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Brakes go to the floor...but still catch on??
#1
Ok so whole back story last year i changed my front manual drums to wilwood 4p disc with a hydroboost. So this system worked flawlessly absolutely no issue, till now. About 2 months ago the pedal started to feel mushy and at a stop light it felt like it lost pressure since the car will suddenly start going forward resulting in me having to put more pressure. thinking it was just air i drive it around for another 100 or so miles. So i did some suspension work and thought might as well bleed the system so i can get on it Big Grin ..except the pedal got worse Sad . Before it didnt sink to the floor but after i bled it, went straight down and barely caught on. at some point i was going down hill i couldnt stop so i pushed it a little harder and my rear drums locked up, but not my front disc. So ok i thought bad master cylinder. Well, i put in the master cylinder, new lines from master cylinder to prop valve, and bench bled the master as well as bleed all 4 brakes. guess what..still having the same issue Exclamation , but the brakes got a little less scary and better! yay! -_-.. So now that leaves me to the prop valve. did that go bad? how can i check? do i need to bleed it? it has never been changed. If it isnt the prop valve then the pedal might need adjustments, since it catches on but, late. if that makes sense. I am no mechanic or expert in brakes, any ideas guys?

1972 Satin Black Coupe, turns better than average, goes vroom with 303 RWHP.
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#2
Old rubber brake hoses can expand giving you that sinking feeling. How old are they?

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#3
Warped rotors or loose front wheels can cause the positions/pads to retract too far for a single pump of the pedal to be able to press the pads against the rotor.



“If you can't explain it simply, you don't understand it well enough.”
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#4
I didn't notice in your post ... Do you still have drums on the back ? If you do make sure to check for leaking wheel cylinders back there. I had the same issue with my 67 F100 when I converted to front discs. I kept thinking I screwed up the installation somehow. After going through all the possible problems the front brakes might have had, I finally went to the back and inspected everything. Wound up being a bad wheel cylinder on one of the back drums.
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#5
midlife;163446 Wrote:Old rubber brake hoses can expand giving you that sinking feeling. How old are they?

the rear hoses were replaced with steel braided hoses about 5 years ago and the fronts when i changed my front brakes

Don C;163458 Wrote:Warped rotors or loose front wheels can cause the positions/pads to retract too far for a single pump of the pedal to be able to press the pads against the rotor.

Hmmm. I am pretty sure they arent warped (i hope not Confused) i will have to check them out, but the wheels are one tight and torqued

phagan63;163477 Wrote:I didn't notice in your post ... Do you still have drums on the back ? If you do make sure to check for leaking wheel cylinders back there. I had the same issue with my 67 F100 when I converted to front discs. I kept thinking I screwed up the installation somehow. After going through all the possible problems the front brakes might have had, I finally went to the back and inspected everything. Wound up being a bad wheel cylinder on one of the back drums.

I'm sorry if it wasnt clear, but yes still drums in the rear. Did the leaky wheel cylinders cause brake fluid to waste?

1972 Satin Black Coupe, turns better than average, goes vroom with 303 RWHP.
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#6
phagan63;163477 Wrote:I didn't notice in your post ... Do you still have drums on the back ? If you do make sure to check for leaking wheel cylinders back there. I had the same issue with my 67 F100 when I converted to front discs. I kept thinking I screwed up the installation somehow. After going through all the possible problems the front brakes might have had, I finally went to the back and inspected everything. Wound up being a bad wheel cylinder on one of the back drums.

+1 on that. Had the same symptoms described in the original post
and it was a leaking rear wheel cylinder.

mike
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#7
oh dam;163478 Wrote:
midlife;163446 Wrote:Old rubber brake hoses can expand giving you that sinking feeling. How old are they?

the rear hoses were replaced with steel braided hoses about 5 years ago and the fronts when i changed my front brakes

Don C;163458 Wrote:Warped rotors or loose front wheels can cause the positions/pads to retract too far for a single pump of the pedal to be able to press the pads against the rotor.

Hmmm. I am pretty sure they arent warped (i hope not Confused) i will have to check them out, but the wheels are one tight and torqued

phagan63;163477 Wrote:I didn't notice in your post ... Do you still have drums on the back ? If you do make sure to check for leaking wheel cylinders back there. I had the same issue with my 67 F100 when I converted to front discs. I kept thinking I screwed up the installation somehow. After going through all the possible problems the front brakes might have had, I finally went to the back and inspected everything. Wound up being a bad wheel cylinder on one of the back drums.

I'm sorry if it wasnt clear, but yes still drums in the rear. Did the leaky wheel cylinders cause brake fluid to waste?

In my instance, yes it did because the fluid was leaking out of the cylinder. I didn't realize it until I actually crawled back there and looked and saw the back plate was a little damp. I think it's possible for them to leak internally without any obvious indication showing on the outside.
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#8
phagan63;163482 Wrote:
oh dam;163478 Wrote:
midlife;163446 Wrote:Old rubber brake hoses can expand giving you that sinking feeling. How old are they?

the rear hoses were replaced with steel braided hoses about 5 years ago and the fronts when i changed my front brakes

Don C;163458 Wrote:Warped rotors or loose front wheels can cause the positions/pads to retract too far for a single pump of the pedal to be able to press the pads against the rotor.

