Rear driveshaft angle and rear seal leakage

JustAnotherSquid · 04-18-2004, 03:25 PM

I've got an SA with the standard suspension and long torque arm. RoundelRider has a Prep with the long shocks and short arm.

I recently installed an Ohlins rear, which is slightly longer than the stock standard shock. But I don't know by how much.

RR's bike in front, mine in back:

While our bikes were parked together, I couldn't help but notice how much shallower his driveshaft-to-rear drive junction was. If I put a short arm on mine, is it reasonable to expect the angle to look more like his bike? Do I have anything to worry about as is?

I also notice some oil weepage out the final drive ... two months after the bike is out of warranty.

Per RR's suggestion, I'm going to drain the Mobil1 and replace it with dino oil and see if the weepage goes away.

If it doesn't, how much does it cost to replace the rear seal? Is it possible that the leakage was caused by the extreme driveshaft angle? Thanks for any insight you can offer.

markjenn · 04:41 PM

There was a lot of discussion about this back when nearly everybody was putting on the shorter GS arm (or a shorter custom one) to raise the rear of the bike and quicken the steering.

Most of the focus was on the loads at the u-joints. Some folks thought the shorter paralever would reduce the load on the rearmost joint since it tends to straighten it out. Others thought it would make it worse because the rear angle needs to be matched with a similar angle in the front, assuming the two joints are properly phased to one another. We've had long discussions also on whether phasing of the driveshaft is even necessary and whether they are phased from the factory.

In the end, there are a lot of people running both short and long paralevers without any strong correlation to problems, so I doubt it is a significant factor on u-joint wear.

And I doubt it has much to do with rear seal problems either. My seal starting weeping right at 25K miles and I managed to squeek in under the warranty for the fix. But it is not terrible expensive - $150 or so at most shops. You may notice that it weeps only in warm weather. Mine sealed in cool weather, but would dribble a bit in warm. Despite making quite a mess back there on one tour, it never leaked enough that I could detect a drop in the level at the fill hole.

BTW, if you have your rear Ohlins adjusted to its shortest length (as they come from Ohlins) then it essenitally matches the length of your stock shock. So your change in shocks probably hasn't affected the geometry at all.

- Mark

pwillikers · 04-18-2004, 05:38 PM

Hey JAS, does RoundelRider's prep thrum?

DavidSoine · 04-18-2004, 05:51 PM

Please take the picture with the bikes loaded - that is the geometry that matters.

best,

Dave

ckcarr · ckcarr's Garage

JAS I just looked at my completely stock 2000 R1100S Sport and it is like yours. The straightening may be due to the shorter arm on Roundel Riders.

motoman · motoman's Garage

These pics are both with no rider and the bike stopped.

Wonder what the angle is with bike running and rider aboard

(like Soine said.. just saw that...)

JustAnotherSquid · 04-19-2004, 02:44 AM

Markjenn, thanks for the insight. If it continues to leak with dino oil in it I'll spend the $150, otherwise dino is good enough.

pwilikers, RR will be checking in soon and he'll be able to answer that.

ckcarr - thanks.

motoman & David, I'm currently running 25mm of sag, and the bike on the sidestand is already using up a portion of that, so the angle doesn't change much with me on it.

repoe3 · 04-19-2004, 03:02 AM

JAS...i am too humble to say i told you so

but those pivot points are normal. my father's all stock S looks that same way as yours. i would highly recommend you get a shorter torque arm. the stock piece is cheap and you dont look short. but yes, drain the mobil 1 and replace with BMW's heavier gear oil. truct me.

repoe3

Flatbutt1 · 04-19-2004, 10:36 AM

I recently filled my final drive with BMW synthetic. Has anyone else who has used it noticed any weepage from their FD?

motoyoyo · 04-19-2004, 11:21 AM

I had some rear end seal leakage after I switched to BMW synthetic. I figured I was going to have to replace the seal, but I first decided to pull the boot back and clean it all up, then just watch it to see if it still leaked later on. It has been several months now and it hasn't leaked a drop since. Here is a link to the post I made about this back when I first noticed it: Check Out This Rear End....

repoe3 · 04-19-2004, 11:22 AM

i have not experienced and weepage with bmw's heavier synth stuff...i did notice weepage with mobil 1 on the prep.

repoe3

roger albert · 04-20-2004, 08:45 AM

I've yet to see any weepage with Mobil-1 on my replaced seal.
Weeped plenty with BMW oil on the stock seal, so it all sounds like another old wives tale on leaking synth to me. From my experiences with a mech, they tend to leak the most when they're old (duh

or when someone changes to synth, but overfills, even a bit. Makes a much bigger difference in weepage than I can understand/explain, but I've seen it over and over. Overfilling usually causes it, a switch to synth doesn't. They just often happen to occur together. I'm sure it's possible there's some truth to it, and it can occasionally happen, but I've yet to see it, or talk to a professional mech who has seen it. Big topic on the 'net though

As for the angle, as Mark said, it's been debated plenty. Personally, I say the angle it's at just sitting there doesn't matter one iota. David Soine, as is typical, has, I believe, the right idea. I'll go furtther and say that the angle really only plays a significant role (if any) at the extremes of suspension travel. A shorter arm will make the joint angle more severe under full compression, and a longer arm will make the angle more severe at full extension. So, it's a tradeoff. There isn't one right answer. However, I'll say that what matters far more to me is the angle of the joint when it, and the other pivots, are most heavily loaded. This is certainly at full compression, not extension, so I prefer to bias towards a less severe angle at full compression, which implies not going too short on the arm. Thus, I chose a custom arm in between the two stock sizes. Also, being pretty short helped move me in that direction

A shorter still arm is academic only for me.

