I won't bore you with how we got here (Lord knows it's a long story) but let me catch you up to speed on what's going on. My '85 WILL NOT push brake fluid to the front calipers. Fluid flows freely through the lines. It will gravity bleed, and if you let it sit and accumulate fluid in the lines you can get one good bleed out of it before it goes back to pushing nothing out of the bleeder. This is of course after trying THREE separate master cylinders on the rig (more on that later). Fluid flows to the rear and the rears bleed just fine. The pedal will even start to build up some stiffness just bleeding the backs. But once you open the front for a bleed, pedal goes right to the floor. This is what we've replaced so far:
- all 4 calipers are now brand new cast ones from some Chinese company on amazon (ask me about my experience with remanned fiero calipers) - all 4 soft hoses - remanned power brake booster (had a friend insist this was the issue) - rotors, pads, all parking brake cables, though that's not really pertinent here - and finally, THREE separate master cylinders, two were remans and one (from the same chinese supplier as the calipers) claims to be new cast, but I can't find any difference between it and the remans - it looks and feels the exact same
We have taken off and blown air through all hard lines, fluid should be going through them just fine. Now, I will say, the OEM(?) master, the one that was on the car when I bought it, will push fluid to the fronts BUT there is a never ending stream of bubbles when bleeding it, makes me think a seal is bad in it because the rest of the system is leak free. It may also be of note that the original master seems to be a different metal, it looks different and is much lighter. Here's the original one:
In contrast, here's how all the ones I've purchased look:
And finally, here's what my current set up looks like:
The little blue thing is a stopper that blocks the prop. valve from closing off the front circuit, as that was an issue at one point.
That's about all I can think to tell you at the moment. Fronts just won't get fluid pushed through them. I've scoured this forum looking for others with this issue, but haven't been able to find one whose problem wasn't solved by replacing collapsed soft lines. My partner in this project/ pedal-jockey-bleeder-buddy will likely be lurking around this thread, and may even throw in his 2 cents, so look out for that. Other than that, I'm open to any and all suggestions at this point, cause I'm sure as hell out of both good and bad ideas.
This post is part of a series of threads in which I attempt to stumble my way through an (unintentional) complete brake overhaul on my 1985 Fiero. Check out the other episodes, if you're having a brake problem, chances are I've had it too!
I won't bore you with how we got here (Lord knows it's a long story) but let me catch you up to speed on what's going on. My '85 WILL NOT push brake fluid to the front calipers. Fluid flows freely through the lines. It will gravity bleed, and if you let it sit and accumulate fluid in the lines you can get one good bleed out of it before it goes back to pushing nothing out of the bleeder. This is of course after trying THREE separate master cylinders on the rig (more on that later). Fluid flows to the rear and the rears bleed just fine. The pedal will even start to build up some stiffness just bleeding the backs. But once you open the front for a bleed, pedal goes right to the floor. This is what we've replaced so far:
- all 4 calipers are now brand new cast ones from some Chinese company on amazon (ask me about my experience with remanned fiero calipers) - all 4 soft hoses - remanned power brake booster (had a friend insist this was the issue) - rotors, pads, all parking brake cables, though that's not really pertinent here - and finally, THREE separate master cylinders, two were remans and one (from the same chinese supplier as the calipers) claims to be new cast, but I can't find any difference between it and the remans - it looks and feels the exact same
We have taken off and blown air through all hard lines, fluid should be going through them just fine. Now, I will say, the OEM(?) master, the one that was on the car when I bought it, will push fluid to the fronts BUT there is a never ending stream of bubbles when bleeding it, makes me think a seal is bad in it because the rest of the system is leak free. It may also be of note that the original master seems to be a different metal, it looks different and is much lighter. Here's the original one:
In contrast, here's how all the ones I've purchased look:
And finally, here's what my current set up looks like:
The little blue thing is a stopper that blocks the prop. valve from closing off the front circuit, as that was an issue at one point.
That's about all I can think to tell you at the moment. Fronts just won't get fluid pushed through them. I've scoured this forum looking for others with this issue, but haven't been able to find one whose problem wasn't solved by replacing collapsed soft lines. My partner in this project/ pedal-jockey-bleeder-buddy will likely be lurking around this thread, and may even throw in his 2 cents, so look out for that. Other than that, I'm open to any and all suggestions at this point, cause I'm sure as hell out of both good and bad ideas.
