Anybody running manual disc brakes? Pics
 

Hi there in order to do some troubleshooting on my 1971 GMC 1/2 ton CORRECTION (71 cab on a 69 chassis) that came with factory drum brakes at all four corners that I have since converted to disc in the front I need to install a non power disk brake master cylinder and I would love to see some pics of how that mounts. My drum/drum setup was power so it had the big vacuum booster can on it

please and thank you

Re: Anybody running manual disc brakes? Pics
 

1971 with drum brakes in front, I didn't know there was such a thing.

I have a 1969 C10, I put on it 1971 donor front disc brakes and spindles with new 1971-72 ball joints and steel brake tubing, and 1971 donor rear drum brakes and new 5-lug conversion rear axle shafts. I did manual brakes. The master cylinder bolts directly to the firewall.

https://67-72chevytrucks.com/vboard/...7&d=1673930048
http://www.67-72chevytrucks.com/vboard//showthread.php?p=9167631#post9167631

Re: Anybody running manual disc brakes? Pics
 

1971 was the first year of disc brakes in all the trucks. There were many trucks with manual disc brakes from the factory.

Re: Anybody running manual disc brakes? Pics
 

Yes that is what I thought, and I didn't know front drum brakes were an option for 1971. Gregski may have had the only one. Or it may be a GMC thing.

Re: Anybody running manual disc brakes? Pics
 

1,000 Super Thanks, this is exactly what I needed to see, shoot I forgot about the proportioning block I bet its a different one for drum/drum vs disc/drum

Re: Anybody running manual disc brakes? Pics
 

sorry its a 71 cab on a 69 chassis, it's been a while since I wrenched on it, please check out this thread:

"Drum to Disc" conversions 67-70 pics and videos

Re: Anybody running manual disc brakes? Pics
 

I do on my squarebody. Master from a '84 with manual brakes.
Aluminum master plastic reservoir

Re: Anybody running manual disc brakes? Pics
 

yes, you can bolt directly to the firewall per djmlambert's great pic (pro looking conversion!). Also note he's got 3/16" lines on the disk circuit and 1/4" lines on the drum circuit, just like the factory 71+ disk/drum set-up. A stock 71-72 combo valve would be perfect, or you can run an aftermarket adjustable prop valve - but you are correct in that the original distribution block from a 69 is not the correct valve for your soon-to-be-modified brake system. It appears you have the correct mc in your 1st post; assuming you purchased a manual brake mc (for disk/drum), it should have the deep hole in the rear piston (as opposed to the little shallow hole that accepts the short intermediate push-rod associated with a booster. Recommend check that your mc has a deep hole piston in the bore where it accepts the brake pedal pushrod. If it doesn't, i.e. just has a shallow little depression where the push-rod goes, then you may have a power brake mc (for disk/drum).

Re: Anybody running manual disc brakes? Pics
 

I sold my 71 gmc 1500 a few years ago. It came with non power discs up front. Master was mounted to the firewall just like in the photo above. It took me a few attempts to locate the proper NON POWER master, finally got it at Napa by going into the old paper parts books. Guy on counter was useless.

Re: Anybody running manual disc brakes? Pics
 

thank you so much for that detailed explanation, no where did it say if this was for manual or boosted, I was just happy to find one for disc/drum instead of drum/drum

I will check like you suggested

Re: Anybody running manual disc brakes? Pics
 

I hear that, I hate going to the parts stores on the weekends as they give the experienced Mon-Fri the weekends off and you are stuck with the new guy in the brand new NAPA shirt on

Re: Anybody running manual disc brakes? Pics
 

my 72 was manual disc/drum but I converted to power.

Here is a pic as it was with stock manual MC

Re: Anybody running manual disc brakes? Pics
 

Gregski, LMC used to carry manual vs power 71-72 master cylinders - here's a part # ref for you - https://67-72chevytrucks.com/vboard/...81&postcount=7

Re: Anybody running manual disc brakes? Pics
 

Love your L6 with power steering !

