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Fork Seal Replacement Comments

  • Thread starter Thread starter kalessin
  • Start date Start date
K

kalessin

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I just replaced my fork seals and fork oil. My bike handles SO much better now!

The old ones were replaced by a mechanic a few years ago, they have the brand name Leak-Proof. They should be named "Leak-for-Sure", the rubber isn't a great quality, the design is generic (added a washer over the seal to my setup, which we ended up discarding), and it was easy to see how they'd started leaking within six months of being installed and slowly getting worse over time. They're *awful*.

I ordered genuine Suzuki fork seals from BikeBandit. They're works of art compared to the Leak-Proof seals. Under normal circumstances, you only need the seals themselves, and new fork oil.

I used Maxima 20 weight fork oil, next time I'll use 15 weight. The actual viscosities and oil quality *are not* the same between fork oil makers; I'll post the chart if I find it. ATF is apparently similarly uncontrolled.

Set aside some time for the repair. I'd say at least four hours if you're slow like me. Get a friend to help if you can, four hands and an extra set of eyes make many things easier.

I held the front up with a big cinderblock and a piece of two-by-four under the exhaust headers under the engine. Remove the front brake calipers, I held them up with a bungee cord over the front end of the tank so they didn't hang by the brake lines, which is bad. Remove the front fender, front wheel, then remove the forks. With my particular bike, there's an air inlet on the top of each fork tube. I let the air out.

Have an oil catch pan nearby. Remove the dust covers on the top of the outer fork tubes. Remove the top of the fork by unscrewing it. We found a wrench that would get around the straight sides of the air-inlet fork caps (over a cloth so as not to mar the paint). Remove the cap being careful to have the oil pan nearby, because right when you get the cap off, you're going to want to get all the fork oil into the pan -- right when it releases the cap will try to go flying. Pour out all the old fork oil, pump the tubes a few times to work it out. Remove the snap ring over the seal.

Clymer's says you have to disassemble the fork tubes to take the seals out. They're wrong. Get a pick-and-hook set from Sears ($7). Push a pick into the seal (not all the way through!) and wedge it out. Don't throw it away, because you'll use it to drive the new seal into place. On the 37mm forks on my 1100GL, a piece of PVC (i forget the size..) fit perfectly, so we took a piece about 2' long and slid it over the fork inner tube and hit it with a mini-sledgehammer to drive the old seal on top of the new seal to get the new seal seated. (Make sure you clean the PVC pipe of dust, shavings, etc!) We had to go the pick-and-hook route because one of the drain bolts at the bottom (which also holds the damper rod in place) stripped out when we were trying to remove it... doh!

The Clymer manual has a table of fork oil measurements that include how many cc's should go in, or the better method we found, of how far from the top of the inner tube with the tube pushed all the way down. First pour in enough oil to cover the damping rod down in the bottom of the inner fork tube. Then pump the fork for a while, to get air out of the system. Then slowly add oil until it reaches the measured distance down the tube. We used the beginning of a regular 25' tape measure for this, just use it like a dipstick.

My bike handles MUCH better now, though the forks are a little stiff. I haven't added any air to the forks just yet, but I'll try and see what happens.
 
Thanks for the tips. I have one seal replaced and will be picking out the other.

Allen
 
Great post. I'll be doing this next weekend sometime, hopefully.
 
Setting the correct fork oil LEVEL is important, and it's critically important that the level is the same within 1mm in both fork legs. The actual AMOUNT of oil is irrelevant, and if you're installing better springs from Progressive or similar, the oil amount will be incorrect anyway because the wire the springs are made of is thicker. Don't just dump in some oil from a baby bottle and button it up.

Your Clymer or Haynes manual will have a photo of a gadget you can make with a large syringe, some plastic tubing, and a piece of coat hanger wire that works beautifully to set perfect fork oil levels every time.

Basically, you attach the hose to the syringe (you can get a "Mix Master" almost anywhere -- it's a large syringe intended to precisely measure two stroke oil.) You then attach the tubing along the wire. Measure the correct fork oil level from a consistent point (I used a large Zip tie to mark the top of the tubing where it rests against the top of the fork tube) then clip a hole in the tubing at the correct point, leaving an inch or so of tubing below the hole.

Dump some fork oil in, making sure you have a little more than needed, then slurp out the excess with your fancy new fork oil level tool. Easy and consistent. If the forks are still on the bike, you may need to compensate a few mm for the angle of the fluid surface within the fork, and you'll need to be consistent about whcih side of the fork tube you rest the tool on.
 
One other bit of fork oil trivia:

You can use this thick yellowish goop called "motor honey" to mix with fork oil and fine-tune the viscosity. Motor honey is intended to be dumped into old junky car engines to help them wheeze along a bit longer (NEVER put it in a motorcycle engine - it'll kill the clutch), so it's a good friction reducer and it also serves to make the oil thicker and "stickier".

In the 70,000 mile forks on my GS850, I used a mixture of 90% 15W fork oil and 10% motor honey, and it works beautifully. The fork action is noticeably smoother with less stiction, and the thicker combination fluid gives much better damping action than 15W fork oil alone. I poured out 100cc from the liter bottle of fork oil, put in 100cc of motor honey, and shook well.

You'll have to experiment depending on how worn out your forks are, your riding style, and your weight.
 
They're probably stiff due to the fork oil you used (15W). What does the manual say to use? I don't have the stock forks anymore since I switched to GSXR1100 units, but I use 5W in them and in my other bikes (dirt and street).
 
The manual didn't say anything... I thought I'd go heavier, and change to lighter if I thought it was too heavy. I do tend to like a stiffer suspension anyway.
 
hungryman said:
They're probably stiff due to the fork oil you used (15W). What does the manual say to use? I don't have the stock forks anymore since I switched to GSXR1100 units, but I use 5W in them and in my other bikes (dirt and street).
Click to expand...


The manual's oil recommendations (often ATF and/or 10W30 motor oil, I think) were written 25 years ago based on factory fresh suspension and 130 pound Japanese test riders.

The damping holes wear over the miles, and some of us are big ol' corn-fed Amurrikin boys, so significantly more damping than stock is desperately needed.

My bike's suspension is set up for me, a large, aggressive rider -- a lighter or slower person would definitely need to decrease preload at both ends and change to a lighter fork oil.

Fortunately, forks aren't all that demanding on oils -- nothing gets all that hot -- so you can freely mix-n-match various hydrocarbons to get the result that makes you happy, including ATF (roughly 7W oil with lots of detergents), various engine oils, motor honey, STP, mouse milk, and even real live fork oil. Foaming could potentially be a problem, so I try to stick with mostly fork oil.

You may have to experiment to find the setup you and your bike like best, but you can generally make a dramatic improvement in fork damping with the right elixir in the forks.

My magic potion of 90% 15W fork oil and 10% motor honey is stiffer than what 98% of GS riders will need, but it's what my heavy, high mileage bike, heavy body, and aggressive riding style demand. (I'm also using so much preload that installing the fork caps is an epic battle. But dang, they work great.)

Most modern forks do use very light oils, like the 5W you mention.
 
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