Clutch Master Cylinder Leak

jfheilman · Dec 13, 2017

The other day I took a 100 mile ride for a meeting. I parked the bike (2007 ST1300A) with the steering locked and when I came back outside, there was what appeared to be some clear fluid on the left side of the tank.

I believe it was hydraulic fluid from the clutch master cylinder that leaked out because of the angle, It could have been from the cover gasket again due to the angel.

Two questions.

1. Has anyone experienced this before?

2. I found what appears to be a master piston set which costs about $45 which seems would be an easy preemptive fix. Is that a reasonable course to take. I would also replace the cover gasket.

Thanks.

Jim

Igofar · Dec 13, 2017

Make sure it was not just this part first DIAPHRAGM
45520-MM5-006, its only about $9 bucks.
.02

mcthorogood · Dec 13, 2017

My reservoir kept leaking after bleeding the clutch. The black rubber diaphragm and the plastic diaphragm plate under the reservoir cap can be finicky. I had to try three or four times putting it back together so it did not leak. I also use a bit of blue threadlocker on the screws for the reservoir cap.

Igofar · Dec 13, 2017

When you go to insert the plastic plate on top of the rubber diaphragm, insert the front part of the plate at an angle, then hold the rubber diaphragm with your thumb to keep from displacing it, then let the rear part of the plate drop into the correct position. Them press down on the cap a couple times watching for leaks before you tighten it down. Only tighten it down finger tight to keep from damaging the rubber. You do not need, nor want, locktite on those screws or near the master cylinder assembly.

Jerseyst · Dec 14, 2017

Mine did the same thing on a trip. It ran down the lever for miles and miles and was very slippery using the clutch. I got a used one off ebay.

dduelin · Dec 14, 2017

Igofar said:
Make sure it was not just this part first DIAPHRAGM
45520-MM5-006, its only about $9 bucks.
.02

This. On older bikes consider the diaphragm a wear item and just replace them at 10 years or so. The rubber ages and gets less resilent and may begin to leak or seep. They are also harder to seat or insert properly. I'd try that first. It's not happened on my ST but it did on two older bikes I owned. I replaced them on the ST a couple of years ago as a preventative measure,

SMSW · Dec 14, 2017

Brake fluid is known to be nasty on painted surfaces. I hope you suffered no damage to your tank's paint.

jfheilman · Dec 14, 2017

SMSW said:
Brake fluid is known to be nasty on painted surfaces. I hope you suffered no damage to your tank's paint.

Thanks for the input and no noticeable paint damage.

I will replace the "cheap" parts first. Then monitor for leaks.

jfheilman · Dec 20, 2017

Update:

I have not received the replacement parts yet. But I did ride the bike about 100 miles yesterday. When I was checking the bike out before the ride, I saw no sign of leakage.

After the ride, some time after (maybe 24 hours), I was out looking at the bike and the clutch lever felt a little "damp" and there was some signs of fluid on the left hand cargo cover (forget what you call the storage compartments). I think the leak might be related to the piston that moves the fluid around. I will check it after I do the diaphragm replacement.

The bike was on the side stand both before and after the ride.

jfheilman · Jan 14, 2018

Update: Yesterday I replaced the diaphragm and plastic cover thingy. I also replaced the little metal cover over the hole in the bottom. It was missing. Will test and see what happens.

Igofar · Jan 14, 2018

When you found the protector, Honda part number 45512-MA6-006, missing, or dislodged, did you replace it back into position correctly? It can be inserted into the housing both correctly, and incorrectly.
You want it inserted so that the shoehorn looking part is in the upward position, and there is a gap between it and the floor of the housing. This is very important. If it is inserted backwards, the corrector will be flush with the floor of the housing and BLOCK the return flow of the brake fluid and lock things up!
When you insert it into the housing, take a small tool, dowel, or plastic chopstick, and press it into place.
My question is, what happened to the missing one? Is it still in the master cylinder housing bouncing around?
The missing part would cause your leak, as the fluid would be shot straight up without the deflector, and force the fluid out the vent holes.

