soft front brake lever
 

Front brake lever keeps going soft around 3days after bleeding. no leaks visable, lines and pads looks ok. trying to figure how to troubleshoot master cylinder isssues. or of it a problem with the master diaphragm. any help would be greatly appreciated. just trying to avoid taking into a dealer if its something simple that i can do myself. Fluid comes out clear without any bubbles when its bled.

Getting air into the line somewhere. Is the reservoir seal in good shape; no small cracks? Caliper pistons/seals clean and lubed? Good seal on your bleeder screws? How old are the brake lines; what type, OE or s/s?

as mentioned by Jeff above, and have you flushed the system and placed new fluids in? Contaminated brake fluid is a bear to deal with and the system should be flushed yearly.

Welcome to KF

bike brake lines are still all stock. i did have some brake fluid i had on the shelf that i opened last yr that i used to top off when i bled the brakes this yr. Maybe i'll get some new fluid and a vac. bleeder and repeat bleeding steps again and see what happens. do u all know how to troubleshoot a faulty master cylinder? If i can just find out if thats the issue, i will get a kit and rebuild it, if thats not the issue, i will replace the brake lines/fluid. thanks for responding.

just a thought. when your brake fluid (in the bike) has been there awhile, the moisture tends to condense behind the caliper piston. You also get very small traces of black rubber which come from the inside of the OE lines and congregate in the caliper. When you have bled the lines, how MUCH did you bleed them? I would recommend getting a fresh bottle of Castrol LME brake fluid, and pumping it through your lines (from "top down" not from the caliper up) to completely purge any contaminated fluid and/or rubber deposit. Go through about 2 complete fills on your master cylinder and flush the lines. Make sure you get only clean fluid (no bubbles) coming out the bleeder catch tube. (Seriously; bleed them till you're sick of it.) I'm not convinced your master needs a rebuild. They WILL go bad if you leave them empty and dry--and the seals rot, but tend to live long if fluid is kept in them.
If that still doesn't work, double-check your banjo connections on the brake lines and/or replace the sealing washers, if you're on a budget (hey, we all are) and not up for spending bucks to convert to stainless lines.
Keep us posted, OK?

Brake fluid is hygroscopic, so you have to use it or lose it. It will absorb moisture once opened. The moisture causes all kinds of brake issues and soft brake feel is just one of them.

Thanks jeff and dragone for the tips. I definitly had black fluid come out after I bled the brakes for the 1st time. So I'm going to get some new brake fluid and bleed the dog crack out of those lines lol.. Hopefully that will do it, I'll keep U all posted. What will be the symptoms of a faulty master cylinder? If this does not work!! Thanks again guys.

[QUOTE=I'm not convinced your master needs a rebuild. They WILL go bad if you leave them empty and dry--and the seals rot, but tend to live long if fluid is kept in them.
QUOTE]

How long is too long? I pulled my front caliper off (08 KX250F) because there was something dragging. I let the brake line hang over a bucket with the reservoir cap and bladder just sitting on the reservoir not screwed down. I went to work the next day to disassemble the caliper (no air at the house) and clean it up. After getting home the reservoir was empty. I reassembled it all and bled until no more air out came of the bleed on the caliper. Held the brake lever to the bar, cracked the relief briefly and closed. Lever is still mushy.

Having no fluid in the reservoir overnight is not long enough to dry out the seals is it? It probably never got over 40 degrees in the garage while working.

Thanks.

Jeff

You'll need to keep bleeding it until you get the last of the air out. Overnight isn't enough for the seals to perish, but you will definitely have air in the system. Use fresh fluid, of the right grade (DO NOT MIX GRADES) and keep going.

Thanks Dark Angel,

I have reading a lot about this situation and I wish I would have let the reservoir cover on screwed down so to create a vacuum. I think tonight I will try tie rapping the lever to the handlebars and leave that for a while. Sounds like people have had success doing that. Plus it is full moon and we are going to go for a ski!

Jeff

No. Seriously. That's like putting a gun in your mouth to cure a headache. There's jut no way it's going to make anything better.
To bleed the brakes you need to PUMP the lever so that you move fresh fluid through the lines and push out the air and other crap. You also need to crack the bleed nipple each time you squeeze the lever and close it when you release the lever or you can suck air back into the lines from the calliper end. Just leaving the lever strapped to the bars doesn't open the ports to the reservoir and will allow the air to stay right where it is and any debris to settle in behind the calliper piston. If this procedure is a little hard for you to reach everything get a brake bleeding tool from an autoparts store or make yourself one using a glass jar a piece of clear hose. About one third fill the jar with brake fluid and push one end of the clear hose on to the calliper nipple. Put the other end of the hose into the brake fluid in the jar. Open the bleed nipple and start pumping the level. Keep topping up the reservoir as it empties. Do NOT let it drain down and suck air or you will have to start again. Watch the clear tube for air bubbles etc. When the fresh fluid has completely replaced the old and there are no more air bubbles or debris in the hose, close the bleed nipple and try the brakes (in the shed, not moving) If it's still spongy and you're SURE the seals are all ok and the brake pads are moving as they should, then keep bleeding the brakes, there's still air in there, most likely in the calliper.

