The rear drive is pumping oil out of the breather

[Petrus Rocks]

First ride for the Guzzi after replacing the cardamon joint.  Went for a ride down to the Curtiss Museum in Hammondsport NY.  Speeds up to 85 mph.  We stopped and found oilall over the back of the bike from the vent hose on the rear drive unit. Put the vent hose straight up- still puking some oil on the ride home.  The drive has been vented for over two years.  thgis is the first time this has happened.  Any ideas?  Bike is an 85 Cal II.

[guzzisteve]

Ride it till it quits puking, then record how much came out changing it. If it's pink crap[ all bets are off, I don't use syn in anything.
If it pressurizes wouldn't the shaft boot blow up like a balloon?

I just drained 10cc out of my Cal2 rear drive that came from my trans. I put Lucas hub oil in it 3,000mi ago to try and swell up the seal. So far it is working, but wow is it thick. It's a pain to pull sidecar and subframes off, plus I need to do lots of 100K mi maint I haven't done in 30K. I don't care, I'm going riding till the crap fails. This u-joint has 100K mi on it, so does the clutch and V700 flywheel.

[John A]

I quit venting that type of rear drive. it should vent to the transmission but doesn't do that so well. I just burp it after an oil change by opening the filler plug to let off the pressure after a good run. seems like I only have to do that the once and its good. then I don't have to fool with it until I check the level. some transfer oil up to the transmission which is good, lubes the driveline, unless it gets excessive. Im with Steve on the purple stuff.

[Rough Edge racing]

 I was riding my bike with  Pete and it was an oily mess....I used to own the bike ..I read here that the lack of venting forces oil up the swingarm tube...So I figured since the oil belongs in the axle drive, why not vent it?.. As Pete says, same rear end, same vent, same hose, no oil was added to the drive ...It's not like the bike hasn't been ridden fast for a period of time previously... Why now?

[John A]

That's curious alright , it's the reason I quit using a breather there. I couldn't get it to act reliably over the long term. I suspect when oil is up the vent at certain temps and attitudes under breaking and acceleration, suspension loaded and unloaded when pressure builds it pushes a slug of oil out.

[pehayes]

You replaced the Cardan u-joint.  Did you do anything to the rear drive?  Did you remove the drive from the swingarm?  Did you happen to pull the input shaft carrier housing from the front of the drive box?  Did you do anything about the oil in the drive box?

https://en.wikipedia.org/wiki/Universal_joint

What oil are you using?  Some brands foam much more than others.  You do not mention having changed or checked the rear drive oil.

I would suggest you drain and measure the gearbox oil volume and do the same for the drive box oil.  Symptom sounds mighty suspicious that you are transferring gearbox oil down the shaft tube to overfill the drive box.  I've been through this issue.

Why did you change the Cardan u-joint?  If it came apart in any way then shards of metal or bearing rollers may have damaged the nearby gearbox output shaft seal.  It can be replaced in situ.

Patrick Hayes
Fremont CA

[John A]

I missed the part where you replaced the joint, I feel foolish for that and what Patrick sez make sense. I still don't vent them, personal preference.

[Rough Edge racing]

You replaced the Cardan u-joint.  Did you do anything to the rear drive?  Did you remove the drive from the swingarm?  Did you happen to pull the input shaft carrier housing from the front of the drive box?  Did you do anything about the oil in the drive box?

https://en.wikipedia.org/wiki/Universal_joint

What oil are you using?  Some brands foam much more than others.  You do not mention having changed or checked the rear drive oil.

I would suggest you drain and measure the gearbox oil volume and do the same for the drive box oil.  Symptom sounds mighty suspicious that you are transferring gearbox oil down the shaft tube to overfill the drive box.  I've been through this issue.

Why did you change the Cardan u-joint?  If it came apart in any way then shards of metal or bearing rollers may have damaged the nearby gearbox output shaft seal.  It can be replaced in situ.

Patrick Hayes
Fremont CA

  Pete is away right  now,,,,,,As mentioned, I used to own the bike..I rebuild the CV joint with bearing cups only , installed a new sealed bearing, replaced the drive oil seals and filled it  with Lucas gear oil I believe...The U joint body was worn and the bearing cups were a bit loose...I actually used JB Weld to glue to fill in the gaps...I also fabricated the vent...
 I rode the bike for a season and sold it to the Pete, OP on this thread...He rode the bike, hard at times, for a few years, maybe a few thousand miles...No oil pushed out the vent during this time period....
  He decided to play safe and replace the whole joint...I was there  when he did the job.. The JB Epxoy job held up, there was no debris anywhere.. Pete replaced the joint with a complete new assembly, a new sealed bearing.. The drive unit was not leaking, no oil leaked out or was replaced during the repair...

[pehayes]

So, it seems nothing was done to the rear drive during this recent repair.  And it seems it was not leaking before the task but developed distinctly after.  All the more to support the symptoms of gearbox oil migrating past the output shaft seal and down the shaft tube to overfill the drive box.  Time to drain and fill each box to the measured specification (not by inspection hole).  Go for a hard ride until it leaks again and do a drain and measure to confirm.

Patrick Hayes
Fremont CA

[Rough Edge racing]

 Ok, I misunderstood you about tranny oil getting into the rear drive, bad rear seal....The new carrier bearing was 2R sealed on both sides but I suppose the oil could get past it? Then the joint boot will be oil filled...

[pehayes]

Look at a used u-joint.  The yoke ends are hollow and internally splined.  The forward splines of the drive shaft fit into the aft end of the u-joint.  Certainly not a 'snug' fit.  nothing that would hold any amount of air pressure or warm liquid.  It would be quite easy for oil to pass down through the center of the u-joint yoke.  No need to go through the bearing.  For the same reason, that is how the drive box is supposed to breathe heating pressure back up into the gearbox and hence out the gearbox's vent.

Patrick Hayes
Fremont CA

[malik]

Was just trading lies with a 750 S3 owner last night. He used to have the same or similar problem with oil coming out the breather on the final drive & all over the wheel. Did lots of things to try to fix it. When he put a breather tube on it, the oil just went up the tube & out of it. Disgusted, he replaced the bevel box with a new one. No problem ever since. That worked for him.

[Petrus Rocks]

Back in town.  I checked the oil in the transmission- clean and full.  No oil in the swingarm boot.
Drained the rear end oil- dirty and low. 
Fresh oil, breather tube with a catch bottle and went for a short ride.  Puked oil again.  Decided to seal the breather tube and see what happens.
Regarding a previous post-I pulled it apart because I knew the old joint was "old".  Replaced the shaft bearing at the same time.  The shaft was out of the swingarm and the hub was removed from the swingarm too.
I have ridden this bike briskly for two years with no significant (if any) oil blowing out.

[Kiwi_Roy]

Did you by chance put your hand on the drive to see if it was hot?

Which bike are we talking about?

[Petrus Rocks]

The bike is a Cal II.  1985.  The catch bottle was not arm after a 7 mile ride.