GSXR250 brake issues

**Pumba** · 7th January 2009, 10:08

Ok I have run out of ideas on whats going on so someone please help.

I have an 89 GSXR250 front end on the bucket, which has the appopriate brake system, twin four pot calipers and a master cyclinder.

In the procces of trying to solve a soft lever problem I have changed the calipers with another second hand set I picked up, and put on braided brake lines but that hasent seemed to make any difference.

When I bleed up the system, especially when I put a cable tie on the lever and leave it over night, the system feels great, but within half a day I am back to a soft lever

Any one got any ideas? The only thing I havent changed in the system is the master cylinder, does this need a rebuild and could be causing my problems?

**NinjaNanna** · 7th January 2009, 10:38

If the lever comes right after leaving it tied over night then it must be air leaking back into the system.

Have you looked very closely for fluid leak after compressing the system over night?

If there's no sign of fluid leak then I'd suspect that one of your seals must be deforming when the pressure is released.

I'd say the most likely culprit would be the master cyclinder seals as they'd have significantly more travel then the pistons.

One test that's probably a bit subjective would be to see just how long you really need to leave the lever tied for before it comes right.

My understanding is that by leaving it tied the air bubbles have enough time to work their way to the top - that being so then surely it would take a lot longer for air leaking past the pistons seals to clear than it would for air leaking in directly at the master cyclinder.

They'd be my thoughts any way.

**motorbyclist** · 7th January 2009, 10:42

Originally Posted by Pumba

The only thing I havent changed in the system is the master cylinder, does this need a rebuild and could be causing my problems?

would sound about right

my little brother had the ~~exact same~~ similar problem and sure enough when we pulled out the master cylinder assembly there was a big chunk missing from the main seal

if i was you i'd replace the seals top and bottom... just did it myself

i'm actually about to post up a big how-to on brake rebuilds seeing as i took photos of the whole process

**SixPackBack** · 7th January 2009, 10:44

Its the master cylinder.
Similar issues on my K6.......re sealed the master cylinder and it helped but still ended up bleeding the system every month, recently that became once a week. I swapped the master cylinder for a ZX10 unit and the problem has disappeared. Note when the original master cylinder was disassembled [again] very little evidence of wear was discovered.

**westie** · 7th January 2009, 10:50

You may need to re-set the brake pots.

Ie, push them apart and with the front wheel in the air, spin it as you squeeze the lever so as to let them contact evenly.

Sometimes with discs they bend or move, especially floating discs, when the pads contact unevenly. ie one side before the other. Then they feel really squidgey.

But a new rubber cup and hone in the master cylinder will help big time too.
Once did it with a drill and some sand paper wrapped around it. Pretty easy to fuck it up tho

**The Stranger:Me** · 7th January 2009, 11:55

I have a nissin radial master cylinder here if you want to try that.
It is surplus, but belongs to Two Smoker - you could deal direct with him re cost.

**Pumba** · 7th January 2009, 12:27

Awsome, everyone else confirmed what I was thinking. Thanks guys.

Westie the brake pads were already set that way, thats some thing I was taught by the old man years ago when I did the seals on a old honda we had in the shed.

Originally Posted by The Stranger

I have a nissin radial master cylinder here if you want to try that.
It is surplus, but belongs to Two Smoker - you could deal direct with him re cost.

That would be great if I could try it to see if it solves the isuue, I could pick it today if you are around home.

**R6_kid:Me** · 7th January 2009, 12:55

that master cylinder of noels is going to give you a completely different feel - i'd say try it before you buy it.

I've got an OLD rs125 master cylinder on the RX125 atm and it has almost no feel - but it gets the brakes on really fast!

**imdying** · 7th January 2009, 13:03

If you clamp the line off when the lever is soggy, does that make it firm?

**Pumba** · 7th January 2009, 15:03

Originally Posted by R6_kid

that master cylinder of noels is going to give you a completely different feel - i'd say try it before you buy it.

I've got an OLD rs125 master cylinder on the RX125 atm and it has almost no feel - but it gets the brakes on really fast!

Yea I know, but that rx had sweet FA feel with the rx master cylinder so sounds like you havent made it any worse.

Originally Posted by imdying

If you clamp the line off when the lever is soggy, does that make it firm?

Didnt seem to make any difference

**Mrs Busa Pete** · 7th January 2009, 15:12

the rx 125 master cylander improved the fxrs front end 10 fold r6 has one for sale

**Pumba** · 7th January 2009, 15:31

Originally Posted by busa pete

the rx 125 master cylander improved the fxrs front end 10 fold r6 has one for sale

What the stuffed one that the fluid dissapeared from that used to be on my bike??

**Mrs Busa Pete** · 7th January 2009, 15:33

Originally Posted by Pumba

What the stuffed one that the fluid dissapeared from that used to be on my bike??

No gravety it all ran out the bottom.

**JMemonic** · 7th January 2009, 15:50

Ok how come no one has pointed out the "washers" in the system ie at the interface between the master cylinder and the brake line are actually gaskets, single use gaskets, (ok you can get away with a couple of tightens) but the can leak air, itsd easier to leak air into the system than fluid out, so along with all the other suggestions made thus far try replacing these, you may be pleasantly surprised.