Need to confirm driveshaft oil amount

[mferguson]

I'm not near my manual but I need to know how much oil is supposed to be in the driveshaft of a 1973 SWB R75/5 (not the amount in the final drive itself). Is it 100cc for a SWB?

[DennisDarrow]

Looking at the last page of my owners manual............ .15 liter.....150 cc....good luck.......Dennis

[20774]

Even 100cc would be fine, really. It just needs some to spash around and get to the u-joint, etc. There's a practical lower limit...not sure what it is. I've heard others say that even 50cc might be OK.

There was something I read in an old MOA news about pressure building in the early /5 driveshafts because there was no vent to the tranny and then to the tranny speedo bolt. The "fix" that was suggested was to put a pinhole on the top side of the boot or maybe a toothpick under the clamp on the top side to allow the tube to breathe.

[mferguson]

There was something I read in an old MOA news about pressure building in the early /5 driveshafts because there was no vent to the tranny and then to the tranny speedo bolt. The "fix" that was suggested was to put a pinhole on the top side of the boot or maybe a toothpick under the clamp on the top side to allow the tube to breathe.

This is EXACTLY what is happening to me now. I even switched final drives to my spare and 50 or so miles into a ride I get off the bike to find gear oil coming out from all 4 sides of the gasket between the drive and the shaft housing. I just put some Hondabond around the gasket thinking that it was not making a good seal but it sounds like it may be making TOO good a seal.

I'll try the tricks you mentioned above. Man I love these forums!

[AnnapolisAirhead]

I'm not near my manual but I need to know how much oil is supposed to be in the driveshaft of a 1973 SWB R75/5 (not the amount in the final drive itself). Is it 100cc for a SWB?

Yes, it is 100cc for a SWB. 150cc for LWB and definitely too much for the stubby SWB shaft.

However, IIRC, Oak wrote something about filling it slightly less than the spec, unless you'd had the swing arm off the bike and know it was 100% empty. So you might want to slightly underfill. As Kurt said, it just needs a bit to slosh around on the u-joints. You could have been inadvertently overfilling it unless you had the swingarm off to completely drain it compounding the vent problem. :dunno

My SWB R60/5 has a vented transmission/negative ground bolt, but it sounds like that may not be enough. I haven't put any miles on it yet, but I suspect I'll encounter the same issue. Good stuff to know. this forum is priceless.

Hope this helps.
:german

[20774]

The MOA website used to have a page which provided an index to topics in previous MOA News issues. I can't find that now...I'm glad I copied it off and have my own copy.

Anyway, the index shows two entires for "Driveshaft Boot" articles dealing with breathing. They were:

Driveshaft boot breather 7.78.26 (month.year.page)
Driveshaft boot, swollen 9.74.15, 9.81.25

The MOA might have back issues which may be worth finding. The 1981 issue actually has instructions on how/where to drill a hole to get that venting capability back. The article says that this affects the /5s prior to 1973, however.

[AnnapolisAirhead]

Does it say what BMW did to address the issue in post-1972 bikes or is that the same fix you are talking about? Just wondering what the factory did versus other Airheads taking care of it themselves.

[20774]

After this, a vent showed up at the 12 o'clock position at the output flange of the tranny. This provided the air path into the tranny and out the breather bolt.

[AnnapolisAirhead]

After this, a vent showed up at the 12 o'clock position at the output flange of the tranny. This provided the air path into the tranny and out the breather bolt.

Ah, probably a tiny one is all that is necesary, visible only with the boot removed? In otherwords, if you were looking at the back of the transmission without the shaft attached, the hole would be from back to front , as in the direction of travel? If so, I'm thinking that's a better fix...if you can be careful with the shavings when drilling. :thumb

[20774]

Yes, that's it. The '81 article gives a diagram on where to drill. If you severely greased up the bit, did things slow, and flushed the tranny, seems like it could be done.

[AnnapolisAirhead]

Very good info Kurt. As usual, many thanks for sharing your knowledge. :thumb

[woodgrain]

Driveshaft housing capacity is 3.2 ounces or 94.7 cc.

Woodgrain

[mferguson]

I'm happy to report that I tried the pinhole in the driveshaft boot technique with 75cc of new oil and all is well. I put a couple hundred miles on this weekend during an AMA Museum fundraiser and it ran flawlessly. Thanks everyone!