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419xr Stripping diff sun gear and its shim

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419xr Stripping diff sun gear and its shim

Old 04-21-2020, 07:07 PM
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Default 419xr Stripping diff side gear and its shim

Iv been having a problem lately stripping the sun gear and the sun gear shim not just coning the shim but being completly deformed by the outdrive pin

Any tips to look out for when rebuilding?

Iv used the 0.3mm and 1mm large shim kit shims, somtimes with the 1mm shims the diff lasts longer but end result not smooth and still leaking and eventually stripping a sun gear.

Using 6.5t if that makes a difference... Thanks

[Edit: diff side gear not sun gear]

Last edited by b3master; 04-22-2020 at 11:18 AM. Reason: Side gear not sun gear
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Old 04-21-2020, 09:09 PM
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Not sure you mean the sun gear. A sun gear is the center gear of a planetary gearbox. The 419 doesn't have a planetary gearbox. If you are talking about the Diff gears, there are the side gears that drive each axle and the spider gears that mesh with the side gears. It sounds like you are stripping one of the side gears. The way you describe it, it sounds like the gears are too tight. If they were too loose I think you wouldn't destroy the shim. Does it feel really tight after you build it? If not, is there a lot of slop. Good luck, problems like you have can drive you nuts! See if you can find a spare diff and compare the two diffs to see if anything is different.
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Old 04-21-2020, 11:06 PM
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Oh side gear yes indeed my bad.

Well i never felt a tight diff, but how do i know if the slop is too much or just right... I do have a spare but it had also busted the side gear (pin slot) and 2x 0.3mm shims that i had installed on the same side the last time i built it... So i been replacing the side gear and a shim and haven't replaced the spider gears... But have been putting a thicker shim where the side gear strips (at the pin side)
The gear teeth are not stripping, its the pin slot that strips and either deforms or cones the shim.
I will replace all the gears on one diff this time and the spider gears on the spare diff and hope i have fresh side gears in it...
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with respect to the slop what do i aim for? How do i accurately check it?
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Old 04-21-2020, 11:12 PM
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Originally Posted by b3master View Post
Iv been having a problem lately stripping the sun gear and the sun gear shim not just coning the shim but being completly deformed by the outdrive pin

Any tips to look out for when rebuilding?

Iv used the 0.3mm and 1mm large shim kit shims, somtimes with the 1mm shims the diff lasts longer but end result not smooth and still leaking and eventually stripping a sun gear.

Using 6.5t if that makes a difference... Thanks

I believe you are talking about the large bevel gear. If you have chance to read the instruction manual for TRF419X or TRF419XR, you will notice that Tamiya changed the differential gear's small shaft (the short shaft through the differential drive shaft) from 8mm to 9mm. Changing of the longer shaft, it reduces the gap there and to save the stripping of the bevel gear.

There is aftermarket replacement pin may able to help...


Last edited by cruise; 04-21-2020 at 11:44 PM.
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Old 04-21-2020, 11:32 PM
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Im looking at the manual as you noted indeed they did use the 1.6x9
i got my car used, seems the user had busted a diff and swaped using the diff rebuild set pins 1.6x8

Im on way to lhs to get the 42221 set that has 9mm pins

As for the slop how do i know if two 1mm shims is too much? If i can feel bevel gears teeth while rotating that would be too much? Even if they rotate freely but with gear feel? Unlike a ball diff that would be smooth or gritty but no gear feel...
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Old 04-21-2020, 11:56 PM
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Thought to share..

There were couple building tips has been shared, you can read below, it sure can help,..
Building a TRF419 diff ? THard.co.uk

Ahhh.. the new Tamiya Differential kit for TRF420 (part code 51649) has better performance and saves the leakage as well, it also fit TRF418/419.
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Old 04-22-2020, 01:59 AM
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Great thanks!

Originally Posted by cruise View Post
Ahhh.. the new Tamiya Differential kit for TRF420 (part code 51649) has better performance and saves the leakage as well, it also fit TRF418/419.
What size shims do i need to make up the size difference of any?
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Old 04-22-2020, 11:13 AM
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Ok found a major problem that i i been falling for:

The large shim set 42313 in almost all website descriptions notes that it has:
5 x 15 x 0.3mm Shims x2
5 x 15 x 1mm Shims x2
2.6 x 9.5 x 0.1mm Shims x4

When the manual calls for the use of 0.3mm shims i simply use the thinner one without measuring it

Go figure that its a typo that still exists on some tamiya sites (like tamiya.de) and all shops simply copy paste the content.

If translated from Japanese item description (and tamiya.com, and if you measure them) you will find out they are 5x15 shims of 0.1mm and 0.3mm thickness, hence the thinner shim is too thin for the application... and hence the stripping, regardless that its easier to strip when using the 8mm pins...

for curiosity sake:
I tried putting both shims as 0.4mm for the side gear but with black Oring causes too much drag, with red Oring much less drag, but when completly closed had more drag than i i liked and that test was done to one side only, so both sides with red Orings and 0.4 shims is probably too much drag.

I even went as far as to try shimming the center gears each with 0.2mm pushing them closer to the side gear which in turn keeps the side gear further pressed into its pin to prevent pin stripping... After closing the case was a bit tight...

Will try the xray Orings soon but thats just to minimize leakage... With the 9mm long pins that come with the xr and the 42221 set i think ill no longer accidentally strip anything...
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Old 04-22-2020, 10:13 PM
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There is another gentleman has posted the gear diff assembly and types of O-rings at another thread " Tamiya TRF419 "

Tamiya TRF419
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