How To Rebuild Harley Master Cylinder
If your motorcycle master cylinder isn't holding pressure when you pull the brake lever, the internal seals may be worn or damaged.
![rebuild master cylinder Harley-Davidson Sportster Harley Sportster master cylinder rebuild](http://www.classic-motorcycle-build.com/image-files/x1976-harley-davidson-sportster.jpg.pagespeed.ic.L_Zfv0Ze1p.jpg)
Other things that would cause no brake pressure are low brake fluid and leaking calipers, so check those two things out before blaming the master cylinder! If you find that it is bad, consider rebuilding the old one as an alternative to buying a new one.
The bike in this article is a 1976 Harley Sportster. The master cylinder is actually a chrome aftermarket replacement, but rebuild kits work just the same as with original Harley units.
![Harley front master cylinder assembly how to rebuild Harley master cylinder](http://www.classic-motorcycle-build.com/image-files/xsportster-master-cylinder.jpg.pagespeed.ic.sCXFxfiM5h.jpg)
Master Cylinder Rebuild Kit
This master cylinder rebuild kit replaces Harley # 45063-72. It fits 3/4" bore master cylinders from many 1972 through 1981 Harleys, including FL, FX, and Sportster models.
![Harley master cylinder rebuild kit master cylinder rebuild kit for Harley FL FX XL models 1972-1981](http://www.classic-motorcycle-build.com/image-files/master_cylinder_rebuild_kit_for_harley_fl-fx-xl-1972-1981.jpg)
NOTE: The rebuild kit does not include a M/C cover gasket. If yours is damaged, you can buy one here.
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Getting Started
Although you can rebuild a master cylinder while it's still mounted to the handlebars, it's a whole lot easier when it's sitting in front of you on a work bench.
Removing the brake fluid from the reservoir was done with a two-ounce (60 ml) syringe.
![Harley master cylinder rebuild rebuild Harley master cylinder](http://www.classic-motorcycle-build.com/image-files/remove-brake-fluid-with-syringe.jpg)
Once the reservoir was empty, the front brake line was disconnected, and the four Allen bolts were removed. Disconnect the two thin wires from the stoplight switch.
![Harley Davidson master cylinder rebuild rebuild Harley master cylinder](http://www.classic-motorcycle-build.com/image-files/harley-master-cylinder-removal.jpg)
Moving over to the workbench, disassembly can begin.
![rebuild motorcycle brake master cylinder rebuild Harley master cylinder](http://www.classic-motorcycle-build.com/image-files/harley-master-cylinder-rebuild-76.jpg)
To remove the hand brake lever, remove the retaining ring (E-Clip) that holds the pivot pin.
![Harley master cylinder rebuild rebuild Harley master cylinder](http://www.classic-motorcycle-build.com/image-files/harley-master-cylinder-rebuild-77.jpg)
I'm using a small flat-blade screwdriver to remove the E-Clip, then pushing the pin through to release the lever.
![Harley master cylinder rebuild rebuild Harley master cylinder](http://www.classic-motorcycle-build.com/image-files/how-to-rebuild-harley-sportster-master-cylinder.jpg)
Brake lever removed.
Remove Master Cylinder Piston
You now have access to the retaining ring that holds in the piston assembly. Remove it with snap-ring pliers.
![Harley master cylinder rebuild rebuild Harley master cylinder](http://www.classic-motorcycle-build.com/image-files/how-to-rebuild-motorcycle-master-cylinder.jpg)
It's a little tough to get to the snap-ring because it's recessed.
Switching from straight tips to right-angle tips on the snap ring pliers made this task easy.
![snap ring pliers motorcycle tools swap straight tips for right-angle tips on snap-ring pliers](http://www.classic-motorcycle-build.com/image-files/snap-ring-pliers-motorcycle-tools.jpg)
Pull out the piston, O-ring, piston cup, spring cup, and piston return spring.
![Harley master cylinder rebuild rebuild motorcycle brake master cylinder](http://www.classic-motorcycle-build.com/image-files/xrebuild-harley-master-cylinder-76.jpg.pagespeed.ic.2S3fE9R9_N.jpg)
Clean and inspect all parts.
![Harley master cylinder assembly how to rebuild Harley master cylinder](http://www.classic-motorcycle-build.com/image-files/how-to-rebuild-a-harley-master-cylinder-80.jpg)
If you find a little corrosion inside the bore, you can try cleaning it with some Emory cloth, but if there's a lot, it's best to replace the master cylinder.
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Reassembly
![Harley master cylinder rebuild rebuild Harley Sportster master cylinder](http://www.classic-motorcycle-build.com/image-files/harley-master-cylinder-illustration.jpg)
Assembly is basically reverse of disassembly.
![rebuild motorcycle brake master cylinder rebuild Harley master cylinder](http://www.classic-motorcycle-build.com/image-files/rebuild-motorcycle-brake-master-cylinder.jpg)
Before installing, lubricate new parts with DOT 5 brake fluid.
![Harley Davidson master cylinder rebuild how to rebuild Harley master cylinder](http://www.classic-motorcycle-build.com/image-files/how-to-rebuild-motorcycle-master-cylinder-92.jpg)
Install the spring and piston into the cylinder bore, making sure they go in the correct way. If you're not sure of the sequence, refer to the illustration.
![Harley master cylinder rebuild remove e-clip Harley master cylinder](http://www.classic-motorcycle-build.com/image-files/harley-master-cylinder-rebuild-90.jpg)
Getting the brake lever back in was a little tricky. It helped putting the master cylinder in a vice between two soft jaw pads so that both your hands are free.
Test Master Cylinder
Here's an easy way to test a motorcycle master cylinder before hooking everything back up. Hold a finger over the outlet, then pump it several times. As you let your finger go, you'll hear the air escape.
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Bleed Master Cylinder
There's several ways to bleed the master cylinder. I took a piece of 1/4" x 8" brake line from an auto parts store, cut one end off, and bent it so that it fits into the reservoir.
![motorcycle master cylinder bleeding bleed front Harley master cylinder](http://www.classic-motorcycle-build.com/image-files/motorcycle-master-cylinder-bleeding.jpg)
Fill reservoir with DOT 5 brake fluid. Pump the hand lever slowly until air bubbles stop appearing in the fluid. On this one, it took about 10 or 15 pulls for the air bubbles to stop. The steel line was then removed and the front brake hose was attached.
![Harley-Davidson FL/XL caliper rebuild Sportster caliper rebuild](http://www.classic-motorcycle-build.com/image-files/xbleeding-motorcycle-brake-caliper.jpg.pagespeed.ic.n9eyLqyGWR.jpg)
Bleeding the front brake caliper.
As an alternative to rebuilding a Harley master cylinder you can buy a new one here.
![Ironhead Sportster brake master cylinder motorcycle brake master cylinder](http://www.classic-motorcycle-build.com/image-files/new-master-cylinder-harley-sportster.jpg)
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CAUTION: Working on brake systems is not something to be taken lightly. If you don't feel that you are 100% capable of doing it correctly, leave it to a professional.
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Related Articles:
Best Thread Sealant For Brake Fittings
Harley Pie-Slice Caliper Rebuild
Harley Dual Caliper Rebuild
Replace Fork Seals
![1976 Ironhead Sportster Ironhead Sportster project](http://www.classic-motorcycle-build.com/image-files/xironhead-sportster-replace-starter.jpg.pagespeed.ic.m4bZYEhfrW.jpg)