Leaking Fork Seal

[worker1]

Hi all,

My left fork seal is leaking on my 2015 FZ-07.

I was going to buy a fork seal kit (4EB-W003B-00-00) and have the mechanic look at it when I'm there in a couple weeks.

But then I was reading that people used a seal cleaning tool to push the debris away from the fork seal.

So my question is, a lot of fork oil came out. Won't we need to refill it somehow? My forks have a cartridge installed and are filled up to a specific level from the top. If oil leaked out it seems like we'll need to put it back in, right?

Anyone have any suggestions on what to try first and how to approach this?

Thank you!

 

[Pursuvant]

15 minutes ago, worker1 said:

...My forks have a cartridge installed and are filled up to a specific level from the top. If oil leaked out it seems like we'll need to put it back in...

Did you have the cartridge suspension installed and/or what cartridges? How long has the forks gone without service? Do you have fork gaitors?

You are going to need to open up the forks to see what cartridge you have, and what springs (they should be stamped). Once you have identified the suspension you can look up what oil to go with your suspension and your weight, and service procedure.

Without gaitors, your fork oil is probably a dead mosquitoes swamp. You also want to have a look at the sliders / spindles for wear, and cartridge has its own service procedure.

Look at this as an opportunity to service the forks and tune suspension for your preferences/weight) riding style. 

[worker1]

I probably only have about 2500 miles since serving my shocks, 3 1/2 years ago

The cartridges are Cogent Dynamics DDC FZ07

We reused the OEM springs

Fork fluid is 85/150-5w Spectro

Thanks for the suggestions, we'll check everything out.

[Lone Wolf]

4 hours ago, worker1 said:

... I was reading that people used a seal cleaning tool to push the debris away from the fork seal.

... a lot of fork oil came out. Won't we need to refill it somehow?

One of my bikes is an old Honda 750 that started to leak fork oil about 3 years ago.

I used this to get between the seal and the metal fork tube, and was amazed at the grit I was able to pull out. It stopped the leak, then it started up again. I ended up getting the "Seal Doctor" which was easier to slip into the tight area and pull out dirt. You can also cut a similar tool out of a plastic jug, such as old oil container, water bottle, etc.

That worked OK for a couple years, then when it started leaking again I pulled the forks apart and replaced the seals (mine were 30 years old). 

Only one seal was leaking, but when I dumped oil out both forks they were about the same volume of oil. 

You see this big mess and think it is a lot of oil, but it isn't. No you don't need to add oil (right now). Wait until you get around to doing the seals. The article you linked to has comments of people that never needed to replace their seals once they cleaned the junk out. It is a common issue with dirt bikes.

When you think about it, some bikes have compression damping only on one fork leg, rebound on the other leg. The axle joins the 2 legs and the stresses from the difference in damping would be much more than what you are dealing with if there is a slight difference in oil level between your fork legs.

Edited July 16, 2023 by Lone Wolf

[worker1]

2 hours ago, Lone Wolf said:

...

 

Thanks, I ordered a Seal Doctor. Your explanation about the volume of oil was very helpful.

[Impulse.Movement]

13 hours ago, Lone Wolf said:

One of my bikes is an old Honda 750 that started to leak fork oil about 3 years ago.

I used this to get between the seal and the metal fork tube, and was amazed at the grit I was able to pull out. It stopped the leak, then it started up again. I ended up getting the "Seal Doctor" which was easier to slip into the tight area and pull out dirt. You can also cut a similar tool out of a plastic jug, such as old oil container, water bottle, etc.

That worked OK for a couple years, then when it started leaking again I pulled the forks apart and replaced the seals (mine were 30 years old). 

Only one seal was leaking, but when I dumped oil out both forks they were about the same volume of oil. 

You see this big mess and think it is a lot of oil, but it isn't. No you don't need to add oil (right now). Wait until you get around to doing the seals. The article you linked to has comments of people that never needed to replace their seals once they cleaned the junk out. It is a common issue with dirt bikes.

When you think about it, some bikes have compression damping only on one fork leg, rebound on the other leg. The axle joins the 2 legs and the stresses from the difference in damping would be much more than what you are dealing with if there is a slight difference in oil level between your fork legs.

I would agree that a little oil difference of a couple ml isn’t going to cause a huge issue but if it’s leaking I would recommend fixing it immediately. It’s is true many bikes only use one fork for compression and the other for rebound, but that’s usually in upside down forks where the forks legs are strong enough to handle the difference in force. The axle on upside down forks is also substantially thicker to handle the difference in force. Bike with thin forks do not like the forks to be unbalanced  with force and can cause random speed wobbles. 
Loosing damping also leads to a less predictable bike as the energy from the extra oscillation can throw you off a line.

performance and handling aside, if any oil gets on your brakes you are going to loose most of your available braking force. It can happen at the most inconvenient of times sending you hurling into corner without warning. 
I was hesitant to mess with my forks when I first got a bike but was glad I did. You will learn a lot and have options to improve your handling. 

[shinyribs]

Nobody take this personal, it's just my opinion, but I believe the myth of unbalanced forks causing handling issues is entirely impossible. 

 

For this to happen the front axle would have to be either bending or flexing it's mountings. The cast aluminum wheel hub and axle mounts on the forks would simply explode under this type of pressure. It physically can't endure those forces. 

 

Once the axle is in and tightened, those forks are locked together and will move in unison. 

Edited July 16, 2023 by shinyribs

[Lone Wolf]

4 hours ago, Impulse.Movement said:

... if any oil gets on your brakes you are going to loose most of your available braking force.

Agreed. I did get some oil on brake shoes, and soaking in Acetone, brake cleaner, etc. did not help once they were contaminated.