Re: Anybody running manual disc brakes? Pics
 

If its mine your talking about, yeah it is factory PS. I pulled the huge stock steering wheel and put in a smaller one as at 6'2" My leg was sideways to hit the brakes. Easy turning with the power with smaller wheel

Now power disc/drum brakes to....

Re: Anybody running manual disc brakes? Pics
 

I was able to stick a pen cap [Science] in that hole 1 1/2" deep would that make it the deep hole?


Some Specs


BrakeBest Select Brake Master Cylinder - New - NMC11339


Warranty: Limited Lifetime Warranty
Unit of Measure: Each
UPC: # 848074025655
New Or Remanufactured: New
Dust Boot Included: No
Number Of Ports: 2
Bore Size (in): 1.130 Inch
Reservoir Included: Yes
Bore Size (mm): 28.58mm
Reservoir Type: Integral
Number Of Pistons: 1
Sensor Included: No
Number Of Mounting Holes: 2
Gasket Or Seal Included: No
Bleeder Kit Included: Yes
Pedal Rod Included: No
Brake Booster Included: No
Port 1 Thread Size (Forward) (in): 1/2-20 Inch
Port 1 Thread Type (Forward): Inverted Flare
Port 2 Thread Size (in): 9/16-18 Inch
Port 2 Thread Type: Inverted Flare
Master Cylinder Body Material: Cast Iron

Re: Anybody running manual disc brakes? Pics
 

I don't know for sure about the master cylinders for manual disc brakes in our trucks, but I do know that in Pontiacs that the manual disc master cylinders were a one year only option and they had a different bore diameter than the power brake master cylinders did.

Last time searched for one I had to have the counterman look the number up in a BOOK! :ack:There was no listing in the computer for a manual master cylinder.

I would bet the bore diameters are different for our trucks also.

Re: Anybody running manual disc brakes? Pics
 

thanks, that sounds boring [sorry couldn't help it]

Re: Anybody running manual disc brakes? Pics
 

Yes that looks like a deep pushrod hole so it is for manual brakes. On our trucks the bore diameter is 1-1/8" for both manual and power brakes. Keith Seymore shared the engineering charts with us on what I think is the definitive thread about manual brake master cylinders for 71-72.
http://67-72chevytrucks.com/vboard/s...30#post8909230
This is the same thread where 54blackhornet discussed his research at NAPA going into paper parts books to figure out the correct master cylinder.

http://67-72chevytrucks.com/vboard/s...30#post8909230

Re: Anybody running manual disc brakes? Pics
 

I used this master on my Studebaker to go from manual drum to manual disc .

https://www.speedwaymotors.com/GM-Co...ore,51673.html

Some pictures I used an inline portioning valve for the rear .

Re: Anybody running manual disc brakes? Pics
 

yep, 2nd the motion that you have a deep hole non-power brake mc - good news!

Re: Anybody running manual disc brakes? Pics
 

and a few hours and a bucket of sweat later she's on

Re: Anybody running manual disc brakes? Pics
 

hey bro, hey bro, what kinda carburetor are you running is that one of them organic Holley Carter Rochester Quadrajet Edelbrocks?

Re: Anybody running manual disc brakes? Pics
 

That's funny right there! Keep that truck organic!

Re: Anybody running manual disc brakes? Pics
 

I think they're called Quadrazaps.

Re: Anybody running manual disc brakes? Pics
 

that's the one! lOl

Re: Anybody running manual disc brakes? Pics
 

Late I know, but square bodies did manual discs. Here is a picture of a '73 with a '74 Master. Seems real '73 masters are hard to find and this one had already been replaced. I put it back the way it came off but doing some research I found that the front and rear was reversed. I swapped the lines and got rid of the adapters show in the photo. If you look the small compartment is in the front for drums and the big one is for discs. Compare to the one in post 1 and they are opposite.

