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JMFL36 10-27-2019 03:09 PM

54 Mercury Power Brakes Troubleshooting

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Hi all. I'm looking for some advice on tracking down an issue with my '54 Mercury power brakes. I am experiencing 2 symptoms while braking.

1. When braking, the car slows normally till the pedal is depressed about halfway down, then brakes sharply as if I've slammed on the brakes.
2. After braking, the brake pedal does not return as it should, but the brakes do release. When I manually raise the pedal with my foot, it feels like there is some vacuum or hydraulic backpressure to my raising the pedal.

I'd like to narrow down the possibilities before tearing into the master cylinder. It looks like it was rebuilt not too long ago (fresh paint and gaskets). Attached are a couple of drawing from the shop manual. Any advice would be greatly appreciated.

KULTULZ 10-27-2019 06:33 PM

Re: 54 Mercury Power Brakes Troubleshooting

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Yours is a BENDIX TREADLE-VAC SYSTEM common to most cars of that period.

In the 54 MERC SHOP MANUAL, is there a diagnostic sequence offered to isolate problem(s)? What is your manifold vacuum?

It seems a major concern is the MC being an aluminum casting and if the system is not service as scheduled, the brake fluid crystallizing.

Read this -

Rebuild Kits are available -

JMFL36 01-20-2020 05:44 PM

Re: 54 Mercury Power Brakes Troubleshooting

I took the unit apart and found a couple of problems with it, the biggest being that the piston endplate was warped and the vacuum seal was shot. The seal is easy enough to replace, but I'm afraid the warped endplate can't be straightened and needs replacing. Does anyone know where I might find replacement parts for these Bendix Treadle Vac units?

dmsfrr 01-20-2020 07:21 PM

Re: 54 Mercury Power Brakes Troubleshooting

I'm guessing there are more than a few places but I just recently looked up this shop for a different style of vacuum brake booster rebuilding so their name came to mind first.

Blowerbob 01-21-2020 10:29 PM

Re: 54 Mercury Power Brakes Troubleshooting

try brake systems inc in portland or 503 236-2116 they have a lot of old stuff

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