poor braking power

[sbujtas]

On my 1992 bronco 351w, i had a soft pedal when i bought the truck. I bled the lines thinking that would help and it didnt do much. I then bought new wheel cylinders and a drum rebuild kit with all the springs and brand new shoes for the rear and changed them and that didnt help much either. The shoes are all set at the correct height because i could barely get the drum on, and when i put the drum on i turned the adjuster a little bit more to make sure they were snug. That only did a little bit but once again didnt help significantly either. I then changed the calipers and shoes in the front and the master cylinder. i bench bled the master cylinder exactly how it told me to do in the instructions and installed that. I adjusted the brake linkage into the master cylinder to make it a little bit longer thinking there was too much play in that because there is a lot of peddle travel. I have bled the brakes at least 7 times and i still have a soft pedal that does not grab the brakes until it is 3/4 down by the floor. Also sometimes i feel a little bit of vibration on the brake pedal itself and the way the pedal feels always changes. I am completely stumped on why the brakes are not up to par. I do have 35 inch tires and a 6 inch lift but i still dont feel like thats an excuse for the pedal to travel so much before the brakes kick in. I also havnt noticed any leaks on the brake lines. I could really use some help. Thanks

 

[Seabronc]

What was your brake bleeding procedure?

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[sbujtas]

for the lines i started at the rear passenger side and had someone pump the brakes until they were hard. they then held it and i cracked the bleeder and had them push it to the floor. I did that 3 or 4 times then went to rear driver then front passenger then front driver. For the master cylinder i plugged the brake line holes on it with the plugs they gave me and i pumped the piston until it was really hard

 

[Krafty]

if you keep getting air out each time you bleed the brakes then you have either a huge air pocket or you are not closing the bleeder ***** before they let off the brakes and **** a bunch of air in.

did you buy a new master cylinder?

 

[sbujtas]

Yea i bought the new master cylinder 3 weeks ago, but no air is coming out of the lines when i crack the bleeder.

 

[Rons beast]

Do a gravity bleed. It may be the only way to get all the air out of the system. Be sure to have a qt of fresh fluid. Open the bleeders on the master, and let the fluid drain down about 1/3rd way out of the resvoire. Close the master bleeders, ( providing you have seen no more air bubbles), then open the bleeders at all 4 wheels. Allow fluid to run out for some time. Keep watching and filling the master so it doesn't run dry. I have watched plenty of fluid run out and then air follow. So it can get trapped, and pumping sometimes moves it back and forth, or if someone pumped fast it can cause the fluid to foam. It can take up to an hour if there is alot of air trapped in the system, but it is the best way to bleed brakes. Be patient.

Good Luck

 

[sbujtas]

Do a gravity bleed. It may be the only way to get all the air out of the system. Be sure to have a qt of fresh fluid. Open the bleeders on the master, and let the fluid drain down about 1/3rd way out of the resvoire. Close the master bleeders, ( providing you have seen no more air bubbles), then open the bleeders at all 4 wheels. Allow fluid to run out for some time. Keep watching and filling the master so it doesn't run dry. I have watched plenty of fluid run out and then air follow. So it can get trapped, and pumping sometimes moves it back and forth, or if someone pumped fast it can cause the fluid to foam. It can take up to an hour if there is alot of air trapped in the system, but it is the best way to bleed brakes. Be patient.

Good Luck

ok great i will give that a try. Thanks a lot!

 

[sbujtas]

ok great i will give that a try. Thanks a lot!

where are the bleeders on the master cylinder? Where the brake lines go through?

 

[Rons beast]

Yep, just crack the lines about 3/4 turn and let some fluid bleed out.

 

[BroncoJoe19]

Ron's suggestion for a complete gravity bleed may do the trick. If on the other hand it does not, then maybe your rear abs proportioning valve is to blame.

I very vaguely remember reading a couple of threads about it. It seems that if it gets stuck that pressure can bleed off into a return line, when you don't want it to. I never had the issue so it never became personal to me, and I have not had first hand experience with it so I didn't LEARN it.

I think that there is information about it in my Haynes manual. IIRC it describes how the system works, but not what symptoms one would get if it failed.

