Joined: Mar 21, 2017 Posts: 25 Location: Peoria, AZ
Posted: Sat Apr 15, 2017 12:59 pm Post subject: Brake Master Cyl/Lines advice needed
Rebuilding my 53 M38A1 and brakes go to floor - Master Cylinder was empty of fluid - filled it and tried bleeding to one front and one rear wheel - no fluid or air. Pedal goes to floor easily and linkages look good. Suspect Master Cyl needs rebuilt and will do this next - when I remove this what is proper procedure to insure lines clear? Loosen all bleeder fittings and blow pressurized air or....? thanks!!!! _________________ Lee Long
1953 M38A1 USMC
Ex-military brake system usually left the military with DOT-5 silicone based brake fluid. The standard civilian fluids DOT-3 & DOT-4 are glycol based. The two are not compatible. The DOT-5 is the hardest to flush and remove all traces of. I won't get into the rediculous arguments between using DOT-5 and DOT-3 or -4. You can educate your self on what is the best choice to use from now on by just googling DOT-5 vs DOT-3/4. Suffice it to say I do not use DOT-5 and 99% of the automotive industry does not use DOT-5.
If you have no idea what your system has in it then just buy a can of DOT-3 and compare smells!
When dealing with an empty system you will normally have to fill the master cylinder several times. Now if you filled the master cylinder and pumped the brake pedal full stroke over twenty times and the master cylinder is still full then you have an issue with the master cylinder bypassing internally
In your case I would start by flushing the entire system with Iso-propyl-Alcohol. Strip clean with (Iso-propyl-Alcohol) & rebuild the master cylinder and all four wheel cylinders.
Joined: Feb 20, 2007 Posts: 581 Location: Illinois
Posted: Sun Apr 16, 2017 8:54 am Post subject:
If your brake master cylinder was dry you may want to carefully inspect all the lines and wheel cylinders for rust and gunk. If the vehicle had not been properly maintained the brake system may be gunked up to the point that a alcohol rinse will not really do much good. When I started working on my M38 the brakes worked but a look at what came out of the master cylinder and lines convinced me I would have to re-accommodate some parts.
Replacing the lines/hoses is pretty easy and will assure you that you can use any brake fluid you choose without contamination from what was used previously. _________________ 1 - 1953 M38A1
1 - 1951 M38
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