Fast Attack Vehicle Gearbox Advice

[tamiya monkey]

hi there can anyone give me some help, i have a fav that i got off ebay not so long ago, first run after a strip and ballraced complete car was at the wrexham meet when i got a nasty clicking noise from the gearbox when putting full power on, also seems as though not much power going to the wheels, the transmission feels free enough, i have used frog re-re dog bones and outer shafts etc to make the gearbox better. so what have i done wrong, heard poeple talk of shims, if these are to fitted, where do i get some from also where do they go.

[94eg!]

Check for free rotation of drivetrain by hand at all possible suspension positions (full droop to full compression). Sometimes the suspension can bind at certain wheel positions, but will spin free & smooth at others. This typically is caused by dog bones that are either too short or too long, so you'll have to look VERY closely. If you do come across some binding problems, you'll have to figure out exactly where and how so you can fix it.

Typically, shimming only helps if your axle is just slightly too short. Then all you have to do is add shims between the out-drives & out-drive bearings, and between the axles and axle bearings. This brings the dog-bone cups on both ends slightly closer together and allows the shorter shaft to stay seated in the cups throughout the full range of suspension travel. As for the shim size, you just need some that have the same inner diameter as the out-drive and axle bearings (typically 5mm). Tamiya sells these shims in sets of varying thickness (5mm ID = part #53587)...

If your axle is too long, you may have to do something to limit suspension travel in the direction where the binding is occurs. If the axle binds when the wheel is fully compressed, you need to add "bump-stops" to the shock shaft on the outside of the damper body. For this you can use rubber tubing cut to the proper length to keep the wheel from traveling up so high. If the binding occurs as the wheel droops down, you need to add "droop limiters" by installing the same cut lengths of rubber tubing on the shock shaft inside the shock body. In either case, only add enough rubber to quell the binding issue. Otherwise your car will won't have enough suspension travel and will handle like garbage.

[Shodog]

My guess is that clicking is the bevel gears starting to strip. The best fix is a Thorp ball diff but if your budget doesn't permit that then grab a new set of re-re bevel gears and some thin 5mm shims. Experiment with the shims between the out drive bearing and bevel gears. When it's almost too tight to get smooth diff action then you have it just right for running.

[tamiya monkey]

thanks for the help guys.

[tamiya monkey]

thanks for your help, took my fav out today to test and it runs great, know does moving to the larger pinion gear make that much differance, plus want a little more speed but not wanting to go mad, what motor would you advice, what kind of turn would it accept, was thinking of anything from a sport tuned 23t to something around a 15t motor.

[94eg!]

thanks for your help, took my fav out today to test and it runs great, know does moving to the larger pinion gear make that much differance, plus want a little more speed but not wanting to go mad, what motor would you advice, what kind of turn would it accept, was thinking of anything from a sport tuned 23t to something around a 15t motor.

To get more top-speed, you can either use a larger pinion gear, or get a motor that spins higher rpms. Either way you will loose low end torque (punch). If you have a stock silver can motor, the easiest all around performance mod would be a tamiya Sport Tuned motor. It has slightly higher rpm (top speed), but still plenty of torque (acceleration). This means you won't need to re-gear the car to make it run properly, and might still have enough left-over torque to switch to a larger pinion for even more top-speed.

If you install a 15-turn motor, you will definitely have to swap in smaller pinions to gain back the lost torque of a mod motor and keep it from overheating. The only problem is that a lot of these older cars were not designed with high performance mod motors in mind. Therefore they have EXTREMELY limited gearing options. This makes using mod motors VERY difficult as they simply spin too fast with too little torque to work properly.