Ok, so I'll try to explain but it may seem drawn out so bear with me....
I have been working on a brake issue on a 1995 f350 DRW for some time now. I am at the point of just giving up because I have no where else to turn. Here is what's happening, this truck has only RABS disks in the fromt drums in the back. With the truck off and all the vacuum blead out of the booster the pedal is solid as a rock as it should be. I start the truck and build vacuum and depress the brakes, I get one press with a "normal" pedal and then as if I was at a stop light I hold my foot on the pedal and it slowly creeps to the floor. If I pump the pedal a couple of times it starts up high again and then repeats itself again. Here is what I have done,
1) new brake lines steel and rubber all around.
2) 6 new master cylinders.
3) new brake booster.
4) new rear drums, shoes, spring kits.
5) new calipers, pads.
6) new RABS valve under driver seat.

I have blead the entire system over and over again and it will not change a thing. The vac is producing 23 hg but the recovery timie when the vacuum is depleted is slow to return back to 23 hg. I also read a few things about the RABS system and have checked the fuse and the sensor in the top of the pumpkin all seems to be initact and working as advertised. I also ran a "diognostic test" on the RABS by grounding the orange and black wire under the dash. I got 16 blinks total telling me that everything is ok with the RABS. Another thing I have read about this kind of issue is problems with the third brake light???? I took it off and found that the bulb was bad and the socket was slightly melted but not enough to create such a problem. I'm not sure where to trun next and for all the posts on the web I have read there hasn't been one that I hve read that pin points how to fix this problem. It seems that every guy that has had this issue has change one thing or another and it either fixed it or didn't. I'm kinda sick of trial and error isn't there a way to trouble shoot down to a component? HELP!!!!!!!!!!!!!!

 

If you didn't replace the master cylinder (or you replaced it 5 times I'm not sure which) you need to . If you did, it sounds like you still have air in the system ...Are the rear brakes adjusted properly ?...

Also , a new master cylinder needs to be bench bled ...( I have seen re mans that weren't any good also)...

 

I have replace the master cylinder 6 times thinking every time that there meay be a problem with the new one. But come on what are the chances of getting 6 bad ones??? I also bench blead every one of them until there were absolutly no bubbles left. I have blead the entire system 3 different ways one with the two perosn method the next with a vacuum and the last with a "home made pressure bleeder". Yes I agree there may still be air in the system but how do I get it out????

 

what order do you bleed the brakes?? are you starting with the wheel farthest from the master cylinder and working your way to the shortest distance from the master cylinder?

 

yes I start with the RR,RR,RABS valve,RF,LF.

 

Here is a link that might help you out.

 

Thank you for the link but I have already gone this route. I just put a new booster in (zero loss) from for three days ago with no good results. I've been doing alot of studying on this brake booster and vacuum pump and thought that the booster was the ultimate fix and was let down when it didn't work. I also found out that ford admitted that the early on boosters and masters were being produced wrong by the vender and now all of the big bore masters and zero loss brake boosters are standard ford parts that you order for what ever truck you need it for.

 

Well here a couple of things you could try. Presuming there are no leaks anywhere. The rears are properly adjusted. The calipers aren't upside down ( I have seen this happen on other vehicles ).

1. Reverse the order of the bleeding procedure. Closest first farthest last. This worked for me on the 86 when I had a similar issue. Using a second person in the cab apply pressure to the pedal and bleed. Do not pump the pedal. Keep the reservoir full as you go. See if it helps.

2. Gravity bleed. I have never done this myself. I have read about it a couple of times. Can't say where to start with this method but front to back seems most logical to me. I'm sure you have some hose that will fit over the bleeder valves. Open each valve and let it drain keeping the reservoir full as the level drops. You can figure the rest out. It takes allot of time but at this point what the heck. Its only brake fluid.

Thats about all I've got off the top of my head. If I come up with anything else I'll let you know.

