I have noticed that my brake pedal gets really firm at random times although it seems to happen more when I am towing my 5th wheel. When the pedal gets firm, I really have to stand on it to get the truck to stop. I have replaced the vacuum pump twice when it went bad but it doesn't seem to be the culprit this time. I was planning on bleeding the entire system since the fluid is very dark and cloudy but wondering if I should plan to replace the front calipers as well. I would hate to lose brakes at a key time like towing my 14,000lb 5th wheel down a steep windy road. Anything I am missing here?

97 F350 Single rear wheel
Pads, shoes, rotors and drums relatively new
308,XXX miles

 

Hmm my truck did this one time only, when i was towing a 11,000 trailer and skid steer. luckily i was going slow enough to make the turn! Mine seemed to be from overheating. Id imagine old black fluid doesn't deal with heat as well?

If you can afford it, I'd replace you're calipers when you do a brake flush. Just for piece of mind. You said your pads and rotors are still relatively new. (As long as the pads are evenly worn you should be fine there, and no grooves in rotors etc). Rock auto usually has some good prices. I found OEM Motorcraft remanned calipers for a good deal there years ago.

Or honestly, for about $500-600 you can upgrade the rotors, pads and calipers to Z36 towing brake system. I've heard only great things about them from friends and online.

Other than the master cylinder and vacuum pump, you have the rear abs module on the drivers side frame under the cab.

 

I have upgraded the rotors and use the best pads from NAPA Auto parts. It does pull a bit to the left when I brake which does make me think I have a bum caliper. Wanting to hold off on any more big spends until January but didn't want to have massive failure between now and then.

 

I've never had a vehicle act like it had no power brakes due to a bad caliper. If a caliper were leaking, you'd expect to see fluid on that side and possibly a soft pedal. If it were sticking, you'd be able to tell it was heating up badly, but shouldn't cause your pedal to get super firm like that. A firm pedal, like it has no power brakes seems to me like it'd be a brake booster issue or lack of vacuum to the booster. Also, some of these trucks did have hydroboost right? Did yours?

 

vacuum brakes or hydra-boost?
your description sounds like a weak vacuum pump.

 

First thought was a leaking booster or a leak off the vacuum tree from the pump.

Contaminated fluid is never good...so flush it all. I have a Motive power bleeder and it works great. 100% recommend fresh hoses as they could be part of the issue. Technafit and Crown both make or can easily make for these trucks. I run Raybestos drums and rotors on the dually. Porterfield R4S pads and shoes. Smooth and quiet braking with minimal dust. Big stopping power too.

Doubt PO has hydroboost, but possible if swapped.

The pulling could be air in system, caliper not fully released/applying, front end wear, etc.

 

I will check for a vacuum leak first and definitely replacing the fluid soon. I also will replace the calipers in January but planning a trip at the end of December so hopefully it's just a simple vacuum leak for now. Any suggestions on brake fluid? I use one in my motorcycle that is meant for higher temps but would be very expensive to use in the truck.

 

Just regular DOT 3.
I have a high suspicion that your vac pump is about to give out. If you have never replace it and have no records of ever being replaced change it.

 

I've replaced it twice. It went out one time while I was driving on the freeway (almost crashed) and the replacement one ended up lasting for a week or so and then went out. Replaced it with an upgraded pump and haven't had any issues since. It has been about 2 years or so but not too many miles. I am going to pull it off and check it just to be sure but since the problem is intermittent I am thinking it may be something else.

 

Hard pedal is an assist problem. Vacuum pump, vacuum leak, power brake booster.

Dark fluid suggests you need a good flush, but shouldn't make for a hard pedal.

IF you are going to open up the lines for front calipers, consider replacing all hard and soft lines as well. Most of your time will be bleeding, so open once / replace all / bleed once rather than re-bleeding with each piecemeal replacement may make sense. Master cylinder and rear wheel cylinders, as well as rear brake small parts, are fairly inexpensive.

Since you're towing heavy, you might also consider converting to hydraboost. Note that increased line pressures from hydraboost will find weak points in your system. When I converted, I blew a line and had a sticking caliper, so I decided replace all the pressure parts and the small parts in the rear drums.

I've had a vacuum pump fail 1/4 mile from home, twice blown brake lines in my driveway, and blew the high pressure steering line on a curvy climb. I'm now a proponent of pre-emptive replacement of steering and brake components.

Even if you don't convert to hydraboost, check your high pressure steering line. The design is vulnerable to the line fatigue cracking at the pump fitting. If it hasn't been replaced, consider replacing it before it fails. And definitely if you do hydraboost.

 

Thanks for this. I will be checking for vacuum leaks this weekend and bleeding the whole system. I already had a blowout of the high pressure steering line while driving on the freeway and changed it out in an O'Reilly's parking lot so it's pretty much brand new.

 

UPDATE:

After a lot of back and forth and looking over the entire system, I ended up replacing the booster which did make a difference. However the problem has not gone away entirely. It seems to happen mostly when I am towing my 5th wheel. I am considering replacing the vacuum pump..again but I really don't want to spend another $100 on something that may or may not be the issue. I haven't found any vacuum leaks yet. It seems to happen if I pump the brakes (i.e. stop and go traffic or if I apply the brakes to slow down and then off and back on). Towing over the weekend there was twice when I had to stand on the pedal to get the whole rig to slow down. My son gets his license soon and I want to let him drive my truck to school but not if it is acting up like this. Any help is appreciated.

 

put a vacuum gauge in the line somewhere. you should see minimum 19 inches vacuum.
hit the brakes let off and see how long it takes to reestablish 19 inches. should be almost instantly.
then hit the brakes twice and see how long it takes. again, it should be almost instant. if not, you either have a good vacuum leak, or a bad pump.
by the way, the crap pumps coming from china are nothing like the quality American made pumps that easily lasted 10 years.
i have seen china pumps die within 6 months.

 

The first time I replaced the pump it lasted 2 weeks. I ended up buying a better one but couldn't find one that was made in the US. The Mexico made one was better though. I will need to get a vacuum gauge but that make perfect sense. I do see that the vacuum pump goes into a distribution block but not sure if those are prone to leaking. What should the vacuum be if I hook it up directly to the vacuum pump?

 

over 19 minimum. over 21 is better.
i just realized this is the 94-97 forum. those numbers are for the IDI powered trucks, but i would think it should be the same for the powerstroke pump.