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Front disk brake conversion ?
Posted by: toms73novass ()
Date: March 06, 2021 06:51AM

Those that did the front disk conversion, did you install residual pressure valves ?

I have read else where that some put 2lb on disk circuit and 10 lb on drum to sync the breaking.

Let me know what you did.

-Tom


63' Monza Spyder Convertable (in process) MY Build Thread
65' Monza MY Build Thread
73' NovaSS 454 Big block (Sold)
86' BMW 325es
98' VW Jetta TDI, for daughter
01' Audi Allroad Stage 3 twin turbo
67' UltraVan 211 "Violet"
NFCC, UMCC
Grand Island, NY

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Re: Front disk brake conversion ?
Posted by: jamesolefjensen ()
Date: March 06, 2021 07:52AM

I have not done a disc brake conversion but I am slowly collecting parts to do so. I ran across some useful information on residual pressure valves on the Wildwood sight.

[www.wilwood.com]

Note: Master brake cylinders designed for drum brakes have residual pressure valves build in.

James
65 Corsa
SF Bay Area

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Re: Front disk brake conversion ?
Posted by: v8vair ()
Date: March 06, 2021 08:09AM

Ive never used them. Both race cars dont have them and i never found the need on the street cars ive done. One thing is ive started using is the Wilwood master cylinder. Always a good firm pedal. Expensive but worth every penny IMHO
[www.speedwaymotors.com])

1965 Crown V8 Racer
1964 Bill Thomas Monza Replica Racer
1964 Spyder Street Car
1979 Mazda RX7

Mike Levine

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Re: Front disk brake conversion ?
Posted by: 66vairman ()
Date: March 06, 2021 09:40AM

I'm not a disc brake expert, but over the years designs have evolved.

Early on their was an issue with the pads traveling too far from the rotor causing excess brake pedal travel unless the brakes were re-applied (pump the brake pedal) in short order. Also a "slight" pad drag was thought to help "dry out" the pads after they got wet. Different approaches were used to "fix" the issue.

Next the issue of reducing brake pad drag and extending pad life was addressed to reduce vehicle operating costs.

Also eliminating noise requires proper hardware and pad combinations.

Modern disc. brakes may NOT need the addition of residual pressure valves.

Best to do some research regarding the disc brake setup you use or you could compromise the disc brake function.



Edited 1 time(s). Last edit at 03/06/2021 09:41AM by 66vairman.

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Re: Front disk brake conversion ?
Posted by: dryenko ()
Date: March 06, 2021 10:22AM

Yes, I have used them.
Especially with rear disc brake conversions.
Drum brake wheel cylinders need some small residual pressure to keep the cups sealed against the bores.
Thus their inclusion in MC meant for drum brakes.
Not using them can lead to a "long" pedal and possible leakage at the wheel cylinders
Race cars may be different depending on the systems used.
BC

Bob C aka Dryenko
Dobson, NC 27017

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Re: Front disk brake conversion ?
Posted by: CoCoCo ()
Date: March 06, 2021 11:54AM

Some of that "preload" action was negated by the inclusion of internal springs in the wheel cylinders I believe. At least that's what I've heard recently
Is that what you've heard as well?

And while this may not be the case with Corvair replacement master cylinders, it's been a very long time since I've seen dual reservoir master cylinders for other vehicles come with residual pressure valves in either circuit.
Seems like they would still be helpful no matter what, but apparently to save a few pennies per unit they just don't bother including them anymore.
Perhaps it's because of the assumption of internal springs, and the knowledge that the master cylinders are higher than the brakes. Which was the other function (perhaps the main function?) of the RPV in the first place. To keep brake fluid from backing up into the master cylinder from the wheels, when the master cylinders were mounted down under the floorboards on the frame rails back in the old days.

Might be worth double checking any master cylinders you receive to make sure they are in there. It's good to have a firm pedal with short travel!
I've driven with and without them too (but not on Corvairs), and don't have any trouble when they're not present either with disc or drum brakes.

Paul

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Re: Front disk brake conversion ?
Posted by: v8vair ()
Date: March 06, 2021 01:19PM

I did use them on my 40 Ford where the master cylinder was under the floor, Keeps the fluid from going back into the master. It had Disc Drum

1965 Crown V8 Racer
1964 Bill Thomas Monza Replica Racer
1964 Spyder Street Car
1979 Mazda RX7

Mike Levine

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Re: Front disk brake conversion ?
Posted by: 66vairman ()
Date: March 06, 2021 02:09PM

I've never encountered MC residual pressure valves on the all drum GM brake systems in the 50's and 60's. I know they did have restricters built in to keep folks from damaging the seals during a "panic" stop.