Pardon us for not welcoming you to FTE!


Welcome!!!

 

Thank you for the fast replies guys. This problem is haunting me and we need this truck for work. I will try all of that and see if it works. Another thing I was thinking about trying was, I have two 200psi guages I was thinking if I could find some adapters I would tee one in to the front circuit and one to the rear circuit and see if when the pedal is depressed if I'm getting constant pressures or if they are falling off as the pedal sinks.

 

I dealt with a 95 F250 that did the same thing, never got it to quit, finally I just put raybestos advanced technology slotted drilled rotors and raybestos advanced technology ceramic pads on and it had more than enough stopping power, the pedal still goes down slowly but no problem stopping. also have the same problem on my '90 F250 nothing fixed it.
sorry this isn't any help but at least I feel your pain

 

This sounds like the Master Cylinder. I read that you have changed it 6 times and properly bench bleed it too. If you have a brake shop close to you, they can pressure bleed your system for you.

The gravity bleeding takes a long time. Fill the Master Cylinder with brake fluid, open the bleeder screws on all four wheels and keep checking the fluid level.

 

I know you replaced it but it sounds to me that both you and helifixer have a bad RABS valve module. Easy to confirm.
If you look at the module there is a large hex bung on the end of it. Unscrew the bung (against spring pressure all the way) and remove the spring that is behind it (no fluid will come out). Replace the bung and pump the pedal a few times to fill the chamber.
If the brakes are now good then the module is faulty. If still the same then replace the spring and and look elsewhere.

 

I have personally recieved 4 bad remain master cylinders in a row before the 5th one was good.

After installing the first and 2 master cylinders I recieved 3 and 4 master cylinder and dissasembled them first before installing them in the car. 3 was missing a seal all together and 4 had a load of sand blasting sand in it. The 5th was built properly and worked fine.

the brand is fenco that I had problems, check the rabs like mention on the post above me.

 

Also, if the rabs is good and you find yourself going after another master cylinder you can buy the master cylinder with a larger bore from ford. You will have more sensitve brakes with this master cylinder as it will push more brake fluid.

Got this information from a tech. service bulliton. 98-5A-34

F6TZ-2140-BA with cruise
F6TZ-2140-AB without cruise

This has nothing to do with your problem, I'm only mentioning it if you decide to go the route of replacing your master cylinder again and to get a bit of a brake upgrade.

 

Article No.
98-5A-34

03/18/98

BRAKES - HIGH BRAKE PEDAL TRAVEL OR LOW
BRAKE PEDAL FEEL

LIGHT TRUCK:
1995 F-250, F-350

ISSUE:
The brake pedal may feel low or there may be long brake pedal travel on some vehicles. This may be due to the master cylinder bore size.

ACTION:
Replace the master cylinder with a revised master cylinder which has a larger bore to displace more brake fluid when braking. Refer to the following Service Procedure for details.

SERVICE PROCEDURE

1. Perform the diagnostics outlined in the 1995 F-Series Service Manual, Section 06-00 for long brake pedal travel or low pedal.








2. If adjustment is unnecessary or does not correct the concern, replace the master cylinder. Refer to the 1995 F-Series Service Manual, Section 06-06 for removal and installation procedures. Refer to the Application Chart for correct part usage.


PART NUMBER PART NAME

F6TZ-214O-AB Master Cylinder
F6TZ-2140-BA Master Cylinder
F6TZ-2140-EB Master Cylinder
F6TZ-2140-FB Master Cylinder

OTHER APPLICABLE ARTICLES: NONE
SUPERSEDES: 96-25-19
WARRANTY STATUS: Eligible Under The Provisions Of Bumper To Bumper Warranty Coverage

OPERATION DESCRIPTION TIME

985A34A Replace Master Cylinder 0.6 Hr.

DEALER CODING
CONDITION
BASIC PART NO. CODE
2140 16

OASIS CODES: 301000