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Author Topic: possible causes of gearbox oil leak on left side  (Read 1371 times)

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Offline CraiGORE

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possible causes of gearbox oil leak on left side
« on: November 25, 2011, 06:52:43 PM »
hey dudes. my rd350 has been leaking a substantial amount of "fresh" gearbox oil when on the side stand. have only owned the bike for a few months so am not sure if this was a problem before. i've got the bike on a stand, seems that it's coming from the left side case (could be because it's on the side stand). took the left side cover off, noticed it was GUNKED up with old oil and who knows what. almost looked like the leak was coming from the"Blind Plug" as part of the gearshift mechanism (#27 in the picture). It looks like a rubber seal of some sort.


I've cranked down the clutch side case to spec, haven't replaced the gasket yet but I have it on the shelf and will be getting to that soon.

Just looking for ideas as to what this could be. need suggestion.. engine seals, oil drain plug gasket, etc. etc. etc. etc. I know that this question is like calling a doctor to diagnose a cough over the phone...  :suicide: but hoping you guys could shed some light

Offline jzanutto

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Re: possible causes of gearbox oil leak on left side
« Reply #1 on: November 25, 2011, 06:59:36 PM »
best thing to do is spray that all down with some good cleaner, wipe it all out clean and then lean the bike over and watch for a while.

good possibility its the countershaft seal.  but, my old saying is 'you cant fix what you cant see'. clean it good

Offline MarkT

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Re: possible causes of gearbox oil leak on left side
« Reply #2 on: November 25, 2011, 07:25:10 PM »
There are 2 blind plugs, the clutch push rod seal, the countershaft seal...  but most of the leak I had seemed to be coming from the plastic neutral switch o-ring. 

All the parts can be changed without splitting cases. :mrgreen:
1963 Yamaha YG1-T - stock
1965 Yamaha MG1-T - stock
1972 Yamaha R5 - frankenstein project bike
1979 DT175

Offline DreamWarrior

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Re: possible causes of gearbox oil leak on left side
« Reply #3 on: November 25, 2011, 07:25:58 PM »
there's like 4 seals in the left side..neutral  switch O-ring, countershaft sprocket seal, clutch push rod seal an shift shaft seal,
all can be replaced with just the side cover off an sprocket
some of the gunk could just be chain lube flung off in there also
THE SWARM WILL FLY AGAIN!

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Offline jzanutto

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Re: possible causes of gearbox oil leak on left side
« Reply #4 on: November 25, 2011, 07:45:33 PM »
mine was a little easier to isolate, because the oil from the countershaft seal would run down onto the sprocket and oil the chain. then the chain would sling it all over my nice powdercoated white wheel. Actually turned out that the PO installed the countershaft seal inside out, with the garter spring facing outwards. easy fix, I just flipped it over and that stopped

Offline mopardiver

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Re: possible causes of gearbox oil leak on left side
« Reply #5 on: November 25, 2011, 11:25:13 PM »
I had a shift shaft seal issue with my R350 and it wasn’t hard to figure out without doing this.  If I were you, I would just remove the cover, lean it on the side stand, put some folded paper towels under the possible areas of concern and look where oil accumulated.
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Offline CraiGORE

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Re: possible causes of gearbox oil leak on left side
« Reply #6 on: November 26, 2011, 09:09:02 AM »
I had a shift shaft seal issue with my R350 and it wasn’t hard to figure out without doing this.  If I were you, I would just remove the cover, lean it on the side stand, put some folded paper towels under the possible areas of concern and look where oil accumulated.
+1 good suggestion

Offline CraiGORE

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Re: possible causes of gearbox oil leak on left side
« Reply #7 on: November 27, 2011, 01:08:55 AM »
looks like partsnmore has a "engine oil seal kit" for $32. can't really beat that. am going to but the coils soon anyway, might as well spring for this as well.