Need a little help with Brakes

[3Kp]

Yes I spelled brakes correctly

Here is what I had going on. Time to time by brake pedal would be hard as a rock. (brake booster) But then I had a caliper pin come out and did some damage to my rim. Got a new pin in checked the pads (looked good) so I put the wheels back on. Went for a test drive. brakes worked as they should but pedal was slow to return back up.

Today I took the brake booster and master cylinder (MC is brand new) off my donor truck since they are the same part # Me and my son bled the brakes and the fluid looked a little dark but it's coming out clear now. Pedal feels pretty good. I take it for a test drive and I press the pedal down to stop and it's slowing down but not stopping as quickly as it use to. so I got down the road further and slam the brakes still doesn't stop it just keeps slowing down. It does stop eventually just need a lot of room to stop. SO what am I missing?

Thanks

 

[cpdenton]

How is the adjustment in your rear brakes? The self adjusters are junk and rarely work. You have to adjust them manually quite often.

 

[dunk]

Yes, check rear adjustment. Tighten up until you get slight drag in one spot of rotation spinning by hand as you adjust tighter. How is the pedal feel? Should be high and tight. Are hoses new? Sometimes they can fail internally and cause funky symptoms if they collapse.

 

[icanfixall]

Heres how to tell if the rears are out of adjustment. Press down the parking brake. Does it nearly reach the floor when it sets? If so then the rears are way out of adjustment. Another idea is apply the parking brake slightly and go for a test drive. Does the brake peddle feel better and stops the truck better with plenty of travel. If so your rears are out of adjustment. Another symptom is does the truck slip forwards at a stop light after you have come to a stop. If so then its the rears again. Does the brake peddle sink down after stopping. Same problem again. Hope this helps you out. Most have changed the vacuum brakes to the hydroboost brakes. Then you have twice the available braking pressure the vacuum brakes had. So you stop much better and safer.

 

[IDIoit]

i vote that the caliper you re-pined is donski.
i agree with adjusting your rear "breaks"
but the back breaks only do 70ish percent of the broking.
break open your wallet for some new front calipers, rotors, and pads.(brakes)

 

[dunk]

Does the brake peddle sink down after stopping. Same problem again. Hope this helps you out.

Agree with all previous, but not this. If pedal sinks after stopped you have a bead seal in the master cylinder bore. It's bypassing internally and allowing you to hold the truck stopped until you run out of travel as it slowly sinks. Been there done that. Either hone and rebuild or buy a new MC if this is your problem, but every time I've had this the vehicle has stopped fine, just wouldn't stay stopped as the pedal sunk.

Most have changed the vacuum brakes to the hydroboost brakes. Then you have twice the available braking pressure the vacuum brakes had. So you stop much better and safer.

Not sure I believe this. It's the same master, calipers, and wheel cylinders. You have exactly the same pressure for the same force on the master piston, it just takes less pressure fmr your foot to get a given psi at the wheels. Manual brakes, vacuum assist, or hydroboost assist should all stop the same. I've never driven hydroboost, but after having the truly extravagant luxury of vacuum assist brakes since I got my first 80-86 truck I do appreciate power brakes on lifted trucks with larger tires... But you're not stopping any quicker with small tires, just easier. With larger tires I can see how it's difficult to apply sufficient brake pedal pressure to stop as quickly as the truck actually can. Call me old school but power brakes and steering on anything other than a lifted truck with large (heavy) tires is purely luxury, for the weak.

 

[3Kp]

I don't drive this truck very often. 2 weeks ago I drove to scrap yard to drop off some water heaters. That's when I lost my caliper pin. Last weekend I found that I lost the pin and replaced it and took it for a drive. Stopped great! just noticed the pedal came back up slow after taking my foot off it. Today took brake booster from my F150 that has new master cylinder which has never been driven on the road since installed. (been parked in a barn for 6-7years). The pedal seems firm when I push it down it goes about 1/4-1/2 way down and no further. Truck does stop eventually and stays stopped. But if I stomp on the brakes like a car or animal ran out in front of me I'm going to hit it! (Doesn't stop barely slows down) I was only doing 20-30MPH when testing this out. Wondering if brake booster is bad as well?

Reason I knew original booster was bad is that at time to time I have to really push down on the pedal and it barely moved and truck was hard to stop. Then the next time I had to stop I was fine. very intermittent.

Hope this help more. Tomorrow I will try out the E brake and see how it does.

Just trying to get this thing safe for the Midwest Oilburners Rally. Next week replacing Axle joints and rear u-joints.

 

[icanfixall]

Agree with all previous, but not this. If pedal sinks after stopped you have a bead seal in the master cylinder bore. It's bypassing internally and allowing you to hold the truck stopped until you run out of travel as it slowly sinks. Been there done that. Either hone and rebuild or buy a new MC if this is your problem, but every time I've had this the vehicle has stopped fine, just wouldn't stay stopped as the pedal sunk.



