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Please help - locking front brake

H

husmar

Joined Feb 2004
12 Posts | 0+
Atlanta GA
Bike is 96FE600E that had been sitting for a few years. Front brake locking while on the trail and I waited untill pressure realeased - couldn't even move lever. Got it home and cleaned master cylinder, line and caliper. Fulid was pretty bad so I flushed with brake clean and used DOT 5 to fill. Manual said DOT 4 or 5 and I didn't know what was in there so I took a shot. Checkout ride went fine - 30min dual sport - and then today after ~1.5hrs on the trail it started locking up again. Took 3 cool down/pressure release stops one of which I bled fluid to releave pressure to get ~10 miles. After I got it back I pumped the break and let it sit for several hours after which it was still locked up. Took salve cyclinders out and marred one with pliers (used compressed air after that) little dirty but bike is 15yrs old so nothing shocking. Now I'm thinking of replacing the following parts - #'s from http://www.ktmpartfinder.com/

Master cylinder - repair piston 11mm 50213050000
Slave cylinders - reapir piston 28mm 54613206000
Slave seals - 28mm 54613205000

Are they the correct parts and will they fix my problem?

Thanks in advance for your responses
 
I would'nt use DOT 5 brake fluid. it's a silicone based fluid, it is not interchangable with DOT 3 or DOT 4. you could use DOT 5.1. you could be filling up the brake reservoir to much, I have done that on an older bike of mine. so when the fluid heats up and expands it has nowhere to go. If it was my bike I would go with DOT 4 fluid and fill up the fluid between the min and max mark and see how that works before replacing parts in the master
 
HI

I think helithumper is right, I would use DOT4, the manual says DOT 4 or 5, but in earliers manual they allways say DOT 4 or 5.1, not 5.

Everything helithumper says is right, I would also take very good care in cleaning the line (I use one kind of industrial alcool, don't know the name in english), and cleaning the cilinder and pistons. Most of the times is nothing wear is just something dirty and sticking.

I would also check the pins where the pads slide, they wear with time and don't let the pads slide, and the pins where the piston slides.

If you need parts I have the 89-96 parts cat. let me know, I send you by mail. Can't put it here because its over 2 MB.

:cheers:
ZAGA
 
Hello.
If you have an lever adjustment screw adjust it so there is a gap, if it`s too tight it will lock the brakes when they got hot.
Regards
Jampe
 
husmar,
i would think if when on your ride and brake locked, if you released pressure by releasing the bleed screw and the and the caliper piston moved back in and allwed the brake to turn then something in the hydraulic circuit is sticking and the caliper is for sure good if it moves on its own, i would check the hose for pinches and make sure that there is flow through it from both directions with low pressure air (if this was a car i would have deemed the brake hose defective from that test, they collapse internally all the time, dont look bad, but hold pressure one direction)
if you saw caliper release the brake when you unscrewed bleeder would also think the caliper pins are not binding but very important to check as zaga says....
and unless there is too much pressure for the adjustment lever or if the fluid level too full (also said already) i would have to think the master is bad, doesnt it say the brake fluid type on the master cylinder lid?
i was always told dot 3&4 brake fluids mix and dot 5 is silicone base and wont mix 3&4, i thought 5.1 mixed perfectly with dot 5? the only difference being 5.1 has a higher boiling point...?
my 1997 600 has 3÷5 as its brake fluid type on the front master cylinder, i have no idea what this means....
rear one is dot4..
using the wrong weight fluid will cause problems over time but not imediatly in calipers, masters, and such due to incampatiblity in the seals and plastics...
should have everything you need in this thread...good luck
 
BERGINI, DOT 5 is a silicone based synthetic. harley davidson used it for a while because it does'nt eat through paint . what people found is that DOT 5 would destroy seals and start to leak unless used with proper seals. DOT 5.1 is a lighter viscosity poly glycol fluid of the DOT 3&4 fluids. from what I read they created the DOT 5.1 fluid for use is ABS braking systems because of there faster cyclic paterns.
 
The fluid information is all excellent. I would definitely heed that great advice.

This sounds something similar to a streetbike (1000 Interceptor) I had back when I was 18 - which is 25 years ago now. I had issues three times when the front brakes would just clamp on hard. Twice this happened in traffic, including once at 100km/h. Not a great situation when you're braking as hard as you can with the front without touching the lever!!

Each time I would release the pressure by loosening a bleed valve. Then I'd take it to the shop, and each time they'd do something to try to fix it, including a caliper rebuild kit. (Can't remember what else they did). In the end, it turned out that a small piece of metal had broken off from the master cylinder from an earlier crash. So it would float around, and eventually block the fluid from returning. When I'd release the pressure, it would dislodge, so then parts would be replaced in the brakes, and it would test out fine until it happened again. Just in case this is something similar, I'd carefully inspect the master cylinder by taking it apart completely.
 
Not exactly the same thing happened to me last week... but similar to the last post... the rear brembo brakes on our bikes can exhibit a similar problem.. mine did it last week, it goes like this:

On the rear brake pedal, there is an adjustment that sets how high (or deep) the pushrod goes into the master cylinder... if this is adjusted too tight it will prevent brake fluid from returning back into the reservoir from the caliper under situations where the brake is not being applied. Last week I drove highway speeds with my 2002 550 (110 km/h which I don't normally do) and as the rear caliper got warm the fluid expanded slightly... since my brake was adjusted too tightly the expanding fluid had nowhere to go and the piston started to apply the brakes, generating more heat, expanding the fluid even more creating a "runaway" situation which I noticed when I had to apply more throttle to keep moving, then as I pulled in the clutch the bike slowed very quickly... the rear wheel didn't lock up but it was close. Cracking the bleeder or allowing the caliper to cool would immediately release the pads grip on the rotor (it happened once more before I got home that day). Once back home, I adjusted the depth of the pushrod in the master cylinder and the problem is gone.

So... in your situation I would suggest looking at the master cylinder, probably not the caliper.. just like others have suggested. It would be much scarier to have the front brake lock up unexpectedly... at least with the rear you could ride out a skid (maybe).
 
Thanks for the replys. This was(is) happening with the adjustment on the lever fully released. I had to go out of town last week for work and had a big ride planned for tommorow so I got the parts - they all fit and look identical for future reference. Cleaned system with brake clean, installed parts, used DOT 4 fluid - same problem. Noticed that rotor was warped when I was replacing wheel so my ride tommorow is not happening. I'm taking it in to the shop at this point, will post the out come.
 
Master cylinder was bad. Mostly likely due to corrosion from old, wet, brake fluid on the bore. You can see slight dicoloration on the bore - not much but I guess its enough. Never thought to change the brake fluid and I talked with some other riders and they never do either. This was a $400 lesson - I'm going to flush every year from now on.
 
i pinched my brake line on my folded down mirror the other day when the suspension rebounded after releasing a ratch strap and made me wonder if you figured it out, i didnt think the warped rotor would cause a lock up just a pulsation...brake fluid is hydroscopic meaning it aborbs water from the atmosphere and things like this happen even in a nearly perfectly sealed system...at least its figured out and you dont have to bleed your brake every few miles to get home any more :!:
 

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