Front brake sometimes gives [resolved]

Yesterday in some horrible traffic and much braking, I would find sometimes that my front brake lever would (while holding me at a stop) suddenly give in another inch or so. I would be able to pull the handle fully, the brake would grab at about halfway. When let go, brake behavior would return to normal (almost stiffer than normal), full brake being applied at almost half lever.

From some reading, I've learned that a master cylinder problem (leak or clog in the tiny overflow hole I believe it was) is to blame for spongy or soft brakes. Could it cause an intermittent problem? I also know air in the lines would add softness to the pull but wouldn't that be full time also?

My car has a tiny pinhole sized fluid leak, it takes quite a lot of brake to get a full stop, but this happens every time, so it must be something else on the bike.

As a side note, I find that when I turn the handlebars too far right it throttles, misrouted/too short cable?
Another PS, I've dragged the kickstand on a few left turns that I thought were pretty reasonable, have turned right much deeper (safely). Anyone have advice, or live with it?

[Edit weeks later] Pulled the piston gave it a good clean, I think it was a combination of rubber lines, moisture, and brake fluid tuned sludge that caused the problem.

 

Re: Front brake sometimes gives

It may be the tiny hole, but may also be the seals on the piston giving way. A rebuild on that is easy and not very expensive. Brakes are your life. Get'em fixed before you ride again. (What if that happened in the middle of a "panic" stop?)

Yes, probably mis-routed cable. Have you done anything there recently?

Kick stand spring?

 

Re: Front brake sometimes gives

It sounds to me like your master cylinder is in serious need of a rebuild.

 

Re: Front brake sometimes gives

There's your answer right there PM Chacal, he'll hook you up

 

Re: Front brake sometimes gives

hey Bandit,

[/As a side note, I find that when I turn the handlebars too far right it throttles, misrouted/too short cable?]

I noticed on mine that when the adjustment at the throttle is backed off a bit the problem will cease.

jeff

 

Re: Front brake sometimes gives

Thanks guys, here's the latest,
Had the bike on kickstand, took off the brake fluid filler cap, (stupid) the fluid that spilled out first was clear, as I pumped the brake a bit it became smoky/cloudy and by the end downright black and gunky, got as much as I could out and left it off. Didn't get any on anything it's going to harm. When I tilted the bike left again it started to do the squishy brake thing, I think it's from having bad fluid or something else (air?) go in the little hole in the bottom of the reservoir. Still going to be the cyllinder? Now that I've taken that off and messed it up what do I need to do? Bleed brakes and new fluid along with that rebuild?

The cable, I haven't done anything with myself. The throttle adjustment is the long nut by the metal elbow? I'll play with it, it idles fine bars straight though... The cable should not move at all when the bars are turned if properly routed right? Since ON and RES are vac operated, is it ok to disconnect the tank at the petcock to take it off with fuel in it?

And the kickstand, has a little play, the spring seems sound I think the bolt may be a bit loose, hard to see what's going on down there when I'm holding the bike up myself.

I hope I'll stop asking so many questions when I can finally get my manuals...

Edit: I think I did screw something up, clear coat on tank won't shine like it used to now...

 

Re: Front brake sometimes gives

Do the maxim 650s not have a centerstand? Just a thought.

I take my tank off all the time with fuel in it. Just leave it set to on, unhook vacuum, then fuel, lift her off.

I however don't have a clue on your brake system, just figured I'd chime in since I could answer the tank question.

 

Re: Front brake sometimes gives

Have put some pics of the semi-disassembly in the gallery, haven't touched the brake much yet, wouldn't know where to begin.
Didn't come with centerstand, but thanks for your confirmation about the tank, it inspired me to go way too far, lol.
Far left carb boot has a nice crack in it right along the metal keeper on one side, I think I'll attempt to RTV seal and plastic wrap it without taking anything else off..

When I was looking at that wrong size air filter(?) noticed oily residue and gas smell from airbox, also oil leaking from head gasket, suspect PO overfilled oil? No gas in oil though.

With all this going on, won't be riding it for a while (dang, right as summer was starting), should disconnect battery and drain carbs correct? pic below is the "carb drain screw" right? Also for storage a tbsp oil in each plug hole, and oil change? Have I missed anything?

Amongst all this, I find I'm thankful for a few things though, one being the valuable information I've gotten from this site and its members (I like to think of it as mental tools, without which my garage tools would be useless to help me), and also the fact that other than a few worn shims my entire engine is pretty clean and seems to run great (judging by the nice beige on all plugs)... Its funny to me, before I got this bike my car 'worked' and that's about all I knew about it (simple stuff aside). After getting this bike, I feel more in tune with both my machines, as though I can be a part of what makes it work.
I just hope I can get it rideable again before the summer is too far gone.

Another big thanks to the forum, I'm going to consider this resolved for now, I've got a 14 item list of things to do and or obtain that earlier today I wouldn't have had a clue about.

