Yamaha TRX850 Enthusiasts Forum

The front right 'blue spot' caliper on my TRX is dragging a little. It seems to be the outer two pistons that are being lazy so I had the caliper off tonight and eased the pistons out, gave them a little fine sand papering and fine wire wooling and thorough cleaning and its marginally improved the action, but I think I need to repeat a few times to resolve the problem completely.

I also managed to 'pop' one of the pistons out and had a small drop of brake fluid drip out of the piston. I quickly pushed the piston back in before any great amount o fluid escaped. Is this ok? I won't have done any damage or let any air into the system will I? Should I bleed the brakes? They seem fine. Some reassurance from those more in the know would be appreciated! I suspect I might have to overhaul the caliper(s) anyways to completely cure this problem in the end.

I've also read about some red piston grease that helps aid smooth caliper action. Whats it called and where do I buy it from (auto factors/Halfrauds?)

Thanks in advance.

Corners (developing Arnie arms pushing my bike about with a dragging caliper!!)

You should absolutely bleed the system after popping a piston.
Never leave anything to `I hope it`ll be ok` with a braking system,it`s just not worth it.

Yeah,you must bleed the system even if it seems ok!!
Your calipers could probably benefit from a strip and overhaul,i.e. new seals,clean,etc....
The red grease you mentioned is worth putting on if you already have the calipers in bits,it`s waterproof silicon based compound that does`nt wash off as soon as it rains...it`s called `marine` grease or sometimes just `red grease`.Marine grease is the proper name for it,Halfords don`t sell it but it can be found on Ebay,but check the quantity of grease before ordering as some people sell a thimble sized pot and some sell a larger tub or tube for similer money!!!
Hope this helps and good luck!

As I suspected, thanks for the confirmation. I'll have a scour of evil bay for the grease.

UPDATE: This the stuff?

http://cgi.ebay.co.uk/LUCAS-OIL-RED-N-T ... 240%3A1318

Is stripping the calipers difficult? I have a Haynes manual so will have a read over a brew later, although its a TRX manual and the calipers are Thunderace! Voyage of discovery and fun ahead I suspect....

UPDATE: Search is a wonderful tool!

It's not complicated. You won't need any special tools, although a compressor can be good.

Take out the brakepads.
Take off the caliper, be careful with the brake lining, have something ready for collecting the brake fluid. (It's an excellent paintstripper...)
Try to get the pistons out. If you have a compressor, put a piece of wood between the pistons (they'll be pushed out quite harshly) and blow air into the calipers.

AND IF YO HAVEN'T? DO THEY COME OUT THAT EASILY GIVEN THAT THEY ARE A B@TCH TO PUSH BACK IN? DO YO SIMPLY PUMP THE PISTON OUT BY PUMPING THE LEVER. OR DO THEY COME OUT EASILY ONCE FLUIDSBEEN DRAINED OUT?

Mark the pistons so you can put them back where they sat. Pull out the rubber seals, and start cleaning the calipers and pistons, use proper brake cleaner or spirit.
When assembling, lube the seals and pistons with brakefluid.
Drain the master cylinder completely by removing the cap (once again, beware of the fluid). You'll have loads of air in the system anyway, so it's a good opportunity to change the fluid.
Push the pistons completely in, put the calipers back, tighten up the bolts, brake linings.

And now the fun stuff, bleeding the brakes Fill up the M/C, different schools, either pushing the fluid from the calipers using a syringe or similar, or fill from the M/C and bleed the normal way. Air can get trapped where the linings connect to the M/C, so you might try to bleed the system there as well.

If this explanation's not enough, I suggest you download the workshop manual, which you'll find somewhere here.

THIS COVER IT??

Corners

Pretty much covers it yes.
A compressor isn`t necessary at all but a bloody handy thing to have in the work shop.
Here`s another way:

Loosen the caliper bleed nipple right off,then attach a piece of tubing.
You can then utilise a footpump or even a bicycle pump(fitted with the nozzle adapters most come with to connect to tubes,air beds etc),then you can gently ease out the pistons with if you like, `reverse` pressure.Alternatively it`s the much messier but just as easy,pump them out with the lever/brake fluid pressure.
Anything soft(fingers work well NOT!)between the opposing pistons will enable you to choose which pair you want to remove first.
And yes,definately don`t mix them up on reassembly,it`s easiest to have some small sandwich bags or similar at hand to keep them seperate.
that way you can work on one at a time and when it comes to refitting them you cannot get mixed up.
It`s an easy job but cleanliness is essential,as is care not to scratch or gouge the softer caliper alloy on the machined surfaces.
Bleeding again is easy if you utilise either a pump or vacuum pump.You can buy vacuum pumps for around 20 quid I think,in fact Hein Gerrick do one if memory serves me correctly.I use a large syringe to draw the fluid through the lines and into the caliper from the master cylinder,again using tubing from the bleed nipple.Use a strong rubber band or cable tie,string etc to hold the brake lever fully in.
I have to say though that when it comes to the `final` bleeding point I like to complete the task off the lever,that way you can feel if there`s air left in the system from the brake lever action.Instead of relying on visually seeing bubbles through the tube,a lot of very tiny bubbles is just as bad as one big one!
Brake fluid is hygroscopic which means it attracts moisture from the air,therefore ANY air left in the system is slowly degrading the efficiency of the fluid and affecting it`s hydraulic qualities too,air is easier to compress than oil/fluid.
As for the grease,be very careful with quantities used,it`ll just attract road grime,dust,grit etc to stick in it and remember any oil/silicon based product near the compound materials of brake pads is really NOT what you want.
I`m sure you`ll find it easier than you imagine it to be.

Thanks for the clarification. As you say I think I'm envisaging a more difficult job than it really is and I suspect fairly regular strip downs will occur once I realise how simple the whole operation is! A second set of biker mates hands will be deployed to assist me when I get round to doing this job, partly as a santiy check to what I'm doing and partly cos its easier to bleed 'off the lever' that way!

I'll order up some red/marine grease tonight in rediness (no pun intended!) for getting time to do the job next weekend. The previous owner had managed to smear copper grease everywhere which was a bitch to clean off so there's no fear about me go to heavy with the red grease!

I will update this thread once the jobs done.

Cheers, Corners