brake pedal to the floor

[AMC1]

With the brakes & engine cold the pedal is almost to the top. A couple of pumps brings it up another inch. When I turn on the engine the pedal goes to the floor. I’ve replaced the master cylinder after bench bleeding it, new rotor discs & calipers with pads. The rear cylinders & shoes are a year old. No leaks in the system. Even the old master cylinder never required any additional fluid. I’ve bled all 4 wheels 3 times, twice with a vacuum pump & once by foot & hand. The only thing left is the power unit & the vacuum hose there looks good. Does this sound reasonable? I’ve obviously mis-diagnosed the problem. The only reason I’m not more angry is because the replaced parts except the pads were original & 32 years old.

[JayRamb]

I'm having the same problem after I replaced the master cylinder too. Did what you did. The only thing I can think of is that the plunger to the master cylinder isn't adjust right?

[carnuck]

Manually adjust the rear drum brakes. Do it cold or they will drag afterwards.

[AMC1]

I pulled the booster out Saturday. I'll have to pick up a replacement.

[JayRamb]

Keep in touch on what you find out!!

[carnuck]

Make sure the master is for rear drum brakes and not 4 wheel discs!

[AMC1]

I haven't received the booster yet but the Master I had already installed. Knowing what I do now I should have ordered a set & saved a few dollars. I had ordered the Master for a 1983 & I don't recalling them mentioning anything about (4) wheel discs. I don't believe they were offered in 1983.

[AMC1]

Has anyone replaced the brake line coming out of the master cylinder - rear port - front brakes. I've tried four stores with no luck. The fitting coming out is probably a 7/16-28 extra fine thread since 7/16-14 & 7/16-20 don't quite fit. The other fitting at the coupler - 13 inches away and is 3/8-24. I can find the brake line with two 3/8-24 fittings but not that 7/16. Do I have to make my own & if so where would I find that 7/16 fitting.

[AMC of Houston]

Yeah; have to make your own.   The fitting size is 7/16-24 (for a 3/16 tube).   Not hard to find -- you can get 6 mailed to your door for $7.50 on Ebay.   I'd think most parts houses would have those (at least where I am).

[AMC1]

Thanks - I'll have to go to e-bay. The last two bog box stores didn't carry them & I don't think the young fellows really knew what a master cylinder is. Interestingly about that 7-24 fitting. According to my downloaded notes a 14 is a coarse thread & a 20 is fine thread. It shows 28 as extra fine. 3/8-24 is fine & 32 is extra fine. I did call another place on the telephone & he said he did have a 7-24 fitting - not a 7-28 - on a 1/4" line.

[AMC of Houston]

Yeah; I always wondered why the thread count was different for "fittings".   Who made that decision anyway??!!

[carnuck]

To keep people from using regular fuel line nuts and bolts in them due to hydraulic pressures.

[AMC1]

I’ve got brakes - actually I always did but not to my satisfaction. I had to take care of something else but it always feel good to get back in the garage. I believe someone asked to add to this post. My brake pedal was only 2-½” from the floor with the engine running ( vacuum assisted). One of the problems was that the right rear automatic brake adjustment spring had became weak, the adjuster lever was flapping & the teeth in the screw assembly were worn down. I replaced the cable, guide, spring & screw assembly. Another major problem was a small fluid leak in the 14” long brake line from the master cylinder to the coupler for the front brakes. It was wet at the coupler. On this Eagle the factory ran the line under the rear line & bent it up at the coupler. On my other eagle it is a straight shot into the coupler. I made 4 lines until I got it right. Clearance for that line is almost nil because the booster pushes down on the line ergo the factory came in from underneath & bent it up. I wish I would have replaced it when the booster was removed. I still came in with a straight line but the clearance is tight, but finally stopped the leak. I kept blaming my flares but have an Eastwood tool which is very good. Bleeding the brakes without the engine running is recommended. Pumping them however may not reveal a leak. Only with the engine running & pumping them will you then see a leak. I’ll mention some important specs. This brake pedal is 5-3/8” (side & center) from the floor (engine running/not running & not depressed). If depressed when running (vacuun assist) the pedal should move down 25% of the distance to the floor. Mine therefore should go down 1-11/32” leaving 4-1/32” to the floor. Mine moves down 1-7/8” leaving 3-½”. I did pick up 1 full inch & it feels good. I must admit however that my other Eagle does have the 4”.

[carnuck]

Manually adjusting the rear brakes will help too. Do it cold with the wheel on. Tighten till it starts to drag then use a screwdriver or similar to pry the adjuster forwards and backwards a couple times then center again. If the shoes still drag slightly, then hit the pedal and check again. They should only drag slightly when cold right after adjustment. If you do it hot then the drum shrinks as it cools and jams the brakes like the Ebrake is on.

Also, make sure the ebrake isn't sticking when you adjust the brakes. It should also come up with shoe adjustment.

[AMC1]

They should be OK. I use a brake tool to tighten the linings to the point where the wheels won't turn - then back them off one revolution. After that I ran it forward & reverse 15 x  abruptly in the alley to set the adjusters. So far no leaks which is my major concern.