Airhead Tech Pages


Fork Seal Replacement

Eric Seaberg   -  klaatucycles@juno.com


I've done the fork seals on my '83 R100RT (Gudrun the Red Zeppelin) twice now. It's not hard, but kind of futzy. You don't have to remove the forks, just the sliders.

What you'll need:

Here, more or less, is the procedure:

1: Put the bike up on the centerstand (duh), you probably don't need to tie the centerstand as the bike will tend to be rear-heavy and shouldn't flop down onto the fork legs. If you tend to be paranoid you can tie it or weight the back or whatever. I don't.

2: Remove the brake calipers (2 bolts each) without undoing the hoses. Set them up somewhere out of the way where they will not be dangling by their hoses, seems to me they nestle nicely against the headers and jugs. I used zip-ties once to secure them, but last time just set them up there and they were OK. This will also require removing the back fender bolts, as they also hold the brackets which hold the brake hard pipes. Be careful, there is an extra washer on this bolt that's not on the front bolts, note the proper position.

3: This would probably be a good time to loosen those big Allen head bolts on the bottom ends of the fork legs, since everything is still together. Don't take them off yet, just loosen them a bit if they are tight.

4: Undo the pinch bolts and axle bolt, pull out the axle, thus loosening the front wheel. Set it aside, taking care not to drop it as the brake rotors are somewhat fragile. An old milk crate is just the right size for the rotor to sit down inside, resting the spokes on the crate. Otherwise you can just lean it against a wall or use some bricks or blocks of wood. Since this bike is new to you I would strongly suggest you get the front wheel seals, and check/repack the bearings and replace the seals while the front end is apart. Get 3 of the seals, as the left-hand seal for the rear wheel is the same. A tire iron, like in your kit, makes a good seal remover.

5: Remove the front fender bolts and set the fender assembly aside.

5.5: On the tops of the fork sliders are black rubber wipers that are a press fit over the tops of the sliders. Pry them up gently with a screwdriver and slide them up on the fork leg. They should hold their position. I've been told that there are felts inside these that should be replaced, but I haven't done it so can't advise. My wipers are gone, discarded when I installed accordian fork gaiters in the operation Earle helped with. If you have fork gaiters you won't have them, and vice versa.

5.75: If you have a fork brace remove it now. Mine is a tight fit on the top of my sliders, it needs a bit of gentle prying on the seam to get it off. I've heard this is a worthwhile addition to the Airheads, and I have to say my front end feels solid with the Telefix brace on. Not that I have any others to compare with, as my Gudrun is the only Beemer I've ever ridden.

6: Go up top and remove the rubber caps on top of the fork legs. There is an Allen bolt in the center of the fork caps, remove it and set aside. This will open the top of the fork legs and let the old oil drain out more quickly and thoroughly. If you have a ball-end Allen wrench it might be easier to get at these bolts, since stuff like handlebars can get in the way. Try moving the bars to one side or another to increase working room.

7: Put a drain pan under the lower ends of the fork legs. Remove one of the large Allen bolts. Oil will come out, and the fork slider will be loose from the rest of the fork. Once the oil is gone you can slide the slider off the leg. I'd do one side at a time.

8: You'll see the seal in the top of the slider. You can pop it out with the tire iron. Check and clean the area the seal lives in, then press in the new seal, using a socket of the appropriate size, or a piece of wood, or something that won't deform the lip. Take your time and be gentle, it may take a couple of tries to get it going. Seat it so it's just below the top of the slider.

9: Run your hand along the fork tube (the shiny part that's still attached to the bike), perhaps with a piece of cloth, checking for rough spots. These can tear up your newly installed seal. If you find them they can be taken down with very very fine sandpaper or crocus cloth. I've not had to do this, so I can't really advise beyond this that others have told me. Mine have been smooth, but then again my bike only has 25K miles (5K mine in past 17 months).

10: Put a little oil on the new seal and slide the slider up onto the fork leg. You'll most likely have to rotate the slider slightly to get the seal up over the end of the leg. Take care that the lip of the seal doesn't get folded over when you put it on. If it does you may be able to unfold it by sliding and rotating the slider along the leg. You don't want the seal folded over. When you have the slider on the leg and the seal looks good, slide it up all the way and put that big Allen bolt back in. I'd use a new crush washer on the bolt, but that's up to you. Some folks want new washers, some don't. I do. Slide the wiper back down and work it onto the top of the slider. Should not take a whole lot of effort. (note-if you have the fork brace, you have to do the wipers after reinstalling the brace, after doing both seals)

11: Repeat for other leg.

12: When both legs are done reassemble. I'd do the fork brace, fender, then the wheel, followed by the brake calipers. Your Haynes manual should have the torque values, or you can just snug them tight. If you have the fork brace, be careful of the bolts, they snap pretty easily, or at least mine did.

13: Some folks recommend that you not tighten everything down until you bounce the forks on the ground, with wheel and all in place. I haven't done this, but that's up to you.

14: Using some sort of funnel arrangement, put new fork oil in thru the holes in the fork caps. Check the manual for the amounts, Gudrun takes 230cc. Put the Allen bolts back in, followed by the rubber caps.

15: Go for a ride. Check for leaks.

Disclaimer-I am not a professional mechanic and have no training on motorcycle repairs. I'm an addressing data geek for the US Postal Service who's too cheap to pay somebody else to fix his bike. (kid in private school, you know) I was a pro wrench on cars back in the early 80s, but that was a long time ago. I don't know your abilities or skills, and my description of this stuff should not substitute for your own good judgement. If you see something on your bike that contravenes what I've said, well, deal with it.

I love my RT, she's exactly what I need in a motorcycle. I hope you enjoy yours.

Peace,
Eric S Germantown TN


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Last Update: 11 September 2010