Someone

Member
Mar 12, 2001
865
0
My buddy has a 99 RM250. Lately, his brakes have been locking up and need to be slightly bled before they let loose. After that is done, it will work ok for awhile, but it's a pretty scary thing to ride with. Thankfully he can feel it drag before it's totally locked up.

This is what we've done so far:
1) new fluid, multiple times, high temp fluid
2) new caliper
3) new brake line
4) wheel bearings

The only thing we haven't replaced is the master cylinder.

Note: his rear wheel isn't very true, when I ride behind him, it wobbles, not extremely bad, but it wobbles enough to see it plain as day.

What do you think? Could it be that his wheel is wobbling and heating up the pads/fluid? Could it be the master cylinder? His rotor is fine, no wobble and has plenty of wear left (along with his pads).

We've been messing with this for quite some time and would appreciate any insite.

Thanks!
 

nickyd

Member
Sep 22, 2004
873
0
if the rim wobbles, that doesn't necessarily mean the hub is wobbling. rebuild the master cylinder - can you attribute anything to it - ie after he washes it? or right after he passes a mudpuddle? is the master cylinder mounted wrong and too close to the motor? usually when the brakes fail they heat up and go away....not lock up. I would look to see if the plunger on the brake pedal is getting stuck - that would entail pulling the master cylinder apart...might as well rebuild it then
 

placelast

Member
Apr 11, 2001
1,298
1
This happened on my son's RMX once. I carefully wedged the pads off of the rotor and it was fine most of the day; replaced them just ot be safe later in the week.

I believe the slave piston was exercised beyond what it normally had, and perhaps stuch on a non-wear portion of the cylinder - hence, the sticking.

Try replaceing the pads, and rebuild (honing) the slave cylinder.
 

Someone

Member
Mar 12, 2001
865
0
Thanks for the help.

We will check everything stated here, and if needed we will rebuild, or buy a new master cylinder.
 

sick 96 250

Damn Yankees
Member
Jul 16, 2004
1,207
0
are you sure you are bleeding them correctly and getting all the air pockets out? Seen it happen a few time where we thought it was bled correctly but there was always a little air bubble hidden somewhere that would eventually lock it up. Also check the seal in the rear caliper, this could be the reason for the air getting in there in the first place. Good Luck
 

Someone

Member
Mar 12, 2001
865
0
There's no air in his system, we used a mity vac and have replaced the fluid half a dozen times. There's also play in the pedal so it's not dragging.

A new master cylinder is more $$ than he wants to pay, I've seen re-build kits for the master cylinder, but Suzukis crap part numbers make it confusing.

Does anyone know a good place to buy a re-build kit?
 

Rog

Member
Oct 21, 2004
31
0
Had the same prob on my RM. I just bought an aftermarket rebuild kit for the master cylinder. Can't remember the name of it but I just got one from the bike shop. It was only something like $50NZ. Never had a problem since.
 

rodH

Member
Aug 17, 2005
369
0
Had the exact same problem on my bike one day, I replaced the fluid and it was all better, but it seems like you already tried that. Did you ever fix this?
 

Tdel

Member
Mar 1, 2004
47
0
I see that you replaced the fluid several time. Was it from the same source, i.e. can of fluid? Old fluid will absorb moisture. As the brakes heat up the moisture expands causing additional drag, causing more heat causing more expansion....... If the fluid was not out of a brand new unopened bottle drain it and try again with the mighty vac.
 

QKENUF4U

Member
Nov 13, 2005
236
0
sounds like the return hole on the master is plugged causeing the pressure/fluid to stay in the line instead of going to the master cylinder like its supposed to. i would do a rebuild on the master and make sure its SPOTLESS when you reassemble.
 

phranticness

Member
Jan 4, 2006
134
1
Free Play

Any master cylinder has to have free play, be sure that the pedal has free play, this is adjustable, when the fluid heats up, it expands, if there is no play 2mm or more, the brakes will begin to enguage................give it a shot, try backing the adjustment off to about 5mm free play, just to be sure..........good luck
 

Top Bottom