Good luck, please let us know how you make out.

 

[sbujtas]

Ron's suggestion for a complete gravity bleed may do the trick. If on the other hand it does not, then maybe your rear abs proportioning valve is to blame.

I very vaguely remember reading a couple of threads about it. It seems that if it gets stuck that pressure can bleed off into a return line, when you don't want it to. I never had the issue so it never became personal to me, and I have not had first hand experience with it so I didn't LEARN it.

I think that there is information about it in my Haynes manual. IIRC it describes how the system works, but not what symptoms one would get if it failed.

Good luck, please let us know how you make out.

ok thanks. i will look into that too

 

[Seabronc]

for the lines i started at the rear passenger side and had someone pump the brakes until they were hard. they then held it and i cracked the bleeder and had them push it to the floor. I did that 3 or 4 times then went to rear driver then front passenger then front driver. For the master cylinder i plugged the brake line holes on it with the plugs they gave me and i pumped the piston until it was really hard

To be quite honest with you, it doesn't sound like you did the master cylinder completely. To bench bleed the master cylinder, you need to go beyond just getting it really hard. Once you get it to that point you need to have the cover off and pump until it no longer puts out a single bubble in the fluid. You press until you see a bubble, relax, press again, relax, press again and keep repeating until you no longer get a bubble for several cycles. Generally the plugs supplied can't take the pressure. I use plugs made from an old set of lines with the end flattened over and then leave it plugged and full of fluid. Remove the plugs just before attaching the brake lines.

keep the reservoir full and work out any air that gets into the lines, (takes a lot of fluid), wouldn't hurt to have a couple of quarts on hand. Connect a hose to the bleeder with the other end so that it is below the fluid that you bleed out into a bottle or can, that keeps air from getting back into the line if pressure is released on the peddle. Better yet is to get a bleeder pump and **** the fluid through the lines while someone keeps the reservoir full. As long as you have clean fluid all the way back, you can put the fluid back in the cylinder. Do not put old fluid back into the reservoir. Your sequence for the lines was correct, but you didn't mention the front left side.

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[sbujtas]

To be quite honest with you, it doesn't sound like you did the master cylinder completely. To bench bleed the master cylinder, you need to go beyond just getting it really hard. Once you get it to that point you need to have the cover off and pump until it no longer puts out a single bubble in the fluid. You press until you see a bubble, relax, press again, relax, press again and keep repeating until you no longer get a bubble for several cycles. Generally the plugs supplied can't take the pressure. I use plugs made from an old set of lines with the end flattened over and then leave it plugged and full of fluid. Remove the plugs just before attaching the brake lines.

keep the reservoir full and work out any air that gets into the lines, (takes a lot of fluid), wouldn't hurt to have a couple of quarts on hand. Connect a hose to the bleeder with the other end so that it is below the fluid that you bleed out into a bottle or can, that keeps air from getting back into the line if pressure is released on the peddle. Better yet is to get a bleeder pump and **** the fluid through the lines while someone keeps the reservoir full. As long as you have clean fluid all the way back, you can put the fluid back in the cylinder. Do not put old fluid back into the reservoir. Your sequence for the lines was correct, but you didn't mention the front left side.

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i was kind of thinking i messed up with the master cylinder too because that was the only thing i hadnt done before. I dont have an old set of brake lines, do you know of anything else i could use to plug the master cylinder?

 

[Seabronc]

i was kind of thinking i messed up with the master cylinder too because that was the only thing i hadnt done before. I dont have an old set of brake lines, do you know of anything else i could use to plug the master cylinder?

Try a professional auto parts supplier, not one of the big box suppliers like AutoZone or Advance. You also might be able to find plugs at a plumbing supply or some place like Home Depot that have the same thread.

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PS The bench bleeding requires a lot of real hard pressing, to the point of pain, it's not fun. I use a large screwdriver pushing on the but end, it tends to hurt the palms of your hands.

Also, when bleeding the lines, you need to make sure you pull all of the old fluid out, air can be anyplace in the line and the only way to make sure that all the air is out is to **** enough to fill the entire line. Obviously the right rear will require the most.