Master cylinder replace

[jep1701]

Hi. Need some input and you all have been great.
I replaced my master cylinder with one that stated it was correct. Everything went well until replacing the left line. The right line went in fine (7/16) but the left line is too big for the master cylinder (1/2). So...
1. First is this normal? Just one of those Ford thing from the past?
2. If I replace the left line do I sure to get a line that is 7/16 on both ends since the end that attached to the car seems to be 7/16 as well.

When look for the lines they seem very specific and want to make sure I get the right one.

It is a 1973 with front Disk bakes and rear drum if that helps.

 

[Doug's 73 Mach1]

I experienced the same thing with my previous MC that I installed many many years ago. It came with an adaptor so was no issue. That MC eventually leaked and I replaced it with a rebuilt I had. The rebuilt had the original factory port sizes. Local auto stores may have the correct adaptor.

 

[jep1701]

Thanks.
OK. So after taking a break (it was almost 90 in Florida today) I looked in the styrofoam protector and there was the adaptor. Leaked a few time until I adjusted it.
Sadly, I still don't think the breaks work right. Might now need to bleed them and was hoping to avoid that. Or I have another issue.

 

[Sheriff41]

Why do you think they're not working right? What are the symptoms you're experiencing?

 

[jep1701]

Why do you think they're not working right? What are the symptoms you're experiencing?

When I was out Sunday with my wife I went to hit the brakes and nothing grabbed. Finally I mashed them down and got brakes, so made it home carefully. With the new MC when I hit the brakes with the engine off they seem to grab and work. But when I start the car and hit the brakes they feel like they go to the floor. It was late tonight so I did not tray to take it around the block to get a better feel.

 

[turtle5353]

If you replaced the master cylinder, you absolutely need to bleed the brakes. I would not even think about driving it without bleeding the entire system.
Helps to bench bleed the new master cylinder before install also.

 

[Sheriff41]

Bench bleeding a MC takes a little more than most people realize. Once you think you have all the air out, keep cycling the piston and you'll most likely get more air out.

I agree with Kevin, you should bleed the brakes. If you bench bled the MC, bleed the brakes RR, LR, RF, LF, refilling the MC as you go. Once bled you should have a firm pedal with the engine off. Once you start the engine you will notice a difference in the pedal feel. You may also need to adjust your rear brakes if it's been a while.

 

[LloydB]

It can't be stressed enough, bleed the brakes before you even move the car again.

 

[Kilgon]

You need to be careful when bleeding your brakes that you don't trip the proportioning valve. They make a screw in bleeder tool that fits where your brake warning switch is at in the proportioning valve that will keep it from tripping. See pic. You can pick these up at most auto stores.

 

[LloydB]

You need to be careful when bleeding your brakes that you don't trip the proportioning valve. They make a screw in bleeder tool that fits where your brake warning switch is at in the proportioning valve that will keep it from tripping. See pic. You can pick these up at most auto stores.

View attachment 73951

You can always learn something new! In all my 31 years of servicing vehicles and the last two working in an auto parts store, I'd never even heard of this.

 

[Sheriff41]

You need to be careful when bleeding your brakes that you don't trip the proportioning valve. They make a screw in bleeder tool that fits where your brake warning switch is at in the proportioning valve that will keep it from tripping. See pic. You can pick these up at most auto stores.

View attachment 73951

I got mine here: https://www.musclecarresearch.com/brake-valve-tool

 

[Hemikiller]

I've never needed that tool to hold the shuttle centered, and IMO, it's not needed on the 71-73 cars at all. When you trip it, you'll feel it in the pedal and the light will come on. It'll re-center once pressure is equalized. Pump the brakes a couple times and stand on the pedal firmly, it'll pop back to center and the light will extinguish. If it doesn't center by itself, then there's still an issue in the system, or the differential valve.

 

[Kilgon]

You can always learn something new! In all my 31 years of servicing vehicles and the last two working in an auto parts store, I'd never even heard of this.

Been there myself over the years - it's like "Well I'll be damned" lol

 

[mrgmhale]

If you are having problems bleeding your front calipers please look at the attached document showing how mixing up the Left and Right calipers can cause a problem with bleeding them.

 

[giantpune]

I got one of those brake bench bleeder kits that has a bunch of different plastic threaded inserts. Used the inserts to figure out the thread size for the master cylinder and proportioning valve. Then I went to the back of autozone where they have a section of all the fittings and some lengths of brake hose and made my own.

 

[Mark Jones]

Just got my girl (Lucy) back on the road and find that when I have to brake hard, the rear drums lockup. The fronts dont lock at all. I dont have any history with the braking system so I have to start troubleshooting from the beginning. I have the OEM Ford power disk brake system. The M/C looks to be older (rusty). The rear brake shoes are new, and the front pads are new. I have the rear shoes adjusted pretty close (about 1 turn out from contact). The brake pedal does travel about 2" before pressure is felt. The pedal is solid and does not fall. Also, I have OEM 14" wheels and stock size tires.
1972 Q Code Mach1.

 

[will e]

Not that unusual for the rear tires to lock up first. You could add a bit of weight to the back of the car. You could replace the proportioning valve but it's a set value so the 'new' one might act the same. There are adjustable proportioning valves.

I learned to drive on my Mustang 35 years ago and it was my daily for years. Since these don't have 'ABS' you get a 'feel' for when the rear brakes will lock up.

I added traction bars and that helped avoid the 'wheel hop' you get when you lock the rear brakes. Mostly now I just drive like the old man that I am so I tend to anticipate issues.

 

[c9zx]

If the problem persists after bleed ing the system, the "pushrod" in the booster may be too short, it should be adjustable. The procedure is in the Ford service manual. Chuck

 

[ROCKET70]

Have the front flex hoses been changed.

 

[cjstaci]

Worn shock absorbers and / or old tires can be a cause. Master cylinder can be a cause. When you apply brakes hard enough, you should be able to lock all 4 wheels. Adjustment of the rear brakes should have a light drag on each wheel. Apply the brakes after adjustment and then check again. Also it’s important that the primary shoe is towards the front.