Gearbox Breather 1979 1000SP

I have a 1979 1000SP that seems to be blowing a bit of oil from the gearbox breather - its not overfilled, changes gear well (best gearbox ive ever had on a big block) the breather hose is about 400mm long and someone has put a little plastic bottle on the end with a vent hole (a 20cc rotring ink bottle) . The hose runs up from the gearbox on the coil side and bends down to the bottle. The bottle fills up over about 250 miles at which point it needs to be emptied. I recently changed the gearbox oil for Millers SAE 80W-90. ive had to empty the bottle 3 times in the last 900 miles so im about 60ml down on oil.

Any advice gratefully received


You could check the detente plunger isnt stuck or damaged. Unscrew the spigot that the breather pushes onto anc there is a spring loaded plunger that should index the gear drum.
I found taking the breather up vertical to the top rail before turning backward works best.

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Did you overfill the gearbox?
(750ml is the normal amount)

Only filled till it started to weep from the level hole - I did add a further 25ml of moly additive after - but hardly an overfill

I think the problem lies elsewhere


I’ll check the detent plunger this weekend - the existing breather hose doesn’t go as high as the top tube at the moment - I ordered a length this afternoon so should be able to run it up to the top tube and down again, I’ll leave the bottle on the end to see how much comes out ( I’ll top up the oil too to the correct level ~ 60cc ish )



I was wondering if turning the pipe back down isnt creating a syphon effect. From memory standard is to finish pointing backwards near the rear brake splitter

The usual advice is to take the breather up to the top frame tube and extend to the back of the bike. No catch bottle.

There seems to be conflicting advice all over the web (and here) some say up then bend down - others up and to the rear. I thinkl I will try both and see what works best.

Thanks for the input


I had this same issue recently with my T3 Cali.

It turned out that the detent plunger had no hole in it to allow the gearbox to breath. Hence the oil drips on the garage floor.

Replaced with the correct part and, hey Presto - no oil leak.

Good luck finding the solution. Hope this helps.


I’ll pull the plunger out over the weekend and have a look


Just to add, the factory default set-up was to have the hose going UP to the top of the battery compartment lefthand side, top frame rail height, or almost, where there’s a hose clamp to hold the end pointing backwards. At no point does it turn downward. Mine never leaked.

Exactly so

My 78 Spada has the breather running up to the top frame tube and is just left open. It does not turn back down. Virtually nothing comes out of it.
I have never heard of the detent plunger having a hole in it, that doesn’t sound right to me. The gearbox breathes through the vent pipe.
Are you sure you are using the correct hole to check the oil level? It should be filled to the one marked B in this photo from the owners manual.

Mines a 79 and there is a hole in the point of the plunger, its only about 1mm diameter.
I think Russell’s problem is almost certainly the breather routing and reverting to standard should fix it. I think this because when I rebuilt my bike I thought I would reroute the breather bcause of a bigger battery and I got the same issue immediately, so reverted to standard and all was fine.
Note to self - check gearbox oil level!

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Definitely using the correct fill hole - this is my 4th big block Guzzi in 10 years and I’ve been doing my own servicing for the whole lot. Never had an issue with gearbox breather before - had a bit of heavy breathing on engine oil but normally solved with a sump extension. I’m going to replace the hose and run it up to the top tube and backwards then see what happens.


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I’ve replaced the breather hose run it up to the top of the frame and along to the end of the frame rail on the LH side - been out for a couple of 30 mile blasts - so far the end of the hose is dry

Thanks all for your assistance



Im glad it worked