Thanks, Doggo
dude double check that your master is pushing fluid. also those prop valve stoppers may or may not work on fieros. ive had various issues using them so try recentering the valve by leaving a rear bleeder open...at least youll know if the master cylinder is worth anything at that point because it should force fluid through the front. i had a similar problem with my 87 gt and the 84 (both had major brake issues when bought...) that turned out to be a suspect prop valve on both. one is using a 2 door s10 valve and the other is using a vette one (its what we had on the shelf and we have been looking for rebuild kits or prop valves that work as intended and its been hard. s10 seems ok though) only reason im using an s10 one is the master cylinder is litterally a fiero replacement one (fierostore sells them as a "big bore" so my thinking was eh good enough for now since the early s10s share the opposite weight balance but give that 70 percent to the fronts right before lockup (tested at 85 and down to 10 mph. that 84 is quite peppy with some tuning)
[This message has been edited by cartercarbaficionado (edited 03-15-2025).]
Yeah I would say that if all the other parts have been fixed/replaced several times, and your proportioning valve has had known issues, and had been modified to "fix" those issues, then that's probably what's causing your problem.
That "fix" is just a way to stop the prop valve from moving at all. We let the fronts bleed to nothing at one point so we would do one bleed and then the prop valve would get stuck forward. It wouldn't slide back on its own and needed to be manually pushed back if you want any fluid to find its way to the front. Now the prop valve is forced always open just until we get fluid back in the front so the system can self heal itself then we will take that lock out and put the sensor back in. (see pic)
I would also like to reclarify that we can push fluid out of the front with the master that was in the car when it was purchased. You can bleed over and over, but there is super small never ending never changing bubbles on both sides front. With the two new masters we can bleed once and push good fluid but then the pedal is dead for the next about 20-30 min. You can get it back faster if you bleed the backs but its still an ordeal.
Having the car on doesn't seem to help or hurt. I also put a vaccum gun on the front and holding it at 15 PSI for about a minute or two yeilds no results.
That "fix" is just a way to stop the prop valve from moving at all. We let the fronts bleed to nothing at one point so we would do one bleed and then the prop valve would get stuck forward. It wouldn't slide back on its own and needed to be manually pushed back if you want any fluid to find its way to the front. Now the prop valve is forced always open just until we get fluid back in the front so the system can self heal itself then we will take that lock out and put the sensor back in. (see pic)
I would also like to reclarify that we can push fluid out of the front with the master that was in the car when it was purchased. You can bleed over and over, but there is super small never ending never changing bubbles on both sides front. With the two new masters we can bleed once and push good fluid but then the pedal is dead for the next about 20-30 min. You can get it back faster if you bleed the backs but its still an ordeal.
Having the car on doesn't seem to help or hurt. I also put a vaccum gun on the front and holding it at 15 PSI for about a minute or two yeilds no results.
then your master cylinder isn't being properly used. its probably partially applied at all times blocking off fluid flow. its not unheard of.. find a rebuilt kit for the original if you still have it
dude double check that your master is pushing fluid.
Should have mentioned that while bench bleeding, all new masters seem to push fluid fine from the front circuit just fine. Seems I'm in the same boat as you with finding a working / rebuilt prop. valve for this car. That is to say, it's damn near impossible. Interesting about the master being "half applied" at all times, any idea what causes that? I'll probably end up getting a rebuild kit for the original master and see where that gets us. If nothing, I guess I'll have no choice but to jerry rig something up with a non fiero prop. valve. Any thoughts on prop valve delete entirely? I know I know safety safety blah blah blah but can it be done? As always, your insight is greatly appreciated.
Should have mentioned that while bench bleeding, all new masters seem to push fluid fine from the front circuit just fine. Seems I'm in the same boat as you with finding a working / rebuilt prop. valve for this car. That is to say, it's damn near impossible. Interesting about the master being "half applied" at all times, any idea what causes that? I'll probably end up getting a rebuild kit for the original master and see where that gets us. If nothing, I guess I'll have no choice but to jerry rig something up with a non fiero prop. valve. Any thoughts on prop valve delete entirely? I know I know safety safety blah blah blah but can it be done? As always, your insight is greatly appreciated.
most people swap to a Wilwood prop valve applied partially could be the pushrod being mis adjusted. also it will push fluid fine on the bench? could be not bled enough or the seals are bypassing seeing actual pressure. can you see any bubbles still coming out?
We usually stop the bench bleed a few pumps after no longer seeing any bubbles from either circuit. Admittedly it takes much less time than I anticipate (no more than 10 mins of pumping). I was always under the assumption that no bubbles means you’re good to go. Could it be as simple as not bleeding the master all the way through? Wouldn’t there still be bubbles if there were more air in the master? I suppose we could try just giving the thing a REAL GOOD like 30 mins of pumping. But that always seemed like overkill and I didn’t think such symptoms could be produced by trapped air in master. Also on the subject of rebuilding, try as I may I CANNOT find a kit/ new seals for this master. When I looked like a year ago I remember seeing them everywhere (fiero store, rock auto, autozone) but it now appears that they have magically vanished. Figures.
