Brakes

[davidon]

What are symptoms of piston seals needing replacement? I noticed a spongy feel at times even though I know there should be no air. Wondering if the pistons are not retracting all the way sometimes.

 

[SpecOps13]

I'm having trouble with my 89 right now. I'm pretty sure the Brake Master Cylinder is in need of rebuild. The lever travels almost half way before the brakes start working.... And, feels mushy too...


Just a Thought....

 

[Fire-medic]

A cheap fix. Wouldn't be surprised if you have a bad master though or a bad line or lines especially if you still have the stock rubber ones. Don't forget to use new copper washers. You can get some at your local auto parts store, you don't need Yamaha OEM. I have used Dorman brand like NAPA & other good stores carry. They might be slightly thicker but if the I.D. Is the same you should be ok.

I uses to try rebuilding my masters but have just decided to buy new after I was hitting more 'no-good' rebuilds than OK ones. I didn't see any obvious scores on the bore but the rebuilds didn't work often enough so I just buy new now. I was using 'made in Japan' kits but not OEM.

 

[naughtyG]

Spongy feeling is usually simply a sign that your brake fluid needs replacing. It absorbs water over time and lose its uncompressibility.

Simply flush your braking system with fresh fluid, bleed it all properly and you should be fine! If not you can always look a overhauling your M/C and/or your calipers.

 

[one2dmax]

Rarely do the calipers need rebuilding. They do sometimes need to be pushed all the way out and the pistons cleaned (an old tooth brush works well here).

Sean

 

[MaxMidnight]

Spongy feeling is usually simply a sign that your brake fluid needs replacing. It absorbs water over time and lose its incompressibility.

Are you sure about that?
Whilst brake fluid is hygroscopic and will absorb water over time that in itself would not alter braking efficiency.
The point is that the water will reduce the boiling point of the fluid but only becomes an issue when braking hard repeatedly. When the fluid temperature goes over water's BP it will turn to steam. Whist water is not compressible, steam is and you will loose the brakes.
Additionally the water can cause corrosion to internal components.

The sponginesses could be down to air getting in or could be down to the hoses flexing (i.e. expanding) as you apply the brakes.
If you still have the OE hoses it may be the excuse you need to upgrade?

 

[naughtyG]

Hmm yea I was oversimplifying of course it's air/steam that's compressible but it all mainly comes from water + heat..

To that of course you can add the OEM lines' expansion over time which doesn't help either, so absolutely fresh fluid + stainless steel braided lines brings the best possible combination.