JustAnotherSquid · 04-20-2004, 08:49 AM

Quote:

Originally posted by roger albert
Overfilling usually causes it, a switch to synth doesn't.

Roger, if it's returned to the correct level, does the weeping go away, or is the seal permanently blown?

I did change out the rear drive oil myself 2000 miles ago, and filled the housing to the bottom of the fill plug threads. That is the correct fill level, no?

JustAnotherSquid · 04-20-2004, 08:52 AM

BTW, as mentioned before, the driveshaft angle doesn't change much with me on it. At least, that's what KK said when she eyeballed the bike with me off it and with me on it. I'm assuming that is because of the small amount of sag I'm running.

repoe3 · 04-20-2004, 08:55 AM

figured it was difficult to verfill the rear drive as filling to the bottom of the threads is the correct level. where else can you put it?

repoe3

BMW Atlanta · 04-20-2004, 09:16 AM

Personally, the only way I would own/ride an S is with the Short Paralever arm and minimum of Boxer Cup Sport Suspension, but having the Ohlins makes me grin ear to ear. With the Short Paralever arm and rear Ohlins totally adjusted for maximum length I have a severely jacked up rear and the bike just dives into the corners. My father who is a true GS die-hard rode my bike for the first time this weekend and couldnt believe how fast the turn in was for a BMW. I just had the rear drive off at 15k and no signs of premature U joint wear or driveshaft problems. I had a weep when I overfilled my rear drive with Redline. I have since done the 12k service and filled to the proper fill level and no seeping since. So it came and went, my inclination is also on the overfilling if you have a weep with low mileage, not due to synthetic.

Dr. Curve · 04-21-2004, 12:37 PM

Why would you run Mobil 1 in the rear drive for extended periods. Race, or track time perhaps, top end course for sure..........but why on a day to day basis. Assuming you are talking about a 20 50 weight. Just curious, seems too light and a sure way to help a seep start.......in due time. Even more reason why the new drive train as evidenced on the GS12 is going to be so nice.

JustAnotherSquid · 04-21-2004, 12:41 PM

Quote:

Originally posted by Dr. Curve
Assuming you are talking about a 20 50 weight.

That would be an incorrect assumption.

roger albert · 04-21-2004, 01:50 PM

Hey JAS and all,

Bringing it up the the threads will be the right amount if the remaining internals are bone dry, otherwise it's slightly too high and has in my experience been a problem. I like it about 1/8" below the hole and never see seepage that way. I don't think the seal should be considered 'blown' as this is not a pressure seal, so no worries there.

Jim, I don't think anyone meant 20w50 Mobil-1 as reardriveoil.
First, it would be completely the wrong formulation and would result in crappy gear wear. 2nd, it would have little to do with being too light. Motor and Gear oil use completely different measurement standards and are not comparable (on the same scale) I.e. if you could find, say, an 80w motoroil, it would be worlds more viscous than an 80/90 gear oil. I don't recall the exact difference but it's in the exteremly rough ball park of 2:1 if one actually wanted to compare gear and motor oil viscosities. I.e. that's the correct magnitude. It's not just a 10% difference, nor is it really large like 10x. I once verifed it with straight rate 40w and some 80w90 gearoil, and they flowed very very close to the same.

In any event, I'm sure we were all talking about Mobil-1 gearoil, and, as long as no one is using motoroil in their rear drive tor trans, then the fill level isn't that critical. I'd rather be 10% over and have to wipe it with a cloth once in a while, than 30% under and be dry and destroyed.

No worries folks.

Rapid Dog · 04-21-2004, 03:13 PM

I was worried sick about driveline angle during that older thread...it was right around the time I experienced the THRUM...

That's also when I noticed the clunking sound if the bike was in gear on the centerstand...!

I panicked, took it to the closest "dealer"...a mom&pop joint and ask for 5 minutes of the wrench's time.
The greezy tattooed dude came out, looked at my bike with the new Fox Shox, pointed his chewed fingernail at my bike and told me the reason my driveline was "shot" was them aftermarket shocks, "lookit the't drivlan aingle!" sez he...

I assured him that the shocks were set to the recommended length then I pointed out my friend's Prep that was parked next to me did have a lesser angle, but a shorter paralever and longer shock.
He said it was because the Prep was not on a centerstand...

I had him listen to the bike on running in gear on the centerstand.
He told me them aftermarket shocks was "wearin' out yer dravline!"...

Discouraged and feeling worse, I walked in the "showroom" to check out the other bikes...all had similar angles to mine, Rocksters, SA's, RT's...

The only thing I've done since then is put a GS paralever on and then take it off.

I'm tired of worryin' about it.
Oh, by the way, I had another wrench listen to the noise on the centerstand...
he said " Don't NEVER do that! Thay ALL do that! Yer not suppose to DO that!"

O.K., whatEVER!

Forgive me if I've told this story before...