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Username Post: Upgrading to '67 dual master cylinder        (Topic#357142)
Eth727 
Contributor
Posts: 330
Eth727
Loc: San Diego
Reg: 04-17-19
07-07-19 03:05 PM - Post#2770138    

Hey ya'll I'm upgrading to a '67 dual master cylinder on my power brake drum system. I was curious do I need to get a proportioning valve in the back? I'm just running drums all around.
Thanks



 


japete92 
"6th Year" Silver Supporting Member
Posts: 1404
japete92
Loc: No. Virginia
Reg: 01-18-13
07-07-19 04:28 PM - Post#2770143    
    In response to Eth727

No. Brake force distribution (front vs rear) is accomplished by larger brakes (wider shoes and drums) on the front. The hydraulic pressure is supposed to be the same through out the system (as GM designed it).

Pete



Edited by japete92 on 07-07-19 04:30 PM. Reason for edit: No reason given.

 
junky 
Valued Contributor
Posts: 3434

Loc: Northeast CT
Reg: 06-27-10
07-07-19 09:48 PM - Post#2770162    
    In response to Eth727

If you take the time to carefully examine your lines, and do a complete brake service on your master cylinder and wheel cylinders, there will be no need to upgrade your master cylinder. These cars didn't have brake failures, until they were on the road for many years, with people neglecting the braking systems. Twenty years ago, I rebuilt my single master cylinder, and all 4 wheel cylinders, and installed silicone brake fluid, and the brakes work as well today, as they did 20 years ago. I am a strong proponent of regular maintenance. All that I described should be done even if you are still going to do a complete change over to a dual master cylinder.

Never argue with an idiot. He'll drag you down to his level, then beat you with experience.


 
japete92 
"6th Year" Silver Supporting Member
Posts: 1404
japete92
Loc: No. Virginia
Reg: 01-18-13
07-08-19 07:23 AM - Post#2770180    
    In response to junky

  • junky Said:
If you take the time to carefully examine your lines, and do a complete brake service on your master cylinder and wheel cylinders, there will be no need to upgrade your master cylinder. These cars didn't have brake failures, until they were on the road for many years, with people neglecting the braking systems. Twenty years ago, I rebuilt my single master cylinder, and all 4 wheel cylinders, and installed silicone brake fluid, and the brakes work as well today, as they did 20 years ago. I am a strong proponent of regular maintenance. All that I described should be done even if you are still going to do a complete change over to a dual master cylinder.



In my opinion, 100% correct. I'm old enough to have driven many thousands of miles on single master cylinder systems and I never had any sudden failure of the brakes. No one I knew did either. I kept my cars impeccably maintained.

In my experience, the most frequent point of hydraulic 'failure' (leakage) are the wheel cylinders. Keep an eye on them and your fine. Even if they do start to leak, the brakes will start to pull and (unless one is stupid) signal it's time to pull the drum and see what's up.

But, some one intent on the change should to be careful buying parts. The drum brakes require approx 10 lbs of residual pressure (just enough to help keep the wheel cylinder sealed, not enough to over come the spring). That's accomplished by check valves integral to the master cylinder, or external ones installed in the lines. Make certain one has them. Just because a vendor says his master cylinder may be used for either drum or disc, doesn't mean the part has integral check valves.

Pete






 
Eth727 
Contributor
Posts: 330
Eth727
Loc: San Diego
Reg: 04-17-19
07-08-19 09:04 AM - Post#2770184    
    In response to japete92

Yeah for sure the brakes need to be in good working order. I had heard that if one of the brake lines or anywhere in system crapped out you would lose all brakes compared to dual you would atleast have partial brakes? There has to be some redundancy somewhere.



 
japete92 
"6th Year" Silver Supporting Member
Posts: 1404
japete92
Loc: No. Virginia
Reg: 01-18-13
07-08-19 12:52 PM - Post#2770198    
    In response to Eth727

  • Eth727 Said:
Yeah for sure the brakes need to be in good working order. I had heard that if one of the brake lines or anywhere in system crapped out you would lose all brakes compared to dual you would atleast have partial brakes? There has to be some redundancy somewhere.



The mechanical emergency brake was the 'back up' for the hydraulics. That in conjunction with downshifting was the way I was taught to 'stop' should there be a failure in the hydraulics. The dual master cylinder likely provides 'more' emergency stopping capability ( I've never experienced a hydraulics failure), but neither 'back up' is meant to be a fully functional 'redundant' system. They are merely means to bring the car to a controlled stop.

Don't take my comments as opposing the dual master cylinder. I am simply noting (as Junky did also) that there are alternative operational concepts that provide safe driving. Owners should select the concept(s) that make them feel the most comfortable.

I am equally comfortable with either master cylinder set up as long as 'equal' (to the GM) quality parts are used and put together by people qualified (as the GM folks) to do so.

Just trying to be helpful.

Pete



 
Keith Seymore 
Contributor
Posts: 739
Keith Seymore
Loc: Southeast Michigan
Reg: 09-17-08
07-10-19 08:44 AM - Post#2770378    
    In response to japete92

I experienced two hydraulic failures in my '63 Grand Prix the year before last, one of which was a new replacement single pot master cylinder. I am now a huge proponent of the dual master cylinder system.

Additionally - it seemed to improve the pedal "feel". The single system was pretty touchy and difficult to modulate (consistent with the "over-boosted" power steering feel of the car). The dual system is not quite so sensitive and allows for better control during decel and at the termination of the stop. It now stops like a "modern" vehicle.

K



Chevelle Intro: http://www.popularhotrodding.com/features/1005phr_...
My Pontiacs: http://forums.maxperformanceinc.com/forums/showthr...
Pickup: http://67-72chevytrucks.com/vboard/showthread.php?...


Edited by Keith Seymore on 07-12-19 03:39 AM. Reason for edit: No reason given.

 
Keith Seymore 
Contributor
Posts: 739
Keith Seymore
Loc: Southeast Michigan
Reg: 09-17-08
07-12-19 03:41 AM - Post#2770511    
    In response to Keith Seymore

  • Keith Seymore Said:
I experienced two hydraulic failures in my '63 Grand Prix the year before last, one of which was a new replacement single pot master cylinder. I am now a huge proponent of the dual master cylinder system.

Additionally - it seemed to improve the pedal "feel". The single system was pretty touchy and difficult to modulate (consistent with the "over-boosted" power steering feel of the car). The dual system is not quite so sensitive and allows for better control during decel and at the termination of the stop. It now stops like a "modern" vehicle.

K





Incidentally, I made it home safely both times, through the use of engine braking and the mechanical e brake.

The highest level of excitement occurred when I tried to make the three point turn to get into my (sideways facing) garage.

I've added an eye bolt into one of the posts so that I can pull it up into the stall the next time I have a disabled vehicle.

K


Chevelle Intro: http://www.popularhotrodding.com/features/1005phr_...
My Pontiacs: http://forums.maxperformanceinc.com/forums/showthr...
Pickup: http://67-72chevytrucks.com/vboard/showthread.php?...


Edited by Keith Seymore on 07-12-19 03:42 AM. Reason for edit: No reason given.

 


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