Must be something done when disc/drum systems came along, maybe built into the proportioning valves.

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Re: Front disk brake conversion ?
Posted by: MattNall ()
Date: March 06, 2021 02:34PM

Look in the brakeline ports..

MODERATOR
Sea Mountain, between Charleston Harbor and Coos Bay! SW Oregon Coast
Click HERE for My Website...Click HERE for My TechPages!
...............110-PG.................................................Webered-Turbo

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Re: Front disk brake conversion ?
Posted by: 66vairman ()
Date: March 06, 2021 04:06PM

MattNall Wrote:
-------------------------------------------------------
> Look in the brakeline ports..

I believe those are simple orifices that prevent excess brake fluid flow when someone jumps on the brakes during a panic stop. They prevent line and wheel cylinder hydraulic shock. They have no impact on the hydraulic fluid flow or pressure when the brake pedal is depressed normally. AFAIK

No moving parts, nothing to do with pressure.

If I'm wrong feel free to post information of GM 60's all drum master cylinder showing the residual pressure valves.

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Re: Front disk brake conversion ?
Posted by: Brizo ()
Date: March 06, 2021 04:15PM

66vairman Wrote:
-------------------------------------------------------
> I've never encountered MC residual pressure valves on the all drum GM brake systems in the 50's and 60's. I know they did have restricters built in to keep folks from damaging the seals during a "panic" stop.
>
> Must be something done when disc/drum systems came along, maybe built into the proportioning valves.

Remember on those old master cylinders there was a rubber washer in the bottom of the bore, a metal cup, and a big long spring? That was the residual check valve. It maintained about 10 ? psi in the system.

When they switched to dual master cylinders with drums, the residual valve was a rubber plug and spring under the pressed in brass flare seat.

Dan Brizendine, Circle City Corvairs
'64 8 door Greenbrier, +.060, stroked 186 ci.140 PG. "In beautiful Wanamaker Indiana...with one stop light and 5 pizza shops"



Edited 1 time(s). Last edit at 03/06/2021 04:22PM by Brizo.

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Re: Front disk brake conversion ?
Posted by: joelsplace ()
Date: March 06, 2021 08:18PM

I did a bunch of reading on residual pressure valves a few years ago and the only applications I could find for them were drum brakes without springs in the wheel cylinders and systems with master cylinders below the wheel cylinders. Never on disk brakes. More "modern" calipers I think starting in the 80s actually were changed to have more piston retraction to reduce brake drag. Residual pressure valves would work against them. I take them out when I find them.

Joel
Northlake, TX
5 Ultravans, 116 Corvairs and counting...

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Re: Front disk brake conversion ?
Posted by: v8vair ()
Date: March 07, 2021 05:08AM

Modern Caliper piston Seals pull the pistons back for less drag. The master cylinders from GM were called quick take up to move alot of fluid to avoid the long pedal. Michael LeVeque uses them in his Racer. Less drag Better Gas Mileage go faster. Flush your brake fluid every two years and you will likely never see a wheel cylinder or caliper ever leak again,Keep the brake shoe adjusters working properly and the wheel cylinder pistons hardly move which helps give you that firm at the top pedal.

1965 Crown V8 Racer
1964 Bill Thomas Monza Replica Racer
1964 Spyder Street Car
1979 Mazda RX7

Mike Levine

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Re: Front disk brake conversion ?
Posted by: kmart356 ()
Date: March 07, 2021 11:35AM

toms73novass Wrote:
-------------------------------------------------------
> Those that did the front disk conversion, did you install residual pressure valves ?
>
> I have read else where that some put 2lb on disk circuit and 10 lb on drum to sync the breaking.
>
> Let me know what you did.

Hi Tom,
Colt Front disc brake conversion here with dual circuit master cylinder.
No residual pressure valves. Stops like it should. cool smiley

Ken
'62 Spyder
Florida


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Re: Front disk brake conversion ?
Posted by: toms73novass ()
Date: March 07, 2021 04:46PM

kmart356 Wrote:

> Hi Tom,
> Colt Front disc brake conversion here with dual circuit master cylinder.
> No residual pressure valves. Stops like it should. cool smiley

Ken,
Good to hear, seems like not needed.

Thanks everyone.