Re: Anybody running manual disc brakes? Pics
 

thanks so much I had a '74 with power brakes if I recall correctly but I remember arguing or discussing with someone that the front chamber is not always for the front brakes and they must have thunk I was crazy, and yet here you are

I just made a YouTube video where I ask this very question, I hope I link correctly right to the point in time here: Electric C10 - Give Me A Brake

Re: Anybody running manual disc brakes? Pics
 

Wait!? You are building an electric truck with manual brakes!? :metal:

Re: Anybody running manual disc brakes? Pics
 

yes, lol, please watch the video

Re: Anybody running manual disc brakes? Pics
 

So I just stole some great brake info from here Master Cylinders FAQ

here are some highlights

Do disc brakes require more pressure than drum brakes?
Yes.


Can I run disc brakes with a manual brake master?
Yes. The bore size of the master can not be larger than 1" and your leverage at the pedal has to be greater than power brakes.


If I add disc brakes will I need a proportioning valve?
Yes. The addition of a proportioning valve is a must. Without it your braking system will not operate properly.


How does a disc brake master differ from a drum brake master?
A drum brake master will differ from a disc brake master in two ways. The amount of fluid that a drum brake master has to move is less than disc brake. Drum brake masters have 10 lb residual valves at the outlet to keep a residual pressure on the drums. If you use a drum brake master for disc brakes you would move an insufficient volume of fluid and the disc brakes would drag because of the residual valves.


Can I use my manual master on a booster?
Yes.


Why is one fluid chamber larger than the other in a disc/drum master?
As disc brake pads wear the caliper pistons will move outward. The fluid level in the master will drop more rapidly than the drum portion so you need more reserve.

Re: Anybody running manual disc brakes? Pics
 

Before you take all that info as fact, there are things you should think about.

>>The amount of fluid that a drum brake master has to move is less than disc brake<<
Think of that from the perspective that the drum master and the disc master are in the same unit as opposed to a drum/drum or disc/disc MC.

The volume of a cylinder = πr²h (That's supposed to be PI).
On ALL dual master cylinders, the forward piston is called the Secondary Piston and the rear piston is the Primary Piston. The fluid in the Primary Chamber, pushes the Secondary Piston forward until the Secondary Chamber compresses and begins to develop pressure. The primary chamber begins to develop pressure at the same time.
Both the Primary and Secondary pistons move forward the same distance at the same time.

The Diameter (and Radius) is the same for both the Primary and Secondary pistons, so the same volume exits both the front and rear ports and it is under the same pressure.

>>Drum brake masters have 10 lb residual valves at the outlet<<
I think you will find that very few new and rebuilt master cylinders have a residual valve because the cup spreaders have been improved and do a better job of keeping the air from entering.

>>Can I use my manual master on a booster? - Yes<<

There is something they are not considering. If your foot moves the manual master pistons forward a 1/2 inch, the pistons move a specific volume and produce some specific pressure.
If you place a vacuum booster between your foot and the MC pistons and your foot moves that same 1/2 inch, the booster will only move the pistons about 7/16 inch. The action of the booster looses distance.
This is why a MC used with a booster usually has a larger bore. The piston in the larger bore doesn't have to move as far to move the same volume and then produce the same brake line pressure.
The same braking with less foot pressure.

In your video, you are holding a old MC which you describe as being a power MC. It looks like it has a rubber dust boot on it. Rubber boots are used on manual master cylinder to keep dirt away from the exposed piston. The boots don't fit between the MC and the booster.
You should have a boot on your new manual MC.
Your questions about large and small reservoir sizes should be answered by looking at the single reservoir on the MC mounted on your truck. It doesn't matter the reservoir size as long as you don't run out of fluid when the disc pads wear down.
Drum brakes with self adjusters never have an issue with small reservoirs.

Re: Anybody running manual disc brakes? Pics
 

That is a bunch of very good technical info here, I like reading it.

When I had the original 4-wheel manual drum brakes on my 1969 truck, the braking worked very well except my self-adjusters were not the best and needed work. One side would differ from the other after a few hundred miles and the truck would swerve in an emergency stop or slow down. Instead of working more on the drum brakes to fix that, I had the opportunity to change all 4 wheels to a great condition stock 1971 setup due to a posting in the parts section.

