Ok consider the master on my '86 MGM Tudor, there are no apparent leaks as the double reservoirs remain full. Long story short while moving the car I miss judged what gear the car was in.........shifted into N I was half asleep, thought i was in reverse, car started to head to some parked cars, I hit the brake pedal and it went to the floor, then apparently came up and I had a pedal. I thought if a master goes bad signs of leaks would be apparent, no??........but as i said the fluid was full in both chambers. What are the tell-tale signs of the master going bad if not leaks??
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Last edited by Toploader; 06-13-2025, 11:07 PM. -
seal on the shaft can bypass fluid and not apply pressure within the master. I've had that failure before. Also, air in the lines can sometimes do that. If you've managed to have a hot day with some heavy traffic, lots of brake dragging, and lack of air movement, old fluid could boil. If there is water within the fluid, that could create air pockets. So yeah, there are some modes of failure that could cause that. Also, if the car was off and the booster already lost vacuum, that might happen as well.
Only two things are infinite, the universe and human stupidity, and I'm not sure about the former. -- Albert Einstein
rides: 93 Crown Vic LX (The Red Velvet Cake), 2000 Crown Vic base model (Sandy), 2003 Expedition (the vacation beast)
Originally posted by gadget73
... and it should all work like magic and unicorns and stuff.
Originally posted by dmccaig
Overhead, some poor bastards are flying in airplanes. -
I have experienced this problem, on my Plymouth Acclaim (but the mechanical concepts inside a master cylinder are very similar across vehicles of a given era).
I believe the failure was, as sly described, the seals inside the master allowing fluid to slip past them rather than building pressure.
This can happen in varying ways/extents, like bleeding between the front and rear systems, and bleeding gradually/slowly or suddenly.
A quick pedal stab is what revealed it in my case and I immediately ordered a master cylinder after it happened, even though the brakes appeared to resume working fine after that event.
During replacement, it was readily apparent that the master cylinder had been leaking fluid, but the cylinder can have internal seal failures between the front and rear systems without leaking externally.
That car's brakes also felt oddly spongy despite being flushed and fully bled with new fluid. New master greatly improved the feel.Comment
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Any suggestions as to the specific manufacturer and p/n?Comment
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Check out RockAuto for various part numbers and manufacturers. I'd stay away from the "no-name"/economy parts.Originally posted by Toploader View PostWhat I Own: 1993 Mercury Grand Marquis GS
What I Help Maintain: 1996 CV / 1988 CV / 1988 TempoComment
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okComment
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Master cylinders are usually pretty economical at local parts stores, and in the case of reman ones (which the vast majority of them in existence will be), getting your core refund back is far easier if you buy locally.
I'd just walk into whatever you've got locally - Autozone, Carquest or any other - and buy the offering they have available. Or if a shop will be doing the job, just let them find the part.Comment
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Thanks Kevin
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Tomorrow I will go down to the car and see if I have a pedal, but if so at this point have no idea if the pedal will again go to the floor? Maybe just have the car flat bedded out to my buds shop out on LI, about 25 miles from my apt in NYC.Comment
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Any possibility that the brake hoses have internally collapsed??Comment
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Normally when they collapse the brakes won't release and it acts like bad calipers.
The only failed MC I've ever had didn't leak externally. It was brand new in fact, but the first pedal application would go to the floor. 2-3 pumps would give normal stopping and it wouldn't sink but by the time I needed the brakes next time it needed to be pumped again. I think the cup seals weren't staying expanded in the bore and the first pedal push was basically a hot dog in a hallway, not enough fluid movement to build pressure but enough to get the seals to push out enough to contact the bore and make pressure for round two.86 Lincoln Town Car (Galactica).
5.0 HO, CompCams XE258,Scorpion 1.72 roller rockers, 3.55 K code rear, tow package, BHPerformance ported E7 heads, Tmoss Explorer intake, 65mm throttle body, Hedman 1 5/8" headers, 2.5" dual exhaust, ASP underdrive pulley
91 Lincoln Mark VII LSC grandpa spec white and cranberry
1984 Lincoln Continental TurboDiesel - rolls coal
Originally posted by phayzer5
I drive a Lincoln. I can't be bothered to shift like the peasants and rabble rousers
Everything looks like voodoo if you don't understand how it worksComment
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Thain the last thing I need is to attempt to drive out to LI and the brakes crap out on me, can you say brown underwear??Comment
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Went out to the car this morning while in its parking street, and alternated from r to d and yes I had brakes. I also applied stead pressure on the pedal and it did not go to the floor. I still think I will have the car flat bedded out to my buds repair shop and put in a new master, just do not want to play Russian Roulette.Comment
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Not sure if you need to take the L.I.E. to get to your buddy's shop but I would certainly not do it with questionable brakes. Hell, I wouldn't want to drive on it with perfect brakes!Originally posted by Toploader View PostWhat I Own: 1993 Mercury Grand Marquis GS
What I Help Maintain: 1996 CV / 1988 CV / 1988 TempoComment
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The only way out of NYC to Nassau County is via the Long Island Expressway!Originally posted by friskyfrankie View PostComment
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