How to rebuild your rear master cylinder


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How to rebuild your rear master cylinder

Postby WingAdmin » Sun Mar 22, 2009 10:35 pm



I used a rear master cylinder rebuild kit from Partsnmore.com for my 1982 GL1100A Aspencade.

1. Remove the right side cover of the motorcycle, exposing the right side of the fuel tank. At the bottom of the fuel tank you will see the master cylinder.

2. Undo the brake line fitting banjo bolt. Be ready to catch dripping brake fluid.

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3. Remove the two bolts holding the master cylinder to the frame. If your motorcycle has rear air suspension, these two bolts also hold another bracket in place. This bracket can remain in place while the master cylinder is removed.

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4. Remove the bolt fastening the rear brake fluid reservoir to the frame.

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5. Where the pliers are pointing is where the brake pedal is connected to the master cylinder with a clevis pin.

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6. Remove the cotter pin and washer holding the clevis pin in place, then remove the clevis pin.

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7. Open the top of the reservoir and dump the contents of the reservoir.

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8. Unscrew the fastener holding the hose to the reservoir and pull the hose free of the reservoir.

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9. Reaching underneath and behind the exhaust, gently lower the master cylinder and remove it from the motorcycle.

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10. This is what the master cylinder looks like once removed.

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11. Loosen the jam nut holding the clevis in place. This may be stiff, I lifted the boot and used another wrench to hold a nut on the brake shaft while I loosened the jam nut.

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12. Once the jam nut is loosened, unscrew the clevis and jam nut from the brake shaft, then remove the rubber boot.

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13. At the base of the brake shaft is a metal washer held in place with a circlip.

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14. Use snap ring pliers to squeeze the circlip, then remove it.

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15. Pull the brake shaft straight up out of the master cylinder. It will bring the washer with it. It may take some force, if the washer is corroded as it was in this picture. Do not bend the shaft from side to side, you do not want to score the inside of the cylinder. Once the washer comes free and the shaft is removed, the piston will be pushed out of the master cylinder by its spring.

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16. There is a secondary rubber seal and a spring remaining in the cylinder. I used an air nozzle, applied to the brake line fitting, to blow them both out of the master cylinder. I wrapped electrical tape around the nozzle of the air nozzle to effect a seal against the fitting. If you do not use this method, be extremely careful getting the seal and the spring out of the cylinder - the cylinder walls are soft, and score easily. If you use a tool to get them out, use a plastic one that will not damage the cylinder walls.

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17. Clean any corrosion and dried brake fluid from the end of the master cylinder. Use copious amounts of brake cleaner to clean any debris out of the master cylinder, both down the front of the cylinder, down the brake fitting, and down the reservoir hose. Use a dull pick to clean out the inner circlip channel as well as the outer boot channel on the end of the cylinder.

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17a. Remove the two screws holding the reservoir hose flange to the master cylinder. Clean out this area of the master cylinder with brake cleaner.

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17b. For the next step, you will need a stiff, very fine wire (a piece of wire clipped from a wire brush, or a piece of guitar string works well). Grasp the wire with a set of needle nose pliers.

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17c. Using the wire, ream out the fluid return port. This tiny pinhole is found in a small round depression near the edge of the cavity, as shown in this picture. Sediment clogging this port is a common cause of dragging and locked up brakes. Clean with brake cleaner once more, and reattach the flange with the two screws.

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18. The new spring has a metal disc on one end with a hole. This end of the spring will be facing the opening of the master cylinder.

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19. The rubber seal has a fitting that goes into the hole on the disc on the spring.

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20. This is how the seal fits on the spring.

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21. Insert the spring gently into the master cylinder.

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22. Lubricate the seal with clean brake fluid and place it on the spring, gently so that it seals against the top of the master cylinder.

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23. Lubricate the rubber seal on the piston with clean brake fluid, and push it into the cylinder, compressing the spring and moving the first seal down into the cylinder.

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24. Push the rounded convex end of the brake shaft into the concave end of the piston, and push the piston fully into the cylinder, allowing the washer to seat into the top of the cylinder.

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25. While maintaining pressure on the brake shaft (if you let go, the spring will push it, and the piston out of the master cylinder), insert the circlip and fasten it in place using snap ring pliers. This will prevent the brake shaft from being pushed out of the cylinder.

