1984 F150 5.8l H.O. v8 Automatic No A/C AM Radio

Truck had new pads at 43k then got driven very little for 25 years (7k miles). During resurrection the brakes were working fine, had them inspected at the Tire & Brake service center when I put on new rubber and they got a clean bill of health. After driving it for a month loaded & unloaded with normal braking. today the brake pedal went to the floor and took extra long to stop the truck, luckily I was only pulling out onto a quiet street with no traffic, a trip around the block didn't change the braking, pumping the pedal didn't help; it goes to the floor without resistance and only the last 1/2" offers braking and longer stopping distances even at that.

If I am replacing the master cylinder should I do the brake booster also? Is there a highly recommended brand to go with? Anything else while I am in there?

All advice/ideas welcome!


thanks

 

Be sure to keep the old rubber Cap Gasket. The new ones seem to be to thin to seal properly.
Jim

 

It might be good to replace the master but just because the pedal went to the floor does not mean the master is bad.

A brake line could have broke and cause that same problem.
Pop the cap off the master and see if one of the Wells is empty. If so you gave a busted line.
Depending if large or small one will tell you where to start looking.
Could fill it back up, cap on and pump the pedal to see where the wet spot is.
Dave - - - -

 

The brake lines love to rust through on these trucks. Open the master and see if the fluid level is unusually low in one of the reservoirs. If one of them is dry, pour some fluid in it, and then while you watch underneath the truck, get someone to press the pedal. It will become apparent right away what the problem is if you have a busted line.

 

I will look into all of these angles, thanks again FTE. should I be able to see a spot under the truck (medium sized gravel parking spot) where it has leaked? nobody around this afternoon to assist. also the front reservoir was 1/3 lower and I filled it this morning, would my brake safety inspection have looked in there? I did when I got the truck 6 weeks ago but can't remember what kind of level I saw, I only remember the color was ok. I'm gonna give the shop a call just to see if it is on their inspection...

 

The front smaller reservoir is for the rear brakes. The line likes to rust midway between the cab and the rear wheel behind the gas tank, and also around the line clips that hold the line to the rear axle. You can repair this yourself with universal lines you can buy at the store. I would buy the copper/nickel line and not have to worry about it again. They are easy to bend by hand also.

 

Check the wheel cylinder behind the rear drums. That was my issue when my pedal acted just like you described. Replaced the hardware and shoes while I was in there since the fluid glazed onto the shoes. About $150 for both sides in parts depending on brand.

Second the copper/nickel lines. I got mine in various lengths from AutoZone. Their replacement warranty is great when I got lines that were way too long after I bent them up already. Just make sure you have "US" threads listed (least for that AZ lines I got) or you will end up getting pissed off while on your back trying to thread it in. Can ask me how I know that one.

 

I'm on it, called the service shop and they said if it was 2/3 full in the front and 3/4 full in the back reservoir and braking well they would not have mentioned it on my inspection (within reasonable limits). I added some to the front res. and pumped the brakes and pedal still goes straight to the floor, then I started it (didn't drive) and tried to pump it up (no effect) and then shut down the engine with it to the floor and after waiting for the engine to settle it came right up when I let my foot off the pedal (read something about this diagnosing the vacuum). still a little light out here on the west coast I will look for evidence of leaks/failure around those locations now... thanks again ppl!

 

No leaks or corrosion that I can spot on any lines, around the drums or calipers, but with the engine off I hear a louder than normal whoosh of air when I step on the brake pedal, significant? the brake fluid I added this noon is still in there, no signs of losing any.

 

If you topped off both reservoirs and pumped the brakes a few times and checked it again if none were lower than when topped bad master.
As for being able to see a wet spot on gravel hard to say but you may see something.
Dave ----

 

New master cylinder in and brakes are back. thanks again ya'll. bled the system at the 2 lines on the master cylinder, front line spit all fluid first (after 3 times pumping and holding the pedal) the rear took 2 more cycles then the pedal was firm. After starting it up the pedal felt less firm, about 1/2 way down it starts to resist and braking seems normal, is 1/2 way correct for this rig?

 

Lucky you! lol. Doing drum brakes for the first time sucked. Master cylinder sounds lot easier.

After I did the rear wheel cylinders, my normal pedal feel is at 1/2 way. I think it should be more firm so possibly need to adjust the shoes more. 1/2 way was what the brakes where like when I bought it. Which is a laughable standard to go by.

 

Wish I could say if 1/2 is good or not.
You should have bench bled the master before you hooked the lines up.
You may have pushed air into the lines.

My truck did not have good brakes when I took it for a test drive then took it all apart when I got it home.
Now that it moves under its own power, all new brakes the pedal goes almost to the floor.

I have to get my wife to help bleed the system, the vacuum bleeder did not work to well ....... I hope!
Dave ----

 

Oops, when I went to remove the old one I looked on my tool bench and saw 2 line (flare nut) wrenches, the end of one fit the big fitting and the end of the other fit the smaller fitting, after that I just figured the job was nearly done! hehe never got back to search for advice on how to replace a master cylinder, bleeding the lines from those fittings with a stick holding the brake pedal down got me back on the road, So what else should I do to do it properly at that point, don't want to take it on the highway or steep hills if I have left anything out...

 

Crack the bleeders at each wheel is how I was taught to properly bleed brakes. If you see fluid coming out with no bubbles at each wheel, you are golden. Unless you can get a seal on the master cylinder cover (gonna have to fab something), vacuum bleeding will work after letting it go for a bit. Think it's faster at the wheel bleeders and someone in the cab on the pedal.