I too see flaws in your bleeding methods deeppowder.

Deeppower, it helps to understand how the system works.
When you squeeze the lever it pushes a piston full of brake fluid down the hose to the cylinder at the other end. That moving fluid pushes another piston which pushes the brake pad. In order for the pressure in the first piston to transfer to the second one the whole system needs to be sealed, nothing gets in or out. In practice the brake pads wear, requiring the second piston to move further to accommodate the changing thickness. This is handled by having a reservoir of fluid that the top piston can draw on. In order to keep things working properly it's better to think of it as two systems. One does the braking, the other fills to master cylinder. The two systems are never open at the same time. When you pull the lever the piston moves forward doing it's pressure thing and closes the port into the reservoir so that the pressure doesn't bleed back. When you release the lever the piston travels back and at the end of the release stroke opens the port to allow fluid from the reservoir to replace anything that's filled the slave cylinder to been lost to leaks.
That spongy feel at the lever is caused by something in the system not holding the pressure where it should be. Something is either expanding/swelling such as old lines, compressing such as air in the system or leaking such as bad seals. Water in the fluid often shows up as brakes that feel fine when cold but go spongy or vanish completely when hot.
Holding the lever against the bars closes off the only access port the fluid in the reservoir has to get into the system. When you're "bleeding" the brakes what you're doing is replacing the air in the system with brake fluid. That means you have to pump fluid in and push the air out. The key words there being "pump fluid in". Fluid will not just drain in and the air will not just rise out.

I thought that I had a how to brake bleed write up. But there are good how to's on You Tube. I use the mity-vac over the manual method.

I usually teach my self how to do these things the olde fashioned(e) way since I'm usually broke and can't afford much in the way of fancy tools.

It's all good DA. just an option that I use since I have to flush my track rides' brakes(6rr and the 10r twice a yr) and I like to keep the Street ones' flushed yrly. (05 ex500, 07 ex250 and the 92 kz1000) so time is important to me and is why I use the mity-vac.

Know how the system works then make your own decision on what method to use. I totally agree

Don't get me wrong, I don't care if other people have fancy tools. Hell, they can turn an hour job into five minutes in some cases! What's not to like? :D I just do it all on a budget is all because that's my own situation. I don't even have a shed (garage) right now.

Just an update as to the situation with my front brake. Thanks to all for their input. Cut my DIY expensive tool (.50 cent tie rap) off my brake lever. Seems like my brake lever stiffened up to how it felt before. Yep, I realize my process was not the best.

Is all the air out? Not sure so went on a short 1/2 hour ride until snow turned me around. Can't wait for summer! Front brake worked fine. Used it quite a bit on a long downward grade headed back home. All felt normal. Will check brake before riding to make sure it is not soft again.

I would never say I am an expert on hydraulic brake systems but I have worked on them on up to 1000 HP ski lifts for 25 years. That said, my technique was off, caused more work for myself in an unfamiliar system. Reached out for help, got it and will see how it goes.

Thanks again.

Jeff

Well said, Dark; +1^.
Sometimes, even when you "do it right," it takes longer than it should. Pretty sure I recall putting s/s lines on the old GSXR (see album). It took me for-freaking-ever to get the front lines bled!!! I'm SURE there was an air bubble in the "T" where the single line coming out of the master cylinder split into left/right lines, above the front fender. AAAUUUUGGGGHHH. The bubble would shift to the line I WASN'T bleeding. Took like an hour just for the fronts.
I like to use the handy little bleeder I got from Griot's Garage, which has a rubber nipple (to vac line) you put on the bleeder screw. Connect the reservoir to shop air, and it builds vacuum in the line. Open the bleed screw....viola...out goes the bad fluid. Use it on the cars every brake pad change or once a year to keep the fluid fresh.
Whatever works. I've done it the old fashioned way (Dark) MANY times, too!!

Soft front break lever (after 3-5days) replaced master cylinder
 

My front break locked up temporarily last year. Happened at 45-50 mph. Felt like I had an anchor off the back of the bike. Ended up replacing the master cylinder and bleeding the hell out of the system. (From the calipers and resivor bleeder). Afterwards there is plenty of pressure. Go to ride the bike a week later and the lever almost touches the grip. Bleed at resivour again and it's tight, again. Then the process repeats. Goes soft every 3-5 days.