Leaking Fork Seal (K75S)

[ok75]

My 1994 K75S has a leaking fork seal. It was minor enough that I ignored it for a good while, but now it's time to address it.

A couple of questions:

Should I drain and refill the fork oil before doing any sort of rebuilding?

Is there a particular fork oil any of you recommend? Also, is there a preferred fork seal kit?

What does the job entail? Do the forks themselves have to be disassembled? Or is it just a matter of draining the old oil, removing the forks from the bike, popping off and replacing the old seals, putting the forks back on the bike, and refilling with new oil?

Thanks!

[captrusty]

Hi OK       

You just saved me the trouble of posting the exact same question I have a k1100lt exact same problem let it go to long now its a pretty good leak, I hope you dont mind if I ask a additional question, whats risk by leaving it leaking while riding other than the mess?

[Chaos]

It's pretty easy to put in a new seal.  Remove wheel, drain fork oil, unscrew allen head at bottom of slider (#12)  Sliders come off, pop off old seal and pop on new one.  I'd replace the rubber cups that cover the seal too.  May be easier to remove fork brace so you can do them one at a time.  I use 5 wt oil, I believe that's what the manual says.  Mine leaked for the last couple months before I got around to fixing them.  Don't think it hurts if they leak as long as there is still enough oil in the fork. (only way to tell is to drain and refill, though)  Illustration courtesy of MAXBMW.

[frankenduck]

New Lieberry Topic: Fork Maintenance                  

[ok75]

Thanks for the pointers, guys.

My K75S is a 1994 . . . After doing a little more digging, it looks like bikes produced after 8/91 have different shocks and slipping off the sliders from the bottom is not an option. Apparently the forks have to come off the bike entirely and the seals need to be removed from the top of the fork. Is this correct? Anyone have any tips for later model K bike fork seal replacement? 

 

[Phil Marvin]

Hi, OK,
    I've done it a number of times on various K75's, all '94 or '95 models.  First, buy seals from the dealer.  I don't have first hand experience with aftermarket seals, but I've heard of leaking problems with them.  Second, I recommend you install fork gaiters.  You can use genuine BMW gaiters (from /6 or /7 bikes) at around $30 each (including shipping) or go to your local auto parts store and buy 2 Rancho 1952 boots for around $15 total.  
-Remove the wheel, tying the calipers out of the way so the line is not kinked.
-Remove the allen bolt at the bottom of the fork.  
-Remove the fork from the brace and the triple clamp.  Remove from bike.
-Remove the rubber cover from the top of the slider.  Slide it off from the top.
-The seal is held in position by a circlip.  Remove the circlip (can be a bitch to remove)
-The slider cannot be pulled away from the fork tube.  The bushing is bigger than the seal opening.  Sharply pull the slider against the tube, like you would a slide hammer.  The second or third try, the seal will come out and the tube can be removed from the slider.  Remove the seal from the top.
-Clean the tube.  Feel all around the area swept by the seal for any burrs or irregularities.  Remove them with a fine whetstone.
-Fit the tube back into the slider.  Reattach the boltup through the bottom of the slider, using a new seal (gasket).  You may want ti wait to tighten it until the fork is reattached to the triple clamp and the fork brace.
-Seal must now be driven into place.  For a tool I used a plastic pipe union for 1-1/2" pipe.  I removed the inside ridge with a curved and, later, a rat tail file.  It slid down the tube to bear on the seal.  I put a block of wood on the seal and hit the wood block with a hammer - a couple of blows, move 180 degrees, a couple of blows, move 90 degrees, a couple of blows, etc., etc.  The seal is in place when you can see (or feel with a scribe or small screwdriver) the groove for the circlip.  Work the circlip back into position.  Slide the rubber cover down the tube and into position.  Slide the gaiter down the tube , but don't put the end onto the slider yet - you still have to attach the slider to the fork brace.
-Remount the tube into the triple clamp.  
-Repeat above for the other side.
-Reattach the fork brace, but do not tighten bolts.
-Reattach calipers
-Place axle into sliders.  Tighten fork brace. Remove axle.  Pull gaiters over top of sliders.  If Rancho gaiters, heat a nail and punch/melt a small hole in the back of the gaiter so it doesn't blow out as the slider goes up and down.  If you want, you can put hose clamps at the top and bottom of the gaiters.  I don't use the hose clamps on my bikes.
-Tighten bottom bolts in sliders.
-Remount wheel.  If it seems to be slightly cocked or it rubs, you may need to loosen the fork brace, adjust and retighten.
-Refill forks with oil.  I use BMW 7.5 wt, 420cc per side.
Ride

I hope I've covered everything.  If you have questions, ask.


Parts I would have on hand are new fill gaskets, new gaskets for the bottom slider bolt, new seals, new gaskets for the fork drain plug if you drain using that (not necessary, really, as you are removing the bottom bolt), and 2 gaiters. 

[mystic red]

I change the seals without removing the forks. Just me............no problems.

[Skeezer]

I posted this thread on another forum You may find it interesting.

I posted a thread amonth or 2 ago about a product called SEAL MATE. Now before you think this is an unrelated topic hear me out.
I returned from a 2000 km road trip this last Sept .There was a unschedualed Gravel ( Fire Road ) Section that I'm sure had a bad effect on my fork seals. They sarted leaking soon after . As I am new to BMW's I started google'n and came across a product called Seal Mate. It s a small inexpence tool that you use to clean out the crud , Road Grime, Bug Guts and crap out of your fork seal.
I was sceptical even after watching their video and saught advise on this and other Brick forum's . the common responce was thers no way it would work as good as the video claims. The other common responce was that to make your seals last you need to install gaiters to keep the above mentioned crap out of the seals.
My seal was leaking so bad it was spraying back on the cowl and even the gas tank. There was visible drops of oil on the back of the Fork and Dust seal. I mention this so you understand this was a sunstantial leak.
So I ordered the gaiters and had planned on getting the seals locally
but I was still intrigued but the Seal Mate solution.

The Seal Mate was so cheap on ebay I brook down and order a couple. Total $15 Cdn including postage. I used the seal mate and pumped the forks 20-30 times in the garage and there was little or no oil making it past the seal and dust cover. So a road test was required( Normally no excuse needed for me to go on a bike ride) Keep in mind it is Jan 2 and I live near Calgary AB Canada. Todays temp was about +8 C so around +40 F.

160 KM later and No Leaky Seal. No the only problem is I still need to put the Gaiters on which will require the forks to be removed . So I still may install the seals.

Anyway long story but the seals do work in colder temps.

[frankenduck]

Dirt can get trapped in your fork seals.  An old motorcycle mechanic's trick is to use a thin feeler gauge which essentially does the same thing as a seal mate.

[Rick G]

One thing to keep in mind is that when your seals leak some of the oil will go back into the radiator fins and as a result collect dust and dirt and clog the radiator stopping air flow.
This has happened twice, not with any great problem but it could cause an overheating problem at a later time.
I took the radiator off and did a coolant change at the same time, sprayed degreaser into the fins and hosed out about 10 minutes later. Did this 3 times and the third time it was all clean with heaps of crud where I hosed it.
I could barely see through the fins before I cleaned it.
I also have found from experience to use OEM seals. Some of the aftermarket ones are just plain crap and others are really bad.

[Supershooter]

I'm a visual learner, is there a well done video showing the process on a K100? This is a great start for me to get started. I'd prefer to replace the seals with the least amount of disassembly as possible.
Supershooter