gearbox oil advise - Triumph Forum: Triumph Rat Motorcycle Forums
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post #1 of 13 (permalink) Old 12-04-2015, 12:11 PM Thread Starter
wol
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gearbox oil advise

is there anything negative about using a fully synthetic oil ( something like 75w90) in the gearbox of a T140 - assuming the gearbox has at 10K miles on it so any "running in " would have occurred -
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post #2 of 13 (permalink) Old 12-04-2015, 01:25 PM
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Not much harm can be done as long as there is oil in the box.I use any make of gear oil of the correct grade and change it at engine oil change time.Very cheap to buy and i usually pay about 3 for 500ml bottle.Using a mineral Duckhams one at the moment as i bought a few bottle cheap at a jumble.
I look after the gearbox well with frequent oil changing and very little wear showing.I did break a tooth off the little cog on the mainshaft a few years back and changed the whole shaft for a new old one i found at Netley.
I feel this Duckhams oil in at the moment is working better than the last fully synth Mobil 1 change.May be coincidence,but i was missing my 2nd to 3rd change a few times.
The use of synth quite often,has not dissolved anything yet,or eaten the yellow metal bits so give it a try.
I like the 500ml bottles as i dont check the level after tipping in a full bottle.
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post #3 of 13 (permalink) Old 12-04-2015, 03:26 PM
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Our local Vintage Guru recommends semi-synthetic G/B oil.
From observation, the box gets a lot of condensate moisture in a short time.

http://farm3.staticflickr.com/2880/9419068358_fe3bbd6508_t.jpg
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post #4 of 13 (permalink) Old 12-04-2015, 05:38 PM
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Local vintage Triumph shop sold Amsoil and used their gear oil in his tranny. He said it ruined the gears. I'd never heard of such a thing. He stopped selling Amsoil and sells Cenpeco now.

Because there are yellow metal parts in the tranny, the standard recommendation is to use a GL4 oil. That does not mean a GL5 which will say "meets GL4 specs" should be used because the GL5 is not recommended for trannies with yellow metal parts.

A number of folks here, whose opinions I respect use GL5 oils with no bad results. But, since I can buy it at my local NAPA, I simply stick with GL4 gear oil.

You really cannot use any oil, ie. motor oil if you do not plan on changing it frequently as Rambo does. Motor oils do not have the additives to help the oil survive in a heaving shearing application. The gears tend to chop up the oil molecules and reduce their ability to lubricate in high pressure areas, which gears are. So, although motor oils have been used in transmissions and are recommended for those that share the crankcase oil with the tranny, they also require more frequent changes.

Morris' point is also well taken and often forgotten about. Since the tranny does not get hot like the crankcase, it will not boil off condensation that forms inside. So, over time, especially on a bike that sits a lot, it can collect in low points and cause corrosion. So you want a oil that will protect your tranny from this. I have seen what condensation can do to a tranny. In a BMW I have, it corroded thru two oil deflectors and big pieces of iron oxide would have gone thru the tranny and bearing had I not stripped it and rebuilt it. Bike had 13K miles on it and sat for a long period.

regards,
Rob
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post #5 of 13 (permalink) Old 12-04-2015, 05:56 PM
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Just to clear a point,i only use gear oil in the 75/90 range.Not engine oil.What Rob says about oil being chopped up was true especially on the Norton Commando boxes.The term used was long chain polymers if anyone recalls.
I actually prefer the mineral Hypoy gear oils to synths having used both types.I cant pin it down,but the gearchanges do feel better.
On condensation,i never get any in the gearbox and that might be the mildish weather in my area and the bike being in an insulated garage.Never used for less than a 30 mile run.
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post #6 of 13 (permalink) Old 12-04-2015, 06:15 PM
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After searching all my local stores I as only able to find one gearlube that specifically stated it was safe to use with yellow metals, and it was a gl5. I actually couldn't find any gl4 at all. Several of the others stated they were safe for all transmissions, but nothing specific about yellow metals.
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post #7 of 13 (permalink) Old 12-04-2015, 06:52 PM Thread Starter
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Ok - thanks for the advise - i will stick with mineral gear oil -- my question was prompted by a problem i have with the gearbox on my suzuki van which forums tell me will be cured/improved with fully synthetic gear oil -- so i was going to buy 5 litres to also use in my T140s (cheaper in bulk)
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post #8 of 13 (permalink) Old 12-05-2015, 04:12 AM
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Wol,its worth trying it out on the T140 to see if it makes any difference.I have not seen any signs of the yellow metals deteriorating after my use.Stick 500 cc in for a trial.The Mobil synth i was using was leftovers from a car gearbox change and i would use it to get it out of the way.
First though,see if the Duckhams product is notably better than previous oils.
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post #9 of 13 (permalink) Old 12-05-2015, 08:41 AM
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With the top quality gear oil synthetics and synthetic blends, is it really necessary to change the gear box oil every change? The motor oil 'grabs' debris from the clutch and the motor's combustion. But a well broken-in gear box doesn't seem to generate much debris. I noticed how clean it was during the last service. Made me wonder why it is recommended so frequently. Maybe every other engine oil change? Longer?

Steve
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post #10 of 13 (permalink) Old 12-05-2015, 01:08 PM
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Its not really required to change oil that frequently.I just do it more often as it is such low cost.The fact it can be left in a car gearbox for 100,000 miles suggests it does last a lot longer than my 1000 mile changes.
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