Brake master cylinder

[geasson]

Well, it is running. Rough but it is running. It has no brakes and fluid is leaking out the back of the master cylinder and leaking on the inside. I suspect a new master cylinder is needed or at least a rebuild kit. My issue is that I have the rectangular master cylinder and according to the catalogs, a 1966 should have a round master cylinder. Did the PO change to an older master cylinder or did the 1-tons continue using the rectangular master cylinder. Which one should I buy???

[Keith Seymore]

I would take this opportunity to go to a dual pot system (especially if you drive it much).

K

[cgrocen]

According to Rock Auto, a 1966 C30 1 ton with manual brakes has the rectangular master cylinder. If it had power brakes, then a round style master cylinder is used.

https://www.rockauto.com/en/catalog/...+cylinder,1836

[jayoldschool]

Yep, the answer is "use neither". Convert to dual master. Order whatever a 1967 one ton used and swap it in and run a couple new lines.

[jocko]

if you're interested in the dual reservoir conversion (and it is a worthwhile safety upgrade - keep in mind that the dual res mc was mandated on all vehicles the following year) here's how I converted my 66: http://67-72chevytrucks.com/vboard/s...d.php?t=487384

[slepysal]

dual master swap as others have said is your best bet!

[arcticman]

Another option is to keep it original. I have a 61 k10 with the same single reservoir master cylinder (millions of vehicles left the factory with this system) Dont believe for a minute that there not safe or somehow prone to fail more than a duel system. you should check the complete system all the way down to all 4 wheels. those old steel lines get rusty and the rubber hoses and seals rot. Im sure you already know this
Today I will be changing out the master cylinder and all 4 wheel cylinders with AC Delco replacements. I will also install new brake lines from Inline Tube and rebuilding my clutch slave cylinder. Once this is completed im confident the brakes will stop me every time. Good luck on your project. keep it original whenever possible.

[slepysal]

Originally Posted by arcticman

Another option is to keep it original. I have a 61 k10 with the same single reservoir master cylinder (millions of vehicles left the factory with this system) Dont believe for a minute that there not safe or somehow prone to fail more than a duel system. you should check the complete system all the way down to all 4 wheels. those old steel lines get rusty and the rubber hoses and seals rot. Im sure you already know this
Today I will be changing out the master cylinder and all 4 wheel cylinders with AC Delco replacements. I will also install new brake lines from Inline Tube and rebuilding my clutch slave cylinder. Once this is completed im confident the brakes will stop me every time. Good luck on your project. keep it original whenever possible.

Very valid point. There is nothing I repeat nothing wrong with keeping it original. But from a safety point a dual master cylinder provides you an advantage of having two separate cylinders in case of a failure in one.
If you are restoring your truck to OE specs stick with the one cylinder, but if yo are going modify it... dual. my 2 centavos

[jocko]

Originally Posted by arcticman

Another option is to keep it original. I have a 61 k10 with the same single reservoir master cylinder (millions of vehicles left the factory with this system) Dont believe for a minute that there not safe or somehow prone to fail more than a duel system. you should check the complete system all the way down to all 4 wheels. those old steel lines get rusty and the rubber hoses and seals rot. Im sure you already know this
Today I will be changing out the master cylinder and all 4 wheel cylinders with AC Delco replacements. I will also install new brake lines from Inline Tube and rebuilding my clutch slave cylinder. Once this is completed im confident the brakes will stop me every time. Good luck on your project. keep it original whenever possible.

And how many of the millions that left the factory with single res mc's crashed due to brake loss, prompting the 67 dual res mandate? "It's never happened to me" does not constitute data. While maintaining one's braking system is important, regardless of how many reservoirs one's mc has, this discussion isn't about good maintenance - in other words, when you take your truck out for its first drive with all its new brake parts and everything functioning perfectly - and some sort of road debris damages ANY of your brake lines - you will shortly have no brakes. If you had a dual res mc, you would have front or rear brakes and be able to safely, and easily stop. The dual res mc system is inherently safer than a single res mc system as it has a built in backup system if any single line is damaged. I'm all for keeping things original too - but implying the systems are equally safe is incorrect.

[AcampoDave]

Yep, I did all the routine maintenance stuff on a '61 and felt I was "good to go" and I was for a while,....then the anchor pin for the brake springs on a front wheel snapped off where it threads at the spindle right at the top of the backing plate. The wheel cylinder blew apart and all brakes were lost. Luckily, I was on a country road (that time). I told myself it was a fluke, one in a million...besides, converting it would be hard, what with the hydraulic clutch and all... So, quick trip to the junkyard and I fixed the anchor and rolled on...later it happened again in a Carl's Jr. parking lot (thank God). That scared me enough to yank the single pot and go dual resevoir with front disc. Back then, I had to go automatic trans too because there was no internet and I never heard of Capt. Fab and I couldn't figure a way to keep my hydraulic clutch.