We usually stop the bench bleed a few pumps after no longer seeing any bubbles from either circuit. Admittedly it takes much less time than I anticipate (no more than 10 mins of pumping). I was always under the assumption that no bubbles means you’re good to go. Could it be as simple as not bleeding the master all the way through? Wouldn’t there still be bubbles if there were more air in the master? I suppose we could try just giving the thing a REAL GOOD like 30 mins of pumping. But that always seemed like overkill and I didn’t think such symptoms could be produced by trapped air in master. Also on the subject of rebuilding, try as I may I CANNOT find a kit/ new seals for this master. When I looked like a year ago I remember seeing them everywhere (fiero store, rock auto, autozone) but it now appears that they have magically vanished. Figures.
i forget if you can see into the bores on the fiero from the top and im too lazy to shovel snow off mine to go look. i belive they removed all kits after someone had a incident recently. it just sounds like theres a massive airlock or litterally 0 fluid flow to the fronts. ironically we had the opposite problem on my 87 and our 84
Originally posted by Doggo: Any thoughts on prop valve delete entirely? I know I know safety safety blah blah blah but can it be done?...
If that stock thing is indeed a proportioning valve, it's probably very unwise to eliminate it. You never know when you want your brakes to work to their full potential.
I'm one of the people who has installed a Wilwood proportioning valve but because I changed brake calipers and rotors. Note that its not a simple replacement. It means a lot of bending and flaring of tubing.
If that stock thing is indeed a proportioning valve, it's probably very unwise to eliminate it. You never know when you want your brakes to work to their full potential.
I'm one of the people who has installed a Wilwood proportioning valve Note that its not a simple replacement. It means a lot of bending and flaring of tubing.
Yeaaaah, it's probably not a good idea (not that the duke will go fast enough to get into a high speed collision anyway lol) but I'm really at a loss here and am kinda just throwing out ideas that have any chance of working.
On the prop. replacement, I've pretty much already ruled that out as looking into it, it looks far and away above my skill level anyway. Unless I can find a part out fiero and get another stock one, which at this point isn't off the table
[This message has been edited by Doggo (edited 03-17-2025).]
I have had issues like this myself, bought one of these type of vacuum bleed system and it made a world of difference and seemed to have solved my issue.
I have had issues like this myself, bought one of these type of vacuum bleed system and it made a world of difference and seemed to have solved my issue.
A vacuum bleeder is far superior to gravity bleeding or pressure bleeding.
I can't believe anyone even tries gravity bleeding. I thought it was a joke. You have to FORCE the air out(or force fluid in), vacuum is the only way to do that right(or use a pressurized fluid forcer thing). But seriously people, get a vacuum bleeder or don't bother.
Could you post a picture of your calipers? 1) When you installed the new calipers, you installed them with the bleeders up correct? I know when I did the Grand Am brake upgrade you have to swap the calipers right to left to point the bleeders up. 2) Have you tried putting the old calipers back on to see if they bleed? It would at least tell you if the calipers are the problem
I know when I did the Grand Am brake upgrade you have to swap the calipers right to left to point the bleeders up.
Ah yes, I remember reading your thread about the upside down grand am calipers. Multiple times, in fact. I’ve kid you not spent hours typing in different combinations of keywords into the search to find threads of people with similar issues, yours was one that came up frequently lol. As for my calipers, I can assure you they are on the right sides, left on left, right on right, all bleeders point up. Interesting point about trying the old calipers, we may have tried that, don’t quite remember. It will go on the list of checks to be performed if the vac bleeder that was suggested earlier in this thread yields no results. I can post a pic of my front and back calipers soon.
I can't believe anyone even tries gravity bleeding. I thought it was a joke. You have to FORCE the air out(or force fluid in), vacuum is the only way to do that right(or use a pressurized fluid forcer thing). But seriously people, get a vacuum bleeder or don't bother.
Yeah I’ve always been a bit skeptical about gravity bleeding myself. Can’t the bubbles like stick to the sides of pipes and hoses and just let fluid drip past? But plenty of old school DIYers and mechanics alike who know much more than I have vouched for its effectiveness so I’ve always tried to suppress my own doubts about it. I bought that vac bleeder that Mr. Moose linked a few posts ago, so here’s hoping!
Yeah I’ve always been a bit skeptical about gravity bleeding myself. Can’t the bubbles like stick to the sides of pipes and hoses and just let fluid drip past? But plenty of old school DIYers and mechanics alike who know much more than I have vouched for its effectiveness so I’ve always tried to suppress my own doubts about it. I bought that vac bleeder that Mr. Moose linked a few posts ago, so here’s hoping!
