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I have a 1973 Coupe with a 351C and disc front and rear drum brakes. Last year while backing out of the garage, the brake pedal went to the floor and the instrument panel brake warning light came on. There are no leaks anywhere that I can tell. There is fluid still in the master cylinder. I think I want to change the booster, master cylinder, and prop valve altogether anyways. Can any of you recommend a good company or kit? Thank you.

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More than likely the master cylinder is bad! Recommend to get a new one! Remanufactured ones make the bore bigger thus Lowering pressure!



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mustang7173 🇺🇸

"Courage is being scared to death but saddling up anyway" -- John Wayne

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I just did mine and just put the master cylinder on yesterday.

Like stated Booster Dewey did mine but the shipping for both ways was like $130 for me on the east coast and he is in Oregon.

What has happened is the brake fluid attracts moisture and it settles to the bottom of the master cylinder which then rusts and makes a low place that the fluid blows by the piston. I rebuilt my own with a kit from NPD. I have brake hone and the amount you hone out is minimal. If you are going to keep the car forever, lol. You can send the master cylinder out and have a bronze sleeve added and it will never rust again.

To avoid more issues you should probably at least pull one caliper and take apart and check it. They are very simple and easy to put a kit in. There is one piston and one seal and dust boot. The hardest part is getting the boot on. I would not order the kit for the caliper with the new piston. The originals are hard chrome plated and never seen one bad. Do get new seal and boot and brake bleeder valve.

I would also pull the rear wheel cylinder and if rusty they are cheap and just replace them. Rear brakes a little harder than front but no science there. Just take pictures before you tear it apart and do one side at a time.

So I would do the following. Get the master cylinder back on if booster is still working I would not touch it. One of the most aggravating jobs is to take off and put back.

Once the new master cylinder is on fill with fresh fluid and go to the right rear and pump fluid or vacuum fluid until clean comes out. Refill the master cylinder as needed. Then the left rear do the same. Then the right front and then left front. Now you have all the old fluid flushed out do the calipers and wheel cylinders. Change the pads and shoes if needed. If you need to turn the drums or rotors be sure to have the shoes ground to fit the drums to maximize your brakes. If front calipers are too thin just get new ones.

I always put anti seize on the threads of the brake bleeders to keep them from locking up. You can get the little packs of brake lube to put on the areas of the disc and backing plates that need lube. Wash braking surfaces with brake cleaner, no grease of finger prints here.

On the front of course get new grease seals and wash out all the old grease and put in new grease using Moly type for disc brakes. In the back if any sign of rear end grease leaking good time to change the seal in the axle housing.

If you don't a brake vacuum pump just get one at Harbor Freight since you do not do lots of brake work. No other special tools needed unless you are going to hone your master cylinder.

I would keep the original the new ones are different if trying to stay original.

With the brake master off be sure and check your rag joint in the steering the brake fluid usually attacks them and might need a new one there.

I used Advance Auto, ORiley and NPD for components. Pretty much nobody does an exchange for the brake booster. Each year has some differences also.

When a man is in the woods and talks and no women are there is he still wrong??:P


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Don't underestimate the possibility of the Proportional valve leaking. I changed every single part in my brake system and it still sucked ass till I put in a new Proportional valve. That was even after putting a repair kit in it. I'm thinking it was leaking from the front circuit to the rear circuit thru the prop valve. Now the pedal is hard and it stops on a dime.

"I drank what?" - Socrates

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  • 4 weeks later...

Hey all, thanks again for the replies. In the interest of time and working this problem via long distance (car is at my mother’s house), I’ve decided to order the parts through NPD and have a professional mechanic do the job. I’m going to replace the booster assembly, master cylinder, and prop valve with new lines so that it’s done. My mother wants the car out of the garage and it I need to get it down to Florida somehow so I can start enjoying it. I’ll keep you all posted on what the problem turned out to be.


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