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Front fork seal leaking
- Thread starter bobgerman
- Start date
Using the “Tag Cloud” there are quite a few threads on the subject.
Here is one-
https://forums.bmwmoa.org/showthread.php?95743-Leaking-Fork-Seals-and-Warranty
OM
Here is one-
https://forums.bmwmoa.org/showthread.php?95743-Leaking-Fork-Seals-and-Warranty
OM
Boxflyer
Active member
I had a weeping RH fork seal on my 2016RT from the middle of 2019 and changed it out the following winter. (77k to date)
The OEM part number is 31428532723 and is a set of parts for 2 fork tubes.
The service manual is nice and clear as to the process and it only took about 2hrs from start to finish with the bike up on my lift.
A tiny quantity of oil can look like a pretty large leak, it's deceiving how much dirt just a small amount can attract.
I tried cleaning up the original seal to find a cut or some crud on the lips of the seal, but didn't see anything unusual.
I used a universal seal puller to carefully remove the old seal. I'd recommend placing some kind of pad or protection against the edge of the fork to prevent leaving any marks or nicks in the metal.
The next picture shows the black coated surface that takes all the force on the top end of the fork tube before replacing the seals. There is a similar thrust surface in the lower end of the fork as well, but I didn't replace anything other than the top seal and wiper.
Next I poured out the fork oil into a graduated cup and it was about 500ml. The manual calls for 545ml as well as measuring it during reassembly to be 90 +/-2mm from the top of the lower fork tube. The original fork oil was not contaminated/dirty, so I topped up the volume to 545ml in my pitcher and poured it in the lower tube. With this new volume, it measured from the upper lip of the tube about 75mm, so I kept pouring it out until the measurement was at 90mm...which just about equaled the 45ml I added in the first place...so almost no measurable loss of fork oil. A couple of drops of oil can look like a mess over time.
The oil in the lower slider leg is not going thru any orifices or shim stacks, so the weight of the oil is not very important…it's just there to lubricate the stanchions on the sliding guide elements in the leg…so 10W fork oil is fine…use 7.5W if that's all you have.
I used the Motion Pro 08-0551 bearing driver to drive the lower seal squarely to the spacer ring in the lower fork. It only took about 4 light hits with a hammer to drive it home. The new OEM seal comes pre lubed and the wiper seal just presses into the top of the lower fork tube.
Sliding the upper shiny tube into the new seals is simple and needs no tools or special procedure with the vent screw still out. When the upper fork slider is up in the top fork bracket next to the handle bar, you install a new top nut holding the slider to a torque of 40Nm, then you replace the vent screw with a new O ring.
Since I only was working on the RH fork, the LH fork tube is the alignment reference with the Quick Release Axle shaft between the 2 for setting the position in the lower clamp.
It instructions were VERY specific about torquing the 2 main pinch bolts in alternating fashion 3 times each to 19Nm.
There was never any degraded performance with the annoying small oil leak on this fork tube, but I was tired of seeing some oil and not knowing if it was a drop or a more serious leak.
This was a couple of hours well spent, I'd had enough of wiping down the fork at the end of each day of riding to see if it was getting worse...because I knew it was not going to get better on it's own.
Hope this is what you were looking for.
The OEM part number is 31428532723 and is a set of parts for 2 fork tubes.
The service manual is nice and clear as to the process and it only took about 2hrs from start to finish with the bike up on my lift.
A tiny quantity of oil can look like a pretty large leak, it's deceiving how much dirt just a small amount can attract.
I tried cleaning up the original seal to find a cut or some crud on the lips of the seal, but didn't see anything unusual.
I used a universal seal puller to carefully remove the old seal. I'd recommend placing some kind of pad or protection against the edge of the fork to prevent leaving any marks or nicks in the metal.
The next picture shows the black coated surface that takes all the force on the top end of the fork tube before replacing the seals. There is a similar thrust surface in the lower end of the fork as well, but I didn't replace anything other than the top seal and wiper.
Next I poured out the fork oil into a graduated cup and it was about 500ml. The manual calls for 545ml as well as measuring it during reassembly to be 90 +/-2mm from the top of the lower fork tube. The original fork oil was not contaminated/dirty, so I topped up the volume to 545ml in my pitcher and poured it in the lower tube. With this new volume, it measured from the upper lip of the tube about 75mm, so I kept pouring it out until the measurement was at 90mm...which just about equaled the 45ml I added in the first place...so almost no measurable loss of fork oil. A couple of drops of oil can look like a mess over time.
The oil in the lower slider leg is not going thru any orifices or shim stacks, so the weight of the oil is not very important…it's just there to lubricate the stanchions on the sliding guide elements in the leg…so 10W fork oil is fine…use 7.5W if that's all you have.