Cleaning the rotor (scotch brite pad, Acetone) and new pads was required.

[Impulse.Movement]

2 hours ago, shinyribs said:

Nobody take this personal, it's just my opinion, but I believe the myth of unbalanced forks causing handling issues is entirely impossible. 

 

For this to happen the front axle would have to be either bending or flexing it's mountings. The cast aluminum wheel hub and axle mounts on the forks would simply explode under this type of pressure. It physically can't endure those forces. 

 

Once the axle is in and tightened, those forks are locked together and will move in unison. 

I defiantly agree that a slight imbalance is not a huge issue and unless you are racing at the highest level you would Never know. 

I can however confirm that huge imbalances like missing all the oil out of one side will give you weird shakes especially if the other side is fully functioning. 

Im currently testing various models of suspension with an after market upgrade that changes damping characteristics. If I don't balance the oil volume and damping of the parts, things get a little shaky at times. I have also forgotten to fill just one fork with oil and the result are not good  

On mid size bikes like the mt07 the effect appears to be very minimal but on a bike with thiner forks and axles like a ninja 250 the effect is more significant. 

Think about how much even a few grams of weight on the wheels can make a huge difference with vibrations/shake. The forks are actually much more bendy than you would imagine them to be. 

[twf]

5 hours ago, shinyribs said:

Nobody take this personal, it's just my opinion, but I believe the myth of unbalanced forks causing handling issues is entirely impossible. 

 

For this to happen the front axle would have to be either bending or flexing it's mountings. The cast aluminum wheel hub and axle mounts on the forks would simply explode under this type of pressure. It physically can't endure those forces. 

 

Once the axle is in and tightened, those forks are locked together and will move in unison. 

Yep. There are bikes out there that have no spring or no damping at all in one fork leg and work just like others.

Once everything is torqued it is single unit. 

[Impulse.Movement]

18 hours ago, twf said:

Yep. There are bikes out there that have no spring or no damping at all in one fork leg and work just like others.

Once everything is torqued it is single unit. 

Many of those bikes also have a brace that sits at the top of lower tubes. Some bikes have that brace in the wheel fender. If a bike has been designed to only use one fork it will have other ways keep the fork from flexing/moving askew. 
A really wild example of this would be the MTB brand lefty Lefty shock on YouTube

Edited July 17, 2023 by Impulse.Movement

[cornerslider]

I have had repeated success with the Motion Pro "seal-mate" on multiple bikes. It was always kind of a band-aid to get me through a riding season. I hated paying $5 for a piece of plastic, but it did buy me some time to get through the riding season (I live in MN)... As far as oil loss goes- most leaking fork seals look MUCH worse than they are. Unless it is leaking onto the brake pads, I wouldn't even worry about oil loss until the off season -

[twf]

3 hours ago, Impulse.Movement said:

Many of those bikes also have a brace that sits at the top of lower tubes. Some bikes have that brace in the wheel fender. If a bike has been designed to only use one fork it will have other ways keep the fork from flexing/moving askew. 
A really wild example of this would be the MTB brand lefty Lefty shock on YouTube

Not necessary. Braces are for side flex because tubes them self are weak part.

Funny you mention lefty, I have cannonade lefty. One of the first ones made.  

[Impulse.Movement]

4 hours ago, twf said:

Not necessary. Braces are for side flex because tubes them self are weak part.

Funny you mention lefty, I have cannonade lefty. One of the first ones made.  

I hope you’re right about that sir. I know my 250 has a weird shake when the levels are off but it could be from something else and maybe it just comes out when there isn’t as much damping. 

If what you say is true I should be able to use a single fork emulator to modify fork performance. I’ll be testing you theory… 
Really fascinating design for sure. 

Ps the lefty is awesome  

[twf]

Gold wing had one damper rod leg and other cartridge. 

Aprilia 250 had damping in one leg spring in other.

Plenty of new cartridges out there where one leg does compression and other rebound. Each leg is single function for damping. 

Some of this bikes had handling issues but it was not because things were not exactly same in both legs. Issue is setup was wrong. Reason why we change them. Isn't that why you making emulators, damper rod simply does not work good enough.

[Impulse.Movement]

10 hours ago, twf said:

Gold wing had one damper rod leg and other cartridge. 

Aprilia 250 had damping in one leg spring in other.

Plenty of new cartridges out there where one leg does compression and other rebound. Each leg is single function for damping. 

Some of this bikes had handling issues but it was not because things were not exactly same in both legs. Issue is setup was wrong. Reason why we change them. Isn't that why you making emulators, damper rod simply does not work good enough.

Thanks for bringing those examples to the table! Definitely agree that a damper rod is not sufficient for real handling performance. I’m going to be tearing the front end of the 250 apart now to find the problem. Maybe head bearings need replacement or cheep tire is just wonky… 

on another note, dose anyone know how the different oils perform over time? Anyone notice more swelling of seals with one brand over another? 
 

[shinyribs]

My 2016 FZ 09 has one active fork leg. Both are sprung, but only one has damping. The oil in the non-danped leg does nothing but lubricate. 

The forks tubes only locate the wheel. Like an A arm on a car.

What's inside the fork controls damping. Like a shock absorber on a car. 

If you're experiencing a wobble then something is oscillating, but it's not low oil levels causing the forks to move independently of each other. 

Some bikes are more sensitive to road conditions or tire designs than others. I love how Conti Motion tire handle on every bike I put them on, but my FZ didn't like them. Something about that particular chassis/geometry, the bars would shake if I let go. It did it with two different Conti Motion fronts, and never did it with any other tires. Sometimes when you have a wobble it's difficult to find what's causing, so keep your eyes and your mind open to new ideas.