Slant Six Forum
https://slantsix.org/forum/

Single to Dual Master Cylinder
https://slantsix.org/forum/viewtopic.php?t=17363		 Page 1 of 1
Author:  60 Pioneer [ Tue May 02, 2006 8:49 am ]
Post subject:  Single to Dual Master Cylinder
After reading past posts here, I am planning on switching my single master cylinder to a dual. Looks pretty straight forward, but on my '60 Dart, there is an threaded electrical plug connection on the underside of my single MC, I believe it is a pressure switch for the brake lights. If I buy '67-'71 dual reservoir MC (4 wheel drum), will it have this fitting?

Thanks again for any and all advice.

Bill
Author:  KBB_of_TMC [ Tue May 02, 2006 10:07 am ]
Post subject:  Mc
I'm pretty sure the newer dual MC's do not have a hole for a pressure switch - the factory went to a simple switch under the dash run by the brake pedal.

It wouldn't be too hard to plumb the pressure switch into the new system, but you'd have to choose whether it ran off the front or rear system and get a little flare/NPT/flare adapter.

You could even get fancy and put 2 in and wire them in parallel so if either side worked the brakes lights would come on, or you could put in the later style switch above
the brake pedal.

Do not be confused by the newer systems differential pressure switch - it turns on only if there is a large pressure difference F/R.

You could gut one to make an adaptor for your brake light pressure switch, but removing the internal piston and connecting both systems would just short the F & R systems together and defeat the purpose of the dual MC.

BTW, I've had a number of brake system hydraulic failures over the years. In my experience, only once has a dual MC held pressure in the intact side for long (hours); every other time the differential pressure blew the seal between the sides and caused the intact side to fail with a seconds. Whether that's a design feature or due to age, I cannot say.
Author:  60 Pioneer [ Wed May 03, 2006 8:35 am ]
Post subject: 
Thanks for the info, KBB. I'll keep that option in mind.

Do the single MCs have a history of failing, or is it just the concept of losing ALL your brakes at once that drives the idea of installing a dual MC?

I've thought about just keeping all the original equipment on it. The car's in good shape, but I don't use it for a daily driver or anything. More a less a toy to wrench on and take out for a drive.

Thanks again,

Bill
Author:  Matt Cramer [ Wed May 03, 2006 8:48 am ]
Post subject: 
Quote:
Do the single MCs have a history of failing, or is it just the concept of losing ALL your brakes at once that drives the idea of installing a dual MC?
After over 40 years, anything that relies on rubber seals might fail. I don't have any information to suggest that single reservoir cylinders are any less reliable than dual reservoir models, but I personally have had one fail and lost all my brakes. While backing down a steep driveway, no less - I'm lucky the neighbor's driveway was directly across the street, or I'd have ended up in their yard.
Author:  Old6rodder [ Wed May 03, 2006 12:27 pm ]
Post subject: 
I'll likely draw a bit of ire for this but.........

I've dealt with brake failures for many years, others' and a few of my own, both dual and single and I've not seen any real advantage to split systems on the street in that time. Of the two instances I know where the second circuit held up, one was in a straight line and was the rears that held. The braking force available wasn't enough to keep him off the next car's bumper. The other one happened to a friend in (admittedly) an oversped corner. The fronts held and looped him rather badly. He was quite fortunate to have an empty field for an exit line (two years later and he'd have wound up in a roadside diner). Both these (in fact most) I've repaired were due to neglected rubber parts and had given the usual warning signs which went unrecognized and/or unheeded.
I've heard (second hand) of some instances where the second system worked as designed and averted an accident but I can't vouch for those as I didn't do the work.

To be honest I have to admit that each of my own brake failures was due to trying to get by with worn parts just a bit longer. I still run a one pot system and haven't had a problem in rather a number of years. I do of course, maintain'em better than when I was a teenager.

In short, a properly kept system of either sort will be reliable enough for the street.

A small trick if you decide to stay with the single, an old fuel pump diaphram makes a far better lid seal than that paper thing.

Another small trick for foot type parking brake systems, rework the release lever into a latchable form and the system may be used as a (weak) left foot brake in the event of service brake failure.
Author:  REDNECKMOBILE [ Thu May 04, 2006 1:09 pm ]
Post subject: 
Quote:
I'll likely draw a bit of ire for this but.........

I've dealt with brake failures for many years, others' and a few of my own, both dual and single and I've not seen any real advantage to split systems on the street in that time. Of the two instances I know where the second circuit held up, one was in a straight line and was the rears that held. The braking force available wasn't enough to keep him off the next car's bumper. The other one happened to a friend in (admittedly) an oversped corner. The fronts held and looped him rather badly. He was quite fortunate to have an empty field for an exit line (two years later and he'd have wound up in a roadside diner). Both these (in fact most) I've repaired were due to neglected rubber parts and had given the usual warning signs which went unrecognized and/or unheeded.
I've heard (second hand) of some instances where the second system worked as designed and averted an accident but I can't vouch for those as I didn't do the work.

