Master Cylinder question

[60sIron]

I'm doing a disc break conversation on my 69 K20, fronts only. Easy right...... Because in 1971 they came that way. The proportioning valve from CPP appear front inlet and outlets to the front brakes, rear inlet and outlet to the rear. The problem is the master cylinder appears to be the reverse. I'm guessing this is so because the rear MC reservoir is larger than the front one. Larger for addition fluid for calipers. And the pre bent lines on the PP valve fit front to rear and rear to front. Has anyone dealt with this? Seems I need a MC off of something else......... or a stock PP valve (which I can't find)
Thanks

[chevytruckguy70]

I see you are working on a 3/4 ton. When I converted mine a few years back I learned that the 3/4 and 1/2 ton were not the same, meaning the 3/4 ton uses the front tank in the master cylinder for the front of the truck. 1/2 tons use the rear tank for the front.

With that being said just make sure you match the upper brake parts which ever way you go. 3/4 to 3/4 or 1/2 with 1/2 and you should be ok.

On mine I kept the 3/4 ton m/c, proportional valve and booster and used them with the 1/2 ton calipers. I wasn't able to mix the upper parts and make them work.

[ck5566]

Originally Posted by chevytruckguy70

I see you are working on a 3/4 ton. When I converted mine a few years back I learned that the 3/4 and 1/2 ton were not the same, meaning the 3/4 ton uses the front tank in the master cylinder for the front of the truck. 1/2 tons use the rear tank for the front.

With that being said just make sure you match the upper brake parts which ever way you go. 3/4 to 3/4 or 1/2 with 1/2 and you should be ok.

On mine I kept the 3/4 ton m/c, proportional valve and booster and used them with the 1/2 ton calipers. I wasn't able to mix the upper parts and make them work.

CTG, you mentioned about 3/4 ton & 1/2 tons being different in what lines coming out of MC going to front or back for the distribution of the fluids. Was that for Power Disc frt.brake/Drum rear brakes setup and not for the Drum/Drum setup? I have a 68 C10 Drum/Drum Manuel Brakes and my frt tanks line goes through the distribution valve then down to the frt brakes, a little different from what you guys are working with but wondering if mine might be wrong or it being right for the 1/2 ton Drum/Drum Manuel system.

[60sIron]

Originally Posted by ck5566

CTG, you mentioned about 3/4 ton & 1/2 tons being different in what lines coming out of MC going to front or back for the distribution of the fluids. Was that for Power Disc frt.brake/Drum rear brakes setup and not for the Drum/Drum setup? I have a 68 C10 Drum/Drum Manuel Brakes and my frt tanks line goes through the distribution valve then down to the frt brakes, a little different from what you guys are working with but wondering if mine might be wrong or it being right for the 1/2 ton Drum/Drum Manuel system.

That was correct for my K20 that had power drum/drum breaks. That's why I'm confused as to why would it change and does it make a difference. From the research I've done the only difference is the size of the reservoir as calipers need more fluid as the pads wear.

[chevytruckguy70]

Yes, mine were disc front and drum rear. The c10 was setup with the rear tank to the front disc and the c20 had the front tank with the front disc. I'm not sure why chevy did it this way.

I converted my '72 c20 to a c10 using parts from a wrecked '71 c10. That's how I found the differences. In the process I ordered prebent brake lines for a c10 thinking I was going to use the c10's master cylinder and booster. In the build I found the c10's booster was bad so I decided to use the c20's setup which is how I noticed the lines were crossed. I had to clean up and use the c20's master cyl to proportioning valve brake lines instead. It all worked out but will really confuse someone (probably me again) in the future.

[B. W.]

You are correct, the larger reservoir goes to the disc brakes. Pictured is a factory 71 K25.