changing manual trasmission fluid

[Goro F]

hello
very basic question, since the filling plug is showed in the manual but not the drain plug

i m going to replace the oil of the gearbox of my R51/2. Are those the right plugs?

is there a way to check the level of the oil? in the manual is mentioned only the quantity to fill in when you make the exchange (should be approx 1 qt, equivalent 1 liter)

[schrader7032]

On my other bikes, the filler hole can be used to check the level. On my R69S, the amount of oil added is to the bottom of the threads on the fill hole. So, if you look in through the hole, you should see oil at about that level.

[Goro F]

ok thanks, i will do so

in the manual is recommended SAE40-50 for summer and 20-30 for winter.

any recommendation from your experience on the brand?

considering the temperature nowadays in my region i would go with higher viscosity

[schrader7032]

Where do you live?

I would certainly measure out the fluid per the specs and see how that fills the transmission. Is it way below the threads? I would certainly not go more than the bottom of the fill hole.

[Goro F]

i live in the middle of italy, in tuscany 15 km far away Pisa leaning tower closed to the sea. So no very low temperature even in winter time

today when i come back home i will open the plug and look better, but if i remember well immediatenly under the plug there is a curve and no oil is visible at this level

yes you 're right, i will measure the quantity of fluid that comes out of trasmission and compare it with the specification

[Slash2]

I’d use Gl4 85/90 assuming you’ve got helical gears in that box. Not GL5!

[schrader7032]

Back in the day, the seals weren't meant to work with hypoid gear oil. That's why specs were for engine oil. Viscosity of a 90W gear oil and a 40/50W engine oil are about the same-ish. If the owner has changed out the transmission seals, then he'd be good to use gear oil.

[cwf]

I started with engine oil in the gearbox of a 50/2 and gearchanging was difficult. So I changed to a GL4 oil and the gearchange is better, not wonderful but back to normal BMW.

Charlie.

[xackley]

for the 45 years I have ridden my 1958 R69, i use 40w VR1 from front to back. Still smooth with minor leaks. I clean once a year for seepage stains. Shifts smooth.
Don

[Goro F]

Thx all for the replies

Unscrewed the filling plug right now. A mark is visible. I assume that the level should reach this mark. I removed the drain plug and no more than 300 ml fluid exit so far… i think that the oil is much less than it should be. In the owner manual it is mentioned 1 qt, which should corrispond approx to 1 liter

I ll leave it drain during the night.