To be honest I have to admit that each of my own brake failures was due to trying to get by with worn parts just a bit longer. I still run a one pot system and haven't had a problem in rather a number of years. I do of course, maintain'em better than when I was a teenager.

In short, a properly kept system of either sort will be reliable enough for the street.

A small trick if you decide to stay with the single, an old fuel pump diaphram makes a far better lid seal than that paper thing.

Another small trick for foot type parking brake systems, rework the release lever into a latchable form and the system may be used as a (weak) left foot brake in the event of service brake failure.
I'm with you on this subject, the parking brake used to be refered to as the emergency brake for a purpose. The only time I have had to use the emergency brake was with the dual line system failing. The money spent to refresh a single line system to me is better than the dual line conversion. Another plus is I have always had better luck bleeding a single line, I wonder how many vehicles with a dual line are bled properly.
Author:  CStryker [ Thu May 04, 2006 4:29 pm ]
Post subject: 
Quote:
I'm with you on this subject, the parking brake used to be refered to as the emergency brake for a purpose.
I thought I was the only one who called it an emergency brake.... Out of curiosity, what are the roots of that name (aside from the obvious usage)? I call it that becuase my dad always called it that when I was growing up, and people kinda look at me funny now when I say it.
Author:  SlantSixDan [ Thu May 04, 2006 4:48 pm ]
Post subject: 
The previous posts in this thread have pretty accurately nailed it: "Emergency brake" was a common term when it was less uncommon than it is now to have a service brake system failure requiring the use of the backup auxiliary "emergency" brake to slow the car down. Most people didn't have the presence of mind to use it, and most emergency brakes didn't have the power to quickly stop the car (see for yourself).

Now that brake failures are extremely rare, the term "parking brake" has become more popular. Most people still don't have the presence of mind to use it!
Author:  60 Pioneer [ Fri May 05, 2006 9:06 am ]
Post subject: 
Yeah, i've always known it as the "emergency brake".

And your right, most people don't know how to use it in an emergency. My daughter is learning to drive right now and I showed her (since her drivers ed class didn't) how to use the "parking" brake in case she lost her brakes. She acted like I told her a big secret.

Seems like some of these things, using an e-brake, driving a manual trans, and working on your own car, is becoming a lost art.

btw, I've decided to use everyones advice and re-furbish my single pot system instead of messing with a conversion.

Thanks again, all.

Bill
Author:  KBB_of_TMC [ Fri May 05, 2006 10:08 am ]
Post subject:  parts
BYW: I got kits to rebuild my wheel cylinders from J.C.Whitney; the quality seems good and they were quite inexpensive.
Author:  Frank McMullen [ Mon May 08, 2006 12:52 pm ]
Post subject: 
I've rebuilt and driven the brakes in about six old vehicles over the last 20 years or so...('41 De Soto; '64 Valiant; '59 Edsel; '55 Chevy dump truck; and some others...)

I've never had a failure in a single-reservoir system THAT WAS PROPERLY REBUILT... :wink:

If I get a vehicle that's more than 20 years old, I plan on replacing ALL the steel brake lines & flex hoses if I'm going to keep it... but I also live in a humid region that uses tons of road salt in the winter.

That said: brake systems corrode from the inside-out, due to the moisture-absorbing characteristics of DOT-3 or 4 fluids.

When I was younger, and tried to get-by, honing old, pitted wheel & master cylinders, and re-use old brake plumbing, then I had problems.


Regarding "Parking" vs "Emergency" brake... for those of us who remember MoPar's drive-shaft mounted parking-brake, you wanted to be careful about using that as an "emergency" brake: if you set it hard enough to lock-up the driveshaft, then both rear-wheels locked, and the car would fish-tail all over creation... :shock:

A dual-reservoir MC gives you better odds, statistically...

But brakes usually don't fail on a vehicle until they're about 10 years-old, minimum...

I think the Dual-MC was part of the same Federal safety mandates that included seat belts, turn-signals, and four-way flashers back around 1967...
Author:  60 Pioneer [ Mon May 08, 2006 2:21 pm ]
Post subject: 
I'll keep that in mind, my '60 Dart has the shaft mounted e-brake.

Athough, I was taught to hold the release open and use the e-brake like a brake pedal, that way you don't lock up the wheels.

That's fine in theory...until your diving a three-on-the-tree with manual steering.

Let's see...
...left hand on the e-brake release
...left foot on the e-brake
...right foot on the clutch
...right hand down-shifting

...hey!...who's steering???
Author:  Old6rodder [ Mon May 08, 2006 6:47 pm ]
Post subject: 
That's why I rework the release lever to be latchable............. :D
Page 1 of 1 All times are UTC-08:00
Powered by phpBB® Forum Software © phpBB Limited
https://www.phpbb.com/