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03-24-2019, 07:04 PM | #1 |
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Shoebox master cylinder help
I put front disc brakes and dual resivour m.c. on my 50 ford Tudor last year. I really like them. Bought them from shoebox central. Maybe they are the same thing ECI sells? Today, after about a 15 mile drive I smelled what I thought were hot brakes. Sure enough, the rear wheels and backing plates were too hot to touch.
I just had the car jacked up for other work and know with certainty that both rear drums turn freely with no drag. I am guessing that pressure must be building sequentially each time the brakes are used. Since both sides are equally hot I would lean to a bad 10# residual pressure valve or a bad m.c. How do I diagnose without just blindly swapping parts? Thanks |
03-24-2019, 07:38 PM | #2 |
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Re: Shoebox master cylinder help
Had a similar issue years ago and after several attempts to bleed the system using conventional methods with no cure for the problem, I installed 'Speed Bleeders' and bled the system that way.
Needless to say the problem was gone. This may or may not work for you but may be worth a shot rather than blindly replacing components.
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DON'T RECALL DOING SOMETHING FOR MYSELF BASED ON SOMEONE ELSE'S LIKES OR DISLIKES Last edited by 51 MERC-CT; 03-24-2019 at 07:44 PM. |
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03-24-2019, 07:47 PM | #3 |
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Re: Shoebox master cylinder help
I had a similar problem with the disc brakes on the front of my hot rod. Problem was the mc rod adjustment...too far out to let the system bleed down after brakes applied.
Easily fixed and sounds like the rest of your system is working properly. Maybe worth a check. |
03-25-2019, 08:00 AM | #4 |
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Re: Shoebox master cylinder help
The pedal should have a good return spring. Adjust the master cylinder push rod for about 1/16"-1/8" clearance, making sure the pedal is fully returned.
A collapsed or defective rear brake hose could also cause this problem. |
03-25-2019, 09:20 AM | #5 |
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Re: Shoebox master cylinder help
crack the line at the master that feeds the rear and see if they turn free could be the mc isn’t allowing the the fluid back in also make sure the mc isn’t overfilled
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03-25-2019, 05:50 PM | #6 |
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Re: Shoebox master cylinder help
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Short (rear) shoe is set to 0.010 clearance from drum IAW Ford shop manual. No noise when turning drums by hand, no whine when driving like bad wheel bearings. I let the car sit for 24 hours and then: Jacked it up and checked tire rotation-- they are turning freely. Pumped brakes pedal 30 times. Tires still rotate freely. Pumped another 30 times. Tires rotate freely. 1/16 to 1/8 push rod free play. Pedal IS NOT riding the m.c. piston. Checked fluid level. Removed a slight amount of fluid from the resivour feeding the rear brakes, now fluid is about 1/4 from top. Car has dual exhaust. Hard lines exiting m.c. are about 1.25 inch from tail pipe. I wrapped some thermo shield around the lines in that area in case thermal expansion of the fluid was an issue. I will test drive tomorrow. Only other thing I know to try is turning down the bias on the prop valve so the rear brakes do less "work". |
03-25-2019, 06:07 PM | #7 |
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Re: Shoebox master cylinder help
It sounds like everything was fine with the system for about one year. Have you turned the drums beyond the recommended specs? I recently went through a similar problem. When I pulled the drums I found that the shoes were slipping off the raised area of the backing plates when the brakes were applied and were hanging up on the drum. I found that someone had turned the drums too far which allowed the shoes to go out to far to make contact. Drove me crazy for two weeks until I looked at the adjusters and could see they were adjusted out almost all the way. Bought new drums and it solved the problem. Check your backing plates and see if they are hanging up. You can see clean metal on the outer edges of the raised areas on the plate if they are hanging up.
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03-25-2019, 06:12 PM | #8 |
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Re: Shoebox master cylinder help
I’ll be looking forward to read what you find. I’m putting a dual master on a ‘51 but staying with drum brakes front and rear for now......Mark
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03-25-2019, 06:27 PM | #9 | |
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Re: Shoebox master cylinder help
Quote:
The short shoes should be the forward linings, long linings to the rear. This is a Bendix servo brake, not a non-servo. Correct total shoe to drum clearance should be .025"-.030", or about 10 adjuster notches back from a locked drum. |
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03-26-2019, 07:46 PM | #10 |
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Re: Shoebox master cylinder help
Drums are NOS Ford.
Thanks to V8 Bob I now have the shoes turned around right! Embarrassing. You know I consulted two ford shop manuals, two ford IPBs, and two Chilton manuals and none of them illustrate a loaded Bendix backing plate with short shoes. I finally found dimensional data in a pocket size service spec booklet for 1950. Anyway, i tweaked one pivot pin and did some light arcing at top and bottom of shoes. I am satisfied I now have even clearance through the full drum rotation. I think a combination of too close tolerances and heat build up from use may have been causing dragging while in use. Anyway, tomorrow I will test drive and adjust prop valve as needed (as if it were a new install since I apparently had the shoes backwardsfor 12 months). Will report back results. |
03-26-2019, 07:55 PM | #11 |
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Re: Shoebox master cylinder help
This may seem like a silly comment, but are you sure you didn't have the parking/emergency brake partially on? Sometimes we forget the easy things
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03-27-2019, 10:13 AM | #12 |
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Re: Shoebox master cylinder help
I once had a Ford Motorhome, around 92 vintage, with front disc brakes. Large size for E-350 chassis. Brakes seemed to work ok when cold , but It had a problem which occurred after driving for an hour or more. The brakes would fail almost entirely, with good pads and shoes, properly bled without warning. Very scary! The e-brake would still stop it, but gradually. I finally figured out the problem, after a long stint on the interstate, the brakes failed on a two lane road with stoplights. Luckily I was able to make a turn and get stopped with the E-brake. I decided to feel of the wheels to see if one of them was hotter than the others and sure enough, the front left wheel was too hot to touch. The conclusion I reached was that the front left caliper was not retracting at all keeping pressure on the rotor, causing it to overheat and boiling the brake fluid. I changed the caliper and rotor on that wheel and had no more problems. Pulled my hair out over that one.
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03-27-2019, 11:32 AM | #13 |
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Re: Shoebox master cylinder help
Paul made a good point I made a similar mistake many years ago one my first brake jobs.
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03-27-2019, 08:39 PM | #14 |
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Re: Shoebox master cylinder help
To all who gave advice I thank you. I found the problem--it was me. The shoes were making poor contact with the drums. I adjusted them once they had worn in some. My adjustment, coupled with having the orientation backwards caused a thermal expansion problem. They were ok cold, but once in use the too little clearance caused heat build up to close down the clearance to the point of dragging.
Factory orientation and tolerances (achieved with a little grinding of the lining material) fixed it up at no cost except time and some slight embarrasment. |
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