Hi everyone,

Just finished a carb cleaning and brake overhaul on my 2009 KLX250SF. Got everything put back together and took it for first ride. New pads and fluid in front and back. Had to rebuild the rear caliper because I had previously lost brake fluid somehow and the caliper had locked the pads shut. The piston and bore were both clean and I installed new seals although the old ones did not look damaged.

The front brakes are working fine, rear seems fine as well and pedal is responsive/pads are not dragging. However I was monitoring throughout the ride to be sure everything was working properly and noticed less brake fluid in the reservoir than when I started. So I think I'm losing fluid somewhere which is probably why I had to rebuild the caliper initially since it lost all fluid and they locked shut.

Looked all over after riding and don't see any brake fluid on the line or connections. Bleeder valve and banjo bolt are secured shut. Only thing I am wondering is if maybe the diaphragm in my reservoir isn't getting a good seal. But the mold on inside of the cap to the reservoir seems like it should hold the diaphragm in place and idk if the pitch of the bike when turning would be enough to lose significant amounts of fluid out the top of the reservoir. Also didn't seem like there was fluid on the outside of the reservoir so not sure that is where it is leaking from.

Just to give some context I have owned the bike since it was new but am just now learning about maintenance and working on the bike myself. There have been a few periods where it has sat for almost a year or more. I have 13,000 miles on it and this is the first time I am doing any brake work. I know this is bad but I'm now trying to learn more about the bike and take good care of it as opposed to my poor habits when I was younger. I'm wondering if my problem could be in the master cylinder although I'm not seeing any fluid around the cylinder or going in or out of it, is there a way to check for this?

Any suggestions for what I should look for to try to identify where it's leaking? Thanks for any help I've learned a lot from searching through this forum so far. I'm including a picture of my reservoir diaphragm below. It is still intact no holes or anything but it doesn't completely cover the sides of the reservoir. Not sure if this is relevant or not.

 

I wish I could give you some constructive advice here, but can only point out what to me is obvious. The problem seems to have exitisted before doing the latest work. I would think that fluid has to going somewhere and leaving some sort of trail or evidence. Brake fluid is some bad "mama jama" when it comes in contact with just about anything.
When I'm checking for the smallest leak is wrap a paper towel around the part(s) in question (such as a line or fork tube) and secure it with painter's tape. I'll then check for seepage which can usually be easily seen on the paper towel.

Also have to ask if you bled the brakes afterwards and have you refilled, bled again to see if you're still loosing fluid? Sorry, just had to ask.

Good for you working on your bike and getting that maintenance done. Wish I could have had a little more direction for you

 

Hi Dave,

Thanks for the input, I'll try the paper towel method. Yes I agree that the problem is probably the same one that I had before doing the work. I did bleed the brakes after install and after noticing the fluid go down in the reservoir, I refilled it and took it for another ride. Didn't have to bleed again because fluid was still in the reservoir. After that ride, I noticed the level went down again leading me to determine there is still a leak somewhere. Hopefully I can find it with your paper towel method.

Thanks

 

Hope you find WTH is going on and solve that hiccup so you can safely ride that bike again. Here's the method I use when changing out the fluid and bleeding the brakes on my bikes. Skip to the 2 minute mark to get to the meat of the subject.

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Yea, wrap some paper towel around the resevior, and run it if you don't come up with something. It has to go somewhere! Sometimes those gaskets get old/hot and warp/leak.

 

Hey durielk, which gaskets are you referring to? I'm about to ride around and do some tests to try to figure it out.

 

I'm thinking that big black thing? It looks like it is totally warped.

 

Yeah, the diaphragm, as it is called in the parts list, needs to be seated around the top of the reservoir in the groove. The top would be relatively dry if it had been properly seated. That one looks like fluid got on top indicating it wasn't seated.

The diaphragm displaces air when the master cylinder is filled, then will draw down into the reservoir as pad wear draws out fluid, keeping air out of the reservoir between it and the fluid. This is done because brake fluid can draw moisture and break down (?) by exposure to the atmosphere. There is a small cut in the reservoir cap that allows air to draw in above the diaphragm.

 

Thank you for the explanation of how that works. I've ordered a new diaphragm and it should be here in a couple days. I think this will help my problem. I appreciate everyone's help here. I'm really happy with the work done on the bike so far and am excited to learn more.

 

Honestly, a brake fluid leak will be very obvious.
Aside from the slick, oily appearance it will attract and absorb any dirt/dust that comes into contact.
A can of brake cleaner to spray off the entire mc/hose/caliper system and ride it.
Another inspection will reveal where it's leaking.