Shimming a gearbox open

[JosephS]

Hello all.

I'm working on building a rc10 DS with a RPM grey transmission. My goal is to make it smooth. So far in my tear down it seems that very lightly oiled bearings with no shields spin the smoothest. There is a really significant spin time difference with the seals in vs out. Then again there was a huge difference with one drop of bearing oil vs two.

I was just dry fitting the parts and it seems that tightening the gear box down all the way reduces the spin time significantly. If I split the box halves very slightly, like the width of the edge of a razor it spins nearly free. Clamped together tight it's like having the rubber seals in the bearings again.

I was thinking maybe some teflon tape between the halves would work. Is there a better way to do this? Am I looking at shimming the wrong parts. Should I be shimming the bearings at the outdrives? Would thin shims between the halves over the screws be the way to go?

[RC10th]

There is actually a lot to this subject but we used to also shave down the gear width.

[JosephS]

There is actually a lot to this subject but we used to also shave down the gear width.

I am intrigued. Isn't the width set by the outdrives? Or are you were you reducing the gear profile?

[GoMachV]

you could use a 3/8" and 5/8" precision reamer to deepen the pockets for the bearings slightly. I would install the top gear, test it. Then the idler tested with the top shaft. Then the idler with the diff. That way you target the correct pockets as some may not be tight at all- like the topshaft iirc is usually pretty sloppy.

[RC10th]

Yes it is, is that the part that is slowing the gearbox down? Is there any side play on the diff when it's tightened down??

[jwscab]

If you had some medium/thin ca glue you could possibly lay a bead along the edge of the housing with the flange. Allow to dry fully on a flat surface and you should get a consistent film. If that doesn't work it's easily removed with acetone.

[JosephS]

you could use a 3/8" and 5/8" precision reamer to deepen the pockets for the bearings slightly. I would install the top gear, test it. Then the idler tested with the top shaft. Then the idler with the diff. That way you target the correct pockets as some may not be tight at all- like the topshaft iirc is usually pretty sloppy.

In this rpm box the bearing don't feel pinched. The opening are a little loose. Though I may test that more. Though I will test it out.

[JosephS]

Yes it is, is that the part that is slowing the gearbox down? Is there any side play on the diff when it's tightened down??

It feel like the sides of the outdrives are slightly touching the box when tightened down Just enough to slow the spin, not stop it,

[juicedcoupe]

Some of it might be the case distorting when tightened.

If you think something is rubbing, look for transfer marks. Perhaps coat the inside of the case with a dry erase marker before assembly. Once you are done, OFF bug spray will easily remove it.

[morrisey0]

Perhaps coat the inside of the case with a dry erase marker before assembly. Once you are done, OFF bug spray will easily remove it.

I wonder how many other liquids around the house, that the guy who came up with this, tried prior to OFF being his Eureka moment?!?!

[juicedcoupe]

Perhaps coat the inside of the case with a dry erase marker before assembly. Once you are done, OFF bug spray will easily remove it.

I wonder how many other liquids around the house, that the guy who came up with this, tried prior to OFF being his Eureka moment?!?!

I heard about it at work.

Over time (several years), it removes the coating from the board as well. Eventually, the board has to be replaced, and the current ones are worse than the older ones.

[JosephS]

Some of it might be the case distorting when tightened.

If you think something is rubbing, look for transfer marks. Perhaps coat the inside of the case with a dry erase marker before assembly. Once you are done, OFF bug spray will easily remove it.

I'll try that out. that may help. When I tighten everything down and back off the screws about 1/2 the depth of the plate things are smooth, if a bit loose.
It also seems helped when I use the gold motor plate since there is one less bolt.

Even then with the bearing shields removed, dry/ lightly lubricated bearings how long should the transmission spin for without a slipper on the top shaft.

cAny extra consideration to take into mind whem pairing this with a 6900k motor?

[jwscab]

Honestly if you aren't trying to run a stock class and looking for weight and friction reduction, and just running some high power motor, you won't see any appreciable different with any of your versions so far. Oil, no oil, seal no seal, screws snug or loose.

[JosephS]

Honestly if you aren't trying to run a stock class and looking for weight and friction reduction, and just running some high power motor, you won't see any appreciable different with any of your versions so far. Oil, no oil, seal no seal, screws snug or loose.

This is just for the satisfaction of the build. I've heard rumors of the transmissions so smooth that they can spin if you blow on the spur. Thought I'd try and make one.

Are there even any classes where a DS could race?

[jwscab]

No not really. It's kind of a standalone class.

If you wanted to get it freer you could look into graphite lubricants that have a carrier that evaporates, so it's a dry lube for the bearings.

Otherwise, if the spur can move if you blow on it, that's pretty frickin' good.