Magical Disappearing Brakes - 92 Mustang
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ok, here's what I did today/tonight::
-Started off my changin out the Combo valve with a different, cleaned valve....Bled system.... No Change
-Then compared the length of a Booster Push Rod to mine (6 3/8" long), then for fun, extended it out to see if I could tell a difference....Bled system... No Change
-Then bypassed the Combo valve all together.... Bled system.... No change
-Started off my changin out the Combo valve with a different, cleaned valve....Bled system.... No Change
-Then compared the length of a Booster Push Rod to mine (6 3/8" long), then for fun, extended it out to see if I could tell a difference....Bled system... No Change
-Then bypassed the Combo valve all together.... Bled system.... No change
How are you bench bleeding the MC?
Just to confirm, when the car iff, if you pump the pedal , it does NOT firm up and get hard as a rock and barely move?
If not, then you still have air in the system....i'd bet in the MC. What's your bench bleed technique?
Just to confirm, when the car iff, if you pump the pedal , it does NOT firm up and get hard as a rock and barely move?
If not, then you still have air in the system....i'd bet in the MC. What's your bench bleed technique?
hotcobra03
Active Member
brakes
very long post,,ill miss something like hissin50...
sounds like you have a piece from this than a piece from that....it sounds like your problem is fluid bypassing back....
things to look at..with drum brakes they must be fully adjusted and make sure parking brake lever/cable isnt frozen...if drum has been cut to far it too will cause problems...
on front calipers....look close at where they sit before and after you let off brakes...even upside down wrong side,
what happens if you just clamp off front brake lines and try brake when running?
very long post,,ill miss something like hissin50...
sounds like you have a piece from this than a piece from that....it sounds like your problem is fluid bypassing back....
things to look at..with drum brakes they must be fully adjusted and make sure parking brake lever/cable isnt frozen...if drum has been cut to far it too will cause problems...
on front calipers....look close at where they sit before and after you let off brakes...even upside down wrong side,
what happens if you just clamp off front brake lines and try brake when running?
I bench bled the MC by::
-Lightly clamping into a bench vise.
-Install MC Bench bleed kit. (three plugs that go into each port that have nipples on them to attach rubber lines to which go back into the top of the MC reservoir)
-Fill reservoir with brake fluid and make sure all three of the rubber lines are fully submerged in the fluid.
-I then started by depressing the inner "thingy" of the MC with a long screwdriver all the way in, then all the way back out, slowly.
-This was done until absolutely NO air was coming out of the lines into the reservoir. (i did this for about 40 minutes, no lie, just to make sure as much as possible was out of the "system")
When I pump the pedal with the car off, it does NOT get firm, it acts as if there is air in the system still. Which I know leads to symptoms off a bad MC. I have bad luck, but as I've stated before, I've been through 4 MCs already with no change at all. The one thats on there currently is a NEW unit from AP (which is a REALLY good hydraulics component company) and is Aluminum.
As far as my system bleed techniques. I start at the RR, then LR, then RF, then LF. But looking on Mitchell last night, apparently the factory recommended bled procedure is RR, LF, LR, RF... so i'm gonna try that today... But anyway, at each corner, i pump the brake pedal 4 times, hold it down while my buddy cracks the current bleeder, releases air and/or fluid, then closes it, and I repeat the process until only fluid comes out.
(At this point and time, i no longer get any air out of any line)
the drums are adjusted correctly and parking brake is not frozen. also, I mic'd the drums and they are within spec.
I haven't tried clamping off a line and tried the brakes yet. I can try that today.
--Ryan
Is it possible someone before you had some sort of petroleum based product in the system and all the rubber seals have gone south in the calipers, brake hoses and wheel cylinders?
Just trying to think of options..
Just trying to think of options..
Good thinking, but no.... I owned the donor car that all the V8 parts (rear end and calipers) came off of and I drove that car before it became the donor and the brakes and everything worked great on it.... wierd huh?
--Ryan
hotcobra03
Active Member
Good thinking, but no.... I owned the donor car that all the V8 parts (rear end and calipers) came off of and I drove that car before it became the donor and the brakes and everything worked great on it.... wierd huh?
--Ryan
was thinking ,,i cant see your bleeding as the problem,,,
in orig post you changed rotors.... are the 4 lug or 5? did you change spindles also...
came across this mustang brake upgrade ..cant answer what is the difference between spindles but depending on what you changed spindle would be changed in some cases...
79-93 4 Lug Ford Fox Body Mustang Brake Upgrade
hotcobra03
Active Member
brakes
if the link is right you need to change spindles
Front Brake Upgrades for 1979-86 Mustangs and 1987-93 4cyls:
To upgrade the brakes on the 4 cyl, pre-'94 V6 or 1986 and older GTs, you will need to upgrade the spindles and rotors. Consider if you are going 5 lug as the SN95 spindles would be the better option. Check my SN95 brakes page for help. If you want to stay 4 lug, then you will need the spindles and rotors from a 87-93 5.0L mustang to complete this along with new brake lines. Check this link for more info and all the parts needed.
i looked into bendix for a buyers guide no luck but did see the rotors are different in height,,,
your story on brakes hard with engine off than pedal fades ect,,,points to mc/booster..you changed that,,
now understand what a booster does...it takes your foot pressure of say 200 lbs and converts it to 10thousand lbs...
