I had a wheel cylinder fail in the right rear wheel on my '65 F-100, which caused a catastrophic fluid leak. Thankfully I have a dual pot master so I still had my fronts and was able to get home.

I replaced the wheel cylinder on that wheel, along with drums, shoes and hardware on both rear wheels. I haven't replaced the wheel cylinder on the left side yet as the flare nut was totally stripped, so I'll do that when I replace the hard lines. After bleeding I still had a very soft pedal, and it felt exactly as it did with no rears at all.

At that point I decided to replace the master cylinder as well. Did a bench bleed on that, and then bled all 4 wheels with a Motive pressure bleeder afterwards. The rears are now working but I have a strange set of symptoms:

• The pedal is no longer as soft, but it's not always as firm as it should be, either. After 2-3 pumps of the pedal, it firms up. Test driving it around town (rural area with low traffic), this seems intermittent. Sometimes when I hit the pedal, it's firm right away.
• If I brake fairly hard, I can feel a distinct pulsation from the rears. Could be that one of the new drums arrived warped?
• The oddest symptom: the pedal seems to firm up when turning/cornering at low speed. I can physically feel the pedal rising when this happens.

There are no leaks in the system at all. Everything is new apart from the hard lines, though I did flush those back in May.

Anyone have any ideas?

 

Did you bench bleed the M/C?

 

Yes and also pressure bled the system several times.

 

Do you have the correct master cylinder for drums? Does the plunger allow full travel? I have experienced bad master cylinders that produce some of the symptoms that you describe. How are your brake hoses?

 

You have vacuum booster? If so, check that the pushrod to the MC has no slop, or very little, they are typically adjustable. Do you have a booster vacuum leak?

I'd be inclined to put the old MC on it and bleed system again. Also, the parts we are getting today aren't very good, even out of the box.

Years ago I replaced the rear end from one out of an '81 and rebuilt everything when I put it in, figuring I'll never have to mess with that again. Wrong. Many years later was loosing fluid in the rear circuit, but could find no external leak. Bad WC. Rebuilt it all again at probably 3X the cost. Brakes are awesome though(power, discs, dual piston/ drums, 12 x 3).

Post back when fixed please. Good luck

 

If your brakes were working fine before the wheel cylinder failed I would bleed the system again at each wheel starting from the shortest distance to the MC going backwards. Sounds like an air problem in the brake lines somewhere and you might want to inspect the other wheel cylinders as well to make sure they're in good condition. JMO

 

If it firms up after 2 or 3 pumps, you need to adjust your shoes. How I was taught, and what I have done for the last 35+ years, jack up each tire, and slowly spin as you tighten (adjust) shoes outwards, once you start hearing the shoes rubbing on the drums, go a few clicks more, I usually go till I feel just a bit of drag from the shoes. I have done this on all my trucks with drums brakes and have never had an issue.

Did you have the new drums turned?

 

No vacuum booster, no. It was upgraded to two-pot but is still manual.

Yes, it's a direct replacement for my old master cylinder, which matches a mid-70's F-100. Hoses are all new, like I said everything is new apart from the one wheel cylinder and the hard lines.

I've bled it several times, unfortunately. There's only one other wheel cylinder. It looks and performs fine right now. I have a replacement for that one as I said in the OP, but not planning to install it until I replace the hard lines.

I was thinking along these lines too, and wondering if something like the new drum being out of round could cause symptoms that dramatic. I have already tried adjusting them several times. I took another test drive yesterday, and after about 2.5 miles i went over a rough section of road, after which the right rear wheel started making an awful racket. There was a rhythmic knocking sound which varied with speed, an occasional screech, and I could hear the brake dragging, loudly.

I managed to drive it home, very slowly. Oddly enough, the brake pedal firmed up and remained firm throughout this little "incident". I took that wheel off today and based on the noises it was making, I expected to find carnage after I pulled the drum. Nope, it all looked normal but there was a bunch of brake dust everywhere from that shoe dragging.

Before taking it apart, I got the back of the truck up on stands, and spun the wheels and heard no odd noises at all. After watching some Youtube videos I am not confident I lubricated things well enough, either. So right now my plan is:

• Put the wheel back on, start the truck and use the motor to spin the wheels a bit while it's up on stands.
• If it doesn't make noises, then take it off the stands and do a brake test in my driveway. If I still have to pump 2-3 times to get a firm pedal, put a clamp on the rear brake hose and try again. If it's still spongy then the problem is in the m/c of proportioner valve, and if it's firm then that would mean the problem is in the rear brakes.
• Either way, take apart both rear brake assemblies and lubricate better. Only one of my old drums was trashed. If the problem is in the rear as I suspect, I will try installing the good drum from the old set on that wheel, and see if the symptoms persist. If not then I know the new drum is at fault.
• If I get this far without fixing it, I guess I start asking here for more ideas again.

 

You need to resurface that new drum. You will probably find it egg shaped. When you adjust it and it starts to drag it is just hitting on the closest to the shoe area but when you actually brake it is doing all kinbds of odd things like pushing the cups in t6he cylinder in and out. Turn that drum, and any other suspect ones and I guarantee your brakes will be 100% better. Or I will refund what you paid for my advice.https://www.ford-trucks.com/forums/i...ons/icon10.gif

 

Sounds like to have a "floater" air bubble....try jacking the back end of the vehicle up about 1 foot and bleed the brakes again!

 

Well, the most recent symptoms are not related to the brake work. After driving it in the driveway again and giving if a more critical listen, I think my assumption that it was a rear brake issue was coloring my perception a bit. It wasn't coming from the front at all. I put the back of the truck up on stands and spun the wheels and everything sounded perfect.

Decided to check the front wheels. It was immediately obvious the passenger side wheel was the problem as soon as I spun it. Took the wheel and caliper off, and now the rotor is just flopping around barely attached. The spindle moves with it, so I guess it's a king pin issue? Haven't finished taking it apart yet. Got to take care of that before I turn my attention back to the brakes.

EDIT: OK, had some time to take a closer look. My brain sure is inventing a lot of stuff lately. I only looked at it briefly earlier, and misremembered what I saw. The spindle does NOT move around and has no play at all. I had a wheel bearing disintegrate. Individual rollers started falling onto the floor as I was disassembling. At least it happened close to home and is an easy fix.

 

Good you had "Lady Luck" on your side and you didn't end up with a wheel passing you on the freeway! IMHO, when it comes to wheel bearings stick with OEM or Timken (who make them).

 

Already picked up some O'Reilly Masterpros. Not sure who manufactures those. I suspect that this was what was causing my soft brakes, too. My theory is the loose caliper compressed the piston in that caliper. Pumping the brakes would bring the piston back out and bring the rotor somewhat into line during braking. Let up on the brakes and drive a bit more and the caliper would compress again.

Nothing else looks damaged in there, and nothing heat welded itself together. Amazing that this didn't leave me stranded and I was able to limp home, even. "Ford tough" indeed. This is what the (I think) inner bearing looked like.

 

Mmmmm Toasty!

 

Might mean I need a bit quieter exhaust. This thing has probably been howling since I owned the truck and I couldn't hear it. I did start to hear what I thought could be a bearing noise only a few days ago, but it was so quiet relative to the engine noise that I ignored it, and didn't put things together until I decided to check the front wheels. Then everything came together pretty quickly. Never seen a wheel bearing that bad though, especially from a vehicle that wasn't towed home.