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26. Lubricate the inside of the boot with clean brake fluid and push it over the brake shaft, making sure its ridge fits into the channel on the brake shaft.

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27. Pull the boot over the top of the master cylinder, ensuring its ridge fits into the channel on the master cylinder.

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28. Screw the jam nut onto the threaded shaft, followed by the clevis. While holding onto the clevis with pliers, tighten the jam nut against it.

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29. Lift the master cylinder into place and fasten it to the frame with its two bolts.

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30. Using new crush washers, connect the banjo fitting to the master cylinder with its bolt, and tighten it to 22 ft-lb.

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31. Apply grease to the clevis pin and smear it around the pin evenly.

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32. Lift the brake pedal lever into the clevis, and push the clevis pin through it to fasten it to the clevis. Put the washer over the pin, and fasten it in place with a cotter pin. If a replacement cotter pin is used, ensure it is stainless steel.

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33. Connect the reservoir hose to the reservoir and tighten its fitting.

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34. Replace the reservoir and fasten it to the frame.

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35. Fill the reservoir and bleed the system. I would highly recommend using a Mity-Vac to do this.



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Re: How to rebuild your rear master cylinder

Postby WingAdmin » Fri Jun 05, 2009 12:22 pm

A note about subsequent brake pedal height adjustments: You can adjust the brake pedal height without disassembling any part of the master cylinder. Just loosen the jam nut from the clevis several turns, then turn the threaded shaft, threading it either farther into the clevis (lowering the pedal) or farther out of the clevis (raising the pedal). The threaded shaft will turn easily without turning the piston, because the convex end of the shaft will simply rotate in place against the concave end of the piston.

Once you have the pedal adjusted correctly, retighten the jam nut against the clevis to lock it into place.

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Re: How to rebuild your rear master cylinder

Postby tumunga » Wed Jun 24, 2009 9:42 am

Nice site. I really love the detailed "How-to" sections.

I noticed you used the front master cylinder rebuild kit to rebuild your rear master cylinder.Is there an advantage to using the front rebuild kit on the rear master cylinder?

Eric - Pittsboro, IN
1980 GL1100i
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Re: How to rebuild your rear master cylinder

Postby WingAdmin » Wed Jun 24, 2009 9:53 am

No, I most definitely used the rear kit for the rear master cylinder - I don't believe they are the same (although they are similar).

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Re: How to rebuild your rear master cylinder

Postby tumunga » Wed Jun 24, 2009 7:43 pm

HA! I could have swore the first sentence said you used a front master cylinder rebuild kit from Partsnmore.com when I read this the first time!

Boom goes the dynamite!

Eric
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Re: How to rebuild your rear master cylinder

Postby jacobite » Wed Jul 15, 2009 7:34 pm

i had problems with my rear master brake cylinder and pulled it off, only to remove the rubber boot and find it full of rust, im thinking of just scraping the rear master brake and replacing it with a new one if i can find the parts :ugeek:

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Re: How to rebuild your rear master cylinder

Postby WingAdmin » Wed Jul 15, 2009 7:50 pm

They don't make new ones...so my advice would be to pull apart what you've got, scrape (gently) the rust and crud that's in there, and rebuild it using a commonly-available rebuild kit. Mine was completely full of rust and crap (as you can see in the pictures) and it cleaned up quite nicely. I think you'll be surprised at just how clean it comes out. Just use lots and lots of brake cleaner, and be gentle when scraping the channels clear - more than anything else, make sure you don't scratch the bore of the master cylinder.

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Re: How to rebuild your rear master cylinder

Postby lobabooby » Fri Aug 28, 2009 9:07 am

As far as bleeding brakes.. They now have replacement bleeder fittings with built in "check valves"... So expensive vaccum bleeders are no longer needed. Niether is the second person to help you bleed them!.. You can check these out at, www.speedbleeder.com Finally, it's a one person job.

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Re: How to rebuild your rear master cylinder

Postby WingAdmin » Fri Aug 28, 2009 9:11 am

Those are great if you are just bleeding your brakes periodically as part of maintenance, or flushing your brakes by adding new fluid and pumping it through. However, if you have drained your brake system, there is really no practical way to bleed it without a vacuum pump - you can try to fill the reservoir and let it sit for a day or two, but until you've got some brake fluid into the master cylinder for it to pump, you're not going to have much success. A vacuum bleeder will do that quickly and easily.

