I had to ask myself again why did my brake light come on after I pumped the ell out of it... I did not offer help when i first read the post because a master was recommended. Well just let him put one on if its a no go then I will ask a few questions. Most guys are looking for a EZ out so no need to get deep when they are going with the EZ answer lets call it human nature just like the human nature of me not questing why my brake light came on so took the EZ out...
Second page near the bottom seams to be the most logical fix to the issue... A large bore master cylinder I remember the issue on fords but don't know what models were effected so score a win for the one that posted it......
I've just been really busy for the past month and unable to post the solution for my problem.
PLC7.3 posted a TSB regarding the vacuum booster. I researched the TSB further and this is the complete TSB that I found;
Subject: Low Brake Pedal
Vehicle Involved: 1997 and Earlier F350 Diesel Power Truck with Vacuum Brakes
Condition: Brake Pedal is Low and Creeping / Falling to the Floor
Repair Procedure: Many owners have realized a low or creeping down brake pedal on their trucks. This condition may be corrected with several possibilities as solutions. Bleeding the brake hydraulic system because of air contamination. Adjusting the drum brake mechanism to correct the shoe to drum gap tolerance. Replacing a defective electro hydraulic dump valve because of a defective dump solenoid. In addition an approved Ford repair to increase the master cylinder bore diameter by using a F450 Super Duty master cylinder specific to the vehicle being repaired. Lastly, a new repair possibility exists involving the vacuum booster on a diesel truck. If the condition occurs after the vehicle has come to a stop, and no other brake concerns are found the condition is considered normal as the result of the vacuum pump replenishing the vacuum inside the power booster. Ford has developed a Zero-Loss Travel brake booster to correct this condition if the customer finds this condition unacceptable. This part is only for use on diesel-powered trucks P/N F5TZ-2005-CA it is not a service replacement, it must be ordered by the part number specifically, not the vehicle application.
Thus, this led me to submit another post "Diesel Master Cylinder" asking the general consensus on the bore diameter on the M/C for the diesel vehicles. Only one response.
I dug into my service papers and found a ford part number for a master cylinder that was replaced at the dealer years ago. I checked that number against what was supposed to be the original part number for the M/C and they didn't match.
What was the difference???
I took the original part number and cross referenced it in the NAPA web site and it returned the part that my local NAPA gave me when I replaced the M/C in December. This M/C has a bore diameter of 1 1/16" and was listed for a diesel powered vehicle.
I took the part number that I found in the service papers and did the same cross reference. This revealed a M/C with a bore diameter of 1 1/8" and was listed for a gas powered vehicle.
Now revert back to the above TSB. It talks about increasing the bore diameter of the M/C. It's all starting to make sense. Also, seeing Jeff Dodson's post about him using a F-450 M/C, which he drilled out the ports a bit, solved his problem.
I took my new M/C NAPA p/n 47-39634 and had them give me a new, not rebuilt, p/n 47-39635 M/C.
I bench bled the M/C with no foreign materials coming out of the bleed hoses, and installed it in the truck.
After bleeding everything, the pedal was nice and solid, just like the previous M/C. Here's the moment of truth. Will the pedal sink to the floor when the vacuum pump is supplying vacuum assist???
OF COURSE NOT!!!
The pedal performed just like it did before the rear steel brake line failed. I adjusted the rear brakes a little and off into the sunset I went!
If I never found the change in the M/C from the service papers, I would have went down to NAPA and gotten a F-450 M/C which would have been pretty much the same fix as Jeff Dodson, but I would be hesitant to drill out the ports from the start.
No misplaced brake lines. No problems with the brake hoses that were replaced two years ago. No air trapped somewhere in the lines after I've gone through a gallon and a half of brake fluid. No faulty master cylinders that contained metal shavings. No air infiltration from the threaded fittings. No problems with the RABS valve. I didn't have to replace the vacuum booster and vacuum pump. I never gravity bled the brakes either.
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