Topic: Leaking master cylinder


fordv8j    -- 09-11-2015 @ 7:17 PM
  Just replaced the master cylinder on our 38 coupe with a new NAPA one,went to Motorfest...came home put in garauge..it was dripping fluid..I use dot 5 fluid...they are going to replace it...who makes a good rebuild kit if this one leaks? I think it was made overseas...their kits probably are too....THANKS


shogun1940    -- 09-14-2015 @ 4:35 AM
  the rubber seals probably not made for dot 5,,


TomO    -- 09-14-2015 @ 7:47 AM
  If it is dripping fluid, the master cylinder is bad. DOT 5 is compatible with all rubber brake parts or it could not be sold. That is the reason for the DOT specifications.

Tom


fordv8j    -- 09-14-2015 @ 6:42 PM
  Just replaced the NAPA master cyl. with another Napa one..Ihave been using dot 5 fluid for years,also in our 38 conv coupe without any problems...but maybe the rubbers are different now...time will tell..thank you all


42oink    -- 09-15-2015 @ 8:30 AM
  Hi, At risk of sounding silly, where is it dripping from? Sometimes I over-complicate things and then find it is a simple problem. Are all fittings tight? Or is the pressure only forcing it out a connector. Just a thought. oink


fordv8j    -- 09-15-2015 @ 6:15 PM
  it was leaking out the rubber boot


fordv8j    -- 12-12-2015 @ 2:45 PM
  The 2nd one from NAPA also leaked..they refunded my money...got one from Advanced Auto..it is also leaking..looks just like the NAPA ones...MACS has them that they say are made in the USA...anyone have any experience with them? maybe mechanicals are not that bad after all...I use dot 5 fluid


TomO    -- 12-14-2015 @ 9:14 AM
  A couple of years ago, we tried several master cylinders that were made in China on a 47 Ford, They either leaked or could not be bled. We went to our local parts house and asked for one from the US. They provided us with an re-manufactured one from Wagner. We bench bled it, installed it and and it is still working fine.

I like to buy parts locally if I can, because the local suppliers will usually stand behind their products and I don't have to pay shipping charges for returning the parts.

The Wagner P/N is MC1050. Rock Auto, Amazon and E-Bay list some for sale, if you can't find one locally.

Tom


len47merc    -- 12-14-2015 @ 9:53 AM
  Agree with TomO on the US-made reman Wagner. Bench bled and installed the same on my '47 Merc and has been working without problem for four thousand miles+/2+ years.

While Dot 5 should work fine as noted above, I've been running Dot 3 since installing the new unit without problem - just because I had it and it needed to be used up.

Steve


TomO    -- 12-14-2015 @ 10:15 AM
  Steve, only use fresh brake fluid in your system. Dot 3and 4 are glycol based and attract rust forming water. They should be flushed every few years to reduce the damaging rust in the wheel cylinders and lines.

Tom


len47merc    -- 12-14-2015 @ 10:24 AM
  Thanks Tom - will do. Had 2 unopened quarts of Dot 3 in inventory when overhauling the complete brake system on car receipt in '13 and went forward with using them for initial system charge and bleed. They're now consumed after a project my son was working on and I'm due now for a change in the '47. Any thoughts on how to efficiently and properly purge the current system of Dot 3 when changing to Dot 5 greatly appreciated.

Steve


TomO    -- 12-15-2015 @ 7:40 AM
  The only way that I would change from DOT 3 to DOT 5, is to completely rebuild all cylinders, replace all rubber hoses and flush the metal lines with denatured alcohol.

Since you have recently rebuilt your brake system, I would stay with DOT 3 or DOT 4 and flush the system on a regular basis not to exceed 3 years between changes.

Flush by removing all of the brake fluid from the master cylinder, refill the MC and then bleed the brakes with a fresh can of fluid. You can keep the left over fluid in a small container, stored with the opening at the bottom, for 1 year, then discard it.

Tom


len47merc    -- 12-15-2015 @ 4:43 PM
  Thanks Tom.

Steve


alanwoodieman    -- 12-17-2015 @ 8:50 AM
  I had the same problem and ended up looking into the bore--not finely honed, rough not shiny surface. re-hone the cylinder and it has not dripped since.


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