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Disc brakes
Posted by: Dave Decker ()
Date: December 06, 2018 10:13AM

Anyone out there using GM metric calipers front and rear? What would you recommend for a power brake booster master cylinder combo with a booster small enough to fit. TIA Cheers, Dave

Dave, Kamloops, B.C. '65 Crown V8, 2017 Mazda CX3

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Re: Disc brakes
Posted by: Seth Emerson ()
Date: December 06, 2018 05:41PM

Dave - I run that set-up, but no power. I am running a pair of 3/4" piston master cylinders, and have no braking issues. An in-line 3/4" master should be fine.

Seth Emerson

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

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Re: Disc brakes
Posted by: BobV66Vair ()
Date: December 07, 2018 06:03AM

I am running them on all four wheels. No need for power brakes, they are easy to pedal. Much easier than the drum brakes were. I run a single 1-1/8" MC. I found that the extra fluid was needed to make the pedal stay higher under braking.

Bob Vinnacombe
Sandy, Oregon
1965 Corsa 140 stock
1966 Monza Soon to be race car
1968 Monza Parts for now

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Re: Disc brakes
Date: December 07, 2018 07:47AM

Seth Emerson Wrote:
-------------------------------------------------------
> Dave - I run that set-up, but no power. I am
> running a pair of 3/4" piston master cylinders,
> and have no braking issues. An in-line 3/4" master
> should be fine.


Maybe not. Total area of Seth's dual 3/4" master cylinders is about 3.5 square inches. Total area of BobV66Vair's 1-1/8" master cylinder is about 4.0 square inches. A single 3/4" master cylinder has an area of about 1.76 square inches, so there would be a lot of pedal travel, and perhaps not enough fluid movement to fully apply the brakes. it would seem that at least a 1" master cylinder would be required, with 1-1/8" being about optimal.

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Re: Disc brakes
Posted by: Dave Decker ()
Date: December 07, 2018 08:29AM

Thanks all. Anyone know of a site with master cylinder specs? Is there a bolt on from the GM family? Wilwood is pretty, but I'm trying to retire ;-)

Dave, Kamloops, B.C. '65 Crown V8, 2017 Mazda CX3

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Re: Disc brakes
Posted by: 66vairman ()
Date: December 07, 2018 09:01AM

BorondaFarmRacing Wrote:
-----------------------------------------------------
>
> Maybe not. Total area of Seth's dual 3/4" master
> cylinders is about 3.5 square inches. Total area
> of BobV66Vair's 1-1/8" master cylinder is about
> 4.0 square inches. A single 3/4" master cylinder
> has an area of about 1.76 square inches, so there
> would be a lot of pedal travel, and perhaps not
> enough fluid movement to fully apply the brakes.
> it would seem that at least a 1" master cylinder
> would be required, with 1-1/8" being about
> optimal.

Good point and don't forget - with a DUAL master cylinder you have to have enough capacity in both chambers so if one circuit fails the inner dual MC spring can collapse and STILL provide enough volume for the other circuit to work. I've known folks were the dual MC worked fine until one circuit was open and then there was not enough volume to activate the remaining brake circuit - pedal to floor and no brakes.

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Re: Disc brakes
Date: December 07, 2018 03:38PM

Good point, but bad math! My bad!

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Re: Disc brakes
Posted by: joelsplace ()
Date: December 07, 2018 09:15PM

66vairman - that isn't how it works. Each piston provides fluid to half the brake system. If one half fails you still have the other half. No reduction or increased need for volume.
There will be more travel since the bad half has to bottom out and if the pedal can't go that far you have an issue.

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Re: Disc brakes
Posted by: MattNall ()
Date: December 07, 2018 09:52PM

Typical of cars converted to Dual MC... pedal ratio is wrong..





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Re: Disc brakes
Posted by: gnrand ()
Date: December 08, 2018 08:00AM

I got an old unused Stinger Motorsports front disc brake conversion. Several MC's were recommended and the one I used is a 1975 GM 1/2 ton truck non power assisted. It stops OK but requires a lot more pedal pressure vs stock. I did adjust the rod to give more pedal travel but it still takes a lot of effort. If someone has this setup and wants to change the brake pads; the ones listed are not correct instead of 1988 Olds Delta 88 it should be 1988 Olds Cutless Supreme 5.0

Wildomar,Ca

1965 Corsa Hard Top
!965 Corsa Convertible
1968 Monza 140 Convertible 4 speed
1966 435 HP Crown
1986 Buick GN

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Re: Disc brakes
Posted by: joelsplace ()
Date: December 08, 2018 08:17AM

I have non power disks on a 65 they have a lot of travel and take a very strong push to stop.

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Re: Disc brakes
Posted by: MattNall ()
Date: December 08, 2018 08:25AM

joelsplace Wrote:
-------------------------------------------------------
> I have non power disks on a 65 they have a lot of
> travel and take a very strong push to stop.
===========================================================


Then you need a power booster and a larger Dia. MC.





