Re: Manual Disc master cylinder
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????????????????????????? I'm trying to give you all info to get what you want. If you look at the part it's got the larger opening for the longer rod as what manual brakes use. I just got back from installing the master on the booster and it worked perfect. Just because LMC say's it's 71-72 doesn't mean it was. They could have done what I just did and now use it as the stock parts. I'm not saying they do are not but I wouldn't be surprised if they don't. If LMC can get it then I would think any parts store could so why don't they list them? :chevy: |
Re: Manual Disc master cylinder
Andy they all don’t say that ! You have to dig deeper for the truth.
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Re: Manual Disc master cylinder
I'm thinking that the issue is the parts stores may carry exactly the correct part and can have it for us tomorrow, but computers and documentation about what is the correct part number for the application has been lost. Probably because there is not a lot of demand. There's probably a dozen people in the country right now that may be interested in manual disc brakes on their old truck, and 100,000 people interested in Chinese disc conversion kits with drop spindles.
I am mostly interested in C-10 because that's what I have. I recall reading somewhere that the heavier duty trucks always had boosters even with drum brakes, because they have to stop a heavier gross weight and manual brakes just don't cut it. I didn't retain that info, I just read it and moved on, because I have a C-10. So, until I see evidence otherwise I don't believe in C-20 and C-30 manual brakes of any kind. And I have doubts that a master cylinder that was made for a C-20 or C-30 would have come out of the Chevy factory on a C-10, because I doubt they mixed them. Sooner or later somebody with a 71-72 C-10 and manual brakes will be able to chime in and see what bore size they have and other details. |
Re: Manual Disc master cylinder
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Re: Manual Disc master cylinder
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Re: Manual Disc master cylinder
You know, Jocko, I stared at that pic enough that I was just getting confused. It absolutely makes sense for the holes to be in different places. But when I went out and looked at my truck, the hole is pretty close to the pivot. It has power brakes from the factory. I suspect that the difference may not be as big as is shown in the pictures. Maybe that is what was throwing me off.
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Re: Manual Disc master cylinder
Good question Steevee. I've had some trucks that had two holes and they weren't as dramatically spaced out as the pic above implies - the upper hole was about like the upper one in the pic above, the lower one was only about an inch, maybe two, below. Above was the only ref I could find in the crazy Assembly Manual, and it was somewhat generic, i.e. not specifically 71-72, etc. My 66 did have two holes - it was where I first stumbled across all these little weird brake system nuances - I was converting from single to dual reservoir and non-power to power - but accidentally bought a non-power mc, not realizing it was wrong until I went to put it all together and discovered the piston pushrod hole depth difference. I ended up skipping the booster and installing a non-power system because that was the mc I had. Was kind on the fence about the booster at the time anyway, so didn't mind :)
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Re: Manual Disc master cylinder
Guy's I'm not arguing the point about different master cylinders for the 71-72. I just stating that the computer guy's don't know enough to tell you this difference. They rely on the computer to tell them. They are not 71-72 gooroo's that spend all their spare time on these trucks like us.
So if the computer doesn't state it for the 71-72 model year then they don't know. But when the computer states there is a difference for the 74 to 86 model then they can look for the right part. The master cylinder in my last post is for a C-20 truck of the 74 to 86 model years. Is it a 71-72 model also, who knows but it does work are at least it bolts up any way. Time will tell if it works are not. My 71 C-10 is factory disc brakes with booster. I have changed it over to full disc now though so it's no help.:chevy: |
Re: Manual Disc master cylinder
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Boy has this thread gone off topic ? I went to Napa this morning and returned with part # M36280 . This is a MC that replaces the original GM master 29881. This is a new, not rebuilt master. As you can see it has the deep recessed hole necessary for NO POWER FRONT DISC BRAKES. (Attention ANDY) ! It has the large front reservoir, small rear reservoir as per the original GM design. I hope that this information might help folks looking for the proper master in the future. I will not have the opportunity to install it for a week or two..:metal:
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Re: Manual Disc master cylinder
Can someone reorient the photos
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Re: Manual Disc master cylinder
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here u go
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Re: Manual Disc master cylinder
Thanks Jocko !
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Re: Manual Disc master cylinder
Specs I see on the Internet say it's 1 1/8 bore size. Is the large reservoir for the rear drum brakes? Is the combo valve for C-10 something also available from a car parts store?
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Re: Manual Disc master cylinder
You can probably find one on buy sell forum section.
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Re: Manual Disc master cylinder
The larger reservoir is always for the front (disc) brakes.
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Re: Manual Disc master cylinder
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The old parts books probably had two columns to fill for the C20 just like the C10 had and put the same power disc part number in both spots. |
Re: Manual Disc master cylinder
You do realize that you are arguing over a picture in the service manual that is hand drawn by one or more illustrators. Humans make mistakes.
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Re: Manual Disc master cylinder
So, has anybody outfitted their 1/2 ton truck with manual disc brakes, or has a 1/2 ton truck with factory manual disc brakes, who can give more information such as the bore size and part number of the master cylinder? Is there a part number of a combo valve or proportioning valve from GM/ACDelco (not junk yard but auto parts store source)? Did you guys who were working on this a couple months ago get it done and can give an update?
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I am just about to do this exact thing to my '68.
This is what the local Federated Auto Parts Store got me. They also didn't show 2 different PN#'s. I ordered this for a 72 C10 with a l6 and no options. I sure would like to figure this out before the truck gets tore down. I'm thinking about sending it back and getting this instead: https://www.speedwaymotors.com/Alumi...nder,8905.html ---> Subscribed <--- Attachment 2043525 |
Re: Manual Disc master cylinder
I wanted to bring this back up. Can we confirm the factory never produced a 1/2 ton 71-72 truck with factory manual disc brakes, or nobody can provide a picture of what the master cylinder looked like or provide any evidence it happened? If power brakes on a C-10 were an option, they must have been such a popular option that 100% trucks got the option. Is that right? Or is it too long since 1972 and every truck in the years has been messed with to add the power brake option by going to junk yards or parts stores?
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Just a couple of weeks ago I removed a master cyl from a 71 that didn't have power brakes and before that saw a 72 in a junk yard that didn't have power brakes.
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Re: Manual Disc master cylinder
If it doesn't say anything about a booster on the SPID, it came with manual disc brakes...unless there was an option that ended up including power disc brakes without calling them out on the SPID. The reason I say that is because I have 16.5" wheels on my truck, but it doesn't say anything about them on the SPID. I suspect that this was because they came with being a Longhorn or some thing like that. I don't see any indication that the 61A alternator should be on my truck either, according to the SPID. Maybe that came with UY1 Camper Wiring? It would make sense.
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Re: Manual Disc master cylinder
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