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Old 11-08-2013, 06:12 PM   #1
KGER OP
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Eh? Transmission Flush?

Hey all,

Just went thru a fluid check on a newly Craigslisted 75/7 and came up with a ton of milky brown tranny fluid. Way over-filled, and a bad dirt brown milky coloration.

Is there any product or method to clean out the gearbox before I refill the gearbox with fresh oil? Do I need to?

The bike only has 13K miles on it and it's possible this is the original fluid that has just absorbed a ton of water over that many years.

As an aside-the old fluid smells like cheap tequila and lime, so there's that.
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Old 11-08-2013, 06:21 PM   #2
Big Bamboo
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Fill with fresh oil, ride until warm, drain oil and repeat until oil comes out clear.
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Old 11-08-2013, 06:31 PM   #3
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If it's really nasty you could flush with kerosene or diesel, then run it with some ATF standing still on the centerstand, then put your 80/90 gear oil in. I've done it once on my ST, it mustve been parked outside.....milkshake for the first 1k miles. then I did the diesel trick and it worked well.
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Old 11-09-2013, 08:01 AM   #4
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Quote:
Originally Posted by hardwaregrrl View Post
If it's really nasty you could flush with kerosene or diesel, then run it with some ATF standing still on the centerstand, then put your 80/90 gear oil in. I've done it once on my ST, it mustve been parked outside.....milkshake for the first 1k miles. then I did the diesel trick and it worked well.
Damn straight!

This is an old 'farmer' solution. Kerosene is harder (and more expensive) to get than #2 diesel, btw, and works just as well for this. It's a good solvent & you can run the trans (on the center stand, no load) with it in without harming the bearings or gears. Kerosene has some oil in it. Farmers did it on their engines too--good for engines that worked hard for 6 months of the year and then sat outside idle for the other--gets water and sludge out (back in the old days of really crappy motor oil.) In and engine, tho, only a 20% solution of kerosene/motor oil was recommended by the old farmer I used to know.

Use synthetic gear oil after you get it all cleaned up. And a very small residual diesel in the bottom of the gear box isn't worth worrying about--the lighter elements (the kerosene portion) will eventually evaporate out.
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Old 11-09-2013, 08:34 AM   #5
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13k, on a bike that old, and that much water,in the gearbox...

I think you probably have a pretty fair amount of rust and pitting on a whole bunch of stuff in there.

But, I also like the kerosene plan, assuming your goals are to just ride it, and see what happens. If you are restoring the bike for the long run, I'd break open the gear box and see what's what.
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Old 11-09-2013, 10:26 AM   #6
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Rust in gear boxes. Seems almost a miracle that any of them don't have rust given the tendency to leak at the speedo boot. If the trans works after rinsing I suggest not opening it unless you are prepared to go forward with a rebuild. Replacing a lot of parts costs a lot of money.

Gear teeth will whine if pitted very much from rust but they will often work. Bearings will not last if they are rusted but they often escape because they are higher up in the trans.

It's really a damned if you do but damned if you don't situation, ain't it?

If you have never opened an Airhead transmission before there are several special tools needed, the main one being the holder/puller for the out put flange. Cost of tool is $80 currently (I think)
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Old 11-09-2013, 11:43 AM   #7
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Change the oil and ride it. It's a waste of time and effort (as well as fluids) to flush it. If you're still worried about it, check the oil in a hundred or so miles, if it looks dodgy, change it again and go ride it some more.
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Old 11-09-2013, 02:10 PM   #8
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What Disston and Pokie said. I got a lot of miles out of my ST's transmission that had sat and pitted the gears. It was only after many thousand miles and the usual output shaft bearing failure/whine that it became necessary to open the box up.

And until I replaced the aged speedo cable boot, campouts at ADV rallies that involved heavy rain usually saw me just flushing milky lube oil with fresh lube and riding until it came clear again.
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Old 11-09-2013, 02:31 PM   #9
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So are we maintaining our bikes as to the standards of old farmers? I bought my GS from a farmer and the thing was a mechanical disaster of his creation until I got it sorted - he even couldn't do the oil filter replacement task without majorly screwing it up.

I would never run a mechanism without the recommended lubricant installed - certainly not some kerosene cocktail to flush it out with. On airliners we flush with the recommended lubricant at all times. There is no guarantee that all of this flushing fluid will be removed before you introduce the factory recommended fluid after the flushing sequence. Running bearings and gears in this media will not be good for long term serviceability. +1 to Pokie on his recommendation.
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Old 11-09-2013, 03:12 PM   #10
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Quote:
Originally Posted by KGER View Post
Hey all,

Is there any product or method to clean out the gearbox before I refill the gearbox with fresh oil? Do I need to?
I recently bought a '95 R100GS that sat outside under a tarp for a year. During the post purchase tuneup and flush the transmission fluid came out like yours, very milky.....obviously water contaminated. After looking for a transmission flush product as you asked about, and not finding any for manual transmissions I drained, rode and refilled the transmission five times before the drained fluid showed no signs of more water.

This bike did have the classic dried and cracked speedometer boot going into the transmission....clearly the source of the water getting in.

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Old 11-09-2013, 03:40 PM   #11
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I don't think it needs as many flushes as some people do. I'd let it drain for a LONG time, maybe use compressed air through the fill hole to blast more of the crud out the drain, fill it and ride it for a while. If I had some good used gear oil coming out of a bike I'd use that for a sacrificial flush or two, but otherwise I'd give some good riding (100 miles or so) before the next change and then probably call it done. A trace of water isn't going to hurt it; many bikes have that.
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Old 11-09-2013, 03:42 PM   #12
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Any Hot/Cold environment will create condensation. Rear Drive, Tranny, Motor. Especially if it's not been run.
Drain everything. Fresh fluids. Run 50 miles. Drain again. Run 1000 miles. Drain Again. Ride!
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Old 11-10-2013, 11:43 AM   #13
KGER OP
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Question Thanks

Great posts everyone. Thank you.

Seems like the two options are kerosene/diesel flush and refill or just refill, ride, drain repeat.

I'm planning on doing a more thorough resto next year, but for now just need to get a couple thousand light duty miles out of it before then.

I think for now I'll just drain ride refill and see what it looks like. If the improvement is minimal maybe I'll try the kerosene/diesel trick.

What does this output shaft bearing whine sound like, and is potentially dangerous to ride with it (could it lock up the rear end)? I've got some rubbing type noise in 3rd and in all gears during deceleration (clutch in and out). It's not a metallic or high pitched sound, more like a tire rubbing (it's not) or brake shoes.

Thanks again everyone for the great opinions.
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Old 11-10-2013, 12:02 PM   #14
Big Bamboo
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I personally would never add any kind of solvent to a gear box. The possibility of getting it all out are minimal and the resultant consequences are dismal. "It worked on my tractor" stories notwithstanding...
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