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: Disc brakes
Posted by: Dave Decker ()
Date: December 08, 2018 08:30AM

gnrand Wrote:
-------------------------------------------------------
> I got an old unused Stinger Motorsports front disc
> brake conversion. Several MC's were recommended
> and the one I used is a 1975 GM 1/2 ton truck non
> power assisted. It stops OK but requires a lot
> more pedal pressure vs stock. I did adjust the rod
> to give more pedal travel but it still takes a lot
> of effort. If someone has this setup and wants to
> change the brake pads; the ones listed are not
> correct instead of 1988 Olds Delta 88 it should be
> 1988 Olds Cutless Supreme 5.0

Do you know the bore of that '75 truck MC? Also, is the mounting flange the same? (One can hope ;-)

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Re: Disc brakes
Posted by: 66vairman ()
Date: December 08, 2018 08:38AM

joelsplace Wrote:
-------------------------------------------------------
> 66vairman - that isn't how it works. Each piston
> provides fluid to half the brake system. If one
> half fails you still have the other half. No
> reduction or increased need for volume.
> There will be more travel since the bad half has
> to bottom out and if the pedal can't go that far
> you have an issue.

Joel - I suggest you review a dual MC function. Some good illustrations online. Note the two pistons have a spring between them. When one circuit looses pressure that spring compresses and reducing travel of the piston on the other circuit with respect to pedal travel. That's why it's common when one circuit fails and looses pressure the brake pedal goes nearly to the floor. If the MC volume to wheel cylinder is not adequate you end up with the pedal to the floor and NO brakes if one circuit fails. Easy to check when doing a brake system bleed. I've seen folks with poorly thought out disc. conversions have this problem.

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Re: Disc brakes
Posted by: joelsplace ()
Date: December 08, 2018 09:44AM

That's exactly what I said except for this statement "If the MC volume to wheel cylinder is not adequate you end up with the pedal to the floor and NO brakes if one circuit fails." One side failing does not change the volume to the other side it only changes the pedal travel the distance of the failed side. If that makes the pedal hit the floor that is a different issue, not an issue of volume requirements changing due to one side failing.

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Re: Disc brakes
Posted by: BobV66Vair ()
Date: December 08, 2018 09:45AM

In a dual MC the rear chamber runs the front brakes and the front chamber runs the rear brakes. The idea being that if one circuit fails, the other can stop the car. No major difference would be felt since both chambers are always working. A slight drop in the pedal would be because the bad circuit cased fluid to leak out of that circuit. You will feel something but the pedal should get you stopped, once. It's a "get you to the side of the road" system, not a "drive home" system.

I have seen two separate MC's for the brakes, one for the fronts and one for the rear's. That would get you home.

Bob Vinnacombe
Sandy, Oregon
1965 Corsa 140 stock
1966 Monza Soon to be race car
1968 Monza Parts for now

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Re: Disc brakes
Posted by: gnrand ()
Date: December 08, 2018 05:47PM

Dave Decker Wrote:
-------------------------------------------------------
> gnrand Wrote:
> --------------------------------------------------
> -----
> > I got an old unused Stinger Motorsports front
> disc
> > brake conversion. Several MC's were recommended
> > and the one I used is a 1975 GM 1/2 ton truck
> non
> > power assisted. It stops OK but requires a lot
> > more pedal pressure vs stock. I did adjust the
> rod
> > to give more pedal travel but it still takes a
> lot
> > of effort. If someone has this setup and wants
> to
> > change the brake pads; the ones listed are not
> > correct instead of 1988 Olds Delta 88 it should
> be
> > 1988 Olds Cutless Supreme 5.0
>
> Do you know the bore of that '75 truck MC? Also,
> is the mounting flange the same? (One can hope ;-)

Advertised as 1" bore size.

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Re: Disc brakes
Posted by: 19sixty5 ()
Date: December 08, 2018 05:54PM

On my Corv8 project, I added a Clarks dual master setup... does anyone know the bore of this unit? I plan to upgrade to discs when I get this sorted out.

65 Crown Hardtop

Huntsville, AL

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Re: Disc brakes
Posted by: MattNall ()
Date: December 08, 2018 08:00PM

Here's a true "Dual" MC setup with balance bar! no need for a proportioning valve..

Pro Series Forward Swing Mount Dual Master Cylinder 7:1 Brake Pedal Balance Bar







MODERATOR
Sea Mountain, between Charleston Harbor and Coos Bay! SW Oregon Coast
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Re: Disc brakes
Posted by: v8vair ()
Date: December 09, 2018 06:44AM

Ive pretty much tried every master cyl size. The best combo i found on my 68 was the stock 7/8 bore master with the std bore GM calipers. A very inexpensive soft metalic pad gave great initial feel and good overall stopping power with our light front ends. A high performance pad just doesnt work well for street driving.

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