now as you are bleeding the brakes are clamping on and off..but to a lesser pressure,,,
you need to look good for something flexing or cocking.because once you use the booster the part moving will go further than you can push,causing very low brake,hence losing your pedal
its not an air thing its the amount of fluid needed during braking..
clamping off the front wheels will lower the amount of fluid moving as will the rear using less fluid..doing this the pedal should stay rock hard while running..which you go from there step by step
if the link is right you need to change spindles
Front Brake Upgrades for 1979-86 Mustangs and 1987-93 4cyls:
To upgrade the brakes on the 4 cyl, pre-'94 V6 or 1986 and older GTs, you will need to upgrade the spindles and rotors. Consider if you are going 5 lug as the SN95 spindles would be the better option. Check my SN95 brakes page for help. If you want to stay 4 lug, then you will need the spindles and rotors from a 87-93 5.0L mustang to complete this along with new brake lines. Check this link for more info and all the parts needed.
i looked into bendix for a buyers guide no luck but did see the rotors are different in height,,,
your story on brakes hard with engine off than pedal fades ect,,,points to mc/booster..you changed that,,
now understand what a booster does...it takes your foot pressure of say 200 lbs and converts it to 10thousand lbs...
now as you are bleeding the brakes are clamping on and off..but to a lesser pressure,,,
you need to look good for something flexing or cocking.because once you use the booster the part moving will go further than you can push,causing very low brake,hence losing your pedal
its not an air thing its the amount of fluid needed during braking..
clamping off the front wheels will lower the amount of fluid moving as will the rear using less fluid..doing this the pedal should stay rock hard while running..which you go from there step by step
I don't remember...is it possible to mount Fox calipers upside down, so that the bleeders aren't at the top? If so, they'll bleed, but they'll still have air trapped inside. It happens all the time on SN95 calipers but it's been a long time since I touched the fox ones.
This is an odd one.
The pedal not firming up when enine off makes me think that either their is air in the lines...or one of the hoses or seals are expanding or leaking.
Really digging into this. How are your lines plumbed? Line on bottom of mc direct to drivers front caliper. Other two lines to prop valve.....rear line to front brakes, front line to rear brakes.
Wish there was a way to remove then brake hoses and cap them to see if the issue can be isolated to the drums or the calipers.
The pedal not firming up when enine off makes me think that either their is air in the lines...or one of the hoses or seals are expanding or leaking.
Really digging into this. How are your lines plumbed? Line on bottom of mc direct to drivers front caliper. Other two lines to prop valve.....rear line to front brakes, front line to rear brakes.
Wish there was a way to remove then brake hoses and cap them to see if the issue can be isolated to the drums or the calipers.
On the prop valve, the Front line (closest to the radiator) coming out of the bottom goes to the Front Right line, and the Rear line (closest to the firewall) coming out of the bottom goes to the Rear Line.... Matching this diagram....
Obviously #3 isn't used in Fox prop valves... so just ignore that one. haha, and obviously again, my car doesn't have ABS.
Ok, so that is right.
If you are absolutely sure there is no air, I'd look for sources of expansion....brake lines, wheel cylinders, etc.
If you are absolutely sure there is no air, I'd look for sources of expansion....brake lines, wheel cylinders, etc.
hotcobra03
Active Member
Ok, saw some progress this weekend, but still not quite there. Friday, I swapped in yet another MC for a New unit. This time, I didn't bench bleed it at all, I just put it on the car, then immediately pressure bled the system. My thinking for replacing the MC yet again was I had a feeling that thru all the testing I had done (both methods of bench bleeding, plus pressure bleeding, changing Booster rod length, etc) I may have damaged other one. Anyway, I got the newMC on the car and everything pressure bled (still not running a Prop Valve)....
First Push of the Pedal = To the floor
Second Push = Just a tad up from the floor
Third Push = Up from the floor even more, starting to feel good
Fourth Push = Felt Great!!!
Not to get excited yet, I waited about two minutes and tried the pedal again.... Same thing happened (to the floor, then up a little, then felt better, then great pedal). So then we once again pressure bled the system thinkin there was still some air in the system. Got a LITTLE BIT of air out but that was it. we proceeded to pressure bleed the system about four more times after this with the same resulting pedal each time. Decided to put the Prop valve back in the system; no change.
What I'm wondering now is if there is air trapped in the lines that run along the firewall (being as they are higher that the MC).... but beside from pressure bleeding the system even more and goin thru even MORE brake fluid (been thru 2.25 Gal already), How I can get air out of the firewall lines? Unbolt the MC, raise it above the height of the firewall lines and pressure bleed again?
--Ryan
First Push of the Pedal = To the floor
Second Push = Just a tad up from the floor
Third Push = Up from the floor even more, starting to feel good
Fourth Push = Felt Great!!!
Not to get excited yet, I waited about two minutes and tried the pedal again.... Same thing happened (to the floor, then up a little, then felt better, then great pedal). So then we once again pressure bled the system thinkin there was still some air in the system. Got a LITTLE BIT of air out but that was it. we proceeded to pressure bleed the system about four more times after this with the same resulting pedal each time. Decided to put the Prop valve back in the system; no change.
What I'm wondering now is if there is air trapped in the lines that run along the firewall (being as they are higher that the MC).... but beside from pressure bleeding the system even more and goin thru even MORE brake fluid (been thru 2.25 Gal already), How I can get air out of the firewall lines? Unbolt the MC, raise it above the height of the firewall lines and pressure bleed again?
--Ryan
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