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Re: How to rebuild your rear master cylinder

Postby MJSantos » Sun Jun 20, 2010 11:36 am

Another interesting symptom dealing with the master cylinder that I ran into was the small hole being partially plugged. With the bike sitting there idling the rear brake would lockup without even touching the pedal. Since it's a linked system you would think that this would affect the front but it didn't. After the bike cooled down everything was fine. I rebuilt the rear caliper but still had the same problem. Did the master found the small hole problem, everything is fine now. Shows how much expansion there is with brake fluid at the back wheel due to the close proximity of the exhaust.

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Re: How to rebuild your rear master cylinder

Postby WingAdmin » Mon Jun 21, 2010 9:38 am

The expansion of the brake fluid is more due to the heat generated by the brakes than by the exhaust. Brakes perform one function: to turn kinetic energy (bike moving forward) into heat. Ever touch your brake rotors or calipers after a hard stop? (don't) They will be extremely hot - they can be hundreds of degrees. Watch the brake rotors of racing cars, and you'll see them glowing orange and white from heat.

This heat goes into the brake caliper, heating up the reservoir of brake fluid that is sitting behind the pistons and inside the caliper itself. This fluid expands and pushes back up into the master cylinder - so if that return port is plugged, it has nowhere to go. The end result: it does the only thing it can do, it pushes the pistons outwards, which engages (i.e. locks) your brakes.

I have a feeling the brake proportioning valve prevents pressure backing up from one caliper from affecting the other - so that brake runout (causing pulsing) on the rear brake, for instance, won't also cause the front brake to needlessly pulse on and off.

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Re: How to rebuild your rear master cylinder

Postby MJSantos » Tue Jun 22, 2010 2:07 pm

What would be a good drill is to find a valve that's no longer any good an grind it open to see how it ticks. My guess is that it's all in the orifice sizes between the front and back ports. Maybe larger to the rear for great braking power to the rear wheel?

My reasoning for the symptom of it locking up the rear wheel when it's just sitting on the stand idling, was the caliper was heating the fluid which could not escape back to the master cylinder and the fact that there is longer rubber lines on the front that would expand just enough as to allow normal operation on the front.

Anyway we look at it, it still points to the master cylinder and that little tiny hole. Don't we just love mechanic-in on these old machines.

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Re: How to rebuild your rear master cylinder

Postby obed_ned » Sun Aug 01, 2010 4:45 pm

Thanks for the info- this is something I need to do in the near future-

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Re: How to rebuild your rear master cylinder

Postby britman » Mon Aug 02, 2010 6:26 am

Very nice how to . But what do you do if you cant get anything out to rebuild because the two alloys stuck together . If you have just got a new to me wing thats been sitting for a while

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Re: How to rebuild your rear master cylinder

Postby WingAdmin » Mon Aug 02, 2010 7:38 am

Which two alloys? What is stuck together?

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Re: How to rebuild your rear master cylinder

Postby britman » Mon Aug 02, 2010 7:58 am

The piston inside the brake housing . trying to find some kroil to see if that would free um . dont want to heat them up to much as i dont want to melt the rubber inside .

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Re: How to rebuild your rear master cylinder

Postby WingAdmin » Mon Aug 02, 2010 8:00 am

Have you removed the circlip (step 14)? The piston won't come out if you miss this step. Note that you may have to pull the shaft up with a bit of force to remove the washer that the circlip holds in place, if it is corroded.

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Re: How to rebuild your rear master cylinder

Postby oldspool » Fri Aug 20, 2010 10:48 am

****EDIT W/ SOLUTION****

1st a side note. I dont think people who have actively used bike have this problem, but mine had been sitting for 3 years and the master cylinder was bone dry, and I think this is what ultimately lead to the binding of the piston within the cylinder.

Solution to bound piston in Brake Master Cylinder:
One way to extract the cylinder is to VERY CAREFULLY drill a small hole down the middle of the concave top of the piston that has been seized. The take a sheet metal screw and thread it into the hole (the hole should be a smaller diameter of the sheet metal screw so it has some "bite") How you choose to pull it out from here is up to you, but I used a slide hammer (aka: dent puller) by attaching the now threaded screw into the end of the slide hammer and used the impact to pull it towards me. After about 5 firm pulls on the slide hammer, the seized piston came right out. I would recommend you avoid prying it out as that may mar up the cylinder wall. Your action should be as linear as possible. Hope this helps.

