Packard Forum Index » Modification Discussion

Quote:

Keith, I have to say that this is the most un-informed post you've ever made, and you don't make any.

The whole reason why a dual master cylinder was thought up is the exact reason that 55PackardGuy stated,
Quote:

I know I would, and every car I will ever build will have some sort of modern, dual line master cylinder on it. Disc brakes or no, from '67 on, ALL cars were required to have a dual master cylinder, for safety reasons, NOT because of front disc/rear drum setups. I've seen multitudes of MOPAR and Ford and GM vehicles from right before '70 that had four wheel drum brakes, and dual master cylinders. All it takes is ONE component to fail in a single line master cylinder and you're done, you have no brakes. At least with a dual you still have 50% like 55PackardGuy stated.

The Dual-Master cylinder setup is not just there for marketing reasons, it's a DOT (Department of Transportation) mandated safety item. I figure the year that went into affect. 1968? somewhere around there.

If is the same reason that commerical airplanes are required to have redundant backup hydraulic and electrical systems.

I think it was 1967 that dual-chambered (tandem) master cylinders became a requirement - but only for passenger cars.

In fact, the 1973 Chevy C60 wrecker used by the Chevy-Buick dealership where my dad worked came from the factory with a single chambered master cylinder, and they ran that wrecker for nearly 20 years - until the dealer retired and sold the business - without incident. Dad even towed coach-type buses with that wrecker (powered only by a 366-cid engine) - not just for mechanical breakdowns, but out to NJ and back for collision repair.

That a tandem master cylinder is required for disc/drum combinations is NOT TRUE. Tandem master cylinders were actually in use before that 1967 federal mandate. Pop the hood on a 1963 Studebaker Lark with four-wheel drum brakes and you'll find a tandem master cylinder. Yet, pop the hood on an original, unrestored 1963 or 1964 Studebaker Avanti that came from the factory with front disc and rear drum brakes as standard equipment, and you'll find and a SINGLE-chambered master cylinder.

Technically, all vehicles require some sort of proportioning between front and rear brakes. On vehicles with drum brakes at all four wheels, this was originally accomplished simply by using different diameter wheel cylinder bores, front vs. rear. Using disc brakes in conjunction with drum brakes adds a new twist because disc are direct-acting while drum brakes have a self-energizing effect. IIRC, it was only about 1976 when genuine proportioning valves came into widespread use.

Since brake proportioning is based on vehicle weight distribution as well as disc vs. drum, I also don't believe that failure in a tandem master cylinder leaves you with 50% braking. Moreover, while tandem systems were initially spilt front /rear, they started splitting them diagonally by the 1980s - that is, left front tied to right rear and right front to left rear. That always puzzled me because the proportioning is usually biased toward the front brakes. If you blow a rear line in a diagonally-split system, you're effectively trying to stop the car with one front brake.

I've personally experienced rear brake line failure in cars with both types of split tandem systems, but would not have been able to bring the car to a complete safe stop had the parking brake not been in good working order. I also once stopped a VW Beetle that developed a hydraulic failure with a single-chambered master cylinder with nothing more than the parking brake AS A PASSENGER, when the driver didn't know how to react - thanks to the handle being located between the front bucket seats.

DRUM require somekind of residual check valve to keep a small amount of pressure against the wheel cylinder seals.

Disk brakes DO NOT require such a preload. If disk had slight pressure left in the lines after pedal released then the calipers would be dragging all of the time.

HENCE the TANDEM cylinder for rear drum/front disk.
However, this may have been only a very early-on engineering decision when disk(FRONT) was promoted.
I am not sure how various manufactures handled this issue of providing residual pressure to the REAR DRUMS while NO provision for such pressure to the front disk. At some point later on, about 1980 or there-abouts, some kind of a cup preloader was used INSIDE THE rear wheel cylinders.

I do not remember ever observing any check valve in the front most port of any dual cylinder i've worked on.

As for government mandateing, it only takes about $10k OF bribe money and we could probably have dragging our feet on the ground mandated as a brake system.

BUT again. What does tandem v single maste cylinder have to do with the BTV "failures" ?????

If the ONLY problem with BTV is the fact that it is a SINGLE cylinder then that would promote the problem to ALL, EACH AND EVERY NON-btv SINGLE cylinder brake system as well!!! A CONTRADICTION!!

For all practicle and rational purposes we are back to square one: Which is Randy Bergers claim appearing below as my standard signature.

i blew a brake line on my 1991 dodge this winter. It has disks in the front, drums in the back and a split master cylender. That dual resivour shure didnt do me any good as i went sailing down a hill, through a stop sign. Thank god for the e-brake!

Quote:

Thank you, that's pretty much the whole point I was trying to make. The biggest flaw with the T/V is that it's a single system prone to the same essential problem of all single braking systems--sudden total failure.

The only contradiction made is to the idea that dual braking systems provide no safety advantage, which I find hard to buy. I also am a little hesitant to believe that someone bribed a politician to get the DOT to require them.

But that's just me--a skeptic. Although I do still remember believing the daily radio broadcasts in the '60s that gave the year-to-date "death toll" on the highways. Since then, I have slowly come to be a believer in relatively small, painless changes in automobiles that exponentially increase safety and survivability whilst driving them. Weird, huh?

This appears to be a bone of contention here, but I'll give my take on it anyway. In the last 15 years I've had about 30 some different cars with quite a few different systems and setups. Single res. drum/drum manual and power
Dual res. drum/drum manual and power
Dual res. disc/drum power (never had manual yet)
Dual res. disc/disc power
Dual cylinder disc/drum power
and yes, there's a difference between dual system and dual reservior. So far, the only total hydraulic failures I've had were on the dual system/single res. type and on disc/drum dual res.with power assist. On a lot of dual system cars with power brakes, people tend to not notice when the rear brakes have failed or started to. I recently sold a 78 LTD that has no rear brakes but most people wouldn't notice. In fact, lots of vehicles I've worked on appeared to have not had functioning rear brakes for years. If you have a front system failure and your rear system is not up to par, then you're in for trouble. Another 2 cases were an 85 Olds and a 87 Merc. When these blew a line, the other half of the system worked but only once as both systems draw fluid from the same reservior and when it's been emptied neither will work.
Cases like those are where the false sense of security is apparent. If you maintain both sides of the system as you would a single system car, then you're ok. That includes the proportioning valve and warning light system. All too often, these are stuck or filled with crap and the warning light never comes on to let you know that something's wrong. Maybe I've been lucky. How many times has anyone let a leaking rear wheel cylinder go until they have time on a dual system car? How many vehicles have never had their brake fluid changed or flushed till something failed? I'll take a properly maintained single system any day over a neglected dual.
Bottom line: Dual system is no safer than a single unless properly maintained, in fact it may be worse.

55Packardguy. Thank you. And thank you to everyone else for their patience with me.

IT HAS SUDDENLY dawned on me that:

****** No one finds any MORE fault with the BTV than any other single cylinder set up. ******

OR to put it another way:

Everyone would agree that the BTV is no better or no worse than any other SINGLE cylinder set up.

Altho i disagree with the above 2wo statements and i disagree that Tandem cylinder is any safer than the singles, i suddenly realize that my analysis SPECIFICALLY OF THE BTV is somewhat of a moot point relative to the general consensus.

SO, as Craig would put it, i'm "moving on" with this topic.

We need to determine if any transplant master cylinder has a residual pressue valve. Is such a valve even needed??? Seems to me like it's needed. More study on the residual pressure valve for the drum brake application is in order.