Hey guys, it's been a while since I've been on here, partly cause I drifted back to my gun forums for a while and partly cause I haven't had any problems with my trucks for a while! lol. The other day I acquired a 35' fifth wheel camper and since I don't have a fifth wheel hitch in my '00 F350 yet, I pulled the camper home with my '93 F250. The brake pedal in my '93 has been a little soft for a while but not to the point that it was a problem. Well with the 35' 5'er behind me, it was a problem! I was thinking that it was probably a master cylinder problem because in the '94 I use to have, the vacuum pump went bad and that caused the pedal to be really hard. I checked and I don't have any fluid leaking around any of the wheels, I have new calipers on the front, I checked the vacuum pump just for kicks and at idle it's pulling 24 lbs of vacuum. I installed a new master cylinder today. I bench bled the master before installing and then bled both front brake lines until no air came out. My pedal is still REAL soft! Even softer than before, in fact it's so soft now that I have to pump the pedal several times just to be able to stop the truck! Could this be the booster? I thought the booster would give the same symptoms as the vacuum pump but I may very well be wrong.

 

First it sounds like there is still some air in the system, should bleed it all out at each wheel.

Second if your rear breaks are not set up properly you will have a soft break feel and petal will go down quite aways before breaking properly.

 

I guess its possible for some air to still be in the lines but I don't see how. I bled each front brake line until no air at all came out, only fluid. It took forever and by the time I was done, I was covered in brake fluid. The pedal don't just go quite a ways down, it will go all the way down and won't stop the truck unless I pump it up. I will check the back brakes cause it probably needs them anyway.

 

yes. it could be the booster has gone bad.

 

the booster is just your assist.it makes stepping on the brake pedal possible without the need to stand on the pedal.sounds like that's working fine.
check the rear brake shoes,wheel cylinders,front pads,rubber hoses,and calipers.
of course the brake system isn't nowhere powerful enough to stop a large 5ver.the poor outdated vacuum system was hardly enough for an empty HD truck lol.you need the brakes on that doing most of the work for you,not the truck brakes.

 

then what would explain SOFT breaks with EVERYTHING new and good in the brake system except for the booster? rears adjusted correctly and everything. no air in system.

just the other day i found a thread on here that talked about how a bad booster (diaphragm inside torn) causing a soft pedal with poor stopping power. i wish i could find it again.

 

LSO, do you get a whooshing sound from the booster area on the fire wall?

 

Alright! i found the thread i was looking for. This one

in my searching i also found this thread as well.


i suspect my booster is bad. sometime this summer i want to hook a hand held vacuum pump to the booster and draw some vac on it and then see if it holds the vac. if it does not hold vac then i WANT to go hydroboost. right now just sitting over night i will loose about 5-10 inhg of vac. that could be other parts of the HVAC system though as well.

 

The front calipers and pads are new. After the new master cylinder install today the pedal is worse. The 5'er has brakes but the controller inside the truck had a loose connection while I was towing it home which I've since fixed.

I do get a wooshing sound from the firewall area when I hit the brakes.

 

My van has the same problem, really low/soft brake. Brakes good, but the pedal goes down alot.



And when you step on it, you hear this whooosh sound. I think the booster is bad.

 

that is the same for me John. sometimes stops are a little hairy though LOL.

in my searches on here and over on obn, it seems like a LOT of people experience decent/good brakes but still have a sinking pedal. i just read another thread where a guy had a sinking pedal that was soft, he replaced the vac booster and after it had nice feel, good brakes, and no sink.

i have been thinking about this some more. i know i said earlier that i wanted H-boost, but that would be over $200 more than if i just got the updated vac booster. i have driven my friends truck and his factory vac boost system works just fine. i think for a daily driver not hauling/towing heavy all the time vac brakes would be just fine. that and i really don't feel like messing with my P.S. pump to do the h.b. conversion.

 

LS, check in between the rubber cups on the rear wheel cylinders.
Sometimes, theres a small leak there that can't be noticed without lifting these cups, and may be causing air intrusion.
Also, make sure when you adjust your rear brakes, that there's a slight "drag" on the wheel's, when turned by hand.
If the pedal doesn't improve after all this, I've read where there has been poor master cylinder design for these truck's, where the bore is only 1/16" and should be 1/8th.
Someone here quoted the new part # for this, napa 47-39635, but I can't get a read for it?
They said after replacing this with the new master, brakes were awesome.

 

X2 If you changed the master you should bleed all four wheels in this order: RR,LR,RF,LF.

 

First bench bleeding the master before install. Otherwise you're wasting time and brake fluid trying to get all the air out.
Don't forget to bleed the RABS system I believe that would fit in between the rear and front brakes.

Another cause for a soft or sinking pedal would be the RABS system if I recall correctly.

 

With this truck having rear drum brakes and it being a '93 model does it have rear ABS? I bled all 4 brake lines today in the order: rr, lr, rf, and lf. The pedal is definitely better but if you are setting still holding the pedal down like at a stop light it will slowly go down almost to the floor. If the truck is not running and you good the pedal down it will not do this and stays firm. This leads me to lean toward the booster?