A gripe about Master cylinders

I agree with Spider Web, HAMMER DOWN! COME ON! WIND HER UP TO 2100 and make her blow black coal like moon dust with 24 ton on!

I HEEEEAAARRRR DAT, COME ON!

 

Obviously if you lose half of a dual-circuit you're going to have no more than half the brakes, which to many will feel like no brakes at all. I've been there, and it worked. If you still have fronts, you'll have a low pedal but real brakes; if you only have rears, it may not be much better than driving on ice.

That said, in 35 years of street driving and a fair amount of road-course time I've never lost a wheel hose. Internal master-cylinder seals, yes. Wheel cylinders/calipers, yes. I've run a couple cars that had a caliper design notoriously susceptible to the body bending and spreading the pads apart, even. But I've never lost a hose. I'm prepared to accept that my situation is unusual.

 

Drove home my first car, a 29A coupe, in afternoon rush hour traffic. Broke one brake rod, two others lost a clevis pin and had only the left rear and emergency brake. Scary ride. First thing I fixed on the car. Also, lost the master on an OT 84 Mazda. Had enough juice left in it to get me to a place to park it and swap out the dual MC. I'm a believer in the most modern braking I can get.

 

Not that anyone here's going to do this, but my remark earlier is incorrect ni at least one specific application.

In '60s and early '70s Volvos the brake system was plumbed so that one circuit operated one side of the dual-piston opposed front calipers plus one rear brake, and the other operated the other side of each front caliper plus the other rear brake. That meant TWO hoses to each front caliper, but it also insured that (if you were prepared to pump the pedal a bit) you would have SOME front brakes regardless which circuit failed, and since the front brakes do 70-90% of the braking, that matters.

It's also expensive, and doesn't work with a single-piston caliper, so it died out eventually.

 

I had the master cylinder fail for the front brakes on my 70 f-100 while on vacation. I was several hundred miles from home. I drove it home very carefully with no problems.

 

I put a dual chamber 67 Mustang drum/drum master cylinder on my 48 Ford sedan. I went under the car to bleed the right rear wheel cylinder, and my good wife operated the brake pedal. When I cracked the bleeder at the wheel cylinder, the pedal went to the floor. So much for dual chamber safety...

 

The pickup I plow snow with rusted through a rear brake line a few years ago and I used it for the rest of the season with front brakes only. One side of the master cylinder would run out of fluid but the other held it's level and I didn't add fluid. The pedal went almost to the floor but it stopped. I kept the transfer case and front wheels locked so the front and rear axles were connected. I removed the line going to the rear brakes from the brake light warning switch and plugged the port to get the pedal back to the top. Plowing snow requires using the brakes quite a bit and it stopped quite well.

When I replaced the brake lines with stainless steel, I also decided to replace the master cylinder and I had to put 4 in before I got one that worked. After the second one didn't work, I thought I still had air in the system but the new master cylinder wouldn't build pressure with plugs in the ports. I put the original master back in and the brakes worked fine so I kept trying until I got a new one that worked. The parts store didn't seem at all surprised that the new ones didn't work. I assumed that this rant was about a problem like that.

 

I had a single system on my 39. I lost my brakes going down a hill. It turned out to be a hose in the rear. Was able to pinch off the rear brakes and drove home with front brakes. Not wanting this to happen again, I replaced the single system with a Wilwood racing dual brake system. It was a small inexpensive master cylinder. Problem solved.

 

This is still an interesting question: Why engineer a dual master cylinder that has a transfer slot which defeats the independence of the systems? Was it a compromise to have the largest reservoir volume available in the event of a brake failure? A darn poor idea if so.

Where an internal dual MC seal fails and fluid can bypass from one side to the other, you have the very same situation. If you continue to drive on "half" the brakes you'll pump all the fluid out, obviously.

Brake warning lights can sense pressure difference or low fluid level. A sensor in the MC itself between the ports (where fluid and pressure should NOT be present) could potentially warn that the master cylinder has failed internally, and should be repaired or replaced.

 

In the 60s British sport cars had dual M/C before the US. required a dual system in 1968. The British had two complete m/c like the race car setup. I like the dual m/c tandem race car set up.



Ago

 

Bringin' this one back from the dead, with a long article from a Hot Rod Journalist. Why Not, it's a good one - the topic I mean.
by Skip Readio
skip.readio@compaq.com

NSRA has recently added dual master cylinders to their list of not required but neat things to have on your street rod from a safety inspection standpoint.

