HOW TO: Rebuild Your Master Cylinder

This is going to be a real quick how-to on rebuilding a master cylinder. The cylinder we'll be working on comes off an 1982 XJ650. Yours may be different.

About two weeks ago, I was getting ready to go for a rather long ride. While doing my pre-ride inspection (you do those, right?) I noticed my brake fluid level was a bit low in the window. No problem, I thought. I grabbed my #2 Phillips screwdriver and removed the first screw from the master cylinder lid. It's when I went to remove the second screw that I ran into trouble. I slipped the screwdriver into the cross and gave it a slight counterclockwise twist. The head of the screw literally came right off. Every part of me screamed obscenities all at once. I was none too happy and a little concerned my "long ride" was officially over before I had even left the driveway.

I pondered my predicament and came up with this as a quick fix.



I filled the master cylinder with fluid and clamped it down with both the remaining screw and a radiator hose clamp. It worked fine; didn't leak once in the last two weeks of use. I knew, however, that this was not a permanent fix so I placed an order with chacal for new screws, a reservoir gasket, sight glass and adhesive, and a rebuild kit.



Luckily I had another rebuildable master cylinder I had picked up at a garage sale last summer. I asked one of my customers to clean it up a bit with his sand blaster. Here's our rebuild candidate:



Not the best paint on the outside, but the inside cleaned up real nice. Anyone have a suggestion on what kind of paint to use that brake fluid won't melt?

Okay, I think we're ready to get this thing torn down, cleaned up, and put back together.

Here are the steps:
1. Remove the rubber dust boot from the rear of the master cylinder bore.



It fits into a grove in the cylinder piston. Our kit contains another, so don't be afraid the give it a good hank to remove it. It fits snuggly into the bore above the retaining E-clip.
2. Remove the E-clip using a pair of snap ring pliers.



You may need to use a pick or some other pointed tool to remove corrosion to get at the E-clip.
3. Push the cylinder contents out of the bore by placing a screwdriver into the bore via the threaded hole where the brake hose screws in.
4. Take your time and do a thorough job of cleaning the bore, the groove where the E-clip goes and the two small orifices that connect the reservoir to the cylinder bore.





5. Install the rubber cup onto the piston. The cup's taper should be tapered toward the rear of the cylinder.
6. Install the rubber cup onto the end of the tapered spring. The nub sticking out of it's center will fit into the hole in the end of the spring.



7. Slide the spring with the rubber cup into the bore followed by the piston. Use a little brake fluid (DOT 3) to lube the cups.
8. Depress the piston and install the E-clip.



9. Install the rubber dust boot, making sure it is seated firmly against the E-clip.
10. Using a small amount of sealant, lay a bead in the grove of the sight window seat.
11. Carefully set the sight window into the recess and apply pressure to bed the window into the sealant. Allow it to cure before filling with brake fluid.



That's about it. Your master cylinder is pretty much done. Reinstall it on your bike, fill it, cap it with a new reservoir gasket and screws, and, after bleeding your system, you're good to go.

 

Very nice, you didn't show us the removal of the broken screw, though.

 

That's cuz it's still in there... just not in this one. I'm sending that one to my machine shop to be fixed.

 

O.K. it was a doner M/C.
Regards paint, havn't found any, I just pollished mine, less ag'

 

Yeah...paint. Duplicolor "brake and caliper" paint doesn't hold up AT ALL; their engine enamel does a bit better; PJ1's black epoxy frame paint...sorta. It doesn't immediately dissolve and come right off, but brake fluid still "attacks" it. I'm going to do an experiment with baking it in a low-temp oven to ensure it's fully cured and try it again. (I'm experimenting using a fluid reservoir cap that was so corroded away on the underside as to need replacing.)

Polished looks fantastic, Wiz; but there are some bikes that need it to be black.

*EDIT* Nice write up too Don, thanks.

 

Don fantastic write up as we have come to expect from you. Thanks!

 

gun kote
NOTHING but sandblasting takes this stuff off

 

I was just thinking either gun kote or Por-15. I've got Por-15 at work. I may try that. It world probably work for repainting the levers, too.

