I hate to admit this but the brakes on my truck are whippin me right now. I could use some help if anyone out there knows what's going on. Here is a list of what has been happening-

2 months ago I replaced my ball joints. I noticed that the front passenger side hub seemed too warm, like the caliper might be sticking. When I got the caliper off it looked OK, but the surfaces that the caliper slides in were very dirty. I wire brushed everything thouroghly and put a thin coat of anti-sieze on the sliding surfaces. I pressed the caliper piston back in place with the proper tool and cleaned everything well. After I reassembled the front end everything worked well, and after a few test drives i noticed that the hub was not heating up like it had been doing before.

Two weeks after that I was sitting in a parking lot of a hotel while I was out of town. When I got in the truck and tried to leave, the shift lever would not come out of park and the brake pedal felt mushy. This continued for several days so I got my vacuum pump out and flushed all the brake lines, longest one to shortest one, not running the master cylinder below half full. I repeated this process twice and used all but a few ounces out of a new gallon of DOT 3 fluid. The pedal felt better now and the shift lever would move when the brake was applied.

One more week went by and i was sitting at a stoplight with my foot on the brake and I noticed that the pedal was creeping down slowly. I checked all my lines, proportioning valve, and each wheel for leaks but I found none. The level of fluid in the master cylinder had not dropped any since I had flushed the system. This led me to believe that the master cylinder was bypassing internally so I got a replacement from O'Reilly's. I bench bled the new unit, disconnected and capped my lines, put the new master cylinder on, and reconnected the lines. I then bled all the lines as before. The brakes once again seemed fine and the pedal was at the top and firm when pressed, and did not creep down.

Another week goes by and the pedal started to feel mushy again, and within a day or two the shift lever would not move again. I knewthat I must have missed some air in the lines so I bought a set of check-ball bleeders for all 4 wheels and one for the proportioning valve. I ran another gallon of fluid through the system and got a small improvement but not quite right, still mushy.

This morning it took almost 30 minutes of pumping the brake pedal before I could get it out of park. I could see the reflection of my brake lights and at first the lights would come on when the pedal first started to move, but would go out if the pedal was pressed harder. After about three glimpses of the brake lights they did not come on again for about 30 minutes, when I got it out of park. When I got off today I immediately went to O'Reilly's and exchanged the master cylinder in the parking lot. I bench bled again and everything seemed fine except for a slight amount of red assembly lube that was in the bench bleeding lines. Before I bled again I got a 6 ft. piece of clear tubing and hooked it to the bleeder. I ran the tubing up to a bottle so I could see from the cab what was coming from the lines. I got about 40 strokes on the rear wheels, and there was some air in the first 15 strokes or so, but none after that. When I moved to the front, the passenger side had a significant amount of air that never did clear out after 60 strokes. I moved to the driver's front and cleared all the air out in the first 10 strokes, then went on to a total of 40 strokes with no more air. I moved back to the pasenger's front and after another 60 or so strokes with the bleeder barely cracked open the air was still as plentiful as it was the first stroke.

Now I am questioning the front passengers side caliper, but only because that is where I see the air. This is the one I mentioned in the beginning that was also getting hot, but I think it was due to dirt. Here is some general info that seems to hold true throughout all this ordeal=
It is worse when it is colder ( less than 55 or so)
Eventually, the pedal will pump up and feel firm
There has never been any leak or fluid usage throughout this
Once the pedal is firm, it acts better if you use the brakes frequently, as in city driving
If the brakes are not used for an extended period, the pedal may go all the way to the floor
The pedal is mushy, the shift lever stays locked, and the brake lights don't work all simultaneously.
When the pedal is firm, the shift lever unlocks, and the brake lights work.
If the brakes are appied without pumping it feels like the front brakes are not working
If the brakes are applied after thre small pumps it feels like all wheels are braking
This info applies to the truck in my signature.
I have no trouble codes on my SCMT (except the P0360?, the one that the tuner causes.)
I have no brake warning lamp, or flashing OD light.
The truck does not pull to one side, there is no vibration in the brakes, and the rotors, pads, drums and shoes all seem fine.

Any info I left out I will be happy to get to you. I would really like to get this one figured out because it's not supposed to be this dang hard! Thanks for reading this and I welcome your suggestions.


A week

 

WOW, that is a tough one.

It sounds like you've covered all the basics. Did you check to see if any of the lines going into the master cylinder or brake cylinders were cross-threaded?

If you find a cross-threaded line, it might not leak, but air could possibly get into the line.

I'm sorry to say I have no ideas on what is happening with your brakes.

I have a '97 F-350 XLT 4x4 Crew Cab Long-Bed. I had Sears flush and replace the brake fluid on my truck. The brakes work fine, but the pedal gets within 2 inches of the floor. This is better than before flushing the fluid. I'm beginning to wonder if my brake system is heading towards the way yours is acting.