While I do not dispute the fact that they are a great safety item, I do have a problem with the blanket acceptance of the device as the "end-all" to everyone's brake failure problems.

First off, the dual master cylinder is a pair of pistons not mechanically connected to each other (unless there's a failure and we'll get to that later)

The piston closest to the brake pedal has a pair of packings, both facing forward, that cause brake fluid to flow when the pedal is depressed.

When you step on the pedal fluid is forced by the rearmost packing out into the brake lines to actuate the front brakes (they do 60% or so of your braking, depending on vehicle weight displacement).

The frontmost packing forces brake fluid against an opposing packing that's on the rear of the front piston. i.e hydraulic pressure within the master cylinder is employed to actuate the piston controlling the rear wheel cylinders. the front packing on this piston sends fluid out to the rear wheels.

If there's a loss of pressure in the rear cylinder (the one controlling the front brakes) the rear piston comes into physical contact with the front piston (the one controlling the rear brakes) and the pedal is now mechanically connected to the rear brakes.

The problem with this scenario is that there isn't enough pedal travel before you hit the carpet to get adequate application of out-of-adjustment rear brakes.

With disc brakes, no decent amount of fluid flows back into the master cylinder after application of the brakes so they're "self-adjusting" and any hydraulic pressure increase has an immediate effect on the application of the brakes.

With drum brakes, you have to re-fill the wheel cylinder each time because the return springs on the shoes force the brake fluid back into the reservoir.

That's why disc brake reservoirs are larger than drum brake reservoirs. The drum fluid is "recycled" while the disc fluid isn't.

So, HERE'S WHERE THE FALSE REASSURANCE PROBLEM ARISES. In most systems, the front brakes will more than adequately stop a vehicle in normal driving conditions. The pedal resistance will be pretty reassuring and even if there's a hole in thne rear brake line, it won't be readily apparent because the pedal "feel" tells you everything's OK. Not perfect, but OK. What WILL happen if there's a hole in the line is the brake warning light will come on.

But let's say there isn't a hole in the line but the shoes are just way out of adjustment. The spring pressure (brake return springs) is going to present enough resistance against the switch in the combination valve so that, UNDER NORMAL BRAKING, the light won't come on telling you there's an imbalance in the braking systems. This can go on for months and although you're still actuating the rear brakes (and wearing them down) you're never ever lighting that lamp on the dash that says you got a problem UNLESS you panic stop and really bear down on the pedal. THAT'LL get your attention.

Anyhow, I've lost the front brakes in my '72 Dart and, because the rears were well enough along, I lost everything. THAT was a fun ride home ...dropping the trans into low when I anticipated stopping, left hand constantly on the parking brake lever (yea, it's a pull it out then rotate to release type)

Just before I left for Australia this past February, I blew a brake hose on a front caliper on my wagon. Again, rears were on the loose side and Bingo, no brakes. Luckily the car's a 4 speed and it was fairly late at night. Got that one home, too. Fixed it when I got back 5 weeks later.

My old Volare wagon lost caliper hoses twice with the same results and my GTX did it to me once way back in 1971.

Now, I currently own two vehicles with single master cylinders. One's my hemi-powered '34 and the other is the '48 Chrysler 7 passenger sedan. Both of those cars have lost wheel cylinders and master cylinders but on EVERY occasion there was prior warning that things were about to fail.

Spongy pedal, rebuild the master cylinder. Low pedal, top off the master cylinder and rebuild the leaky wheel cylinder. Drop of brake fluid on my toe, top off the master cylinder then rebuild it when I got home.

Normally, low brake pedal, adjust the brakes.

I'll probably convert the '34 to a dual master cylinder but not because it's the politically-correct thing to do, because it isn't. I can't get rebuild kits for that old Ansen swinging pedal assembly any more.

Skip Readio
skip.readio@compaq.com
Early hemi s.m.e.
Street rod wiring consultant
Freelance rod & custom journalist

 

Good info: Make sure that your master cyl. will bottom the cyl with no fluid in it( enough pedal travel). Or if you loose a brake line it won't stop you.


Ago

 

I always prefer a dual master over a single. A single system is only as good as the condition of the components. I actually only lost brakes once on my '65 Belair when the longest (of course) line let go on me. On a dual system with rear drums and you lose the fronts, you'll stop better depending on the rear shoe adjustment. Low adjustment = a low pedal.