 

Is that gun kote generally available in local stores? I am looking in redo-ing my MC within the next week or so (am going to do the same, rebuild a spare I have). I was thinking about just polishing it, however my MC is a Seca dual disk which is jammed behind/under the headlight. So I think a black finish would be best just to 'hide' it. So I am interested in anything for painting it ;-)

Great write up!

 

I'm not sure where you'd find gun kote.. Here's an online source. If they have a contacts page, you could call them to see if they had a local distributor you could go to.

On a side note, I forgot to give instruction on removing the sight window. I know there are two kinds out there. I'll see if I can get a picture and put together something later on.

 

i'am pretty sure brownells is online only, they are the only place that has gun kote in spray cans also
you can get 16oz cans from the mfg. to use in a air brush that will last the rest of your life, 2oz does all the covers on a engine

 

Being that I am lazy, i'd go for the aerosol so I don't have to go buy a airbrush ;-)

Any other recommendations for paint? if I had a sprayer i'd just get some black powder coat and coat it and bake it in a toaster oven.

 

Ouch, I just went to that link. Pricey. Averages 30$ a spray can

 

Quote: "On a side note, I forgot to give instruction on removing the sight window. I know there are two kinds out there. I'll see if I can get a picture and put together something later on."

Anybody got anything about this? I'm putting a shopping list together for chacal and wanted to ask him or anybody for that matter, how do you know which type of sight window to get?? I feel like mine is glued in but don't wanna waste $ on the wrong sight window.

ps. not sure if I quoted this the right way but you get the point

 

Now if we can get something like this for a Seca MC, I'd be all set ;-)

 

Also:

If the "Guts" of the master Cylinder you are about to rebuild look as funky as the Guts in the Model used for this instructional; it would be a good idea to examine the MC Bore after it has been cleaned with Disc Brake Cleaning Fluid.

After cleaning, visually inspect the Bore.
Look for Build-up or Pitting.

The Build-up needs to be removed.
Heating it with a Pencil-Tip flame of a Butane Torch will soften it and allow it to be cleaned without scraping the Bore.

If the Bore is Pitted ... You'll have to "Hone" the Bore.
Roll a tight Cylinder of 800 Finishing Paper on a Wooden Dowel
Lube the Roll of Finishing Paper with WD-40
Stuff the Rolled-up Cylinder of 800 into the Bore so that the roll does not unwind when rotated.

Use a Variable Speed Drill and Rotate the Roll in and out ... at different speeds to refinish the Bore and (hopefully) eliminate the Pitting.

 

There two types of original sight windows that were used, and depending which type your original master was equipped with will determine which type of replacement glass window to order, since both the original and replacement windows differ in size depending on which style was originally used:

a) Sight window Type A was originally pressed into the cavity in the master cylinder body....there may have been some type of sealant used, but I'm not sure. This type of sight window is larger than the Type B below. This type of sight window can be a beast to remove from your original m/c, as you have to sometimes pick it out, piece by piece.

This Type A sight window is, to the best of our knowledge and experience, used in ALL versions of the large-bore master cylinders (dual-disc bikes) and only in SOME of the smaller-bore master cylinders used on single-disc bikes (including the 1100 front master cylinder, which is a small-bore m/c).

b) Sight window Type B was originally retained in the cavity in the master cylinder body via a "C"-shaped clip that is inside the reservoir....and once you remove this c-clip, the entire sight window can just be pushed out from inside the m/c. This type of window is relatively easy to remove, and uses a smaller window than the Type A window above.

This Type B sight window is, to the best of our knowledge and experience, used in MOST versions of the small-bore master cylinders (single-disc bikes, including the 1100 front m/c) and NEVER in the larger-bore master cylinders used on dual-disc bikes. This "clip-retained" style of sight window seems to have been an "earlier" design, and phased out over time, and replaced completely by the pressed-in style (Type A) window by the 1982 model year (which is when the larger-bore, dual-disc m/c's started being used on the XJ models).

 

Here's how chacal explained it to me:

I hope that helps. It got me into the right parts (I was a Style B).

 

Gamuru, thanks for relaying the message. I have the 81' 650 as well and suspect I have the style B kind as well.

Chacal, expect a list from me asap. Thanks for the descriptive comments on different sizes also!

 

Thanks, Rick, for the tips! All are excellent suggestions.