what you see is that it is possible to overwhelm the synchronizer’s ability to perform its function as the speed of shifting is increased.
With any short shift kit it can be assumed that the time interval for all of the required "gear braking" CAN be reduced since the spaces to shift from gear to gear are closer together. If you select gears at the same speed as when your car had a stock shift linkage then there is no difference and your synchronizers have plenty of time to do their job. Basically what I'm saying here is that the faster you change gears even with a stock shift linkage the greater the chance for gear grinding. And so if you speed shift your gears with your new short shift kit then you run a greater chance of getting gear grind. It's that simple. It doesn't matter whose kit you are using, either. If you overwhelm the synchronizer’s ability to do its job then you will eventually get gear grinding and you will also overheat and destroy your syncronizer for the particular gear that is grinding. The only recourse in this case is to replace the brass synchronizer ring inside the transmission. The syncro rings aren’t really expensive but the specialized labor is. And if you grind gears for too long you might break a tooth off of one of your gears and that’s not very good for the guts of your transmission.
It is extremely important to note that if you already have a bad synchronizer for a certain gear BEFORE you install ANY short shift kit then you will only put more stress on the synchronizer and you will likely get more lovely grinding than before. I recommend that you DO NOT speed shift your transmission or install a short shift kit if you have experienced significant gear grind at any time. You will wear out your syncros or break a tooth if you do. A grind every once in a while is normal since we can't clutch and shift perfectly every time but you must realize that if you have a persistent grinding problem it will likely get worse if you shift faster. If you have to "granny shift" (wait longer to engage a gear after pushing in the clutch) your transmission to avoid grinding before installing a short shift kit then DON'T install a kit until you diagnose a bad clutch or syncro and have the tranny fixed. In summary, as with guns, short shift kits don't kill transmissions, PEOPLE kill transmissions! Knowledge is power.
With all of this said, I recommend two quarts of Redline gear oils (MT-90 or MTL) for all VW transmissions since they have the best frictional properties for the brass synchronizer rings in my opinion. If you want the best for your car then change the gear oil (two quarts) and fix all leaks! Almost every VW transmission failure I have seen is from running a transmission out of gear oil from final drive oil leaks. The other leading cause of failure is by breaking off a gear tooth by letting gears grind and/or NOT replacing a worn, broken, or slipping clutch which will also increase the chances for grinding.
Jim Royston
September 5th, 2001