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Hey folks, I got around to servicing the master cylinder and brakes on my sled today. I figured I would do a quick write-up on this little project.

This is based on my sled, 2001 Formula Deluxe 500 (Liquid)

Tools needed:
Phillips Head Screwdriver.
11mm Wrench (or whatever size for your bleeders).
A 10" length of appropriately sized tubing for bleeding.
A small container for bleeding.
Syringe/suction device for removing old fluid from master cylinder.
A small piece of wire, or jet cleaning kit (for cleaning the return port in the master cylinder).
A small container of brake fluid.
Rags.

First, carefully remove the master cylinder cover:

Mine was good and dirty in there...

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Remove as much old fluid from the master cylinder as possible:

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Inspect and remove any large debris found:

Here you can see the "rusty" type residue left from the moisture that made it into the system.

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Clean out the master cylinder using brake cleaner and brushes:

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Use small wire/jet cleaning kit to clean out the return port (small port) in the master cylinder:

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Refill the master cylinder with fresh brake fluid:

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Install tubing on the bleeder, open the bleeder on the caliper:

NOTE* My caliper has 2 bleeders. I bled the "left" bleeder first, then moved to the right.

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Bleed until fluid runs clean, taking care to not let the master cylinder run dry (then you'll have to bleed all that air out):

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Top-off master cylinder, test brakes for proper operation. Caliper should relax after releasing the brake lever.

Ride safe out there everybody!
 

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Yeah, I think it's because the lube oil tank behind it is causing the color to look off. In person the fluid was nice and clear.

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Yeah, I think it's because the lube oil tank behind it is causing the color to look off. In person the fluid was nice and clear.

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Right on. Hey what size hose did you use over the bleeder valve? I'm going to have to go buy a small chunk and don't want to have to take the caliper with me.

-Doo02
 

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Discussion Starter · #6 ·
Right on. Hey what size hose did you use over the bleeder valve? I'm going to have to go buy a small chunk and don't want to have to take the caliper with me.

-Doo02
I want to say it's 1/4" nylon. I'm not 100% sure, it's stuff I've had laying around for years...

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I did it to my 2000 FD 700 when the brake seized up on the trail. The return hole was plugged. Had to stop on the trail 3 times before we got home to relieve pressure on disc. The last time I didn't notice it was hanging up until it was too late. By too late, I mean, I just so happen to glance down by my right foot to see pretty little red lights in the foot well. Stopped and popped the hood, the disc was cherry red!

So my question, this is a sealed system, how does the fluid get so yucky?
 

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I did it to my 2000 FD 700 when the brake seized up on the trail. The return hole was plugged. Had to stop on the trail 3 times before we got home to relieve pressure on disc. The last time I didn't notice it was hanging up until it was too late. By too late, I mean, I just so happen to glance down by my right foot to see pretty little red lights in the foot well. Stopped and popped the hood, the disc was cherry red!
So my question, this is a sealed system, how does the fluid get so yucky?
It's a mystery to me too. How does water get in and cause metal to rust? Must be a "not so sealed" system.

-Doo02
 

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Discussion Starter · #10 ·
The master cylinder cover can (and does) over time leak minuscule amounts of air in. This air has moisture in it, and then this condenses into the fluid in the reservoir time after time. Eventually it settles to the bottom and gaks up the bottom of the MC.

I mean, it takes years and years. I likely did the first clean & flush on my machine, and it's 17 years old.

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Yea, mine is 16 years old and never been done... no issues, but my wife's, same age, locked up. Think I will clean and bleed mine when doing hers.

-Doo02
 

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Just finished mine. Man there was a ton of air in the line! Actually took caliper back off, compressed pads, and the when pushing back pads, a tons of air bubbles came out master cylinder. Still seems a hair soft so gonna bleed it more, but it did harden up. When I started sled and hit brakes, she stopped the track no problem. Gonna hopefully test her tomorrow!

Pic of fluid that came out. MC was very orange in color.

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-Doo02
 

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I thought moisture get in there because of a mix of warm /cold conditions of the fluid and temp out side- kind of like storing a gas tank low on gas for a period of time it will condensate inside and then you’ll have water in fuel issues
 

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Could this be the solution for my mxz 800? When the temps are below zero the brakes like to stick and not release, wondering if my return port is plugged or partially
 

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Discussion Starter · #15 ·
I'd say this is something that should be done every 5 years. It's such an important part of the sled, takes very little time and effort, and costs almost nothing to do.....why not just do it?!?

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Stupid question. I used DOT 4 fluid to replace the old stuff but I noticed that the new stuff was synthetic. Does this matter?
My first guess would be no. Every time you hear Synthetic, it is expected to be better. I would thing you would be okay, but I am sure someone would chime in that has a better idea.

DOT4 opposed to DOT3 has a higher boiling point. Synthetic over non-synthetic is probably one of those "preference" deals.

I would be curious to hear if someone has been using syn without issues though.

-Doo02
 

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Did this a couple of weeks ago to a NTM 97 MXZ 670. Everything was working as intended the first couple of trips I went on. Then, 2-3 weeks ago, I put on some bar risers and throttle extension. Was going to extend the brake line, but my local auto parts store didn't have what I needed. Turns out that just relocating the brake line gave me enough slack. Once I cleaned the MC, I couldn't get anything to bleed. Verified flow through the MC. Blew the caliper out with air, but couldn't air through the brake line itself. Had 140 psi on my compressor, but nothing would squeak through. Leaving the next morning, so I had to come up with something. Ran my welding wire through the line several times and finally cleared out the blockage. Took almost 4hrs to do a 15min job. Geesh!
 

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Nice write up. After having my 1995 Mach 1 catch fire from a dragging brake this winter, every hydraulic brake on any sled I restore gets cleaned and rebuilt. The backflow port gets plugged = when the brake is applied it does not fully disengage. As it drags, the heat generated causes the brake fluid to boil and expand, causing the caliper to clamp tighter - eventually turning the rotor red hot and ripping it apart - sending red hot pieces all over under the hood. Not pretty.

A neat little trick for refilling the system.... I filled a pump oilcan with brake fluid, and put a piece of 3/16" gas line on the tip of it - connected the other end to the inner side brake bleeder. Cracked open the bleeder, and slowly pump the fluid into the system from the oilcan. You'll see bubbles in the master cylinder - when it stops bubbling, the brake system is fully bled and full.

Otherwise it takes FOREVER to refill the brake system.
 

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Always remember to use a sealed container of brake fluid too. Brake fluid will absorb moisture from the air over time and make your brakes feel ''pillowy''/ not function correctly.
 
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