Hmmm. I am pretty sure they arent warped (i hope not Confused) i will have to check them out, but the wheels are one tight and torqued

phagan63;163477 Wrote:I didn't notice in your post ... Do you still have drums on the back ? If you do make sure to check for leaking wheel cylinders back there. I had the same issue with my 67 F100 when I converted to front discs. I kept thinking I screwed up the installation somehow. After going through all the possible problems the front brakes might have had, I finally went to the back and inspected everything. Wound up being a bad wheel cylinder on one of the back drums.

I'm sorry if it wasnt clear, but yes still drums in the rear. Did the leaky wheel cylinders cause brake fluid to waste?

In my instance, yes it did because the fluid was leaking out of the cylinder. I didn't realize it until I actually crawled back there and looked and saw the back plate was a little damp. I think it's possible for them to leak internally without any obvious indication showing on the outside.

what would be a way to check it? just remove it and inspect it?

goodnigh;163479 Wrote:
phagan63;163477 Wrote:I didn't notice in your post ... Do you still have drums on the back ? If you do make sure to check for leaking wheel cylinders back there. I had the same issue with my 67 F100 when I converted to front discs. I kept thinking I screwed up the installation somehow. After going through all the possible problems the front brakes might have had, I finally went to the back and inspected everything. Wound up being a bad wheel cylinder on one of the back drums.

+1 on that. Had the same symptoms described in the original post
and it was a leaking rear wheel cylinder.

mike

interesting. i think ill have to really check them out. This is scary and it sucks :/

1972 Satin Black Coupe, turns better than average, goes vroom with 303 RWHP.
  Reply
#9
oh dam;163437 Wrote:Ok so whole back story last year i changed my front manual drums to wilwood 4p disc with a hydroboost. So this system worked flawlessly absolutely no issue, till now. About 2 months ago the pedal started to feel mushy and at a stop light it felt like it lost pressure since the car will suddenly start going forward resulting in me having to put more pressure. thinking it was just air i drive it around for another 100 or so miles. So i did some suspension work and thought might as well bleed the system so i can get on it Big Grin ..except the pedal got worse Sad . Before it didnt sink to the floor but after i bled it, went straight down and barely caught on. at some point i was going down hill i couldnt stop so i pushed it a little harder and my rear drums locked up, but not my front disc. So ok i thought bad master cylinder. Well, i put in the master cylinder, new lines from master cylinder to prop valve, and bench bled the master as well as bleed all 4 brakes. guess what..still having the same issue Exclamation , but the brakes got a little less scary and better! yay! -_-.. So now that leaves me to the prop valve. did that go bad? how can i check? do i need to bleed it? it has never been changed. If it isnt the prop valve then the pedal might need adjustments, since it catches on but, late. if that makes sense. I am no mechanic or expert in brakes, any ideas guys?

There are rubber seals in the proportioning valve that wear and cause them to stick. Before I replaced mine I was not getting the proper amount of fluid to the brakes so sloppy brakes, just throwing this out as a suggestion.
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#10
oh dam;163645 Wrote:
phagan63;163482 Wrote:
oh dam;163478 Wrote:the rear hoses were replaced with steel braided hoses about 5 years ago and the fronts when i changed my front brakes


Hmmm. I am pretty sure they arent warped (i hope not Confused) i will have to check them out, but the wheels are one tight and torqued


I'm sorry if it wasnt clear, but yes still drums in the rear. Did the leaky wheel cylinders cause brake fluid to waste?

In my instance, yes it did because the fluid was leaking out of the cylinder. I didn't realize it until I actually crawled back there and looked and saw the back plate was a little damp. I think it's possible for them to leak internally without any obvious indication showing on the outside.

what would be a way to check it? just remove it and inspect it?

goodnigh;163479 Wrote:
phagan63;163477 Wrote:I didn't notice in your post ... Do you still have drums on the back ? If you do make sure to check for leaking wheel cylinders back there. I had the same issue with my 67 F100 when I converted to front discs. I kept thinking I screwed up the installation somehow. After going through all the possible problems the front brakes might have had, I finally went to the back and inspected everything. Wound up being a bad wheel cylinder on one of the back drums.

+1 on that. Had the same symptoms described in the original post
and it was a leaking rear wheel cylinder.

mike

interesting. i think ill have to really check them out. This is scary and it sucks :/

"what would be a way to check it? just remove it and inspect it?"
I'd start with the easiest and move toward the more complex. Get up under the car and behind the rear wheels where you can see the the back plate of the drum assemblies and look for any signs of dampness. If you can't, pull the rear wheels off and look from that perspective. If it still looks dry I guess the next step is to pull the drums themselves off and inspect each wheel cylinder. After that ... I'm not sure because I found my problem before I got that far. Good luck to you. Hope it turns out to be something simple.

I was just thinking some more about your problem and a question came to my mind. You said you converted from front drum to front disc brakes. I'm sure the conversion was done correctly but sometimes little things slip past us. Did that conversion include a new proportioning valve ? I didn't read anywhere in your original post if you had changed out the original distribution block with the proper proportioning valve. If by chance you didn't, this could be the source of your problems. Just a thought.
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