Brake line fittings

[Beaker60]

I am replacing a single brake master cylinder in my 1960 Pontiac with a dual master from a 1975 Pontiac and need one or two brake lines to finish the job. Does anyone know where to get information on what the thread sizes are on the master cylinder and how that would compare to what is on the car today? I've tried a few of the major brake tube shops and they have been less than helpful. Thanks.

Cam

[wheelman1917]

To do it right you will also need a proportioning valve. Brk. lines are pretty standard until you get into abs. Most lines are either 3/16 or 1/4 in. available at any auto store
do not use compression fittings as they are illegal for brk. lines in most states. They have thead in fittings for line to line . hope this helps Wheelman

[Beaker60]

Thanks, wheelman. I know all the parts that are required including the prop valve. All I need to know are the fitting (thread) sizes. If I guess by using the color coding on the master cylinder, I believe that one of the connections there is 7/16" - 24 thread (red) and the other is 9/16" - 18 thread (blue). Would that be right?

[MagicRat]

Most cars made in the last 20 years use metric fittings and flares. You want to use old-school standard fittings and flares. Both the 1960 and 1975 Pontiacs used such 'standard' fittings and flares. Most decent auto parts places will have these lines in stock, in pre-made lengths, with all the necessary fittings and flares included.

Don't use the metric lines! They have the same line diameter as standard but are not compatible.

All you need to do is to measure the length you need, get the closest size (but never shorter than you need) and bend it to fit. It's best to get a line bending tool to do this, although you can bend them around large sockets (from your tool box) to get a nice radius.

Also, note the lines need to have a couple of coiled turns in it where they go into the master cylinder. Unit-body cars do not need these, but seperate-frame cars, (like yours) do. These coiled turns allow enough flex so the body can move on the rubber body mounts (as it is designed to do) without breaking the new lines from metal fatigue.

Also, use proper retainer clips for the lines. If they are not secured properly, they will vibrate, fatigue and break.

[Beaker60]

Thanks MagicRat. That is all great advice. All I need now is to know what the thread sizes are for the fittings and I'll be set. That's the info I've been looking for.

[wheelman1917]

You want american standard thread . Blue & red fitting that I've seen were metric . take the master & proportioning valve with you. buy a piece 3/16 & 1/4 american thread to test fit. small lenths are very cheap. You can then test fit your wheel cylinders Valve & master.

[wheelman1917]

The thread size you need is already on the premade brake lines 3/16 should be 3/8th 1/4 7/16.

[Beaker60]

The 1960 has 3/16 lines, so it must have 3/8th fittings. The front MC port would typically have 1/4 lines for disc brakes, meaning I'll need an adapter to convert the 1/4 to 3/16 to hook into existing. I think I got it now. Thanks.

[MagicRat]

One more thing.... get a proportioning valve from a car with a dual master cyl and 4-wheel drum brakes.

Many GM cars made from 1968 through the early '70's had this, because, back then, drum brakes were only optional on most models.

But by 1975, pretty much all GM cars had standard front discs..... so the valve from a '75 Pontiac will not do.

[Beaker60]

I'm actually converting the front to disc brakes, so a later model prop valve would be appropriate. The ones that were on the mid 70's and up cars were distribution blocks with proportioning valves built in (that were not adjustable - they were set to a specific ratio). However, I won't be using this type of prop valve since I'll be leaving the original distribution block in place (and plugging the hole where the rear line used to be). I'll be using an adjustable one, inline from the MC to the rear line. Like this:

http://www.ssbrakes.com/commerce/det....cfm?nPID=8341

[MagicRat]

Originally Posted by Beaker60

I'm actually converting the front to disc brakes, so a later model prop valve would be appropriate. The ones that were on the mid 70's and up cars were distribution blocks with proportioning valves built in (that were not adjustable - they were set to a specific ratio). However, I won't be using this type of prop valve since I'll be leaving the original distribution block in place (and plugging the hole where the rear line used to be). I'll be using an adjustable one, inline from the MC to the rear line. Like this:

http://www.ssbrakes.com/commerce/det....cfm?nPID=8341

Actually I considered suggesting both a conversion and an adjustable valve.

Excellent ideas!!

And, if you do your projects like me, they will be finished just in time for winter to start..... which, (given our cool Toronto summer thus far) is not too far away.

[Beaker60]

Actually, I don't think *any* of my projects are finished, just abandoned.