With disc brakes I noticed some things changed. 1) the swerving problem went away. 2) the pedal braking effort reduced. 3) the total pedal travel reduced such that with full application of the brake the pedal no longer went down as far, a difference of about 1 inch. 4) the brakes have a better feel and are very smooth.

When I drive my truck with manual front disc brakes, it makes me wonder why there appears to be a great amount of interest in power brakes for a C10. I can't imagine having the desire to add power to mine.

But who knows, I could change my mind in the future. I wonder if the majority of posts dealing with brake problems are related to booster failure and vacuum or hydroboost problems, and we just don't hear from the manual brake crowd very much because the systems are simpler and less prone to problems and therefore superior. Or maybe there's only a dozen people left with manual brakes and we're just missing out.

So, anyway, it appears I'm long-winded, my point is I'm not just running manual disc brakes, I'm liking them a lot and would recommend them. Specifically I recommend manual front disc rear drum brakes for a half ton truck.

Re: Anybody running manual disc brakes? Pics
 

Personally, I'd like manual disc, even on my 3/4T truck (don't have that- it's power). If the engine quits and the vacuum disappears, it isn't yet a problem for me. I can stand on the pedal. My frail wife, though...different story. Though she did manage to get our Astrovan off the freeway and stopped when the fuel pump failed. No Hydroboost brakes or power steering. Luckily she drives like a snail and was on an offramp that had a "Yield" sign at the bottom when it happened. Could have been way worse.

Re: Anybody running manual disc brakes? Pics
 

super info thank you and I picked out the quote above because we thought the same thing after making the video and taking some measurement of the recess of the piston in the old rusty "power" drum/drum master cylinder to only find out it was also just as deep as the new manual disc drum one so about 1 1/2"

in my defense I bought that "power" one maybe 5 years ago and I specifically asked for a power drum/drum master cylinder, I am not sure i bought it as a kit with the vacuum booster but maybe, not pointing the finger but I wanted a power MC and I ranned it with a booster for like 5 years, hence me posting that FAQ about can you use a manual MC with the booster

anywho thanks for the tip on the rubber boot, that was the first thing I asked the counter guy at Oh Really's when he took it out of the box for us to stare at it, I said shouldn't it come with a rubber boot? he shrugged his shoulders

as a heads up, I didn't see any of the computer screens at AutoZone, Oh'Reilly's or NAPA say manual or power for any of the MCs we looked at they just specify drum/drum or disc/drum so I wonder if they are saying they are interchangeable, I don't know

once again I really appreciate you taking the time to write all that info up, I love learning this stuff, thank you very much

the pic below is from like 6 years ago when I first got the truck and put a new drum/drum brake MC on it

Re: Anybody running manual disc brakes? Pics
 

Most manual MC have the deep hole and most power MC applications use a shallow hole.
CPP, supplies MC's with an adapter plug to use as a manual or with a booster. You still have to decide what bore size you need.

Re: Anybody running manual disc brakes? Pics
 

Yeah, having three trucks I forget which one this happened on, but I installed the booster and the MC and then found that little pinky finger in the box and thought oh shoot, where does this go... and I had to remove the MC and shove it in there LoL

Re: Anybody running manual disc brakes? Pics
 

My 71 c10 had manual disc brakes very hard to stop. Found a booster and brackets off a c20 what a difference in pedal pressure

Re: Anybody running manual disc brakes? Pics
 

Hearing things like that makes me wonder what's up, since mine is easy pedal effort with manual disc brakes from a 71.

Re: Anybody running manual disc brakes? Pics
 

happy to report brakes are done and all working, son helped me bleed 'em! thank you Michael you won't hear me talk about them ever again, sheesh enuff of that, we have an electric truck to build!

just wanted to say THANK YOU so much to everyone on this thread who offered help, this had me in a funk for 6 months, I really appreciate the exchange of know how on this forum, thanks again