Final drive

[Namor]

forgive my ignorance in advance. I know how bikes work, but am excellently unfamiliar with the final drive on the BMW. my father let his 98 rt1100 garage sit for the last 4 or 5 months.

the dust cover over where the rear wheel mounts. between the swing arm? and rear hub? is leaking. what i would guess, is it is transmition fluid. I pulled the boot and about 3 ounces of oil came out.

can someone point me in a direction here? i own a duc and know how to work on it, so i figure this BMW isn't too much.

since it does not belong to me I don't have a repair manual. can someone guide me to picks, etc. for some knowledge.

and how big is that alen screw? 18-22mm or more?

[snod]

Quick answer, don't ride it until you have the leak fixed and the rear drive refilled with grease! The transmission and rear drive both use 90W140 gear grease. The bellows type seal that you took loose is one of two seals on the rear drive. The other one is "difficult" to get to. Replacing the bellows requires removing the rear drive. You need to do a little reasearch if that is what is required. The 12mm allen head that your are refering to holds the rear drive on the swing arm. I wouldn't start the job without either a Haynes or Clymer manual to guide you. The rear drive has to stay lubricated!. DO NOT ride until you solve this problem!

[Paul Mihalka]

I don't think the situation is quite as critical as Mike paints it. With the little oil you found in the boot, there is still a reasonable amount left in the rear drive. The likely defect is a bad oil seal on the input shaft of the rear drive. If you are a good home mechanic it can be done by you. Some tools and a good service manual are a must. The correct recommended oil is SAE 80/90 G5. A 75/90 or 75/140 syntetic will do very nicely.

[Ken H.]

Some seepage in that area is rather common. You could replace the rear drive seal, but the problem may return.

 

My suggestion, clean it all up, and check the level in the final drive, add if necessary. Ride the bike for 3-5K and check the boot again. If all you are seeing is a small amount, don't sweat it. OTOH if the boot is flooded, new seals are in order.

[Stan Walker]

My '02 RT was always weeping at the boot, not a lot, but enough to make it look dirty. At 40,000 miles or so I drained the boot. 30,000 miles later I checked again and there was almost nothing in the boot.

 

Sometimes they self-heal.

 

Stan

[smiller]

What the last three guys said, all of which I usually agree with so they must know their stuff. If you are only seeing the 'usual' few teaspoons of oil every few thousand miles then it's more of an aesthetic concern than anything else since you won't lose enough oil between scheduled changes to matter. If you have an extended warranty or something might as well get it fixed but otherwise I'd ride to your heart's content and just keep an eye on it.

[Ken H.]

all of which I usually agree with so they must know their stuff.

LOL! Now there's a ringing endorsement you can take to the bank!

 

Cheers!

[Stan Walker]

Another comment.

 

On my '96 RT the boot always stayed pristine clean. Never a trace of seepage. I naturally assumed that it had a good seal in the final drive. With 71K on the bike I opened the boot for the first time and found lots of oil, much to my surprise.

 

The early 1100 bikes used screw clamps on the boot, not the cable ties used on the later bikes. This can make a much tighter seal and prevent the external mess.

 

Stan

[smiller]

On my '96 RT the boot always stayed pristine clean. Never a trace of seepage. I naturally assumed that it had a good seal in the final drive. With 71K on the bike I opened the boot for the first time and found lots of oil, much to my surprise.

 

The early 1100 bikes used screw clamps on the boot, not the cable ties used on the later bikes. This can make a much tighter seal and prevent the external mess.

I had the same experience... thought that I was somehow immune to the leaking final drive input seal syndrome until I had reason to crack the boot open and find out otherwise (my bike being equipped with the metal bands rather than the cable ties.) Maybe a more cost-effective solution for a seeping FD input seal would just be a couple of metal band clamps off of the older bikes?

[Stan Walker]

Maybe a more cost-effective solution for a seeping FD input seal would just be a couple of metal band clamps off of the older bikes?

 

Sadly, they don't fit, too big.

 

Stan

[cgdR]

Sometimes they self-heal.

Stan

I agree! Sometimes an oil flush will stop the leak. I have read somebody's claim that switching from synthetic to mineral would fix most leaks. Mine stopped leaking after I did the opposite, so I don't think synthetics have anything to do with it. Come to think of it, maybe the oil flush didn't have anything to do with the self-healing either!

[smiller]

Maybe a more cost-effective solution for a seeping FD input seal would just be a couple of metal band clamps off of the older bikes?

 

Sadly, they don't fit, too big.

 

Really? That's interesting. I thought that there were no exterior changes to the swingarm or final drive in the 1100s until the 1150 came out so why would the diameter of either end of the boot change?

[Stan Walker]

That's interesting. I thought that there were no exterior changes to the swingarm or final drive in the 1100s until the 1150 came out so why would the diameter of either end of the boot change?

 

Well, I may have been hasty, let me clarify. The metal rings from an early 1100 do not fit my 1150. That I know for sure.

 

Looking at a parts list for the R1100RT I only see one swingarm and one rubber boot listed so I suspect you are correct in that all 1100's use the same size straps.

 

Stan

[smiller]

Well, I may have been hasty, let me clarify. The metal rings from an early 1100 do not fit my 1150. That I know for sure.

 

Ah, OK.

 

I can certainly see how the boot would not be oil tight with just a tie-wrap on there. I hope BMW saved a whole nickel with that one.

[Clive Liddell]

My 2001 R1100RT (or 2000 USA) had one metal & one tie wrap - got the metal one to replace the wrap and started "filling" the final drive to just below bottom of threads (One litre of 90 GL5 fills final drive and g/box). There's been no sign of a leak externally for the last 50000 km (now on 65000km).

 

The '96 R at 70kkm now has never leaked (It came with two metal hose clamps).