Got Shaft Rot.... again WTF

Warlord said:
This issue has been going on for years...

https://forums.bmwmoa.org/showthread.php?37675-Final-drive-gator-not-sealed-water-in-swing-arm
Click to expand...

Post number 20 in that thread is interesting to read, may not be relevant today, but who knows, read below

Actually -- the boot should seal off the driveshaft.

The open hole in the rear-drive bottom is outside the boot. The accordian boot fastens at the rear-drive to the round boss the input shaft is in - and on the swingarm end, it has a lip that goes inside the casting, and is held moderately tightly in place with a plastic expanding ring inside.

As noted above - if this ring is damaged (or not installed correctly) - then you do have a chance for water intrusion (and no way for it to get out..) and that's what I think happened in this instance. The front of the boot to the swingarm was mentioned as being a loose fit ("and looked like the large swing arm side was not sealed") - allowing the water to get in. Since the rear seal for the boot is sealed to the rear-drive, it became a reservoir to keep the water in.

A possible cure would be a small (1/8") hole in the last pleat of the boot near the rear-drive. That should allow any water to drain out, and unless you're submerging the rear drive regularly, minimal water would intrude. Or just make sure your plastic ring is properly in place and put a bit of lithium grease on the casting surface to help seal it.
 
I've had a look under the rubber boot and there is nowhere obvious to drill / make a drain hole in the boot itself. It's squished together on its folds too tight.

I've washed the bike as normal today, not avoiding the rubber boots or swing arm.

I'll run it until next service and tear it all out for another inspection.

See where we are then...
 
if you're drilling holes, I woulod have though it best in the bevel housing, so it does not build up in there around the nut and splines.... 3mm should do it ;)
 
beaver said:
if you're drilling holes ....
Click to expand...

I would have thought to be best at the lowest point ;)

Like the Austin Maxi when water was getting in to the boot area and spare wheel well ... instead of looking to stop water getting in BMC merely drilled a hole at the lowest point to let it out :blast

:beerjug:
 
beaver said:
if you're drilling holes, I woulod have though it best in the bevel housing, so it does not build up in there around the nut and splines.... 3mm should do it ;)
Click to expand...

IF I have any problems with water... or rubber boot collapsing in 3000 miles time, I will seriously consider drilling a drain hole.

I'll go from the inside out on the swing arm so I can see exactly where it's located for best drainage and least stress....

A stress fracture on my swing arm is not a good fix to an otherwise fairly annoying rust issue....

Another consideration is will one hole allow water to drain out easily... if there isn't another hole for air to get back in?

BMW put a valve on the FD for this exact reason.... why not on the swing arm side?
 
Where's an Engineer when we need them? :D

Am I running a serious risk of stress fractures if I drill a hole... ??

Anyone want to take a guess?
 
Warlord said:
I've just had a closer look at this, on the expanded .pdf document..... and that valve is on the final drive, aft of the splines seal.

So it won't effect the pressures inside the swing arm. there isn't a valve on the swing arm side (which is where the problem is...)

Once you seal the top rubber gator and the bottom rubber gator... that's it, it's sealed.
Click to expand...

Just picked up on this from Jim Vonbaden, might be helpful for some later.

https://forums.bmwmoa.org/showthrea...-Final-Drive-change-and-Spline-Lube-Pictorial!


Now you can see the condition of the splines, and the area inside the final drive. Both bikes looked exactly like this, and the 14K mile bike had a lot of off roading, presumably with water crossings. If you find oil in the swingarm, look up inside and see if there is an oil trail. If so, it will be the transmission output seal. If not, look at the dropped final drive for wet oil indicating a leaking final drive input seal.
 
Just fill the swingarm with oil, problem solved :D
 
For what it's worth.

This how it was on my -15, and my way of interpretation of the picture:

47738664102_5c1c60ca5c.jpg


Blue Arrows: These are the hard plastic hooks that keeps the gator in position by gripping behind the flange in the end opening of the swingarm.
Red Arrow: This lip makes a seal that fills the opening in the flange, I.e this lip does not go all the way behind the flange, it just press against the wall inside the flange.
Green Arrow: This makes out the gutter that allows water to flow towards the bottom
Yellow Arow: This is where the water leaves the gutter and drips into the opening between the swingarm and the bevel gear.
Sealing it is a matter of a very thin layer of lubricant along the lip (Red) and the gutter Edit: Green Arrow, not Yellow just to make sure it sets properly in the opening.
Due to the tightness of it all there will not be much water flowing, and there will be no heavy pressure.