[arcticman]

Thats the problem with these sites today the original poster never asked for advice on how to improve or upgrade to disk or duel res. only wanted info. on correct master cylinder. Jocko I see you have my post in your replay so I consider your statements a response to my post. I dont know who your quoting when you quote "It's never happened to me" does not constitute data." but it sure did not come from me. Secondly not all of us fall for you scare tactics. you make false and misleading statements when you say and I quote" and some sort of road debris damages ANY of your brake lines - you will shortly have no brakes." Thats BS the good folks at GM gave us a secondary mechaniclal braking system seperate frome the hydraulic system. Its called the emergency brake. Designed to stop your vehicle if the priamary system fails. The big black handle under the steering cloumn. Unless by chance that same road debris that ripped your brake hoses or lines or wheel cylinders apart also tore the steel cables apart and If thats the case maybe that persons needs to find a different means of transportation. Honestly the only reason I even originally responded to geassons post this morning was to encourage him to stick to his original plan, take a moment and read his post. then read the others. one person answered his question. the rest of you guys dont even bother to ask him if he wants to keep it original. It comes across like this man's not smart enough to really know what he wants or is asking for, so we'll just enlighten him with are wisdom on what he needs to do to his truck

[jocko]

I wanted to edit this post (#12), hope you don't mind. Perhaps this is a better way to make the point I was trying to get across.
arcticman, apologies as I was not quoting you directly - more a general mindset we all see on here sometimes where we feel someone bases their statement more on personal experience than fact - yet, we all do it, I've done it.
Nobody has stated that a single reservoir mc is unsafe - several have only stated that a dual reservoir mc is safer than a single reservoir mc. That is inherently true if a line failure occurs for any reason.
You make a good point regarding backup system, however, it's worth pointing out that the same GM engineers that brought you that parking brake, also saw fit to add the dual reservoir mc to the brake system in 67 as parking brake use for an emergency stop at speed is not as ideal as coming to a stop with an intact front or rear brake circuit.
I do not think offering a suggestion of a dual res mc to the op when he's in the process of changing out an mc, the perfect time to upgrade IF one wants to, is in any way offensive to the op, nor is it a scare tactic - it's simply a suggestion for awareness to the opportunity if it's of interest. I've owned and driven many single reservoir brake systems over the years and I'm still alive - and they are perfectly appropriate for restorations and even everyday driving. And though no less likely to fail than a single circuit system, the ability to stop on front or rear hydraulic brakes in the event of a failure, is preferred to stopping with a parking brake.

[jayoldschool]

Yes, I lost brakes on BOTH of my single MC vehicles. On the 65 C10, rear wheel cylinder. Ended up in the field next to my house. That got converted quickly. On my mint, very original, rust free Californina 65 Impala convertible... I wanted to keep it stock. I've owned the car over 20 years. No leaks. I thought. Turns out the master had failed, and was leaking very very slowly between the MC and the booster. Pulling into the garage one day... no brakes. Bang, drove right into my tire rack. Thankfully. Bumper bounced me right of the lower set of tires. Used the parking brake pretty quickly after popping it in neutral. Converted that car to dual as well, but used pre-bent/armored lines that look a lot more factory.

Can you put a single MC back in? Sure. Is it going to work? Yes. Is it the best choice you can make? No. Unless your vehicle is a 99 pt show winner...

[geasson]

I appreciate all of the input and while I may eventually go and convert to the dual master cylinder, my immediate goal is to get it running and stopping so that I can see if the driveline needs more work. Thanks to everyone for their input.

[Keith Seymore]

Originally Posted by arcticman

Thats the problem with these sites today the original poster never asked for advice on how to improve or upgrade to disk or duel res. only wanted info. on correct master cylinder.

"Problem"?

I'd say "strength".

I had a single pot fail on my '63 Grand Prix: twice in the same season.

Early in the year I lost all brakes a few miles from home, after driving around pretty much all day. I was able to limp home on back roads using engine braking and the E-brake.

I figured that was a sign from above to convert to a dual system, so I bought all the recommended parts and adapter fittings. When I went to put it on it was obvious that the lines were going to crash hard into the wheel liner/inner fender and I realized I had a "science project" on my hands.

So I thought to my self: "Self - you oughta just put another single on there so you can drive it while you figure out how to make the dual master cylinder fit".

You already know where this is heading. Yep - lost all brakes AGAIN after the brand spanking new just installed single pot master cylinder failed, this time during the Woodward Dream Cruise, about 20 miles from home at the farthest southern point of my circuit. I was able to limp nearly home before pulling off to the side and topping off the master with brake fluid to make it the rest of the way.

You haven't lived until you've tried to put that car through this 90 degree turned garage door - with no brakes (not to mention driving on the freeway knowing full well you have zero brakes). Next time I will winch it up in there.



But - I don't expect there to be a next time. Because now it has a dual pot system on it.

In short: I like to think that because of my many years of experiences (and foibles) I can help people think outside the box to come up a technically better (often less expensive) solution to their problem than what was on their radar, or at a minimum at least make the suggestion for their consideration. The OP can dismiss it outright if he wants, but is making an informed decision. As a result of my profession - including time as a brake development engineer for GM light duty trucks - and my preferences I see my specialty as answering the question they didn't ask - but should have. It's how we all learn.

So - I had all this in mind when I posted. I stand by my original response and recommendation.

K

[Keith Seymore]

This is the only single pot system in my fleet.

I'm reminded the brakes went out on this one, too, while taking my son to a little league practice. But it has 12.5:1 compression and a 4.88 rear gear, so it doesn't really need brakes. You can just take your foot off the gas and it will slow down on its own.

K

[geasson]

Sorry if my simple question caused some hard feelings. I post here to get input from people who know more than me. While I grew up in my Dad's GMC and Pontiac dealership, he started in 1954 and quit in 2004, I appreciate the input from others with more mechanical experience. My experience comes from listening to the mechanics talk and so I listen to people, like all of you, that have more mechanical know-how than I do. Thanks to everyone.