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Username Post: Power drum brakes        (Topic#366711)
57210sportsedan 
Member
Posts: 60

Loc: Germany / Georgia (US)
Reg: 02-06-03
10-16-21 04:34 AM - Post#2829244    

Hi friends!
Am trying to get my car past the German hurdles for a historic tag and they noticed my disc brake conversion (Auto City Classic). The kit is great and I am very happy with the performance compared to the drums but ... the bean counters say it ain't original (every other nut and bolt is) and they won't wink it through.

So if I put the drums back on the front, is there a way to at least keep the dual master and booster and NOT replumb the whole front end again? In other words which drum-drum master cylinder and metering valve would be as close to what I have on the car now (preferably bolt on)?

I know this isn't original either but it is still far safer than that single-pot all-drum setup that has helped me find my way into more than one ditch over the past 30+ years. And they didn't notice that part of my upgrade.

Another way I could go is to prove that disc brake upgrades are "period" (of course GM didn't offer them until 1965), but I just can't find that first JC Whitney ad ... any ideas here?

Thanks!
Markus

Markus
57 Chevy 210 Sport Sedan
70 Triumph Spitfire
bought and sold a few more ...


 


japete92 
"7th Year" Silver Supporting Member
Posts: 1805
japete92
Loc: No. Virginia
Reg: 01-18-13
10-16-21 06:08 AM - Post#2829246    
    In response to 57210sportsedan

My '63 Impala with all drums has the dual master cylinder. It properly does not have a proportioning valve (used only with the disc/drum combo).

The all drums provide for an approx 60/40 (front/rear) braking force distribution mostly by having wider drums/shoes in the front. There is also a minor difference in the size of the wheel cylinders. Hydraulic pressure is equal throughout the system.

If your car has adjustable proportion valve, you may be able to retain it by adjusting it to provide the required equal hydraulic pressure front/rear.

Because your dual master cylinder is for disc/drum combo it likely does not have the correct residual pressure valves (10 psi for drums; about 2 or 3 for disc). They are required for the drums. They keep 10 psi pressure on the wheel cylinders to provide for better 'seals' and keep them from leaking.

Just a few impediments to overcome.

I have driven hundreds of thousands of miles in car with single pot/all drum brakes without EVER winding up in a ditch (because of brake failure). Those system require more frequent inspections and routine maintenance than the discs. Brake failure in those system were/are due to neglect and improper maintenance. Or, improper installation/parts to begin with.

IF you are required to replace the dual master cylinder, I would not hesitate using the 'old' single pot system. Just be prepared to do more inspections/maintenance.

I do believe the dual master cylinder 'upgrade' is money well spent. I would keep it if I did not have to change.

Disc brakes? The only advantage of disc brakes over drums is their ability to dissipate heat better; thus reducing 'fade' when the brakes are applied 'hard' repeatedly (a la racing). 'Fade' is typically not a issue in 'street driving' application.

Just my opinions. Give them what ever weight you wish.

Pete



 
57210sportsedan 
Member
Posts: 60

Loc: Germany / Georgia (US)
Reg: 02-06-03
10-16-21 08:19 AM - Post#2829256    
    In response to japete92

Hi Pete,
thanks for the answer. I too have driven hundreds of thousands of miles on a single-pot drum system (my 57 for example) ... and hundreds of thousands on disc-drum and disc-disc setups. Just never a 1957 Chevrolet with power drums and a dual master.

I live in an area where there is a lot of traffic and tons of expensive newer "cars", not to mention pedestrians, bike riders etc, so stopping power is very important to me. Also it would be nice if the wife would drive the Chevy too, unlikely without power brakes. So I really don't want to go all the way back to where I was.

Do you think power drums on a dual master would be a reasonable compromise? And if so ... which master cylinder do I buy (67 Chevelle, Corvette, for example?). My proportioning valve is just a GM disc-drum metering block (non adjustable). If I remember correctly, they used versions of these on all dual masters, so to keep from replumbing the entire brake system, I hope to find a match here too.

thanks again,
Markus

Markus
57 Chevy 210 Sport Sedan
70 Triumph Spitfire
bought and sold a few more ...


 
japete92 
"7th Year" Silver Supporting Member
Posts: 1805
japete92
Loc: No. Virginia
Reg: 01-18-13
10-21-21 03:55 PM - Post#2829579    
    In response to 57210sportsedan

  • 57210sportsedan Said:
Hi Pete,
thanks for the answer. I too have driven hundreds of thousands of miles on a single-pot drum system (my 57 for example) ... and hundreds of thousands on disc-drum and disc-disc setups. Just never a 1957 Chevrolet with power drums and a dual master.

