help with break problem

[ramon f350]

help with brake problem

well my new drama with the truck is the brakes. I have had problems with the pedal sinking while holding the brakes so I thought it was the master cylinder. I bought a new one yesterday and put it on and it did not fix the problem. I bench bled the master and then bled all 4 wheels and did not get any air out of the lines. after that not fixing the problem I figured that it had to be the brake booster so I stopped and picked on up this afternoon after school. I threw it on and again it did not fix the problem so i thought well maybe i got a bad master cylinder so i tear it down again and go get a new one on the warranty. bench bleed the new one and bleed the brakesa at all four wheels to no avail. does anyone have any ideas at what else it could be I am really at wits end here

thanks for all of your help in advance
Ramon

 

[EvergreenRanch]

have you tried adjusting the brake shoes with a screwdriver on the back of the drum housing (little hole at 6'oclock)? how about propotioning valve (im pretty sure our trucks have one but not 100%)?

 

[olivera149]

are you hearing any clunks in MC area or near the booster? There is a spec on the length of the pushrod on the booster that engages the MC, i dont know it off the top of my head and my little notebook that i jot down all the info on is no where to be found.

 

[dsblack]

Mine was solved by changing the RABS sensor in the rear diff. less than $50.

Mine was solid for a second then would start driftng down.

Good luck

 

[tuckerd1]

From Ford Tech Pub:

Manual Adjustment with Drums Installed


Adjust the single anchor brake by turning self adjusting screw located between the lower ends of the shoes.
1. Raise the vehicle until the tires clear the floor. Install safety stands under the axle.
2. Remove the cover from the adjusting hole at the bottom of the brake backing plate, and turn the adjusting screw (inside the hole) to expand the brake shoes until they drag against the brake drum as shown.
3. When the shoes are against the drum, loosen the adjusting screw so the drum rotates freely without drag. If the drum does not rotate freely, remove the wheel and drum. Using Rotunda Brake and Clutch Service Vacuum, vacuum out any dust and dirt from the linings. Remove brake shoe hold-down springs. Using sand paper, remove any rust from the points where the shoes touch the backing plate while holding shoe away from backing plate. Apply a light coating of lithium-base grease, Premium Long-Life Grease XG-1-C or -K (ESA-M1C75-B) or equivalent or Disc Brake Caliper Lubricant D7AZ-19590-A (ESA-M1C172-A) or equivalent. Do not get the lubricant on the linings. Install brake shoe hold-down springs. Install the wheel and drum and adjust the shoes.
4. Install the adjusting hole cover on the brake backing plate.
5. Check and adjust the other brake assembly.
6. Apply the brakes. If the pedal travels more than halfway to the floor, there is too much clearance between the brake shoes and the drums. Repeat Steps 2 and 3 above.
7. When all brake shoes have been properly adjusted, lower the vehicle and road test to check brake operation. Perform the road test only when the brakes will apply and the vehicle can be safely stopped.

Hope this helps

 

[Mr_Roboto]

Fluid is leaking through somewhere. The Master Cylinder was a good first try.

The laws of mechanics still apply, mis adjusted brakes can't cause the brakes to be firm, then "loosen up".

Let's get this straight: If you hold the brakes long enough, it goes all the way to the floor and you lose brakes, right? I just want to eliminate vacuum level changes which would cause the pedal to "drop" some, but not go to the floor.

If the pedal does indeed go to the floor, I would look at the ABS valve as it can leak internally and cause the problem.

 

[icanfixall]

What you are seing is the rear brakes need to be adjusted up. This is a vary common problem with our trucks. Do this first. Set the emergancy brake. Did it hold the truck but ingage really far down? Now step on the brake peddle. Is the brake peddle holding now and not slowly going down? If so your rear brakes are way out of adjustment causing the master cylinder to slowly sink because its trying to push more brake fluid to the rears that now need more. This problem will also cause the front rotors and pads to wear out and heat up much faster because they are doing all the braking. Sorry you spent so much on parts but this simple adjustment will solve your problems....

 

[Mr_Roboto]

A low pedal and a sinking pedal are two different things....

Misadjustment will cause a low pedal, not a sinking pedal.

 

[EvergreenRanch]

A low pedal and a sinking pedal are two different things....

Misadjustment will cause a low pedal, not a sinking pedal.

i dont like contradicting, but i noticed a distinct differenence in pedal firmness with proper adjustment of my rear brake shoes....i suggest it as at least a starting point as it cost you nothing to adjust those....if nothing else, it rules another piece of the puzzle.

 

[Mr_Roboto]

Hey if we all agreed, what fun would it be?

Drum brakes are funny, the first part of the pedal effort is to overcome the return springs. So you can actually "push" and not get any braking if the adjustment is loose. And once the primary shoe contacts, it wedges and energizes the second shoe, which could produce a sinking feeling once the brakes energized themselves.

It certainly never hurts to check your adjustments.

 

[Full Monte]

Well, if you get tired of it all, you can do what I did and put a hydroboost in it. The technical article on how to do it is in this forum.

 

[icanfixall]

Rear drum brakes out of adjustment will cause a sinking peddle and a low peddle. Just try the test as I have offered and you will see. What I right here is up for interpatation so enjoy and I wont feel bad either way. My skin is tuff. I"m formally from the "other" site. I still go back from time to time just for kicks. This site IS the place. Just look at all the heavy hitters here. I'm really not one of them but I do enjoy this site....

 

[ramon f350]

Thank you all for your help I adjusted the rear brakes today and it didnt help they were only out a little I use my emergency brake all the time to try and keep them adjusted. we did find that the abs dump valve is the problem. I am going to call and get prices on one tomorrow. if I cant afford it i may take it out and just do away with the abs all together I dont like it anyway. Thank you again for all of your help.

Ramon

 

[towcat]

Thank you all for your help I adjusted the rear brakes today and it didnt help they were only out a little I use my emergency brake all the time to try and keep them adjusted. we did find that the abs dump valve is the problem. I am going to call and get prices on one tomorrow. if I cant afford it i may take it out and just do away with the abs all together I dont like it anyway. Thank you again for all of your help.

Ramon

unplug it and see how the brake pedal feels.

 

[Snowman671]

Glad we can all disagree

I will tell you this I just did all this myself. I started at the master cyl, then replaced the front calipers, then the rear cyls, shoes, springs, drums all of it. Everythgin except the RABS. I went by ford's book and adjusted everything !! Twice !!! Finally I bit the bullet paid the 159.00 for the RABS and everything is a hell of a lot better.

Now all that said I still need to re adjust the rear shoes again now that they are broke in but I can stop and the pedal is 100 times better.

Basiclly. I replaced every part on that damn thing and it ended up being the rear shoes needed adjusting and the RABS Valve needed replaced.

Side note : when i unplugged the RABS the pedal did not change. The only way to check and see if the RABS is the problem would to be to bypass it with a custom made line.


dsblack you must have bought a used RABS for 50.00 ?? I looked everywhere for them and NAPA was the only place had access to them and it ran me 150.00


Just my experience in the last month with the brak system

Dave