I used the Motion Pro 08-0551 bearing driver to drive the lower seal squarely to the spacer ring in the lower fork. It only took about 4 light hits with a hammer to drive it home. The new OEM seal comes pre lubed and the wiper seal just presses into the top of the lower fork tube.
Sliding the upper shiny tube into the new seals is simple and needs no tools or special procedure with the vent screw still out. When the upper fork slider is up in the top fork bracket next to the handle bar, you install a new top nut holding the slider to a torque of 40Nm, then you replace the vent screw with a new O ring.
Since I only was working on the RH fork, the LH fork tube is the alignment reference with the Quick Release Axle shaft between the 2 for setting the position in the lower clamp.
It instructions were VERY specific about torquing the 2 main pinch bolts in alternating fashion 3 times each to 19Nm.
There was never any degraded performance with the annoying small oil leak on this fork tube, but I was tired of seeing some oil and not knowing if it was a drop or a more serious leak.
This was a couple of hours well spent, I'd had enough of wiping down the fork at the end of each day of riding to see if it was getting worse...because I knew it was not going to get better on it's own.
Hope this is what you were looking for.
windsailor97
Member
This brings up a good point. I tried to get the fork dust seal loose to clean the seal prior to replacement but there isn’t much space. Has anyone been able to free up the fork dust seal without disassembling things?
bigjohnsd
'21 R1250 GS Adv
I don't know about room on a GS but I did mine from below on my GSA.
Boxflyer
Active member
Yes, the outer dust seal can be pried out of the fork slider and up the stanchion. I’ve been successful using 2 small tip screwdrivers about an inch apart to twist the tips to slide the seal out.
But...you don't always have to remove it to get to the inner seal.
The first time I had a leaking fork seal was on a ride to Alaska in 2014.
Instead of removing the dust seal, I used one of those hotel “Do not Disturb” door knob signs as my scraper tool.
I used some scissors to cut a small rounded hook on one end. This flat sheet formed around the stanchion and I slid it down in past the dust seal and into the lips of the oil seal.
See the pics above to get an estimate of how far that is, but I’d say you need to go in about 1.5 to 2 inches.
Keeping the thin plastic curved around the stanchion, just rotate the hook end a turn or 2 and continue to turn as you pull this scraper out.
I used this Marriott seal cleaner to clean out around the Final Drive small bearing seal as well on 2 bikes and that stopped those seals from leaking as well. This is in my tool bag on my bike to this day!
My calipers show the actual thickness of this kind of tool, and as you can see the "real deal" tool works in a similar way too.
If this "on the road" method of getting the crap out of the fork seal to stop the oil leak doesn't work, then before you go to all the trouble of removing the fork leg to replace the seal like I did above, you can try this tool as well.
You do need to slide the dust seal up out of the way for this to work, because the hook is not long enough to go past the dust seal and get into the oil seal.
It's a bit pricy at $25, but I've used mine about 3-4 times already, so I think it's worth it.
https://www.amazon.com/dp/B006ZTTY6Q/ref=dp_iou_view_item?ie=UTF8&psc=1
But...you don't always have to remove it to get to the inner seal.
The first time I had a leaking fork seal was on a ride to Alaska in 2014.
Instead of removing the dust seal, I used one of those hotel “Do not Disturb” door knob signs as my scraper tool.
I used some scissors to cut a small rounded hook on one end. This flat sheet formed around the stanchion and I slid it down in past the dust seal and into the lips of the oil seal.
See the pics above to get an estimate of how far that is, but I’d say you need to go in about 1.5 to 2 inches.
Keeping the thin plastic curved around the stanchion, just rotate the hook end a turn or 2 and continue to turn as you pull this scraper out.
I used this Marriott seal cleaner to clean out around the Final Drive small bearing seal as well on 2 bikes and that stopped those seals from leaking as well. This is in my tool bag on my bike to this day!
My calipers show the actual thickness of this kind of tool, and as you can see the "real deal" tool works in a similar way too.
If this "on the road" method of getting the crap out of the fork seal to stop the oil leak doesn't work, then before you go to all the trouble of removing the fork leg to replace the seal like I did above, you can try this tool as well.
You do need to slide the dust seal up out of the way for this to work, because the hook is not long enough to go past the dust seal and get into the oil seal.
It's a bit pricy at $25, but I've used mine about 3-4 times already, so I think it's worth it.
https://www.amazon.com/dp/B006ZTTY6Q/ref=dp_iou_view_item?ie=UTF8&psc=1
bigjohnsd
'21 R1250 GS Adv
Yes got me home from Alaska. Replaced the seal precautionarily the following winter.
AjaxTheDog
New member
An old dirt bike trick I used to use was to take your thinnest flat feeler gauge and run it around the seal to clear out any debris. Worthwhile to try before going through all the trouble and expense of replacing a seal.
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