 

Re: Front brake sometimes gives

That gunk that came out black is probably one of the "seals" breaking down. The yellow gunk is going to be throughout the system and is aged brake fluid. Check your lines (they are supposed to be replaced periodically). That gunk is going to be everywhere. A dissassembly of the system, cleaning of everything, and reassembly is the safe way to go. Replace the lines while your at it to increase safety. I did mine with a rebuild of the MC and Calipers and Stainless lines (all from Chacal) and it now stops better than new. With the lines (they are the expensive parts) it was about $200 but for safety, I think its money well spent.

While your dinking around with brakes, have you checked you back for the beginnings of delamination?

 

Re: Front brake sometimes gives

Another PS, I've dragged the kickstand on a few left turns that I thought were pretty reasonable, have turned right much deeper (safely). Anyone have advice, or live with it?

Have you checked the air pressure in the tires? I picked up a brad nail during last weekends ride and the pressure went down in the rear tire. I was dragging the center stand during high speed turns in the twisties. Well, high speed for me anyway. Aired up the tire and limped home and now no more drags.

Sure thought I was really cool there for a while though!!!!

 

Re: Front brake sometimes gives

My digital gauge won't fit my tires but they seem firm enough, I'll get the means to check them soon. Come to think of it PO lowered the bike, maybe it's just too low.

Can't say I'm looking forward to the brake job with no jack or centerstand. I had been doing a bunch of studying up to check my valves, and here this comes. Hoping I won't have the problems I see here on the forum when putting the brakes back on, sounds like it can get difficult...

 

Re: Front brake sometimes gives

What is wrong if my 82' xj650's front brake was sticking really bad even when the brake was not being applied? Master cylinder on the wheel rebuild? The lever seems to work fine. I took the brake line off at the wheel and could see fluid being forced out of the line when applyiny the lever. What do you guys suggest?

thanks

casey

 

Re: Front brake sometimes gives

Shouldn't need a center stand. Wheel stays on, parts come off. Did mine on the side stand the whole way.

 

Re: Front brake sometimes gives

Could be a sticky caliper (Caliper rebuild - easy and fairly cheap). Could be a warped rotor (easy but more expensive). Take the sticky one off the rotor but leave connected. See if you can move it by compressing the lever or some pressure between the pads. If not or hard, that would seem to be the culprit. Pull them both and rebuild them. (Unless you know it has been done recently, you should redo the entire system for safety sake anyway IMHO. My life on 28 year old braking parts is not some thing I want to stake).

If is seems to be moving freely, then perhaps the rotor is warped. A brake shop can check this for you.

 

Re: Front brake sometimes gives

First observation Reptar, is that you shouldn't thread-jack someone else's thread. Please observe proper webiquette and start your own thread.
Second, one of two things is amiss with your brake system. The most common is blockage of the return port in the master cylinder. This is a small hole in the m/c bore but should not be overlooked as it will cause the symptoms you describe. The other culprit is the caliper pistons are stuck. All of this points to the need for a 27 year old brake system to be overhauled, a bit of preventative maintenance normally ignored by most bike owners.
If you are short on cash, and this is NOT the recommended practice, disassemble, clean and reassemble your brake system. This is again not the right thing to do. If you are going to tear it down to clean it, you may as well replace all the soft parts while you are in there and buy yourself peace of mind. All the neccessary parts can be had for under $150 if you don't need new lines (and you do at 27 years). Contact our resident parts guru Chacal for guidance on parts.
Good luck and start saving your money for a complete and proper overhaul, your life and continued well-being depend upon your brake system working correctly.

 

Re: Front brake sometimes gives

Does anyone have a diagram of the 'box' that contains the pads for the front brake? for some reason my pads are engaged even though all brake lines disconnected, pads will not space far enough apart. I can't figure out why they would be doing this. would the piston have seized from pumping the brake with the system dry?

 

Re: Front brake sometimes gives

How can you pump the brake with the system dry? :?

 

Re: Front brake sometimes gives

I meant squeeze the handle with no fluid in it, there's no pressure in the system it seems completely wrong that the pads are grabbing the rotor

The red highlighted area in third picture below, does this come off for more cleaning/parts inside?

In the second picture, is the clearance between the pads, still no pressure in the system, this seems mechanically wrong to me unless the piston is seized.

In the first picture below, is there supposed to be anything other than rust in that hole? It seems an oval object was pushing against the back of the pad from the mark on it. Where's the actual moving part of the brake?

 

Re: Front brake sometimes gives

Is that slightly touching or grabbing and not allowing movement or very hard movement. The latter should not be happening and you need to get the caliper off and check it out. Slight touching is normal for disk brakes. (Theres nothing to pull them back off of the rotor).

 

Re: Front brake sometimes gives

Slight touching is normal? I never noticed it before I started messing with the brake.. Edited the post above with pics of the caliper off..