Correct Master Cylinder

[samkost]

Before the start of the restoration of my 1972 C10, I had an excellent full functioning power brake system.
During the restoration process I had a new power brake booster added and installed.
The resto shop turned out to be a nightmare of mishaps and shoddy workmanship.
Ending the relationship I took ownership of the truck and brought it home.
When I picked up the truck, my power brakes were not functioning with a rock hard brake pedal.
At home I started to correct the many inherited issues.
I later found out and determined, with help and questions answered from this forum site, that a shallow short bore piston was installed instead of the long deep bore piston rod between the OE master and the new booster.
I replaced the short piston with the long and partially regained my power brake function but it wasn’t 100% as before.
I went to a new shop to get the trucks brake system checked and bled.
They advised that my present master cylinder was missing an O-ring resulting in some vacuum loss and had a slight bit of corrosion between the master and booster. Strange they were unable to get new replacement parts?

So, I need to confirm the new correct replacement master cylinder part to order is an AC Delco #18M1036.
Is this AC Delco master a short or deep bore?
I also want to replace the proportioning valve for good measure.
I could use some guidance with the bore size diameter, shallow bore or deep bore and a correct proportioning valve requirements.

I’ve added photos of my present set up because of confusion what may have happened from previous owners add ons or past upgrades.
The present master is a deep bore piston and is taller than the new AC Delco.
Is this master cylinder the correct OE part for a 1972 C10 with front disc/rear drum power brakes?
I would appreciate any recommendations and comments.
Thanks all

[72BBChuck]

I have fought the master cylinder and rod length nightmare a couple times. They both must be the correct length/depth. I am in Centralia and there is a shop here in town owned by a guy that has several of these trucks himself. He has fixed many such problems for local owners. His name is Mike Hagstrom. The shop is Hags Automotive. If you get stuck, I can seperate an original booster/cylinder and measure both.

[samkost]

72BBChuck,
I have an understanding and figured out the piston lengths to get semi functioning brakes again.
Just trying to determine what new replacement parts are needed for the existing older worn master/proportioning valve parts.
My current master on a web site shows it is a non power brake master with my
SPID labeled Hydro Brake Booster adding to my confusion.
I’m learning everyday.

Thanks for the info and reply.

[samkost]

I made some calls to some vendors today and got some insight to the direction I am going to go.
One vendors web photo showed my present style of master cylinder as a manual brake master? Hmmm?
They showed a different style (shape) as a power brake master.
Their tech had to put me on hold to answer my questions.

I asked another vendor about the AC Delco replacement master cylinder.
It is indeed stamped USA on its body but it is manufactured in China.
They couldn’t tell the bore size or piston length.
This master seems to be out of stock on several vendor sites.

I then called POL (Performance Online)after browsing their web site, and spoke with a tech.
He had answers for my application and explained the bore sizes and bore piston lengths.
Their products don’t match my current style of master brake cylinder.
I was told that I require a 1” bore with a deep bore long piston for the 72’.
Going make some more calls tomorrow.

Anyone have opinions or used POL brake products?
Thanks

[Toro]

I have been in the same situation. I can confirm that AC Delco #18M1036 is the deep bore that you will need with your setup. Also GM #19176594.

See my thread link (with photos) regarding similar issue and question regarding if the deep bore/long push rod in booster was correct. On my 72 Blazer it was that way from factory. Details here: https://67-72chevytrucks.com/vboard/...d.php?t=845821

[samkost]

Originally Posted by Toro

I have been in the same situation. I can confirm that AC Delco #18M1036 is the deep bore that you will need with your setup. Also GM #19176594.

See my thread link (with photos) regarding similar issue and question regarding if the deep bore/long push rod in booster was correct. On my 72 Blazer it was that way from factory. Details here: https://67-72chevytrucks.com/vboard/...d.php?t=845821

Thanks for the information and clarification Toro.
So my 1/2 C10 with power brakes is the same as the original Blazer set up. Interesting.
The subject of what a correct master cylinder looks like from the factory for a 1972 C10 with power brakes (2 wheel disc/rear drum) has been a challenge.
I even checked my SPID glove box label and it lists J70 Hydro Brake Booster.
Looks like I can proceed with ordering some new brake parts!
Funny I didn’t see your linked post when searching past forum posts.
Most helpful and much appreciated.
Thanks again

[samkost]

I ordered a new AC Delco Master Brake Cylinder and decided to not replace the original cast iron Proportioning Valve assembly.
I want to maintain that original master and prop valve look.
I researched a lot about aftermarket prop valves and saw many complaints of poor quality and leakage issues of the brass style replacements.
A few forum members commented that they maintained and kept the O.E. Prop valves./
I also found through searching past forum posts about a vendor that rebuilds the O.E. proportioning valve assemblies and contacted them.
$$$ Pricey but guaranteed for life.
I noticed a couple of members here that have used that vendor for rebuilt brake assemblies.
If needed later on, I will rebuild my O.E. unit.
Thanks again to Toro and 72BBChuck for your input posts.

