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njot33 · February 11th, 2008, 10:23 PM

I'd like to caution you when you try to make the switch from a single to a dual reservoir master cylinder... you need to be careful about how you hook the brake lines up. I'm trying to save you time here and much of the #!@$#% aggravation I went through making this swap... though in the end it was worth it since making this conversion could ultimately be the difference between life and death. I ABSOLUTELY think you should make this conversion and should not even consider continuing with a single reservoir master cylinder. On a 42 year old car you could break a brake line easily and have no way of stopping.

I just did this conversion on a 65 F-85 with manual drum brakes. I believe the '66 would be almost identical to the '65's braking hydraulics. I know you said you had power brakes, but if you can't use the original power booster from your '66, and want to try manual brakes, you can do that. You will, of course, need the correct pushrod to connect to the brake pedal.

The main thing you will need is a master cylinder with a 1 inch bore. You will also need to make sure that you get a master cylinder off an all drum brake car, not one with disks in the front and drums in the rear. A disk brake master cylinder will not have the correct check valve in the port that would go to the front brakes.

You will need to make sure that if you decide to go with manual brakes, that the pushrod can pivot properly in the little notch in the back of the master cylinder.

My recommendation is that you go online to Year One, go under Oldsmobile > Cutlass > brakes, and select part number BM679. This is the master cylinder I got for my '65 and it works well. It cost $85 + shipping, tax, etc.

On this particular master cylinder, the front lines hook up to the rear reservoir, and the rear lines hook up to the front reservoir. NOT ALL master cylinders are like this!! Some go front res to front lines and rear res to rear lines. If you get a different master cylinder than this one, just make sure you check before putting it on the car, that you make a note of which port has more fluid flowing out. It is this port that you want to hook up to the FRONT brakes. This is because the wheel cylinders on the front brakes will have a larger bore than the rear wheel cylinders.

What may be easier to notice is a delay on one of the ports when the brake fluid comes out. One port will spurt fluid first. This one that goes to the FRONT brakes. You want the front brakes to engage slightly before the rears.

You should use 3/16" brake lines to hook the master cylinder up to the system. For the rear brake line, use a universal connector to hook the new brake line coming down from ther m/c to the existing rear brake line.

For the front lines, use a steel block off cap to block the old port in the junction block that used to go to the rear brakes. You can get one at an auto parts store. DO NOT simply cut the line, clamp it shut and try to weld it. You are asking for a brake failure if you do that.

For the line coming down from the master cylinder to the top of the junction block, you'll need to use a 3/16" line but one that has a larger than normal fitting so it will screw into the junction block.

For any line you screw into the junction block, start the threads by hand, and screw in the nut by hand as much as you can... reason being the junction block is brass and the threads will be stripped if you cross thread by accident and screw in with a wrench. Only use the wren ch for the final tightening.

You should be using line wrenches to tighten these. You can purchase these at Sears. You should also buy a tubing bender and a flare tool to make new flares on the brake lines (if necessary) if you don't have them already.

I forgot to say that to hook generic lines up to the master cylinder, you will need adapters that screw into the outlet ports on the m/c so that the fittings on the brake lines will conect to them.

You should check the brake lines carefully and if you have an doubt about any of them, NOW is the time to replace them.

Also, make sure to bench bleed the master cylinder, or bleed the air out of the master cylinder on the car by pumping the pedal, by using extra brake lines that curl up over into the reservoirs themselves, with the open ends submerged below the fluid level. This is the best, and perhaps only real way, to get all the air out of the master cylinder bore. THEN hook up the brake lines. THEN bleed the system using the bleeder screws on the wheel cylinders.

That is everything I can think of to tell you to do. I went through a lot of work and trial and error trying to get things to work, but hopefully you won't have to if you can follow some of what I said.

February 11th, 2008, 10:23 PM	#6 (permalink)
njot33 Registered User Join Date: Feb 2008 Posts: 27	hooking up brake lines correctly I'd like to caution you when you try to make the switch from a single to a dual reservoir master cylinder... you need to be careful about how you hook the brake lines up. I'm trying to save you time here and much of the #!@$#% aggravation I went through making this swap... though in the end it was worth it since making this conversion could ultimately be the difference between life and death. I ABSOLUTELY think you should make this conversion and should not even consider continuing with a single reservoir master cylinder. On a 42 year old car you could break a brake line easily and have no way of stopping. I just did this conversion on a 65 F-85 with manual drum brakes. I believe the '66 would be almost identical to the '65's braking hydraulics. I know you said you had power brakes, but if you can't use the original power booster from your '66, and want to try manual brakes, you can do that. You will, of course, need the correct pushrod to connect to the brake pedal. The main thing you will need is a master cylinder with a 1 inch bore. You will also need to make sure that you get a master cylinder off an all drum brake car, not one with disks in the front and drums in the rear. A disk brake master cylinder will not have the correct check valve in the port that would go to the front brakes. You will need to make sure that if you decide to go with manual brakes, that the pushrod can pivot properly in the little notch in the back of the master cylinder. My recommendation is that you go online to Year One, go under Oldsmobile > Cutlass > brakes, and select part number BM679. This is the master cylinder I got for my '65 and it works well. It cost $85 + shipping, tax, etc. On this particular master cylinder, the front lines hook up to the rear reservoir, and the rear lines hook up to the front reservoir. NOT ALL master cylinders are like this!! Some go front res to front lines and rear res to rear lines. If you get a different master cylinder than this one, just make sure you check before putting it on the car, that you make a note of which port has more fluid flowing out. It is this port that you want to hook up to the FRONT brakes. This is because the wheel cylinders on the front brakes will have a larger bore than the rear wheel cylinders. What may be easier to notice is a delay on one of the ports when the brake fluid comes out. One port will spurt fluid first. This one that goes to the FRONT brakes. You want the front brakes to engage slightly before the rears. You should use 3/16" brake lines to hook the master cylinder up to the system. For the rear brake line, use a universal connector to hook the new brake line coming down from ther m/c to the existing rear brake line. For the front lines, use a steel block off cap to block the old port in the junction block that used to go to the rear brakes. You can get one at an auto parts store. DO NOT simply cut the line, clamp it shut and try to weld it. You are asking for a brake failure if you do that. For the line coming down from the master cylinder to the top of the junction block, you'll need to use a 3/16" line but one that has a larger than normal fitting so it will screw into the junction block. For any line you screw into the junction block, start the threads by hand, and screw in the nut by hand as much as you can... reason being the junction block is brass and the threads will be stripped if you cross thread by accident and screw in with a wrench. Only use the wren ch for the final tightening. You should be using line wrenches to tighten these. You can purchase these at Sears. You should also buy a tubing bender and a flare tool to make new flares on the brake lines (if necessary) if you don't have them already. I forgot to say that to hook generic lines up to the master cylinder, you will need adapters that screw into the outlet ports on the m/c so that the fittings on the brake lines will conect to them. You should check the brake lines carefully and if you have an doubt about any of them, NOW is the time to replace them. Also, make sure to bench bleed the master cylinder, or bleed the air out of the master cylinder on the car by pumping the pedal, by using extra brake lines that curl up over into the reservoirs themselves, with the open ends submerged below the fluid level. This is the best, and perhaps only real way, to get all the air out of the master cylinder bore. THEN hook up the brake lines. THEN bleed the system using the bleeder screws on the wheel cylinders. That is everything I can think of to tell you to do. I went through a lot of work and trial and error trying to get things to work, but hopefully you won't have to if you can follow some of what I said.