Good luck.

 

I had a problem like that once & it turned out to be a bad brake caliper. the seals were bad enough to allow air into the system but not to leak fluid. it drove me crazy trying to find it. rebuild kits are not that expensive if you want to try that route .

 

Have you checked your rear brakes? Those usually affect pedal height and could possibly be wore out, also check the wheel cylinders while you check out the rear shoes and drums. They could be letting air into the system every time you let off the brake pedal. check for small leaks around them too. I have an 86 F250 that loses brake fluid every 3 months, everything except for the front calipers has been replaced I just finally got tired of putting money into it.That rabs valve can also give troubles like the ones you describe. But Id check the rear brakes first, they definetly could be the problem. I almost forgot I had an older truck do the same thing yours is doing an it ended up being a front caliper. The seals were bad and let air in the system and did not leak. Let us know what you find out and Im sure we'll get the problem figured out. Casey

 

Thanks for the replies!
I have been thinking about this one all night. I am on the road right now so I think that I am going to replace the pasenger side caliper rather than rebuild it. That wheel stays full of air when bleeding, and it feels like the front is the part that gets the air in it because the truck stops so much better after pumping the pedal. My best guess is like you guys have mentioned- fluid is not leaking out, but air is leaking in. Any other ideas out there?

 

yeah i would replace the caliper like you said. if you still have issues diesel nut gave you good advice about the RABS valve and the rear brakes. Our truck are very picky about rear brake adjustment and even when theyare up tight the pedal drops stlightly. When i bought my truck i had low pedal and it dropped slowly once pumped up. Rear brakes were shot. That helped but the pedal still dropped. so I bypassed the RABS valve that helped. so replaced that. then there is an upgrade for the mastercyclinder that can be done and it involves replacing the MC with one with an 1/8 inch bigger bore. that helped. now i just have to keep my rear brakes adjusted up good and i have a good hard pedal but it still drops sometimes while sitting at a light.

 

You might consider making sure your rear drums are adjusted out... most car's I've been around it didn't matter that much - I guess the rear wheel cylinders on these trucks are fairly large bore because very small adjustments can make a big differece in how far the pedal goes before it engages.

 

another thing u could look at is the possibilty of your master cylinder leaking internanly, you dont see any fuild leaks and the level wont go down either but its passing fuild inside itself this will cause a mushy pedal and all the bleeding and fuild swaps wont fix it. mine is doing this now and have a new one coming in

 

Ive changed about 3 master cylinders and Im still having this same problem too.
I did just change the front pads so the calipers are suspect.
But these things are about $200 a piece. I'd hate to change them and not fix it.

 

I can't think of a way to isolate the calipers. If you just plugged the lines, you would still have air in because there is no way to bleed it out of the lines. rebuild kits are just new seals & dust boots & are normaly cheap. i would try & rebuild it & if it took care of the problem then you could by a new caliper if you wished or just run it with the one you rebuilt.

 

It is possible to pick up a caliper on ebay. I've seen remanufactured for about $60. For example : Item number: 200041812960

 

I just got a caliper from NAPA for about $50. (core charge is $80???) I did check the rear drums and shoes. They looked good to the eye, and they were snug when putting the drum on the shoes. The big thing that convinced me to get the new caliper was the fact that the air is always at that one wheel, and only that wheel when I bleed it.
I kind of understand the role that the RABS can play and I kind of don't.---When the pressure comes out of the master cylinder it has to go somewhere. If the RABS reduces the fluid going to the rear brakes, then it must divert that pressure to somewhere else, right? How can it do that without a return line to the master cylinder? (insert *** scratch and confused look here)

Thanks for the replies and if anyone has anything to add I will be thrilled to read your suggestions also. I will be installing the caliper tomorrow and I will let you how it does.

 

Ive never gotten air out of any of the 4 bleeders.
All fluid.
But I had just changed the pads and I had to push the pistons in.
Could be the rabs who knows?

 

i believe the RABS works like this. fluid comes into a chamber with 1 port fluid in and fluid out. then there is a piston which is attached to step motor. ABS module detects rear wheel skid and the step motor backs the piston up some creating a larger chamber and removing pressure from the rear wheels then quickly step back up sending pressure back. during an ABS stop this happens a couple times a second.

I have replaced a few of these but i have never opened one up cause the core is so stink much. So don't risk you life defending my theory but i think thats what is going on in there. So how could that make the pedal drop. the piston could leak around the sides like blowby but since its a sealed unit it would leak fluid.

 

Check the brake light switch on the brake pedal. Mushy pedal should not affect weather ot not vehilce comes out of park!!!