Not sure I believe this. It's the same master, calipers, and wheel cylinders. You have exactly the same pressure for the same force on the master piston, it just takes less pressure fmr your foot to get a given psi at the wheels. Manual brakes, vacuum assist, or hydroboost assist should all stop the same. I've never driven hydroboost, but after having the truly extravagant luxury of vacuum assist brakes since I got my first 80-86 truck I do appreciate power brakes on lifted trucks with larger tires... But you're not stopping any quicker with small tires, just easier. With larger tires I can see how it's difficult to apply sufficient brake pedal pressure to stop as quickly as the truck actually can. Call me old school but power brakes and steering on anything other than a lifted truck with large (heavy) tires is purely luxury, for the weak.

Yes.. A sinking peddle after stopping CAN be a bad master cylinder but.. Its proven here many tomes over the sinking peddle is the master cylinder trying to fill the rear wheel cylinders. Now as for the brakes have the same pressure as the vacuum brakes have is not so. The vacuum brakes has at the most. About 1000 lbs of hydraulic pressure available. but its not used every stop. But its there in a panic stop. Now the hydroboost brake pressure is just over 2200 lbs so right there you have available more than twice the braking pressure. Now if you change the master cylinder to the larger 1 5/16 bore from the smallish 1 1/8 bore you now have MORE volume per peddle stroke so it can fill the out of adjustment rears easier. No more fading after a full stop sinking brake peddle.. I realize fluids do not compress. You can't force more fluid into a closed system but.. Think about the out of adjustment rear brake wheel cylinders requiring more fluid to open up. Now you have the idea of what hydroboost does for us.

 

[cpdenton]

I think I have found your problem. You say you took the brake booster and the master cylinder off your f-150?

they have a smaller bore master cylinder. 1 1/16th verses your 250 diesel has a 1 1/8th.

That smaller bore will never move enough fluid to fill your wheel cylinders. Get the right master cylinder back on there and I bet you will be back in business.

Edit: the brake booster also has a different part number.

 

[3Kp]

Huh didn't know they were that different. I know the brake booster is the same part number didn't think to check the MC.

So what would cause the pedal to come up slowly with the old system? Never noticed it but never looked down at the pedal. Will try to put old MC back on and see what happens? Well heck may just go buy a new one.

Thanks

 

[cpdenton]

The booster on a 250 is the same part number as a 150 if you are under 7000 pounds gvwr. Yours is the heavier system, because you have a diesel, and is a different part number. According to rock auto anyway....

 

[3Kp]

Tomorrow Going to O Reily to get new booster and MC.

Never mind on same part number it was the power steering gear box and blower motor. that was the same. Sorry been rough few weeks and just found my notes on parts that were interchangeable. Feeling like an

Thanks a lot! appreciate the response time and advise.

 

[3Kp]

Well after correct parts we can stop again. With icanfixall tip on the E brake found my back need adjusted so I'll tackle that later.

 

[dunk]

Yes.. A sinking peddle after stopping CAN be a bad master cylinder but.. Its proven here many tomes over the sinking peddle is the master cylinder trying to fill the rear wheel cylinders.

Proven how? I don't believe it as it makes no sense.Sinking pedal after stopped and holding brake is either external leak or internal bypass.

Now as for the brakes have the same pressure as the vacuum brakes have is not so. The vacuum brakes has at the most. About 1000 lbs of hydraulic pressure available. but its not used every stop. But its there in a panic stop. Now the hydroboost brake pressure is just over 2200 lbs so right there you have available more than twice the braking pressure. Now if you change the master cylinder to the larger 1 5/16 bore from the smallish 1 1/8 bore you now have MORE volume per peddle stroke so it can fill the out of adjustment rears easier. No more fading after a full stop sinking brake peddle.. I realize fluids do not compress. You can't force more fluid into a closed system but.. Think about the out of adjustment rear brake wheel cylinders requiring more fluid to open up. Now you have the idea of what hydroboost does for us.

Properly adjust the rear drums and volume to make up for slacking on maintenance is not an issue. How did you come up with 1000 psi vs 2200 psi? What pedal force is that using and is that pedal force a small woman or a strong man who does leg presses every other day? Reference? If 1000 psi can lock the tires then how is 2200 psi better? This is exactly why I say the benefit comes with larger/heavier tires, as 1000 psi may not be enough to lock them. If you can lock the wheels you have maximum braking capacity for the tires.

 

[TronDD]

found my back need adjusted so I'll tackle that later.

Later? It takes less than 5 minutes with a screwdriver and makes a huge difference. Just get 'er done.

Tim.