Yeah vacuum bleeders are great, except when you forget to add fluid to the reservoir, I've flushed the brakes on at least 4 cars, my Fiero twice now (removed cradle, rear lines were drained) no problems, just pump until the bubbles stop coming (and make sure the bubbles aren't just coming from the bleeder, and that's it! A vacuum bleeder has helped me with the clutch system, although every time I've done it it's been finished up by one person slowly pumping and one person opening the bleeder, except for the last time, with a dry f23 hydraulic throwout bearing, that surprisingly bled really easily, vacuum to get fluid to it, a few pumps of the clutch to get some fluid in it, then vacuum and some slow pumps to mostly fill it, then vacuum to get the last bubbles.
Sad to say that the vaccum bleeder we used did not help. It would only suck out little driblets and the fluid level in the resevoir had no notable movement, certainly not something we saw with our eyes. We had the same results with the resevoir cap on and off. The only time we had any notable fluid movement was when we pressed the pedal while the vaccum was on and as usual we only got the one push and then it was basically dead after that.
We did not try the backs as a control variable. The next step I think we should take is "bench bleed" through the prop valve since we know we can bench bleed straight out of the master. I really really really super hope there is some dumb giblet in there, but what blows my mind is that we have one master that whenever we put it on, it bleeds every caliper fine, but for the infinite microbubbles that never get better or worse in the fronts. The Master we are currently using is a newer one that will only push the fluid once through the fronts then its dead for at least 20 min.
Sad to say that the vaccum bleeder we used did not help. It would only suck out little driblets and the fluid level in the resevoir had no notable movement, certainly not something we saw with our eyes. We had the same results with the resevoir cap on and off. The only time we had any notable fluid movement was when we pressed the pedal while the vaccum was on and as usual we only got the one push and then it was basically dead after that.
We did not try the backs as a control variable. The next step I think we should take is "bench bleed" through the prop valve since we know we can bench bleed straight out of the master. I really really really super hope there is some dumb giblet in there, but what blows my mind is that we have one master that whenever we put it on, it bleeds every caliper fine, but for the infinite microbubbles that never get better or worse in the fronts. The Master we are currently using is a newer one that will only push the fluid once through the fronts then its dead for at least 20 min.
Your procedure is wrong. You should start at the farthest caliper from the MC(passenger rear, then driver rear, passenger front, driver front). It MUST be bleed in that order. Put a dab of grease on the bleed nipple so it makes a good seal with the vacuum hose. You need to be able to pull and hold a full vacuum BEFORE you open the bleeder(also some vacuum bleeders suck and don't work very well, confirm it actually works and holds a vacuum). There is also a way to force fluid through using positive pressure (ignore that it is on a tesla, the tool is the important bit) https://www.youtube.com/watch?v=GVEG3jhG6n0
I didn't every thread here but two things.... Did you 1. Check to make sure the master cylinder returns to its internal stop after being pushed?(take master off, push in and listen for positive clunk/click of the piston hitting the C-clip/stop) and 2. Did you measure the push rod length in relation to the mounting surface to be sure the piston is not being pushed slightly. It sounds like the piston is not coming back all the way and the "compensation port" is not getting uncovered so fluid is not allowed to refill the piston after a pedal stroke.
I didn't every thread here but two things.... Did you 1. Check to make sure the master cylinder returns to its internal stop after being pushed?(take master off, push in and listen for positive clunk/click of the piston hitting the C-clip/stop) and 2. Did you measure the push rod length in relation to the mounting surface to be sure the piston is not being pushed slightly. It sounds like the piston is not coming back all the way and the "compensation port" is not getting uncovered so fluid is not allowed to refill the piston after a pedal stroke.
Your procedure is wrong. You should start at the farthest caliper from the MC (passenger rear, then driver rear, passenger front, driver front). It MUST be bleed in that order.
Sorry, but your procedure is wrong. With a Fiero, due to the way the brakes lines are run, the driver's side rear caliper is the furthest from the MC.
2. Did you measure the push rod length in relation to the mounting surface to be sure the piston is not being pushed slightly
One thing I did NOT do was measure the pushrod length on the remanned booster before installing. Well, that’s not entirely accurate. We TRIED to measure it with the little H shaped tool but it wasn’t compatible with the size of either the master or the booster (don’t remember which). Now, to make myself look like a fool… when we couldn’t measure the pushrod length, my buddy (who keep in mind is a ASE certified tech) said “it’s probably fine” and we continued the installation. I trusted him because he’s done all kinds of stuff to his own car and like I said, literally went to school to become a mechanic. I had totally forgot about this little bit of information… needless to say the very next thing I will be doing is properly measuring the pushrod length.
I trusted him because he’s done all kinds of stuff to his own car and like I said, literally went to school to become a mechanic. I had totally forgot about this little bit of information… needless to say the very next thing I will be doing is properly measuring the pushrod length.
