Final Drive (Shaft) Oil Change

[ST1100Y]

...is it ok to use GL5 80w90 hypoid oil in the final drive...

Yep, its the GL5 spec that IDs it as hypoid oil.

...what is the silver cap fitting at the top of the hub for? is it a breather?...

You'd guessed right: its the breather-cap, prevents pressure increase of the air pocket due thermal expansion, whilst keeping water/contaminations out (unless you're fording with your ST; then an instant oil change is STrongly suggested...)

...the filler plug nut is getting well rounded, anyone know the part number of a good replacement plug for it...

Use of bad/inappropriate tools, like plumbing pliers? ;-)
P/N 41511-ME5-000 CAP, GEAR CASE OIL and P/N 91302-001-020 O-RING (30.8MM) should serve you there.

 

[etalors]

Good point. I do mine every 8K. I think that's what Honda recommends. I'll have to check. The riding season in IL is short about 6 months at the most.

 

[Jim Van]

Because its real easy when doing an oil change, its cheap, and like 'chicken soup' it can't hurt!...
then agn, I never listened to the 8k oil changes either.

Don't know exactly what the original poster means by " shaft oil " . Didn't know the shaft had an oil supply, only know about the rear differential oil supply.

+1 on Tom Mac's post above post. I change mine at the beginning of the riding season. Only takes about 10 minutes and since only about 5 oz. is required, it's cheap insurance. I use 75W-90 full synthetic. I feel it's an "upgrade" to the #80 the manual recommends. I have it on hand for my Jeep rear differential, so I use it.

 

[broc11]

Yep, its the GL5 spec that IDs it as hypoid oil.

You'd guessed right: its the breather-cap, prevents pressure increase of the air pocket due thermal expansion, whilst keeping water/contaminations out (unless you're fording with your ST; then an instant oil change is STrongly suggested...)

Use of bad/inappropriate tools, like plumbing pliers? ;-)
P/N 41511-ME5-000 CAP, GEAR CASE OIL and P/N 91302-001-020 O-RING (30.8MM) should serve you there.

Thanks guys, just hope I didn't tap the vent cap back on too tight, I'll order a new filler plug cap for next time.

 

[Oldbikefixr]

Thanks guys, just hope I didn't tap the vent cap back on too tight, I'll order a new filler plug cap for next time.

That's one of the first parts I replaced when I got my 1991 back in July. The only corroded part on the bike. When the new one came in, I removed the old one. Tried to save it....but. it didn't want to leave home. Slipped a section of fuel hose over it and grabbed it with pliers, rotated and pulled it up. The little cap came right off the tube section, it was glued on, so I removed the tube with vise grips. Cleaned up the inside of the mating surface, applied a bit of silicone grease and tapped the new one on with a small brass hammer and block of wood. Lot of work for such a tiny part. The metal tube section is strong, the chromed cap is wimpy, so be careful with it .

 

[dwalby]

Good point. I do mine every 8K. I think that's what Honda recommends. I'll have to check. The riding season in IL is short about 6 months at the most.

8k is the inspection interval, whatever that means, and 24k is the replacement interval.

When I did mine the first time in 1999 the guy who owns Maxima oils said change it once with synthetic and forget about it. I mentioned I planned on keeping the bike a while and putting over 100k miles on it, he just kinda scoffed like I was being overly concerned. My annual mileage dropped off a few years later, so I finally changed it maybe 10-12 years later after another 60k or so miles, and the magnetic drain plug looked fine. So on one hand the oil is usually just sitting on the shelf anyway, so why not change it more often, but if you don't its no big deal either. And I might be lucky that I live in a place with no humidity and year round riding temps, not sure if that helps or not.

 

[Eagle59]

I’m probably going to ignite a firestorm of responses on this one but here is my experience. I’m actually running synthetic ATF in my rear case right now. This comes from experience I had riding an 82 VF750 Sabre. I bought this bike in 1983 and rode if for 31 years, trading it in for my current 97 ST. The rear case would push the hypoid gear oil out the top and make a mess of the rear end. This was a known issue on these bikes. I tried replacing the vent with a 2” brass riser tube, slotted at the top and a 45auto case soldered on the top upside down. I thought a bit of elevation would keep the heavy oil from pumping itself out. Apparently there is enough centrifugal force inside the final drive to push the oil up and out the vent.
Based on some articles and writings at that time, I decided to try ATF in the rear case to see if a lighter oil would stay put. It did, no more oil pumping out of the vent. Here is where I made some interesting observations. With the heavier hypoid oil in the rear case, it would get very warm after a long ride. If you put your hand on the case, it would be hot. Not so hot that you couldn’t keep your hand on it but it was very warm. After draining and replacing with ATF, the case did not get as warm. I have no empirical evidence or temperature readings to back this up but you could feel the difference. Now if friction generates heat and there is less heat buildup running AFT in the transfer case, what does that mean?
When I got the ST, I performed the same experiment. I took the bike out for an extended ride. When I returned I put my calibrated hand on the rear case. Yup, very warm. I drained the oil and noted the odd smell mentioned elsewhere in this discussion. It seemed a bit dirty but otherwise, okay. After putting synthetic ATF in the rear case I performed the exact same ride on similar weather conditions. When I put my hand on the rear case after that ride, it was not as warm. ATF has many high pressure, high temperature properties that seem to work well inside a gear case. Many manual transmissions in trucks spec out ATF, not hypoid gear oil. My Ford Ranger did.
I’m sure there will be many responses explaining how I have violated many mechanical, and physical laws of nature doing this but this has been my experience. I will probably put synthetic gear oil in as part of this winters’ maintenance to get back in the good graces of the motorcycle gods. Take the observations for what they are. Don’t hate me for running afoul of the maintenance schedules.

