Brake pedal hard as a rock

[JoshT]

This isn't the Ranger, but my F-100, power brakes are power brakes though.

Truck has front disc, rear drum. Fairly new booster and master cylinder, both replaced a few years ago with the front disc swap. Worked great initially (couple years ago), now brake pedal hard as a rock and not stopping well. Wasn't a gradual thing, parked over the summer and bad when came back to it.

Put a vacuum gauge in it. Got good vacuum to booster. Booster isn't leaking vacuum, as evidenced by it sucking in air when I removed the check valve. I get no power assist and weak brakes.

Thoughts? Things to check?

 

[franklin2]

Pull the master cylinder off the booster just a little bit, you do not have to take the brake lines loose. Look behind the master cylinder, see if it's wet with brake fluid. If it is, the master cylinder has leaked into the booster and ruined the booster.

 

[RonD]

+1 ^^^^

This type of power brake system works using outside air pressure
The vacuum in the booster is lower air pressure than outside air pressure
In the cab where the brake pedal push rod is in the booster is the Atmosphere Valve
When you press brake pedal the push rod pushes open the atmosphere valve allowing outside air pressure in and this is what assists you in pressing down the brake pedal

Diagram here: https://www.researchgate.net/profile/Liang-Li-21/publication/326618599/figure/fig3/AS:662375493550080@1534934032966/Diagram-of-vacuum-booster-system.png

Start engine to build up vacuum in booster, shut off engine after 30seconds, doesn't take long, booster stores enough vacuum for 3 or 4 pedal presses, in case engine stalls while driving driver will have enough vacuum to safely pull over still having power assist
Get down low under the dash and press brake pedal, you should HEAR air being sucked in
If not the atmosphere valve is bad, so no assist

 

[JoshT]

Pull the master cylinder off the booster just a little bit, you do not have to take the brake lines loose. Look behind the master cylinder, see if it's wet with brake fluid. If it is, the master cylinder has leaked into the booster and ruined the booster.

I'll check when I get a chance, but I'm about 90% certain that this is not the case. The mastercylinder was a new unit installed about a week before the booster back in 2018/19. Not a lot of miles on it since. Not that new parts can't be bad or fail in short order, but the reservior has not shown any signs of leaking or loosing fluid.

+1 ^^^^

This type of power brake system works using outside air pressure
The vacuum in the booster is lower air pressure than outside air pressure
In the cab where the brake pedal push rod is in the booster is the Atmosphere Valve
When you press brake pedal the push rod pushes open the atmosphere valve allowing outside air pressure in and this is what assists you in pressing down the brake pedal

Diagram here: https://www.researchgate.net/profile/Liang-Li-21/publication/326618599/figure/fig3/AS:662375493550080@1534934032966/Diagram-of-vacuum-booster-system.png

Start engine to build up vacuum in booster, shut off engine after 30seconds, doesn't take long, booster stores enough vacuum for 3 or 4 pedal presses, in case engine stalls while driving driver will have enough vacuum to safely pull over still having power assist
Get down low under the dash and press brake pedal, you should HEAR air being sucked in
If not the atmosphere valve is bad, so no assist

You might be onto something there. Did not really know how the insides of the booster worked. I'm sure I've seen it in years past, but that diagram drove it home. Vacuum goes to both sides of the diaphram until pedal is pressed at which point the back side is opened to atmosphere and vacuum provides braking assist. If when I'm pressing the pedal it doesn't open to atmosphere then I get no assist. That makes sense for what is happening.

Power assist doesn't work at all from the time I start the truck. Truck needs to be tuned, but I'm getting decent vacuum to the booster. Put a gauge in line between the engine and booster and it is showing 18-20 inches. The vacuum check valve flows like its supposed to. There is definitely vacuum building in the booster considering that it sucks in air when the check valve is removed.

The way the booster is mounted on these old trucks it is not bolted directly to the firewall. It actrually has standoff brackets that keep all of the booster outside of the cab with a long pushrod that goes through the firewall to the brake pedal. With the truck running I doubt that the vacuum would even be audible under the hood, but between seeing how it works and reading what you wrote, I'm fairly certain that this atmospheric valve isn't working. This isn;t my setup, but an aftermarket kit for my truck with similar mounting style to stock.

Sounds like regardless of what is causing the problem, the solution is going to be replacing the booster. Guess I need to decide if I'm trying another reman booster (54-73112), or getting a new modern style unit from Battle Born Brakes. The one I have now is a Cardone reman and I think most of the big chain store remans (Wearever, BrakeBest, Duralast) are probably the same booster stuck in a different box. The BattleBorn unit is allegedly new manufacture made for the application.

I'm not returning the core I have. When I was doing the booster upgrade boosters for these trucks were hard to find. I could have sent my booster off for rebuild if I had one, but I didn't. I'll be saving the booster I remove so that if I encounter the issue again I can ship it off for rebuild, so eating the core charge. With that in mind, there is about a $!00 difference in price, $150 for the reman and $250 for the new unit.

