halftrackinfo
brakes => all brake related topics => Topic started by: 8683jb on February 26, 2021, 10:23:55 PM
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I've been meaning to post an update on the o-ring modification I made to the hydrovac a year ago, http://halftrackinfo.com/index.php?topic=2378.0, and thought this latest event would be a good reason. It's been working well, but I noticed lately the pedal was getting a little soft. I checked the master cylinder yesterday and it was very low. No external leaks, so I pulled the hydrovac and when I opened the vacuum control valve and atmospheric valve chambers there was brake fluid present so I knew the piston was letting fluid past it again.
(http://www.surfacezero.com/g503/data/500/medium/20210226_131638.jpg)
I removed the piston and found a nick in the o-ring.
(http://www.surfacezero.com/g503/data/500/medium/20210226_130545_LI.jpg)
(http://www.surfacezero.com/g503/data/500/medium/20210226_140950_3_LI1.jpg)
Looking for the cause, I noticed a sharp edge on the bleed hole in the piston's bore and realized I had to have shaved the o-ring on that during installation.
(http://www.surfacezero.com/g503/data/500/medium/20210226_132917_LI.jpg)
I replaced the o-ring and then temporarily slipped an 1/8" brazing rod into the bleed hole and lifted it flush with the sharp edge so the o-ring could slide into the bore undamaged. I disassembled the rest of the hydrovac and cleaned all the brake fluid out of the vacuum cylinders and it's back on the half-track now. After bleeding the brakes tomorrow, it should be good to go again. I'll do another update after I get more time & miles on the modification if there's any interest.
Jon
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Thank you Jon , good catch, appreciate the update. I’ll have to review your technique on the rebuild once I get closer to it for my halftrack.
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You bet John. Holler if I can help.
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The small cup in the rebuild kits is espcially prone to rot over the years. I used a teflon cup of the same dimensions with very good results.