GS850G gear oil question

[IanFrancisco]

Greetings: It's been a while since I've posted here. My '80 GS450 has been relieved of its duties as daily driver since Apr '06 and gets taken out about 2 to 3 times per month to keep the juices flowing. The small, light bike is a nice contrast from the current daily driver, a '91 Suzuki VX800M. Pics of the GS450 are in the gallery.

Anyway, my buddy Cliff, who recently introduced himself as the new proud owner of a very nice '80 GS850GT, has recruited me as his maintenance trainer and consultant, and we topped off the gear oil today. Oddly, the final drive was overfull when I removed the fill plug, and the secondary drive gear oil was WAY low, darnit. It took about twice as much oil to fill it as it usually does to drain and fill the VX final drive. The previous owner said he had never checked it in 6k miles and we only hope it was not run completely dry. That would be a shame because this GS850 is a very nice original survivor with only 14k miles on it. The previous owner was a weekend cruiser, he had the handlebars and an aftermarket windshield set up all wrong for anybody who rides a lot. So, hopefully the secondary drive gears survived that period of neglect. Everything in the final drive is tight and silent.

Anyway the first question is; Does this middle gear oil sump lube both the tranny and secondary drive gears? Or, Does the trans get lubed by engine oil as is the case with most Japanese bikes? I rode the bike home for Cliff, only about 4 miles on surface streets and the shifting was nice and slick as with most GSes.

The second question is; Is it possible for gear oil from the middle sump to drain past a bad seal and overflow into the final drive unit? That would explain why the final drive was overfull. Otherwise, how could anybody overfill the final drive without going thru quite a bit a hassle? The other possibility is that someone filled it while it was on the bench, but the bolts on most areas of this bike look untouched, and it's unlikely the final drive has ever been removed and replaced.

I know I should search previous posts, but lunchtime is over and my employers want some work to get done for some strange reason...

Thanks, ian

[tomcat24551]

1. Motor oil lubes the transmission. Hypoid oil lubes the secondary only.

2. In my opinion, this would be highly unlikely. In addition to the oil getting by the seal in the secondary, it would have to get by two seals to get into the final drive. I've never been into the final drive, but I'm looking at a blow-up in the OEM shop manual for my info.

An easy way to find out is to check it again later to see if the level has risen.

The final should only be filled to the bottom of the filler hole.

[salty_monk]

It was probably filled when it wasn't level hence the overfill...

Dan

[BassCliff]

Thank you for your replies and for sharing your knowledge and expertise.

I wondered if the bike had been up on a block, with the rear tire higher than the front, when the differential was last filled.

I had another thought: opening the fill plug while warm and recently churned up, there may have been a bubble in the shaft and when we opened the plug the pressure forced the oil out. Perhaps I should check it cold?

Thank you for your indulgence,

BassCliff