 

Bounce some stupid little fucker off the front of your car and then tell me how you feel about brakes. I did. Kids are stupid -they do stupid things like dart across a street on their bikes in traffic. Sometimes their ability to predict how fast cars are coming is also crappy -who knew ! I did nothing wrong, wasn't speeding, wasn't texting, wasn't on my phone, wasn't playing with the radio. I was ACTUALLY driving conservatively AND paying attention - it didn't matter I still bounced the dumb ass off the front of my car. Let's see I did nothing wrong - only problem was - I STILL FELT LIKE SHIT - having nearly killed someone. Several months prior I upgraded my tires from Bias to Radial and the brakes from Drums to Discs. The car stopped 100 times better after my upgrades. Had I NOT UPGRADED - I have absolutely no doubt that this kid would be dead.
So go ahead and argue that you "know" 9 people who had a dual system fail them totally and therefore they (dual) are no better than singles. Aahhh... what about the 10 jillion people who DID have dual systems SAVE their ass or someone else's? Ignore them because they don't support your position? My advice - don't go to Vegas and bet your money.

SO what do we know ? We know that with a single pot system - 100% of them have NO BRAKES when a line (or similar) fails. We know that in a dual system that - 9 people have had 100% failure and 10 jillion have had some measure of brakes - oh by the way - count me as one of the jillion people - I lost a front brake line and my dual m/c kept my rear brakes still functional - although in the excitement it felt like I had no brakes - the reality was I had SOME brakes - just not a lot. Also YES the reason the front line failed was MY fault -it was rusted - I should have replaced it long before it had a chance to fail.
Yes poorly designed and poorly maintained systems will play havoc on our odds.
Argue all you want - you'll never convince me that a single pot m/c is worth a shit. SHIT happens - even when you DO everything right. I can't imagine having to live with myself had I killed this kid. Overly dramatic - well IT SHOULD BE - we are talking BRAKES! They're kinda important.

 

Hemirambler, good points there. When you're out and about in your car, anything can and might happen. So to err on the side of safety.. not a thing wrong with that.

 

On the way to the Nashville Goodguys meet I lost all the fluid in the front portion of a dual master cylinder. I was able to stop just on the back brakes and limped on in to the show. The brakes were not much but it would slow the
truck down, if you gave it plenty of room to stop.

 

I just had the driver side wheel cylinder go out on me while driving. I was able to stop with the front brakes even though they faded pretty quick. I'm not sure this would have been the case had I used a single pot.

 

Well said Hemi.

 

Oh, Man!
Again with the aggression. Everyone with the getting so angry and spouting off emotional rants. It's sad. The post at no time states they are better (single pots). Rather, it states, and I might add, one-thousand ways to Sunday, that the system is not what it claims to be. Dual MCs are of course not worthless in their entirety. I even shared a personal experience where I drove an 80s VW Rabbit home with front lines only, and was able to do so because of a dual master (go back and read the whole post). But I have had other less acceptable experiences.Why? Why are some okay and others horrible? Why are there other people with the same tales? Why do so many MCs have grooves that connect the pots? Why are the bores made of steel and not stainless (and brake lines as well) ? Why aren't there two pots totally separate, side by side, like a Wildwood set up that you pay decent money for - if safety truly is the key objective? And WHY WOULD ANYONE ARGUE THAT A LOW PEDAL IS ACCEPTABLE IN ANY SITUATION. Since when is a low pedal and decreased stopping space of say 3-to 500 feet in difference OKAY? If the system worked as it should fronts or rears would actually be able to stop the average car pretty darn well, and without a LOW PEDAL. Again, if the system was truly designed with people's safety foremost in mind it would not be as it is. You can't argue these points. It simply shouldn't be. And if you do argue, it's pride that now selects the words you type. As a final note, I am using one pot, b/c I have the 65 Chevy PU master that is both clutch and brake setup combined. Many guys have and still do use this MC. It is solid as long as the car is looked after and everything is kept up. Again, people! I am not attacking dual pot builders, I am attacking the flaw in the system - the corporate, money saving, number crunchers, who are paid to care less for your life and more for the four dollars saved in each part, as these total millions of dollars when building high numbers of vehicles. Just think about it- really. There's no tricky business going on here.

 

I even shared a personal experience where I drove an 80s VW Rabbit home with front lines only, and was able to do so because of a dual master (go back and read

The 80s VW rabbit had staggered front to rear dual brakes. If you lost fluid you still had braking on (one) front and (one) rear wheel.


Ago

 

Well ,that makes sense why she stopped pretty darn well then.