I live in an area where there is a lot of traffic and tons of expensive newer "cars", not to mention pedestrians, bike riders etc, so stopping power is very important to me. Also it would be nice if the wife would drive the Chevy too, unlikely without power brakes. So I really don't want to go all the way back to where I was.

Do you think power drums on a dual master would be a reasonable compromise? And if so ... which master cylinder do I buy (67 Chevelle, Corvette, for example?). My proportioning valve is just a GM disc-drum metering block (non adjustable). If I remember correctly, they used versions of these on all dual masters, so to keep from replumbing the entire brake system, I hope to find a match here too.

thanks again,
Markus



'Do you think power drums on a dual master would be a reasonable compromise?'

Yes. Unless the car will see repeated hard stops (producing enough retained heat to cause fade), I would feel confident. Simply adding the dual master cylinder (if done correctly) does not impact brake performance.

You won't be able to tell it's there. No difference from a single 'pot' master cylinder in normal operation. The dual system (see below) retains better emergency braking IF one of the two has a failure.

'... which master cylinder do I buy...'

You likely do not need a new/different master cylinder. You will need residual pressure valves (10 psi) in each of the two brake lines coming off the master cylinder.

Something like :

https://www.summitracing.com/parts/wil-260-13784?s ...

I simply quickly looked that up, there may be something better available, It's just an example.

No proportioning valve. Pipe two completely separate 'systems'; one from the front master cylinder 'pot' to the front brakes; and one from the rear 'pot' to the rear brakes. No connection between the front and rear 'systems'. Each has a residual pressure valve.

If you acquire a master cylinder that already has 'built in' residual pressure valves, separate in-line units are not required.

Recommend you acquire the shop manual for your car to give you the info you will need to install/maintain the OEM type system. It won't address the dual master cylinder, but it will provide all the info on shoes, springs, etc of the brakes.

Pete




 
57210sportsedan 
Member
Posts: 60

Loc: Germany / Georgia (US)
Reg: 02-06-03
10-23-21 09:13 AM - Post#2829650    
    In response to japete92

Hi Pete,
thanks again for the response.

So your are saying I can keep my disc-drum master as long as I use the residual valves? I was hoping to not re-plumb the front of the car again by therefore somehow incorporating a same-sized drum-drum proportioning valve as the one on there now. I would prefer replacing the master with a drum-drum unit and a new valve if you (or anyone else) knows of any comparable replacements. Thanks!

Markus
57 Chevy 210 Sport Sedan
70 Triumph Spitfire
bought and sold a few more ...


Edited by 57210sportsedan on 10-23-21 09:21 AM. Reason for edit: No reason given.

 
japete92 
"7th Year" Silver Supporting Member
Posts: 1805
japete92
Loc: No. Virginia
Reg: 01-18-13
10-23-21 11:11 AM - Post#2829653    
    In response to 57210sportsedan

  • 57210sportsedan Said:
Hi Pete,
thanks again for the response.

So your are saying I can keep my disc-drum master as long as I use the residual valves? I was hoping to not re-plumb the front of the car again by therefore somehow incorporating a same-sized drum-drum proportioning valve as the one on there now. I would prefer replacing the master with a drum-drum unit and a new valve if you (or anyone else) knows of any comparable replacements. Thanks!




The 'all drums' require the hydraulic pressure to be the same thru out the system. And, they require a residual pressure (approx 10 psi) retained in the system to keep the wheel cylinders from leaking.

Somehow your 'revised' system must address those requirements.

Perhaps changing to an adjustable proportioning valve (if it can be adjusted to supply equal pressure front/rear) may save some work/parts. But the residual pressure still needs addressing.