[samkost]

I hope this following information may help someone else when trying to replace this specific style of Master Brake Cylinder.
A frustrating and lengthy update about my previous post from late October.
I had ordered an AC Delco Professional Master Brake Cylinder #18M1036 from Amazon.com
Waiting 2 months I called Amazon to see what the delay was.
Turns out the AC Delco part was not in stock with no update/communications, just a pending on my bank account.
I then called AC Delco customer support and was told the parts would be available mid December.
A week ago, Amazon then shipped the part only to find out the wrong master cylinder part was in the correctly labeled AC Delco box.
I returned the part to Amazon and then ordered from Summit when assured from their Technical support that the photo of the master shown on their web site photo was indeed the correct part depicted.
Received that Summit part yesterday in the AC Delco packaging only to see another incorrect master cylinder.
It’s being returned also.
Calling AC Delco/GM Parts customer support again to find out why a different style of master brake cylinder from two different vendors were wrong, they passed the buck and said to contact Amazon and Summit to correct. Unreal.
I emphasized that the wrong parts are being sent in the correct labeled boxes.
They disagreed and said to order directly from The GM/AC Delco web site.
I found out that you cannot order from their web site and have to order from a GM dealership.
So now I’m waiting for an answer from the dealership to confirm if this style of replacement brake part is even still available.
Here are some photos to describe what I have under the hood presently and what has been delivered twice so far.
Twice two wrong parts delivered from two different vendors in the proper labeled boxes.
Maybe third time delivered is the charm. God I hope so

[volksworld]

just to make you feel more wonderful the AC Delco masters are made by Brake Parts Inc in china and aren't a "real "chevy part...they also make Raybestos and NAPA stuff...found out when they had a recent recall of all 3 brands on a master that was locking up....so i doubt your dealer will source it from them...been at least 15 years since my master swap but i swear manual masters were 1 inch and power were 1 1/16 or 1 1/8...a bore thats too small will give you excessive pedal travel, too large a short throw that's too hard to push...a lot of the aftermarket power disc conversions used the Vette style master with the equal size front and rear resevoir sections (which lets you use them with disc/drum or disc/disc applications) and that's what it looks like they put on your truck...idk if a stock master is compatible with whatever they supplied as a booster...Rockauto is one of the few vendors that uses the actual picture of the part you're getting and not a stock photo of something similar...the Delco one they sent you looks more "oem correct" than the one in the Summit picture...a rock hard pedal is usually lack of power assist...bad check valve or bad booster

[samkost]

My hard pedal was due to the restorations shops failure of installing the wrong short piston rod between the master and the new booster.
I later replaced it with the correct longer rod.
I gained my brakes back but still need to replace the older master and bleed the system anew.
Yes the parts are made in China, says so on the AC Delco labeled packaging.
Their customer service said that they are American made. Untrue.
The customer service personnel need to be better informed.
I gave them my 1972 C10 VIN # for the correct replacement part search and they said my VIN was incorrect not enough characters
Internet vendors, Amazon, Summit Racing, Rock Auto and others show my OE style photos on their web sites (an old generic photo array?). One of several pictures shown on the internet show the bottom of the master stamped “made in the U.S.A”. That’s why I believe the photos are old examples and not current.
One AC Delco Technician that I sent my photos to, agrees with me that there might be two possibilities:
1. The newly stocked wrong parts were misboxed and packaged with the correct parts numbered boxes.
Or,
2. They replaced the OE style with this new replacement (different model) of Master Brake Cylinder.
He believes that they are misboxed. The main Customer service denies this theory.
The wrong or newer Master part is only stamped with a “S” on the bottom of the part. No other casting numbers are present. Strange.

I will report back and see if the dealer will come through with the original style master, I’m not holding my breath .
You did raise a good point though, what is the correct bore that I need.
I was told that a 1” bore is correct.
I would appreciate any input from the forum here to chime in and assist myself and others about a correct choice of an aftermarket replacement Master Brake Cylinder.
Thanks for your input volksworld

[1970cstblazer]

It's hit or miss with the AC Delco 18M1036 recent issue replacements. The first one I received from Amazon was the single bail unequal size reservoir design, exactly as shown above.

The second AC Delco 18M1036 unit I bought from EBAY is the correct equal size reservoir dual bail version, almost identical to the original Delco Moraine unit that came on my 1972 Blazer donor.

[samkost]

Originally Posted by 1970cstblazer

It's hit or miss with the AC Delco 18M1036 recent issue replacements. The first one I received from Amazon was the single bail unequal size reservoir design, exactly as shown above.

The second AC Delco 18M1036 unit I bought from EBAY is the correct equal size reservoir dual bail version, almost identical to the original Delco Moraine unit that came on my 1972 Blazer donor.

Thanks 1970cstblazer,
That’s great information to relay back to customer service and their technician.
Did you purchase the double bail style master from eBay recently or some time ago?
Not sure if I will get an answer from them for the two different styles of parts in the AC Delco 18M1036 labeled factory box.
Thanks again for posting your experience with the Master Cylinders.