-Tom


63' Monza Spyder Convertable (in process) MY Build Thread
65' Monza MY Build Thread
73' NovaSS 454 Big block (Sold)
86' BMW 325es
98' VW Jetta TDI, for daughter
01' Audi Allroad Stage 3 twin turbo
67' UltraVan 211 "Violet"
NFCC, UMCC
Grand Island, NY

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Re: Front disk brake conversion ?
Posted by: 65180 ()
Date: March 08, 2021 11:06AM

I used a 1978 Monte Carlo master cylinder 1 1/8 bore. Added an adjustable proportioning valve and never looked back. It stops straight and true every time. Firm pedal and much shorter stopping distances. Word of advice, just don’t hit the brakes very hard while one of your buddies is behind you with just drum brakes. You will soon find that you have a mid engine Corsair!

Mike Lake
Tucson, Az
65 Corsa 180
65 Corsa 140 sold
66 Monza PG
66 Monza 4sp sold
61 Lakewood sold
61 La[corvaircenter.com]

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Re: Front disk brake conversion ?
Posted by: Seth Emerson ()
Date: March 15, 2021 08:56PM

All disc brake calipers are not alike. Some calipers are hard mounted to the front spindle or rear housing. Pads on both sides of the rotor, float. The pads, as they are engaged, move out to meet the rotor, and stay near there, or close. If there is any runout of the caliper, whether caused by loading from the wheel or, most likely, runout of the actual disc rotor, the pads will be "Knocked back", pushed away from the rotor. When that happens, that pad movement/retraction pushed fluid back to and into the master cylinder. Not a lot, but some. Next time you hit the brakes, the master cylinder has to push the pads back over to the rotor, before the pads can clamp the rotor - and stop/slow the car. The residual Pressure valves keep a couple of PSI in the line between the master cylinder and the caliper. That is supposed to resist the knock-back action of the pad/rotor. Most production-car calipers are "floating calipers. These are attached to the spindle or housing by floating on a pair of pins. Each caliper has a hard mounted pad side and a pad pushed out by the wheel cylinder(s) in the caliper. When those make contact with one side of the rotor, they pull the other side pad against the other side of the rotor, as well and the caliper just floats over the rotor. This style can also be affected by "knock-back" when it actually spreads the caliper open at the pads. Again the first push of the master will be moving the pads into place. Counter-intuitively, this is not a really big race car problem, except maybe at the end of a long straight. But it can be a street car problem, when you could drive a long time between brake pedal applications. So, at the suggestion of most disc-brake manufacturers, I install the low pressure (2 PSI) residual pressure valves on disc-brake racing applications. If I was doing a street conversion, I would do it on that as well. GM installed them, originally, on their 67-up dual masters, drums or discs.

Seth Emerson

Check my new Performance Corvair Web site [www.perfvair.com]

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Re: Front disk brake conversion ?
Posted by: toms73novass ()
Date: March 16, 2021 03:42AM

Seth, thanks for the great explanation. thumbs up

-Tom


63' Monza Spyder Convertable (in process) MY Build Thread
65' Monza MY Build Thread
73' NovaSS 454 Big block (Sold)
86' BMW 325es
98' VW Jetta TDI, for daughter
01' Audi Allroad Stage 3 twin turbo
67' UltraVan 211 "Violet"
NFCC, UMCC
Grand Island, NY

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Re: Front disk brake conversion ?
Posted by: jazzworkerbee ()
Date: March 30, 2021 05:15PM

I am in the middle of replacing my brake lines and adding discs to the front. For the conversion I am using:

Scarebird brackets
Raybestos rotors for S10 4WD
Wilwood 1" tandem master cylinder
Wilwood D154 (single piston) calipers
wilwood APV001 proportioning valve for the rear drums
Braided hoses

After bending some stainless steel line from the blocks to the cylinder I discovered that Wilwood only provides 3/16" and (I think) 1/2" outlet ports and the Corvair distribution blocks use 1/4". Wilwood doesn't sell 1/4" outlet ports, so I need to find another solution, hopefully one that doesn't have an adapter between the port and the inverted flare line. I have located a few adapters, but I'd rather not introduce another potential leak point if I can avoid it,

I would like to know how other folks have solved this problem in the past. I can go to 3/16th port, but that would still necessitate adapters to fit into the distribution blocks for front and rear.

Thank you,

Daniel Atkinson
Tacoma, WA
65 Turbocharged Corsa



Edited 1 time(s). Last edit at 03/30/2021 05:18PM by jazzworkerbee.

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Re: Front disk brake conversion ?
Posted by: MattNall ()
Date: March 30, 2021 05:36PM

But adapters are so simple a fix!

MODERATOR
Sea Mountain, between Charleston Harbor and Coos Bay! SW Oregon Coast
Click HERE for My Website...Click HERE for My TechPages!
...............110-PG.................................................Webered-Turbo

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