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Thread: Cleaning Master Cylinder With Alcohol?

  1. #1
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    Cleaning Master Cylinder With Alcohol?

    I'm rebuilding the master cylinder on my '49 Jeepster. I have an old Motor's Auto Repair Manual that has pretty detailed instructions for disassembling, cleaning, and re-assembling the master cylinder. It says to soak the parts in "alcohol", and I can't figure out what type of alcohol to use. Rubbing? Denatured? Also, I'll probably get a rebuild kit, but if I were to reuse any of the rubber parts, can/should I soak them in the alcohol too? Any advice is much appreciated.

  2. #2
    Senior Member bmorgil's Avatar
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    Isopropyl or Denatured will work just fine. I use 90+% Isopropyl on a lot of things. It is one of the only solvents that will wipe off permanent ink.

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    Super Moderator gmwillys's Avatar
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    One thing to keep in mind when rebuilding your brake components is to invest in a brake hone to dress up the internal surfaces. This will clean up and true up the piston sealing surface.

    To answer your question, most people soak the pistons in brake fluid to prepare them for install. This will help the rubber to seal up better.

    I haven't had a ton of luck rebuilding these components because of salt and rust intrusion. It was time and money well spent to go ahead and purchase new American made pieces. The parts are about double to what these outfits as for theirs, but the American made brands fit exactly as the original did. The Crown or ADA brands are alright, but you have to modify the dust plate to get the mount bolts to fit.
    Last edited by gmwillys; 06-04-2019 at 04:37 PM.

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    Super Moderator LarrBeard's Avatar
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    Quote Originally Posted by JBridd View Post
    Also, I'll probably get a rebuild kit, but if I were to reuse any of the rubber parts, can/should I soak them in the alcohol too? Any advice is much appreciated.
    You will get new rubber parts in your master and wheel cylinder rebuild kits. Don't try to reuse any rubber parts - the old rubber is beyond its "use-by" date.

    I second GMWillys' advice about honing master and wheel cylinders, and don't be surprised if the bores do not clean up even after being honed. Brake fluid is hygroscopic (absorbs water) and when a vehicle sits for a long time, water will settle and corrode and pit the bores.

    Unless you are very sure that the brake cylinders are OK, the cost of new master and wheel cylinders isn't that big a portion of the rebuild budget. I recommend going new all around if there is any question.

    After a discussion from last week on the forum, for a rebuilt brake system DOT 5.1 silicone brake fluid is a good choice. It's expensive, but it only gets changed every five years or so. The silicone fluid doesn't absorb water, so it keep corrosion down in vehicles that sit a lot. And, supposedly, it is compatible with the older glycol based DOT 3 and DOT 4 fluids.

    A personal note: From 1965 when I started driving the '48 until it went into hibernation for 35 years, I had limped along with marginal brakes. The drums were turned way oversize and the bores were corroded; so something was always leaking somewhere. A double pump on the brakes was just a way of life to get it stopped.

    When we put it back together, one of my first observations was "Dern, it stops now!".

    Don't skimp on brakes. We talk about getting our Jeeps to run, but stopping is just as important. As a commercial said a while back "Well, if you do just an OK brake job, something will stop you".

    Show us a picture of your Jeepster - an unaltered Jeepster (especially the first generation VJ's) are about as rare as pink unicorns.

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    Sorry, I tried to post a reply yesterday, but I guess it never made it through. Maybe the pictures I attached were too large.

    Thank you all for the advice. I got some Denatured Alcohol today and am going to try cleaning it up with that. I'm hoping the cylinder will clean up good and then I'll get new "guts" for it. Otherwise, I'll just have to get a new cylinder. Planning on getting a working cylinder back in place and then moving on to checking the wheel cylinders.

    Quote Originally Posted by gmwillys View Post
    One thing to keep in mind when rebuilding your brake components is to invest in a brake hone to dress up the internal surfaces. This will clean up and true up the piston sealing surface.
    Thanks for the hone suggestion. It mentions that in the Motor's Auto Repair Manual. Sounds like I should probably do that.

    Quote Originally Posted by LarrBeard View Post
    A personal note: From 1965 when I started driving the '48 until it went into hibernation for 35 years, I had limped along with marginal brakes. The drums were turned way oversize and the bores were corroded; so something was always leaking somewhere. A double pump on the brakes was just a way of life to get it stopped.

    When we put it back together, one of my first observations was "Dern, it stops now!".

    Don't skimp on brakes. We talk about getting our Jeeps to run, but stopping is just as important. As a commercial said a while back "Well, if you do just an OK brake job, something will stop you".

    Show us a picture of your Jeepster - an unaltered Jeepster (especially the first generation VJ's) are about as rare as pink unicorns.
    Little history on my Jeepster. It was my Grandfather's, who had it for a long time (I believe he rebuilt the engine it in around 50 years ago--rough calculation based on how old my Dad says he was at the time they rebuilt it). I was always interested in it and always took it to the dances in High School. My wife and I actually drove it to prom (we were dating, not married at the time ). So my Grandfather willed it to me. I basically do enough work on it to keep it running because we still like to go for a cruise once in a while, but I haven't done must "restoration" on it. The brakes had been acting a little odd for a while, and when we took it out a couple weekends ago just around town, it was evident something was wrong. When I tried to take the reservoir cap off it was super stuck in place. It ended up breaking, which revealed how sludged up the brake fluid was, which lead to where I am today. Here are a couple pictures of it.

    20190604_180001.jpg 20190604_180223.jpg

    Finally (sorry for the lengthy post), I found this little piece just sitting in the bottom of reservoir, and I can't figure out what it is. I'm not even completely sure it's part of the brake system. My dad thinks maybe it was attached to the underside of the cap before it broke. Any ideas?

    20190602_211424.jpg 20190602_211430.jpg 20190602_211456.jpg

  6. #6
    Super Moderator LarrBeard's Avatar
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    Mystery Part in Master Cylinder

    The mystery item was part of the filler cap. Either it had fallen off a long time ago, or when you broke the cap, it was collateral damage.

    From your description of all of the sludge in the brake system, I'd not be surprised if things don't clean up really well. You'll probably end up with a new master cylinder.

    That Jeepster is fantastic! It is one of the "pink unicorn" variety. From the photo of the dash, I can see that the speedometer is disconnected. If there is a speedometer issue, there is a good guy in Michigan who can rebuild it.

    The engine turned face plate on the cluster is an earlier feature - I don't know when (or if) they changed the style in the Jeepster, but in mid '48 they went from the engine turned to painted face plate in the 2WD trucks.

    At the lower left on the dash looks like an overdrive control. The Borg-Warner overdrive was an option on the Jeepster and it let it cruise at 55 mph, a breathtaking speed in VJ days. We worked with a guy last year to solve an overdrive issue and it turned out to be a bad control relay - the box on the firewall. Look for a nameplate with a VIN - that will tell us exactly how old the vehicle is.

    A third generation Jeep/Jeepster is really neat - but not unusual here on the forum. Jeeps tend to stay in a lot of families for generations. I've been driving my Dad's truck since I was 12 years old - about 63 years now.

    A serious suggestion; buy a Parts List and a Willys Mechanic's Manual for the Jeepster. Those two books will help you be a Jeepster "authority". And, get a KWAS catalog, it is a gold mine of Jeep information; parts, tips, serial number information and even color chips by year.

    Let us know how the project goes, and don't be surprised if it grows a bit.....
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