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McGuiver
03-04-2002, 03:13 AM
Build A Better Front Diff!

In reference to building a none binding diff i have the following solution.

*First check that the brass diff pinion gears(HPI Part #73403a) rotate freely on the shaft pin (HPI Part #73404b) that is supposed to hold them in place. Mine were a press fit and to tight. I did have access to a lathe so I used the next best thing, my drill (cordless).

*Second I chucked up the gear as seen in picture (Pictured Below).

*Third I went through my tool box and found my round needle file. I then proceeded to file the inside bore if the gear. The drill chuck was turning and I used a in and out motion with the needle file. You need to check the looseness of the pin fit carfully. It doesn't take very much filing. About 15 secs. for me on each gear. I have also included picture (See next Picture) to see how the needle filing was done.

*Fourth I didn't like how there was a brass gear spinning on the inside of the diff case (HPI Part#73404-1). I then took the 2 little black washers (HPI Part #Z275c) which were supposed to go on the motor mounting screws. I replaced the motor mounting washers with some other I had that were silver in color (no big deal). I then installed a little black washer (HPI Part#Z275c) between the brass gear (HPI Part #73403a) and the fron diff case (HPI Part #73404-1). All the parts fit in the front diff. case. It is tight but worth it when you feel how silky smooth it is when assembled. Then reassemble as normal.

I figured out that the little brass gear (HPI Part #73403a) was making the pin shaft (HPI Part #73404b) spin in the diff case(HPI Part #73404-1). The pin is not supposed to spin in the case. It gets pressed in place. If it spins it is likely to wear out the diff case and mabey destroy the inside of the puple anodized diff pipe(HPI Part #72338). I forgot to take pictures of the assembly, but will do so if needed.

McGuiver
03-04-2002, 03:14 AM
This is the Picture of me using a needle file on the inside of the gear.
Please read above post.

tc rcr
03-04-2002, 07:12 AM
thanks for the tip

Bbot21
03-04-2002, 12:30 PM
Thanks

I've found that a huge wad of heavy grease does the trick also. The gears last a lot longer without loosing teeth.

TFRMicro
03-04-2002, 02:06 PM
HPI mentioned to use a Xacto knife to shave the brass gear...

McGuiver
03-04-2002, 02:15 PM
I know they mentioned it but that will not give it a smooth finish. As a machinist, part perfection is a must. Especially aircraft. If I wanted to I would take some diamond lapping compound and lap the pin to the shaft. I'm not that anal.

TFRMicro
03-04-2002, 02:17 PM
oh...okok....:o :cool:

Turbo Cloud
03-04-2002, 02:48 PM
Every one is now giving tips on how to build a better diff now i wished someone had done it earlier but that is what all my friends did was bake the brass gears hole bigger

McGuiver
03-04-2002, 03:11 PM
Perfecting and fine tuning your car takes time. It is not like we have a pit crew to fix everything. We are the driver, Pit Crew, and Usually the financeer (money guy).

If I was at work I would have just reamed out the brass gear to the right size. I was at home and did the next best thing.

Mugen96
03-04-2002, 03:25 PM
Not a bad idea. I no longer have the frint stock diff, but I wonder if using a stand body reamer that you get for your lexan bodies would do the trick...be easy and would still leave a pretty smooth cut...

Dan

runtracer
03-04-2002, 03:31 PM
i dont know if a body reamer could survive cutting brass. what i did was installed the steel pin in my drill and spun it over emery cloth till the gears fit snugly on it but spun freely.

McGuiver
03-04-2002, 03:49 PM
I was refering to a machine reamer. Her is a picture. They come in straight flute like this one, and spiral flute like a drill. A reamer is only used to bring to hole to final size.