[1970cstblazer]

Originally Posted by samkost

Thanks 1970cstblazer,
That’s great information to relay back to customer service and their technician.
Did you purchase the double bail style master from eBay recently or some time ago?
Not sure if I will get an answer from them for the two different styles of parts in the AC Delco 18M1036 labeled factory box.
Thanks again for posting your experience with the Master Cylinders.

Yes, I ordered it on the same night, 12/14/23, that I received the first one from Amazon. I made double sure that I was getting the correct style prior to the order.

[samkost]

A picture is worth a thousand words.
Great ammunition to show AC Delco customer service.
Who knows why they deny any misboxed items on their part.
Your timely purchase with this photo should prove that there is a problem on this stocking issue.
One last request, can you direct me to the eBay seller you purchased from?
Wonderful info.
Thanks again 1970cstblazer

[1970cstblazer]

https://www.ebay.com/str/midwesthotrodsinc

[samkost]

Originally Posted by 1970cstblazer

https://www.ebay.com/str/midwesthotrodsinc

Wonderful, many thanks again!

[1970cstblazer]

So, my theory here is that there are two designs approved by GM that will work for the intended applications, just one of them not be somewhat true to the factory issued design.

Here are a couple of listings that show the "wrong" style master for a 1972 C10:

https://www.ebay.com/itm/12570248397...Bk9SR8TL94aRYw

https://www.ebay.com/itm/16582312265...Bk9SR8bL94aRYw

[samkost]

The two wrong AC Delco parts I sent back never had model numbers casted onto the masters.
Curious if the one you have has “made in U.S.A” stamped on its bottom base?
Only a “S” was stamped on the bottom of the two I returned.
More ammo to pass on.
Thanks again for the links.

[1970cstblazer]

I will check and report back

[1970cstblazer]

The marking on the correct master:

[samkost]

Thanks for the photo.
I am still not able to locate an OE replacement style master cylinder with the double hoops.
The link you sent doesn’t offer or list this part anymore.
They haven’t responded to my inquiry yet. You may have gotten the last one from them.
A couple of eBay sellers won’t confirm what’s inside the box and or even attempt a visual check.

The stock Ac Delco photos these vendors show are of the old style and need to be updated.
I’m not giving up and will still try to find this old stock/style of master cylinder that matches the photos.
I am upset with AC Delco with numerous calls, misinformation and failure to admit the different style brake part now offered.
Still waiting on the dealership to see if an older stock part is still available.
Maybe someone here on the forum can help find this elusive part.

[dmjlambert]

I'm curious about your master cylinder problem. Why is it you specifically want the one with 2 bails? Is it because it should work better, or have equal size reservoirs, better looks, or what? I have one with single bail, small reservoir for rear drum brakes, and big reservoir for from disc brakes, on my manual brake setup and it works well. I thought you were supposed to have different size reservoirs for front disc and rear drum arrangement.

[samkost]

Originally Posted by dmjlambert

I'm curious about your master cylinder problem. Why is it you specifically want the one with 2 bails? Is it because it should work better, or have equal size reservoirs, better looks, or what? I have one with single bail, small reservoir for rear drum brakes, and big reservoir for from disc brakes, on my manual brake setup and it works well. I thought you were supposed to have different size reservoirs for front disc and rear drum arrangement.

Just trying to replace my current 50 year+ set up which worked flawlessly before the restoration shop mishaps.
I also want to maintain the current original cast iron proportioning valve.
Having several forum members here post responses to my questions,
I have been told that this AC Delco/GM part # 18M1036 master cylinder is the correct replacement for my 72’ C10 with SPID code J70 Hydro Brake Booster, with original front disc/rear drum.
Unfortunately the O.E. replacement parts are not readily available anymore and AC Delco has replaced the older 2 bail design with the single style bail.
I may go with a Corvette or Camaro style master (deep bore) brake cylinder.
My booster came from P.O.L. I will try them for a compatible master cylinder.

Still waiting for the local GM dealership to locate an older master replacement.

[dmjlambert]

I sent my 71-72 combination valve to White Post Restorations and they did a good job with that. I'm sure they could take care of your master cylinder too, and maybe the original booster and brackets. I'm not sure if they do boosters, but they might. They put a cast iron color epoxy coat on the combination valve, but their paint job was not perfect. There's minor places they missed and you can barely tell the difference between the paint and bare cast iron. It becomes more evident when it gets a little rust on it. I did touch up paint on the valve. Anyway, it would be more expensive but it would likely last a long time and you would be getting the parts that were engineered for your truck and not some generic Chinese not-made-for-your-application-but-sorta-works parts.

[samkost]

I am familiar with White Post Restorations.
I inquired and yes they are pricey.
I am patiently waiting for the GM local dealership to hopefully locate the older OE style replacement master cylinder.
If nothing develops, I will get the Corvette style master for my 1972 C10 disc/drum set-up. My booster is new from and good to go.
Thanks for your replies.