I recently experienced a brake failure and have been posting about it on a number of existing threads. It was suggested to start a new thread to document what went wrong and how the issues get resolved.

About 3-4 years ago, I decided to upgrade to a dual master cylinder, hoping to avoid a total brake failure such as what just occurred. The unit I chose was part no. 5914 from Mid-Fifty's 2018 catalog. Installation went went fairly well but did require some some extra fittings and a homemade adopter.

Since installing the dual master cylinder, I've been under the mistaken notion that in the event of a brake system failure one axle would still have brakes--both would not fail at once.

Just recently, however, returning from a car show, I braked a little harder than normal going into a turn at about 50 mph, and the peddle went right to the floor. There was almost no reduction in speed. Neither axle had brakes, and the emergency brake didn't do much to reduce speed either.

I slowed down to 30-35 mph and made it to the next town using engine braking and the emergency brake. Pumping the brakes did not help. My truck is currently at a repair shop and their initial diagnosis is a master cylinder failure. They are in the process of locating a replacement.

I asked why both axles failed at the same time, and they said because the fluid leak was inside the master cylinder. If a brake line or wheel cylinder failed, I was told the dual master cylinder would have performed as expected.

...so is a dual master cylinder such a great idea after all? Could it be possible that steel brake lines and original rebuilt wheel cylinders are more reliable than the rubber internals of an aftermarket master cylinder potentially made in China?

Thoughts?

Jim

 

Hmmm, food question.

 

Did the kit you purchased tell what MC was supplied? As you mentioned in the other thread, how would a shop looking for a rebuild kit or a replacement MC know what to look for? Usually the kits use an OEM MC as a basis, but which one? If you can find out, I'd source a replacement from a high-quality source, like Wagner.

Leakage between the chambers is how all the dual MC's I've had fail went. As you found, that leaves you with nothing.

 

Nothing is going to be 100% foolproof. But if there's 10 places where brakes can fail and a dual circuit master cylinder will help prevent disaster in 90% of them, it seems like a worthwhile investment. They have been mandatory in new cars since 1967, and we rarely hear of accidents caused by brake failure. Find a quality replacement for the defective parts, move forward and be thankful nothing worse happened. My 2c.

 

Hi Ross. I spoke with the guy working on my truck yesterday. He tried searching for a replacement MC using the numbers on my after market unit but couldn’t find any match-ups. I explained the history behind the MC currently in my truck, and he said he knew how to proceed. He said he would be looking for a GM style replacement unit.

Jim

 

Thanks for weighing in Wayne. I follow your reasoning and what you say makes sense. It is troubling though that a relatively new master cylinder failed. I must have driven a million miles in my lifetime but don’t recall a brake line or wheel cylinder failing all at once without warning like my master cylinder just did.

Jim

..

 

I used a Ford Mustang dual master from NAPA, 67 I believe. I’ll be checking fluid regularly. I did find out yesterday that my parking brake is only stopping the right rear wheel. The truck will remain parked until I figure out why, I suspect mis adjustment.

Jim, I doubt if this was a sudden failure. I’d bet it’s been leaking for awhile and the hard braking pushed the last drops of the fluid out.

As for brake failures. Recently I was stopped at a red light on a 4 lane, divided. There was a left turn lane with no one in it. I heard someone behind me honking like mad, then saw a pickup truck go into the turning lane and blow through the light, crossed over to the right hand shoulder. He managed to stop somehow. It had to be a brake failure. The driver handled it well and didn’t cause an accident, but I’ll bet he needed to change his underwear.

 

I've never been one to check brake fluid levels other than at oil changes. My truck had an oil change and general inspection at the start of the driving season this spring. I specifically asked about the brake fluid level because it's a little hard to check. I asked about the brake adjustment too. It's hard to develop new habits, but I'd be open to hearing about how often others think brake fluid levels should be checked.

Jim

 

Jim, your mechanic is on the right track, the master cylinder I received from midfifty was from a nova according to the paperwork that came with it. Not positive but I think it was an early 70’s model.

 

Thanks Rich. It's good to hear my guy may know what he's doing. From conversation with him, it appears he does quite a bit of work on old vehicles and has one himself.

Jim

 

Jim,

A couple of things. I had a rear wheel cylinder pop on a 64 mustang project. Since it was a "project" I hadn't got around to hooking up the parking brakes. Needless to say I had an accident and the Mustang didn't fair well.

Since you brought up the master cylinder I decided to look at a conversion kit I've still got on the shelf. I've already got 2 installed on my 56 F100 and my 53 Panel. Absolutely no markings except "Made in China". As close as I can tell it's similar to the 1" bore Corvette master with outlets on both sides.

Just food for thought since you've brought this up on your master cylinder failure. I try to keep detailed notes on my trucks build sheet but when you buy a kit???

 

Thanks BJ--Good suggestion on keeping notes. It's easy to kid yourself you are going to remember all the little details of what you do to your truck. As the years go by, good notes are bound to come in handy--just don't loose your notes. LOL.

Any suggestions on getting more stopping power out of your emergency brake? Mine is hooked up with new cables and totally rebuilt brakes in 2012, but at 40 mph, pulling it as hard as I could, really didn't do too much.

In my younger days, I remember pulling the emergency brake of a 1959 Plymouth Sport Fury I used to have. I was on an interstate highway going maybe 70 mph, and what happened was shocking! The rear wheels locked up and started "hopping" all over the place as I struggled to stay in my lane of traffic. I came very close to loosing control and have been vary of emergency brakes ever since. Nothing too dramatic or exciting about the emergency brake on the F1, however. Ideally, I'd like something, in the happy middle, between what I have with the F1 and my long ago experience with the Plymouth.

Jim

 

I think I asked before, but I don’t…what was I talking about?

Is your parking brake on the wheels or on the tranny?

It’s pretty silly to think that these parking brakes are worth anything as emergency brakes. Here in NJ you can’t even take your drivers test if the instructor can’t reach the parking brake. It simply won’t stop the vehicle in a reasonable time.

I can lock up the rear wheels with my handbrake. I doubt if the tranny brake will do that.

 

The emergency brake cables connect to the rear brake shoes. I sure can't lock my rear wheels. You are either stronger, or your brakes work better than mine. If I'm going real slow, there is some noticeable braking, but as mentioned, at 40 mph, checking down to the emergency brake is regrettably going to be too little too late in any kind of situation requiring an urgent need to slow down or stop. Going down a steep half mile grade in the Pennsylvania Wilds would be the stuff of nightmares.

Jim

 

Jim, I would check your rear brakes for adjustment, and then check and adjust your e-brake cables so the handle is 1/2 - 2/3 of the way up when they are firmly set. For that matter, check all of the shoes for adjustment.

The braking forces of the brakes on the trans get multiplied by the rear axle ratio, they are very stout when they are in good shape and not covered in trans oil.