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Gear box lubricants break down just like motor oils do. Yes, many people do not change them, but they should, if for no other reason than to get clean oil in that has become contaminated with metals from wearing parts.
Brake fluid gets nasty and dirty with time. It should be changed as well.
I change the motor oil in my four wheeled vehicles like clockwork, but I'm guilty of procrastinating when it comes to the transmission fluid, rear end grease, etc.
If you notice folks changing the fluids often in their bikes, it's because they want their machines to last longer, and their safety depends on proper maintenance of these items more so than in a car.
How often to change fluids other than motor oil is a judgement call.
Better to change too often than not enough.

 

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Roundman cover most of it for me but brake fluid is a whole nother issue. Brake fluid is Hygroscopic ( I think that is the right word??) Anyway it absorbs moisture from the air. As it does so it allows corrosion and can generally raise havoc inside your brake systems. Standard recommendation is to completely purge yo7r brake systems every two years.

After resurecting several older bikes and haveing to completely rebuild the brake systems I consider a two year change out gospel. The stuff can turn to mud after a couple of years.

 

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n2xwv wrote:

Hi, so i have no idea and so i ask, why do the guys change fluids, brake fluids and gear oil in final drive of motorcycles, never have done it in a bike or a car? just normal engine oil changes and filter changes,, seeya john n2xwv

John, there are different types of brake fluid.. the Dot 3 & Dot 4 are very good at absorbing water & holding it in suspension.. As a rule that doesn't cause much system harm.. After enough time, (depends on how much moisture in the air, breathing cycles of the brake fluid reservoir, temperature swings), the moisture content in the fluid exceeds what the fluid can isolate & then is when the corrosion damage begins.. A second issue is: as the brake fluid absorbs moisture the brake fluid boiling point lowers so brake fade under hard braking then becomes an issue..

Now the Dot 5 (silicone) based brake fluids have other issues (they are by nature not hygroscopic so don't absorb water) but that isn't a good thing either because anywater (moisture) that enters the brake system quickly settles to the lower parts of the brake system & quickly forms corrosion in those areas..

Depending on the brake system, how good it's sealed from the atmosphere, how long the vehicle sits inactive, the brake fluid should be changed anywherefrom between 1 to 3 years.. My BWM "R" bike with power servoABS brakes REQUIRES the fluid be changed every year.. As a rule I change the brake fluid every other year in my other bikes.. When changing out the brake fluid it is a good idea to pry the brake pads back into their bores & wedge them there during the bleed processas that also allows the old fluid in the piston bores to be bled out with the changed fluid..

Now on the gear oil?.. That is subject to "shearing" do to loading from the hypoid drive gears so does loose viscosity as it it goes through the miles.. Also the anti scuff & anti wear EP (extreme pressure) additives in the gear oil degrade over usage so that is also subject to being changed every few years..

A side issue on motorcycle gear oil is the rear drive units on motorcycles have a fairly exposed vent on them.. That vent is also down low & gets hit with a lot of road spray, dirt, dust, washing high pressure water, so the gear oilon motorcycles tends to end up with water in it after a while (a sure way to pit the bearingsthen trash out a rear drive unit.. Seeing as most motorcycle rear drives only hold a quart or so of oil it is a very good idea to change it at least once a year & if possible twice, (spring & fall)..

Twisty

 

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Ok that about says it all, i have taken my 88 wing and replaced everything and anything that it needed, I better go buy some new fluids and get started! i have some more work to do hihi. seeya john n2xwv ride safe