jfheilman · Jan 14, 2018

Igofar said:
When you found the protector, Honda part number 45512-MA6-006, missing, or dislodged, did you replace it back into position correctly? It can be inserted into the housing both correctly, and incorrectly.
You want it inserted so that the shoehorn looking part is in the upward position, and there is a gap between it and the floor of the housing. This is very important. If it is inserted backwards, the corrector will be flush with the floor of the housing and BLOCK the return flow of the brake fluid and lock things up!
When you insert it into the housing, take a small tool, dowel, or plastic chopstick, and press it into place.
My question is, what happened to the missing one? Is it still in the master cylinder housing bouncing around?
The missing part would cause your leak, as the fluid would be shot straight up without the deflector, and force the fluid out the vent holes.

t took me some time but I did finally get in seated/inserted as you described. It took a few minutes to explore the options and it appeared that this way was the appropriate one to fullfill its fucntion. However I will double check before I take it out on the road.

As to what happened to the original one, i suspect it got sucked up when I was vacuuming out the housing. I was cleaning out the system and replacing the fluid and, well, it obviously got lost.

I do believe that you are correct in that this was the reason for the "leakage". But time will tell.

I did verify the fluid shooting straight up, just to verify that it really did as described.

Thanks for the feedback.

jfheilman · Jan 16, 2018

Update: Ok, I took the cover(s) off and removed the little metal thingy (protector). I thought I might have had it in wrong based on the wording used above, but also re-read the words and decided I had it in correctly the first time.

In doing some more cleaning, I found the original one in a corner cleverly hidden from view and removed it. It must have been dislodged when I cleaned out the clutch fluid.

jfheilman · Jan 24, 2018

Update:

Took the bike for 100 plus mile ride yesterday and no clutch fluid leaking. So, the issue was most probably the "protector" not being in the correct location (well it was in the corner and no where it was suppose to be).

So, it appears, the issue has been corrected.

Thanks for all the help.

Jim

MaxPete · Jan 24, 2018

Excellent - well done Jim!

Pete

PS - you’re a lucky dog being able to ride these days.

Gus1300 · Nov 5, 2020

Looks like I also have a leak, but pretty sure it's not from the cap based on the handle/cable stay/piston area. Still looking for a new vs rebuild thread before tearing into the Master Cylinder; any hints? So far no tank paint damage that I can see, despite the drips shown in the photo.

Igofar · Nov 5, 2020

That may be grease dripping down from where someone may have tried to lubricate the lever at the bushing....which by the way is completely worn out and damaged.
Remove the 10mm nut underneath the lever, then unscrew the threaded rod and remove the lever.
You will find the bushing damaged and possibly the lever worn egg shaped as well.
Replace the bushing, lever, and boot now or it will damage the perch (master cylinder housing) which is about $400 dollars etc.

dduelin · Nov 5, 2020

A master cylinder rebuild kit is available under p/n 22886-MCS-G01 for about $45. The entire sub assembly is $250. As Larry points out you probably want to replace the bush p/n 22885-MBO-006 and push rod p/n 22884-MBO-006 for another $25.

I never have had to fix the ST's clutch master cylinder but I think I'd try to replace the wear items.

Gus1300 · Nov 5, 2020

Thanks guys, I will look at the parts list and get them ordered for next week's time off.

heffly · Nov 5, 2020

It all comes in a kit. About 53 bucs. Putting the main plunger rubber over the new slide requires some caution. Its a tight fit..

Clutch Master Cylinder Leak

jfheilman

Igofar

mcthorogood

Igofar

Jerseyst

Official Crown Royal TeSTer

dduelin

Tune my heart to sing Thy grace

SMSW

jfheilman

jfheilman

jfheilman

Igofar

jfheilman

jfheilman

jfheilman

MaxPete

Gus1300

Igofar

dduelin

Tune my heart to sing Thy grace

Gus1300

heffly