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.