 

[ST1100Y]

The rear case would push the hypoid gear oil out the top and make a mess of the rear end.

Happens only if you overfill the case...

 

[Eagle59]

Not in this case. (No pun intended) Factory specs for the Sabres and Magnas of the day was to fill to the bottom of the large fill hole. Mother Honda actually had a replacement vent cap that was supposed to address the oil venting issue. It didn't. They later changed the fill specifications for the read case to put less oil in there. I spent many years with this bike, working on this issue. It was a great machine, fore-runner to our beloved STs.

 

[Jim Van]

Very, very interesting. You may be onto something here with the temp difference ..........

Yes, ATF is used in manual transmissions and in my Jeep, the transfer case too. But since the FD has hypoid gears, they require a hypoid / EP lubricant. So that eliminates the use of ATF. Do a Google search to verify.

 

[CWDUSMC]

I change it when I replace the rear tire (usually around 15K miles) and use synthetic. Since it takes less than a qt, not a major expense.
Ride safe,

 

[dwalby]

Very, very interesting. You may be onto something here with the temp difference ..........

Yes, ATF is used in manual transmissions and in my Jeep, the transfer case too. But since the FD has hypoid gears, they require a hypoid / EP lubricant. So that eliminates the use of ATF. Do a Google search to verify.

Since he has only 31 years of experience with running ATF in his Sabre final drive without problems (maybe less, he wasn't clear about exactly when he switched during his ownership period) he had better do an Internet search to show him how wrong he was. That will teach him.

 

[Eagle59]

To be fair, I ran the ATF for about 20 years in the Sabre. I would periodically open the large fill cap to inspect and check the fluid. It always looked clean and red. I recall changing it a few times as part of normal maintenance. In my opinion, modern lubricants have very advanced qualities. If AFT is being used in a truck transmission, it should be adequate in a lowly motorcycle FD. Imagine the heat and stresses that go on inside an automatic transmission. The forces and stresses inside the final drive are probably not as great as inside a truck or jeep, design and engineering specs notwithstanding. Do this experiment yourself and make you own decision. Running ATF in the rear case will at least clean it out good with all of the additives and ingredients in the magical ATF. If you don't like it, go back hypoid. No harm, no foul.

 

[Fatjock]

LOL......I'm glad this came up the week after I changed the final drive oil on my two bikes.

No doubt it'll be long forgotten by the time they're due again.

 

[broc11]

LOL......I'm glad this came up the week after I changed the final drive oil on my two bikes.

No doubt it'll be long forgotten by the time they're due again.

My fault, I dug the thread up again after 6 1/2 years

 

[dkruitz]

I'd be curious to see how those folks are doing with the ATF in the final drive units.

 

[Jim Van]

Since he has only 31 years of experience with running ATF in his Sabre final drive without problems (maybe less, he wasn't clear about exactly when he switched during his ownership period) he had better do an Internet search to show him how wrong he was. That will teach him.

Don't take my word for it, I'm no lubrication expert. But the experts say only a Hypoid / Ep lube should be used in a FD because of the hypoid gears. Like I said before, do a Google search. I did and I actually learned something from the experts.

Personally, I wouldn't go against the expert's recommendation and take a chance running ATF in my FD. Why take a chance ? But if anyone else wants to, that's their business and their risk to assume.

If anyone knows of a manufacturer ( MC or auto ) that stipulates ATF to be used in a hypoid differential, I would be interested in hearing about that.

 

[SMSW]

Are there any oil gurus out there? Can a chemical engineer (or whoever really knows oils) explain what hypoid gears do that requires a special oil? Is it the pressure between the gears of the metal to metal contact? Does hypoid oil have enormous film strength compared to regular motor oil? How does hypoid oil compare to ATF juice in the defining characteristics - i.e. film strength, and whatever other properties oil scientists use to compare different oils' performance?

 

[Bush]

Is it the pressure between the gears of the metal to metal contact?

More the shearing action of a hypoid gear set that would be of concern, methinks.

 

[st1300r]

Are there any oil gurus out there? Can a chemical engineer (or whoever really knows oils) explain what hypoid gears do that requires a special oil? Is it the pressure between the gears of the metal to metal contact? Does hypoid oil have enormous film strength compared to regular motor oil? How does hypoid oil compare to ATF juice in the defining characteristics - i.e. film strength, and whatever other properties oil scientists use to compare different oils' performance?

Hypoid shaped gears are not on the same axis kind of a spiral shape and don't engage all at once like a noisy straight cut gear like the counter balancers that make the whiny ST noise. On axis would be a bevel gear. "hypoid" oil is another way of saying EP "extreme pressure" oil additive package. Moly is an EP additive that deals with high pressure and slow relative movement between surfaces as opposed to say a high speed relative movement like a ball bearing and its race.

The interwebs suggests the weight scale of gear oil is purposely different so you're not likely to confuse oils. An 80wt "gear" oil might really be a 40wt "motor" oil viscosity or close but it's called 80wt so you aren't tempted to use a "motor" oil that would have an inappropriate additive package.