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Old 10-12-2012, 02:59 PM   #1
jdc_va_usmc OP
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Under tank master cylinder rebuild - installing secondary seal

Any tricks to getting the secondary seal onto the piston? I don't want to use any tools to stretch the seal, but I don't see how I'm getting it on the new piston.
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Old 10-12-2012, 03:35 PM   #2
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got to post #246 for information on correct seals between tank and master cylinder.

to fit new seal, first warm up seal in hot water. dry off seal then use brake fluid as a lube to slowly stretch over metal seal holder.

http://www.advrider.com/forums/showt...730033&page=17
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Old 10-12-2012, 03:50 PM   #3
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Quote:
Originally Posted by _cy_ View Post
got to post #246 for information on correct seals between tank and master cylinder.

to fit new seal, first warm up seal in hot water. dry off seal then use brake fluid as a lube to slowly stretch over metal seal holder.

http://www.advrider.com/forums/showt...730033&page=17
Thanks! Man, I thought my m/c was in bad shape!

How did you get the rust and residue out of the inside of the cylinder of that thing? I have a bit in there that I'd like to get out before reinstalling and refilling.
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Old 10-12-2012, 03:53 PM   #4
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Thanks! Man, I thought my m/c was in bad shape!

How did you get the rust and residue out of the inside of the cylinder of that thing? I have a bit in there that I'd like to get out before reinstalling and refilling.
Oh, and nice thread! I'll check it out more thoroughly when I get time; might answer some questions I have in the future.
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Old 10-12-2012, 04:28 PM   #5
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Thanks! Man, I thought my m/c was in bad shape!

How did you get the rust and residue out of the inside of the cylinder of that thing? I have a bit in there that I'd like to get out before reinstalling and refilling.
carb cleaner is your friend ... cleans without leaving residuals. most airhead master cylinder bores are too small for hone tools.

make your own with emery cloth and wood dowel rod. carefully clean out then inspect bore with a bright light. then carefully sand any pits out to smooth.

objective is not to remove pits entirely. although that would be nice too. for deep pits objective to provide a smooth transition for rubber seal to travel across without cutting up new seal.

normally it's best to replace or re-sleeve master cylinder when pits get so bad it cannot be sanded out. and/or bore diameter gets too large. most quality master cylinder kit will contain a new piston. which will restore piston back to factory spec's. usually that will tighten up tolerances to allow reuse of old master cylinder body.

what kills master cylinders is moisture attracted by brake fluid. it's a good idea to change out your brake fluid every few years. some folks say every two years, that's a bit too much for me.... I've seen master cylinders rebuild fine after 30+ years with same fluid.

so my take is every 5 years of so change out your brake fluids. some may say that's too long, others say too short ... your mileage may veri....

_cy_ screwed with this post 10-12-2012 at 04:37 PM
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Old 10-12-2012, 05:19 PM   #6
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I don't want to use any tools to stretch the seal, but I don't see how I'm getting it on the new piston.
Isn't there a dental floss trick that helps pull the seal into place? I know I've done it, but it's been to long; can't describe the details. I'll see if I can find a link to a tech article.
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Old 10-13-2012, 10:26 AM   #7
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I use the tip of a caulking tube cut to size (piston spool diameter). Take a small piece of 1" x 2" and drill a hole to secure the opposing end of the spool as a good solid base to position the spool in a vertical position. Slide the caulking tip over the other end of the spool, lightly lubricate the tip and rubber cup seal with fresh clean brake fluid and simply slide the cup seal over the caulking tip and into place onto the spool. Very simple and easy. Here's a link with photos showing the procedure, Page 2 of my photo link. Can't remember where I heard of this but is much easier than using string or dental floss.

http://tinyurl.com/3saerp7
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Old 10-13-2012, 10:48 AM   #8
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sure it's a bit tight.. but after softening up seal with hot water, then dry, then lube with brake fluid.

seal slips right over piston. if you think this is bad, wait until you try installing a super stiff Teflon seal on a 6in hydraulic cylinder.

even if you are able to force seal into place. initial stretch could damage seal. on any super tight seal, best to soften seal up by soaking in HOT water just below boiling. then carefully dry, then lube with what ever fluid seal will live in.

on last master cylinder overhaul on R90S, didn't use anything except brake fluid. seal was a bit tight, but with brake fluid as lube. slipped right over piston. just make sure you get direction of seal correct first go. taking a tight seal on and off will probably hurt it.

wouldn't want to use dental floss, be afraid it'd cut into seal. using a cone to slip over edge is a good one. when I did rear main seal on Cummins, seal came with a plastic cone to assist installation. otherwise you'd damage seal trying to seat in place.


_cy_ screwed with this post 10-13-2012 at 10:59 AM
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Old 10-13-2012, 10:54 AM   #9
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Mike V, great idea. Good photos. I bookmarked your page to reference when I rebuilding my next MC.
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Old 10-13-2012, 11:11 AM   #10
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Quote:
Originally Posted by Mike V. View Post
I use the tip of a caulking tube cut to size (piston spool diameter). Take a small piece of 1" x 2" and drill a hole to secure the opposing end of the spool as a good solid base to position the spool in a vertical position. Slide the caulking tip over the other end of the spool, lightly lubricate the tip and rubber cup seal with fresh clean brake fluid and simply slide the cup seal over the caulking tip and into place onto the spool. Very simple and easy. Here's a link with photos showing the procedure, Page 2 of my photo link. Can't remember where I heard of this but is much easier than using string or dental floss.

http://tinyurl.com/3saerp7

Mike, I just used this method (got it from you via the airheads list), and it makes it stupid easy. Finding a spare piece of wood and old caulk tube was the hardest part, and that took all of 5 minutes in my garage.
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Old 10-13-2012, 11:12 AM   #11
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And just to confirm, DOT4 brake fluid? I thought I read DOT 3 somewhere, but my Clymer manual says DOT 4.
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Old 10-13-2012, 11:22 AM   #12
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Mike, I just used this method (got it from you via the airheads list), and it makes it stupid easy.
John,

Great to hear you found this helpful, I agree - almost criminal how quick and easy this is. Amazing how many "special tools" we have hiding in our garages.

Keep in mind the importance of cleanliness for the assembly of the new MC parts.

Yes, Dot3 or preferably Dot4, NOT synthetic for our /7 braking systems.
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Old 10-13-2012, 11:24 AM   #13
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And just to confirm, DOT4 brake fluid? I thought I read DOT 3 somewhere, but my Clymer manual says DOT 4.
DOT 3 or 4, doesn't matter. Do NOT use 5 (silicone type).
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Old 10-13-2012, 12:06 PM   #14
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sure it's a bit tight.. but after softening up seal with hot water, then dry, then lube with brake fluid.
I did soak in warm water as well, per your tip. Belt and suspenders I guess.
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Old 10-13-2012, 12:42 PM   #15
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Change brake fluid at least once a year. Good luck using anything but a good hone. It takes a little luck WITH a good hone. If the pits are not removed completely, it will leak. Good luck.
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