2002 yamaha kodiak--weak brake pedal--whats the problem

[garysaul]

Rear brake pedals very soft,I think all of a sudden as the kids have been riding this one.

Changed pads-calipers in great shape

Bled brakes--no change--apparently need new master cylinder?

Never had any type of vehicle where the master cylinder actually failed

Partzilla-$144---amazon $25 --has anyone used a chinese one 

 

[Gwbarm]

Used one for front brakes on a Big Bear no problems yet.

[Mech]

Are you sure it's the cylinder ? "very soft" is a strange condition.. If it doesn't bleed, and the pads aren't getting pushed back in by excessive wheel bearing play, perhaps the rubber hose is starting to bulge under pressure.

[Mech]

If the pumping seal in the cylinder is starting to wear out even though there's no leaks yet, the common symptom is that if you apply the brakes very slowly and gently avoiding building up pressure, the pedal will creep down. If you jab the pedal down the seals flare out and seal.

I'd try that test.

If it's a disc brake, and it passes that test the cylinder is probably ok. If it's drum brakes and it passes that test, there may be a valve in the cylinder that may be crook and the cylinder may still need to be replaced. To check the hose, you could use a clamp and gently clamp the hose near the master cylinder end and test the pedal. 

Best to try and diagnose things before throwing parts at it.

[garysaul]

O ram I better off trying to rebuild master cylinder--never tried it?

[Gwbarm]

I ve never had much luck at rebuilding these small master cylinders, bores are too corroded, just relating my experience, plus the kits aren't cheap for what you get. Im not telling you not to try, I will try anything once, maybe even twice, plus there is nothing more valuable than getting your own experience.

[Mech]

It's hard to get seals for overhauls these days..  But if it's just the seals and they are available then it's worth a try.. Seals are cheap if you can get them. You wash everything in brake fluid and/or water, not kero or anything petroleum. If it's got gouges in the bore then it's probably not worth doing. If there are no gouges then don't hone it, just polish it up with a rag on a stick. Lube the new seals with brake fluid or rubber grease before stretching them onto the piston, lube the bore with brake fluid or rubber grease..  Fit the cylinder, use your finger to block the outlet while you bleed it, then fit the pipes back on and do a full bleed.

Oh ok GW says the kits are dear..  I generally just bought individual seals..  back in the day.. haha.

Now, for $25 perhaps it's simpler to buy chinese.

[garysaul]

yep-just ordered one--now have to find someone with snapring plyers