therobski

Guys, there are two size lines coming off the MC to the proportioning valve. I have the 3/16th bent and installed the other in the picture ( inboard to the firewall) is a template-what is the correct size line. I know that one is bigger. I'm thinking 1/4 inch? Just want to be sure.

Allan R

All the brake lines on my car are 1/4". The ones to the MC usually have spring around them to protect the lines from any rub areas. So do the areas along the frame rail where there's a chance of movement.

On my lines, there are simply different size fittings to the Prop valve to ensure the lines go to the right ports.

joe_padavano

Not from the factory. On dual circuit master cylinders, Olds (and all GMs) used 3/16" tubing for the front brake lines and 1/4" tubing for the rear brake lines. This is true from the M/C to the distribution block or combo valve and from there to the wheels. You are correct about the fittings. Where it was possible to mis-connect brake lines, GM used different threads on the flare nuts for a given tube size specifically so they could not be mis-connected.

Allan R

Just replaced ALL the brake lines and hoses on my car. The MC to Prop valve lines (replacement) would not thread after over 30 minutes of cursing and trying, even though the fittings are different sizes to ensure no screw ups. All the other new lines and fittings threaded in no problem. So I tested the OEM lines against the prop valve. They caught the thread and locked in within 10 seconds, so I capped the ends, media blasted them, blew out the lines and reinstalled them. They look as good as new. Side by side comparison of new/old the fittings looked exactly the same. But I swear the lines from the prop valve to the front discs are 1/4", same as the rear drums. The anchors for the front lines are labled as 1/4" too.

Professur

I'm just gonna throw in that I wasted a ton of time farting about with the clamp type flaring tool, could not get a consistent double flare. Finally gave up, took a bent line to a local brake shop to have them flare it. Worst $20 ever spent. Looked like a single flare it was so crushed .. and they had the coated steel clamped so tight they had to sand off the coating, and teeth marks .. I don't even want to consider how much material they took off in the process. Finally I broke down and paid the money for the Eastwood flare tool ... total idiot proof. Redid my entire car, not one bad one, and no damage to the coating. Since then I found these but I haven't tried them to speak to the quality.

therobski

Guys I ran 3/16th on all my lines except the one we are talking about and from what everybody is saying the I may as well use the 3/16 template in stead of the 1/4 inch for that one piece in question. I used a product that is almost perfect for the novice I am at building these brake lines car. I used EZIBEND line and fittings www.brakequip.com. This product is super easy to bend and shape, it's on a lot of new high end cars from the factory. Very forgiving too. Based upon this thread I don't think it's going to make that much difference.

MDchanic

The EZ-Bend tubing looks like standard copper / nickel, available in most auto parts stores.

I've never had a problem with the clamp flaring tools - not always the prettiest, but they don't leak.

- Eric

joe_padavano

Every cast iron GM dual circuit master cylinder from 1967 to well into the 1980s uses 1/2-20 threads on the front port and 9/16-18 threads on the back port. Note that these are NOT the standard flare nut threads you get if you just buy a piece of pre-flared brake tube at the auto parts store. The "normal" flare nut for a 3/16 tube is 3/8-24 thread.

Here's a PDF of some catalog pages from Inline Tube. The first page shows the wide variety of inverted flare tube nut thread sizes. The third page shows that for GM brakes, the front brakes use 3/16" tube and the back brakes use 1/4". I would not use 3/16" for the back brakes because of the potential pressure drop in the long tube run to the rear axle. Keep in mind that GM tries to cut every penny possible from the cost of building a car, and even they felt it was necessary to use the larger 1/4" tube for the run to the back of the car. Also keep in mind that while something smaller may work fine under normal driving, GM engineers and tests cars to operate under all types of driving - including panic stops with a fully loaded vehicle. As an engineer, I value their design and testing.

Edit: I just looked at that Inline Tube catalog again, and naturally they have a typo. If you look on the third page at their diagram of a 1967-1970 master cylinder, they show that the rear fitting uses tube nut TN14, which is for a 1/4" tube, but the diagram says it's 3/16.

therobski

Joe thanks a bunch for your thoughts. As mentioned I used EZIBEND 3/16 tubing and all new parts used for assembly, including 1 inch bore rear wheel cylinders would most like work for a stock little driver that's not driven everyday, but I plan on running this car hard. That said I ordered 25ft of 1/4 inch EZIBEND tubing. Any ideas where to get the tube nuts. I think I would need 3/8x24NF-1/4 for the long tube to the rear and the two lines to the wheel cylinders and one 9/16x18-1/4 and a 7/16x20NF-1/4 for the larger line off the MC to the proportioning valve and where to order these tube nuts??

joe_padavano

The tube nuts are pretty easy to find. I've had good luck at both NAPA and AutoZone, though usually you need to force the guy behind the counter to just let you paw through their bins of tube fittings. Summit sells assortments of tube nuts with different threads for each tube size. For 1/4" tube, the steel kit is PN SUM-220115 and stainless is SUM-220215.