My late '94 F350 psd needed a new master cylinder and booster, and a rear wheel cylinder, no big deal. But now I have a soft, low brake pedal, and no amount of bleeding seems to help. A hard, steady push on the pedal will slowly take it right to the floor, I've seen this described in several threads. One previous thread suggested to cycle the ABS system several times, and then bleed to cure this, worked for his truck.

I cycled it 5 times, and sure enough, the pedal became firm and much higher, BUT, I was called away, and didn't get back to work on it again until two days later. You guessed it - by then the pedal had gone back to low and soft!

So, I once again cycled the ABS system, once again pedal improved, and this time I bled it right away, used a pressure bleed system, never saw any bubbles, but hoped it would be the permanent cure.

As soon as I was done, the pedal was back to low and soft again!! The bleeding made it noticeably worse, I don't know where to go next with this.

My take is that the master cylinder isn't leaking by - after the ABS drill, the pedal is firm, doesn't fall to floor any more. Ditto hoses - the whole system works correctly, but only after the ABS system is exercised!!

Can anyone out there tell me if they've been through this one, and if there's a right fix for this?

 

If the pedal firms up and then goes soft again, you have air getting into the system.

Check ALL the connections; even the connections you didn't loosen.

I had a soft pedal (may or may not have contributed to the accident - long story) once. After the accident damage was fixed, the shop sent the truck out to have the front end work done. The second shop determined that my brake hoses were deteriorating on the inside. No damage was visible from the exterior of the hoses. They found the hoses were deteriorating from the inside when they removed the hoses to install new ones.

Since you're having a problem anyway, you might want to consider inspecting the hose interiors.

Was the master cylinder bench-bled before installing? Have you double-checked the rear wheel cylinder? If only one was replaced, the others may now be showing their weakness.

 

Excuse my ignorance but what is the ABS drill? I'm not satisfied with my bleed job eighter.

 

Stupid info...but when doing brakes they say to replace everything in pairs due to the fact that they all get use/abused the same amount...I would check the other rear wheel cylinder. Also...did you check your solid line flares... might have flared it to much causing it to crack and allow air into the system...Just my 2cents...what do I know...im only 18 haha so dont take my word on anything...just brain storming. Good luck

 

Take a look here for a possible fix.

 

to oldbird: the abs drill, as I know it, is to make the system do its thing as designed by creating a wheel lockup situation and initiating the pulsing lock and release cycles of the wheel brakes. I do it by driving in an area of low traction (wet grass here in the NE, lots of that this summer) about 30 mph, and standing on the pedal. Lots of cycling of the abs, obvious pulsing feel in the pedal.

 

Thanx pete for the info - I had heard somewhere about this mystery booster - the "zero loss" unit. So, I'll place my trust in Ford engineers, and I'll install the thing, and then post after it's in to share the results.

 

Racine, I don't know how that booster fixes it, but it sure does. But doing my research on it, I found that there are several people with the same proplem. And every one that put that zero loss booster on, no longer had the problem. Good luck man.

 

Thanks racine, that makes sense. RubberDuck, how would you compare this zero loss booster to the hydoboost?

 

Can't really compare it. SD and OBS are different animals, and never drove an obs with hydroboost. But I do know of a few SD's that after a hard braking, started to whine and you could feel it in the pedal. And it never went away.

 

I have installed the "zero loss" brake booster, ford part no F5TZ-2005-CA, paid $191 for this from ford; and it is very much better than the "standard" booster, for sure. The pedal is much higher, and much firmer; gives you a much greater sense of confidence that you can actually stop the truck! BUT, with the vehicle sitting still, a firm and steady push will still bring the pedal slowly to the floor. My take on all this is that the issue with soft, low pedals on these trucks is usually the booster; not the hydraulic side of the system. For some reason, these boosters slowly bypass with a steady, firm pedal push, and allows the pedal to slowly go to the floor. The "zero loss" unit was a big improvement on my truck, and really helps when driving lightly loaded or towing heavy.
Thank you to all who helped guide me on this thing, I hope this post may help some others who are puzzled by this same issue.

 

Good deal! Glad your squared away.