So, I've got a similar issue to CollinsCD here: https://www.ford-trucks.com/forums/1...9-f-250-a.html


I'm currently trying to diagnose my exact problem and one weird symptom is how long it takes for the pedal to return position after pressing it. This happens even with the master cylinder disconnected. I took a video of my booster off the truck and me pushing on the rear where the pedal would be pushing:


You can see it has a pretty slow return and I'm not sure if that is normal or not. When its all bolted together it takes 2-3 times that long for the pedal to shoot back up. Now I'm wondering if its a small hole in my booster diaphragm.

Some other info about my brakes that I know so far:

• The brakes work... but only until my pedal is nearly all the way to the floor, which is concerning each time.
  
• I've bled the brakes, and gone through 2 different master cylinders, both were bench bled.
  
• I know the booster is working as its supposed to, its assisting the pedal after all. I've got a firm pedal with no engine and with the engine going its too mushy.
  
• It loses 2-3 inches of manifold vacuum. for about 3 seconds, causing the engine to stumble, not die just shake a bit.
  
• If I plug vacuum line to the booster I've got my firm pedal, with no assist and not vacuum lose when I apply the brakes.
  
• The booster push rod is adjusted to spec as far as how much it sticks out
  
• After having the engine running for a couple minutes, pulling the check valve from the booster sure has some pressure to it. It has to be holding some sort of vacuum.

Wondering if its safe to say I need a new booster. Anybody know a good way to diagnose these?

 

anybody have thoughts on this?

 

On my other truck, it would either work like normal power brakes, or it wouldn't and you would have to let the pedal sink until it became manual. When it was power, even then, the pedal would slowly sink down. It was disconcerting to say the least.

I would say if you are having problems, just get a new one. Sure, they are kind of expensive, but on a 30+ year old truck, new parts aren't a bad thing.

 

Hi, did you solve this? how did it work out for you? I've replaced power boosters & M/C's and had the squishy brake problem- its a PITA. bench bleed, screw out the plunger, bleed, bleed, bleed, all to no luck. The last time, the problem ended up being I installed the hardware on my rear brakes incorrectly, and the brake cylinders were smaller than original. thus, they were not pushing the rear pads out enough/not enough power & had to redo spring installation. Ultimately, since I kept my original stock brake cylinders, I honed em, put in a rebuild kit and everything worked fine. The smaller brake cylinders with 10mm bleeders are not enough to handle f250 braking. Need to keep the originals and rebuild, not use aftermarket crap.

 

Was wondering if I could replace my vacuum booster with a hydraulic one?

 

Do you mean a hydroboost setup? If so, yes it can be done but is not a direct bolt in. Do a search on the forum and you will find lots of threads on the subject with several different ways other members have done it. If not, it would be best to start your own thread instead of replying to one that is 5 years old. You'll get better responses and less confusion that way.

 

Pump the brake pedal several times, then step hard on it and hold it there. If the pedal sinks to the floor, there is a leak somewhere in the system.

When the master cylinder leaks, the fluid usually seeps into the booster* .. so it cannot be seen.

*1973/79 F100 2WD: Manual disc brakes were standard equipment, power disc brakes were optional.