 

[RonD]

If it is similar to that image then after shutting engine off you should be able to hear air flow at back of booster when brake pedal is pressed

No vacuum should escape from booster with just its hose removed, but it will if you also pull out check valve

 

[JoshT]

Yes, that's what I said. When I removed the check valve, it sucked in air. The point of that was to verify that it was actually building vacuum in the booster and to verify that the valve was flowing properly.

 

[franklin2]

Cardone is the only game in town on some things, so sometimes you have no choice. I have not been impressed with their products and have had many failures from them.

 

[PetroleumJunkie412]

Brake pedal like a rock

So.... just to double check...


Your truck doesn't currently look like this, does it?

 

[JoshT]

So.... just to double check...


Your truck doesn't currently look like this, does it?

Sorta. As I said in the first post, it's an F-100 not a Ranger. More like this.

Ford Dana 44 converted to Disc brakes using a chevy spindles, calipers and mounts with Ford Rotors and hubs. Basically the only option to get discs on these kingpin Dana 44s.

I'd rather have a later, all Ford, ball joint Dana 44, but they ain't easy to find around here. A disc Dana 60 would be awesome, but hard to get with the right lug pattern and not worth the extra cost to build for my usage. The later D44 with a later and wider 9" LS rear end would make this about perfect where axles are concerned.

Anyway the chevy bits don't seem to be the problem. The truck does stop, just not well due to lacking power assist. I'm using a Ford master cylinder, but sized it to match what Chevy used in the application where these calipers were used. (K5 blazer IIRC, have it wrote down somewhere)

 

[franklin2]

It's rare to have a factory disc brake setup that is not power. Disc brakes need more pressure to work. Drum brakes have what they call a "servo action". They use the drum's turning motion to help assist and apply the longer shoe, making it need a lot less hydraulic pressure for the same braking force.

 

[JoshT]

It's rare to have a factory disc brake setup that is not power.

What you talkin bout willis?

Did you read the thread?

Truck (60s F-100) was originally drum brake all round. Dad says that he converted it to power drum in the 80s using factory components. Seems accurate since what I took off years ago matched factory components. Never stopped great even with the power drums, but better than without the power assist.

In 2018, after the truck was parked for 12 year or so, first thing I did after getting it running was a front disc brake conversion. Only option for this dana 44 is basically to use the outer components (mentioned above) from a K5 Blazer (I bought for a 74), with the rotors and hubs from an F-150 to retain the correct lug pattern. At the time (very brief time) I retained the master cylinder and booster from the drum brakes so see how it worked before throwing more parts at it.

Second thing I did was upgrade the master cylinder because I quickly determined the old master wasn't working (no surprise after sitting over a decade) and undersized for the new brakes. Because the 74 Blazer used a 1 1/8" bore master cylinder, I selected an 84 F-350 master cylinder with the same bore diameter. Considered going newer style with the plastic reservior, but I liked the idea of keeping the original all cast with integrated reservior.

Third was to upgrade the brake booster from a ~8.5" 68-72 F-100 drum brake single diaphram to a ~8.5" 69-76 F-350 disc brake dual diaphragm. FWIW, the 85 F-350 has practically the same booster, but different mounting pattern and the input rod isn't long enough.

So yeah, not sure why you're talking about a non-power factory disc brake setup.

 

[franklin2]

This is what I saw and didn't realize you were talking about the same truck that you started the thread with.

Anyway the chevy bits don't seem to be the problem. The truck does stop, just not well due to lacking power assist.

 

[JoshT]

Yep, same truck. I don't own a Chevy or want one, but some parts can be useful. I guess technically they would be Dana parts since both ford and chevy bought the axles from Dana.

I may not agree with him on everything (EV thread) but I'm pretty certain that @RonD hit the nail on the head here. I stopped on the way home and ordered a "new" rebuilt booster for the truck along with a new IAC motor for the Sniper EFI. I hated buying another rebuild, but atleast it has a lifetime warranty that I can redeem locally almost anywhere in the country. The new unit from the other place was tempting, it had a lifetime warranty too, but almost twice the price and I'd have to ship it both ways for replacement. Same reason I bought the IAC motor there as well, I could get for half the price online, but this is the second one that stopped working on this sniper unit. 4 years, but not a lot of miles. I don't mind replacing them, but I don't want to keep paying for them.

 

[JoshT]

Just to follow up, the booster was the problem. Installed new booster and they are back to working almost like they are supposed to. Do need to play with the pushrod adjustment some more to get them at 100%, but it stops like its supposed to now. Well, probably better than its supposed to since its supposed to have manual 4 wheel drum brakes.

The IAC motor also helped, but now my fuel pressure is down for some reason. Guess next step on that project is to diagnose that and get the new window regulators installed. That's for another day though.