Yamaha TRX850 Enthusiasts Forum

The curse of the piston binding
Mr. Yamaha forgot to tell that the famous blue spot calipers require a specific maintenance : cleaning the pistons. The problem is that the pistons fit in their bores with very limited looseness. Then dust settle around the pistons and soon forms a hard deposit which seize the piston. As a Result, it is not uncommon to have only one piston to remain operational inside each caliper. This lowers the braking efficiency and generates an asymmetric pads wear - maybe other strange figures - and finally makes the brake lever less firm . This is difficult to realize because the phenomenon is very progressive.

The solution : remove the calipers, clean the pistons one at a time while pushing them partially out. Rub the piston with a soft rag, using some brake fluid if the dust layer is hard. There also exists so-called "special calipers cleaning" fluids, but since there does not exist standard for these cleaning fluids, so there's something for brake fluids (including compatibility with seals), I prefer to use only genuine brake fluid on any brake part.

• Remove the two mounting screws and the caliper .
• Push back the pistons with the old pads still in place

• Remove the beta clips, the pad pin and the pad spring .
• Remove the pads & take note of their locating (internal / external).

• Place a wedge (wood or hard plastic) to block a pair of piston.
- Operate the brake lever to push one of the remaining two pistons out , blocking the other with the hand .
• Don't push it out past the casting otherwise the piston may come fully out !
• Clean the piston using a small rag around, add some brake fluid if the dust layer is hard.
• Push the piston back and proceed with the others.

• Replace the pads, swap them if the wear is different between both.

• Replace the pad spring with the arrow-mark pointing forward, replace pad pin and beta clips .


• Install the caliper on the front fork, tighten the screws to 4.0 m.kg.
• Proceed with the other caliper.
• Operate the brake lever several time to push the pads in contact with the discs.

The result is really worth it : stiffer break lever, increased braking power, now it's time to change the front fork oil !

I have a blue, silver, gold spot `key` cnc`ed from aircraft grade alloy hex bar. The spots once removed allow full cleaning to easily take place.
They are not expensive but a damn useful tool :

http://www.ebay.co.uk/itm/Yamaha-Blue-S ... 19ce7828a4

as i have never pulled them apart, whats to discover under the blue/gold/silver spots when you take them out?
do you require new rubbery bits to reassemble them?
cheers
fung

As far as I`m aware there are no O rings or gaskets as such, the `spot` removal just aids thorough cleaning etc.

http://www.oemmotorparts.com/oem5.asp?M=Yamaha&T=YZF R1 1000&Y=1998&L=YA-YZF-R1-1000-1&O=FRONT BRAKE CALIPER&F=YA-YZF-R1-1000-1_bk&L2=YA-YZF-R1-1000-1_bk

No O rings or gaskets shown on the parts listings fung but I`ve yet to do one myself.

i did some digging around, and found that the blue/gold/silver/blackspot screws in thru the caliper and has an o-ring seal on each one.
theory is, blow the piston out then screw out the plug in and out the other side.
full stripdown this is
cheers
fung

Ahaaaa, well done that man

How far out can you push the pistons approx before they fall out? I need to do some brake maintenance and don't want a woopsie moment
Later on: I pushed em out about 7mm to be on the safe side. Thanks for the inspiration to do the job Fung. I also changed the brake fluid for what appeared to be the first time since the bike left the factory...disgustingly muddy semifluid Brakes now lovely...cheers

This of course is called progress - think of the weight saving from not fitting dust seals...................