Or, a 'distribution valve' (it ONLY distributes the brake fluid front/back; does not impact pressure) to replace the proportioning valve. Typically their only real purpose is to supply the 'workings' for a dash warning light. Such a valve MAY take up the same 'space' as a proportioning valve. But, again, the residual pressure still needs addressing.

And yes, you may be able to simply add the residual pressure valves to your existing master cylinder/booster pedal configuration. But the equal pressure requirement (proportion valve) needs addressing.

Said another way; you can replace the master cylinder with a 'drum-drum' unit (with built in residual pressure valves) but you will HAVE to do something to return to a system with equal hydraulic pressure. Your existing proportioning valve has to go.

In general; a GM all drum master cylinder from a 'newer' car; installed with a distribution valve; may reduce some of the 'pain'. There are too many variables/unknown to asses over the internet.

I don't want to say 'buy this master cylinder' for the same reason.

Here's a question to answer to yourself. Will the plumbing to the 'new' front drum brakes be the same as your existing (to the discs)?

Just trying to be helpful.

Pete









 
Rick_L 
Member #409
Posts: 27924
Rick_L
Loc: Katy, Tx, USA
Reg: 07-06-00
10-23-21 04:51 PM - Post#2829663    
    In response to 57210sportsedan

My first question is are they going to allow a later model master cylinder and brake booster, given that disc brakes on the front wheels are not original? Even though it's a safety upgrade.

But let's say they will. You will need a 1" bore master cylinder to work correctly with the original drum brakes, and with the booster you have. I can't think of a "sure thing" OEM looking substitute, as you probably have a "short pushrod" vacuum booster. Maybe you could machine a spacer plug to extend the booster pin, and then use a 67-68 Camaro/Nova/Chevelle master cylinder. That plug would need to be a precision length so that the pushrod had .015-.030" clearance in the master cylinder piston. An alternative would be an early C3 Corvette manual brake master cylinder.

As for the residual valves, they are pretty much required - though I've heard of not using them. Without residual valves, the brake shoes are going to retract a bit more than with them when you release the brake. This means you will have to adjust the brakes very often, otherwise you'll suffer from a low pedal. The 67-68 Camaro, etc. master cylinders came with a residual valve in each outlet port, but very few if any remanufactured m/c's or aftermarket clones come with them these days. So if you want them, you're going to have to use inline residual valves. Wilwood has them. Also note that your current system, if it has a GM-style combination valve, there is a residual valve in the outlet for the rear brakes.

Also, those same Camaros/Novas/Chevelles had distribution blocks (manifolds) which are installed similar to the later combination valves. The only valve in them is a shuttle valve which closes if one end of the system has a hydraulic failure. The shuttle also has a switch that can be wired to a warning light. While a dual piston/dual reservoir master cylinder is a good thing for safety, the shuttle valve gives you a higher pedal if a failure occurs.

Personally before I went to all this trouble, I'd find out if they were going to accept it. Otherwise I'd get rid of the booster too, and go with a manual system and an original style master cylinder.



 
57210sportsedan 
Member
Posts: 60

Loc: Germany / Georgia (US)
Reg: 02-06-03
11-04-21 01:51 AM - Post#2830196    
    In response to japete92

Thanks Pete,
yes I know this is complicated. I have the original lines and can put the single-pot back on but ... was hoping to not scratch up the engine bay squeezing a set of lines under the still miraculously unscratched oil pan for a third time.

Sounds like the easiest path is to just capitulate and go back to the original system, or ... find a technical bulletin, reasonably period ad or nod from GM Heritage about the disc brake upgrade. I am still working on these options. Thanks again!

Markus
57 Chevy 210 Sport Sedan
70 Triumph Spitfire
bought and sold a few more ...


 
57210sportsedan 
Member
Posts: 60

Loc: Germany / Georgia (US)
Reg: 02-06-03
11-04-21 01:55 AM - Post#2830197    
    In response to Rick_L

Thanks Rick,
yes it seems like going back to original for now is the most reasonable path, outside of maybe getting them to accept the discs as a relatively period and/or GM approved upgrade. What a pain ...

Markus
57 Chevy 210 Sport Sedan
70 Triumph Spitfire
bought and sold a few more ...


 


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