Original Post
Any tips on what to do when you remove the brake shaft from the master cylinder, but the piston has been seized to the cylinder on the inside? I think this is what BRITMAN was talking about. I have tried soaking the inside and outside surfaces with PB Blaster, but nothing has come free and I do not want to scrape away or risk gouging the soft metal on the inside of the cylinder walls. Any Ideas would be greatly appreciated.
Currently looks like this:


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Re: How to rebuild your rear master cylinder

Postby Willis333 » Thu Mar 10, 2011 8:53 pm

Great site- very very helpful. Thanks!!!

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Re: How to rebuild your rear master cylinder

Postby habitex » Thu Mar 31, 2011 11:44 pm

16.
There is a secondary rubber seal and a spring remaining in the cylinder. I used an air nozzle, applied to the brake line fitting, to blow them both out of the master cylinder. I wrapped electrical tape around the nozzle of the air nozzle to effect a seal against the fitting. If you do not use this method, be extremely careful getting the seal and the spring out of the cylinder - the cylinder walls are soft, and score easily. If you use a tool to get them out, use a plastic one that will not damage the cylinder walls.


I helped a friend buy a 82 1100i recently. It had been sitting for awhile - we were told about a year or so. We searched the internet and found this forum. What a life saver! Kudos to everyone for all of the information.

We cleaned the bike up, drained the gas tank, cleaned the fuel lines, and replaced the fuel filter and got the bike running. Now we are redoing the brakes. We are having the same problem with the rear master cylinder that Britman described.

Our rear master cylinder has the secondary rubber seal and the spring stuck in the cylinder. We have tried the air method described and will now try the drill and screw extraction method that oldspool described. We will keep you posted.

Wingadmin - you're the tops.

Thanks again to all of you.

Habitex and CCPopeye

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Re: How to rebuild your rear master cylinder

Postby Willis333 » Fri Apr 01, 2011 7:07 am

Just to recapp- if pb blaster and air wont do it- find a grease fitting and attach to the master cylinder. Go and buy a normal sized grease gun and pump the mc full of grease- the piston will slowly make it's way out with each pump. Make sure you have cleaned all that you can clean around the concave head of the piston- and remember it is fairly easy to scratch or damage the piston walls. This trick also works great with a brake caliper. I hope this helps. Willis333-Asheville, NC :geek:

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Re: How to rebuild your rear master cylinder

Postby bandit12 » Mon Apr 04, 2011 8:03 pm

Ok folks i get my rebuild kit from 1 of the venders Parts N More. Open my book too the master cylinder page and look over the diyagram and it said there was a check vavle when i took my M/C apart no check valve. and mine is a cone shape spring. I have a 2nd one so the org. is on the bike it's been afew days from when i took it apart so just to make shere that it's going back right the spring go's big end up or down.faceing the brake padlthanks mike :?
Last edited by bandit12 on Mon Apr 04, 2011 8:16 pm, edited 1 time in total.

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Re: How to rebuild your rear master cylinder

Postby Willis333 » Mon Apr 04, 2011 8:11 pm

I believe the little rubber hat fits on the small side of the spring- that part faces the plunger- twoards the con-caved head- circlip- etc.... hope this helps. Willis- Asheville

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Re: How to rebuild your rear master cylinder

Postby WingAdmin » Tue Apr 05, 2011 8:56 am

Willis333 wrote:I believe the little rubber hat fits on the small side of the spring- that part faces the plunger- twoards the con-caved head- circlip- etc.... hope this helps. Willis- Asheville


That's correct.

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Re: How to rebuild your rear master cylinder

Postby dover02 » Thu Apr 14, 2011 9:24 am

Ok folks as i got wiser i loked for ways to make things easier working on stuff that is froze up and on the rear master cylinder if it is froze up insted of doing all of the drilling u can also take a 1 foot peice of chain or longer if u need atach it to the yoke and to something stable and work it as a dent pulling hammer by takeing the cylinder in your hand and snap it back and fourth untill it pops out . This is the easyest way i have found to get one un stuck good luck and great rebuild pictures and instruction thanks WINGADMIN.




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