But if you fill the gutter with grease, the gutter will overfill and the water will be lifted to the top of the edge and possibly enter behind the lip and into the swing arm.

I will not guarantee that this is correct, but this is what I have done to my bikes, (K's and R's) and to this day there has never been water in my swing arm, in spite of power washing and frequent driving in shitty weather.

What do you think, does it make sense ?

That said, I'm probably jinxed by now, so I better check my swing arm next week. :jager
 
There was no grease on anything when I collected it from BMW.... except a swingarm full of water and rust everywhere
 
knutk said:
For what it's worth.

This how it was on my -15, and my way of interpretation of the picture:

47738664102_5c1c60ca5c.jpg


Blue Arrows: These are the hard plastic hooks that keeps the gator in position by gripping behind the flange in the end opening of the swingarm.
Red Arrow: This lip makes a seal that fills the opening in the flange, I.e this lip does not go all the way behind the flange, it just press against the wall inside the flange.
Green Arrow: This makes out the gutter that allows water to flow towards the bottom
Yellow Arow: This is where the water leaves the gutter and drips into the opening between the swingarm and the bevel gear.
Sealing it is a matter of a very thin layer of lubricant along the lip (Red) and the gutter (Yellow) just to make sure it sets properly in the opening.
Due to the tightness of it all there will not be much water flowing, and there will be no heavy pressure.

But if you fill the gutter with grease, the gutter will overfill and the water will be lifted to the top of the edge and possibly enter behind the lip and into the swing arm.

I will not guarantee that this is correct, but this is what I have done to my bikes, (K's and R's) and to this day there has never been water in my swing arm, in spite of power washing and frequent driving in shitty weather.

What do you think, does it make sense ?

That said, I'm probably jinxed by now, so I better check my swing arm next week. :jager
Click to expand...

Now that makes perfect sense, overgrease the lip and it has an opposite effect........................:clap:clap:clap
 
a small hole at the bottom should be fine.. the loads are on the side of the arm... cant see much stress in the area your talking about drilling
 
knutk said:
For what it's worth.

This how it was on my -15, and my way of interpretation of the picture:

47738664102_5c1c60ca5c.jpg


Blue Arrows: These are the hard plastic hooks that keeps the gator in position by gripping behind the flange in the end opening of the swingarm.
Red Arrow: This lip makes a seal that fills the opening in the flange, I.e this lip does not go all the way behind the flange, it just press against the wall inside the flange.
Green Arrow: This makes out the gutter that allows water to flow towards the bottom
Yellow Arow: This is where the water leaves the gutter and drips into the opening between the swingarm and the bevel gear.
Sealing it is a matter of a very thin layer of lubricant along the lip (Red) and the gutter Edit: Green Arrow, not Yellow just to make sure it sets properly in the opening.
Due to the tightness of it all there will not be much water flowing, and there will be no heavy pressure.

But if you fill the gutter with grease, the gutter will overfill and the water will be lifted to the top of the edge and possibly enter behind the lip and into the swing arm.

I will not guarantee that this is correct, but this is what I have done to my bikes, (K's and R's) and to this day there has never been water in my swing arm, in spite of power washing and frequent driving in shitty weather.

What do you think, does it make sense ?

That said, I'm probably jinxed by now, so I better check my swing arm next week. :jager
Click to expand...

Fair point, and noted.

But you're going to need to be Ronnie O'Sullivan to get and maintain lines at that level of accuracy.

Fitting these rubber boots and not getting grease all over the place is like eating Spaghetti Bolognese with chopsticks in a white suit.... good luck with that idea as well....
 
Ok, here's the weird thing going on with my shaft. Abnormal swelling !!

Best take a look at the pictures.... :nenau
 

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So when it's sat in the garage and cooled right down, the rubber gator is being sucked inwards.

When I go out riding and have a good blast, it swells and looks bloated.

So......

a) It's definitely sealed now !!

b) Is the constant fluctuations in pressure going to effect the final drive oil seal !!?

c) Fuck knows what I need to write on this line

Anyways, it's all getting stripped down again in 2,500 miles as it'll be due it's next service. So I'll see what's going on inside then.
 
Think it needs a good dose of Antibiotics...
 
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