Just replaced all four calipers with Fiero Store rebuilds, replaced brake lines with braided ones and completely flushed fluid and replaced with new stuff. Car had been sitting for awhile when I bought and fluid was gross.
Got it all back together and went for test drive. What’s happening is soft pedal, pump, little stiffer, pump, normal, pump, back to almost the floor. During the stiffest pump brakes engage. It’s a continuous three pump cycle with the brake warning light coming on throughout the process. I figured there’s still air in the line so bought a new vacuum pump as I didn’t trust the one I had and bled the brakes again. Same issue. No sign of leaks.
Further details: had missus pump the brake while I watched what is happening. Pads engage the rotor to stop (at least won’t turn by hand) but piston completely retracts. I have new parking brake springs, but have cables loosened till I get the brakes working right, then planning to adjust. Also, before I installed I used pliers to pump the parking brake lever just to make sure the piston moved. They did and I turned them to fully retract before reinstalling.
I’ve gathered stuff to do The Ogres (man, that guys awesome!) manual adjustment but he says they should auto adjust and needing to do indicates other problems. And I’m feeling there are other things creating problem. So before I start throwing parts and time at these things, I want to figure out what the actual problem is.
[This message has been edited by Tallguy68 (edited 01-12-2023).]
You can validate this by placing a 2" diameter fender washer between the pad and the piston or the pad and caliper (don't drive it with the shim, just install it, start the car and check pedal firmness) - the soft pedal will become firm.
You need to adjust the pistons so the pads are closer to the rotors, proper gap is about the thickness of a playing card. If your auto adjusters in the pistons are still working, you can cycle the parking brake lever to push the piston out several times and check for any movement from the retracted position. If that doesn't work you can rotate the pistons, but you might need to remove the lever arm from the back and sping the whole assembly.
If you have Rebuilt Rear brake(s) that Do Not self adjust... Then the "Rebuilt" job was done wrong and doing any manual adjustment including the cave page won't help. Manual Adjust May seem to work but pads wear down in a few days to a few weeks and back to "square one."
Worse. Often seem to work longer to many but rears have too much gap and other problems and the Rotor will have problem too or Rear can drag a pad causing brake failure or a fire.
Many "Rebuilt" "Fiero" rear calipers also reuse or "rebuilt" the piston. (Same piston design has been used in other models.) Either have big problems. GM didn't make these to fix, only replace them. Even GM Dealers never got parts from GM for Rebuilding this.
Hope you didn't return the cores...
------------------ Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should. (Jurassic Park)
These are my original calipers I sent into the Fiero Store for rebuild. Unfortunately there isn’t much of an option for 88 rear brakes. I looked everywhere for calipers, rebuild kits, anything. This was the only option I could find.
So even if I do th manual adjustment I’m screwed? What exactly is failing that won’t allow them to self adjust? Is there anything else that could possibly be the problem? I mean, I’d like to get my $350 bucks back from the Fiero Store if I can determine if it’s bad rebuilds. If it is the calipers, then what are my options? I can’t believe these 88’s could be such a headache! Looks like even the master cylinder will be a problem to replace if I ever need to.
The next step at this time is to try adjusting the piston position. Everything Ogre has listed are potential issues, but unfounded until you test and figure out they are actual issues.
Every caliper change on the rear of a Fiero needs to have the piston clearance checked/adjusted as part of the process. This is the same for all years of Fieros, it isn't just an 88 thing.
That’s pretty much my plan. Printed out The Ogres how to instructions, got sheet metal to make the shim and will be following it to a T and we’ll see what happens!
Just another thought...years ago I had a similar problem...car running- had soft pedal and felt like "air" in lines...bled over and over issue continued. When the car was off I would have a good/ hard pedal... start car and it would go soft again....Observation led me to see I had functional fronts but little to no rear brakes...I bought new rears and swapped. Issue continued. In my case issue was the proportioning valve......replaced with one off a parts car and had brakes after bleeding one last time....this was on a fiero that had set for couple of years with engine issues...Brakes worked when parked.
If it does not self adjust (the gap closes up) then it is s a problem with the inner piston not functioning properly - I suspect the shaft for the inner piston it is not allow to rotate freely inside the inner piston when the parking brake lever is retracted. The inside of the piston and the shaft for the parking brake are a worm gear type assembly that allows the inner piston to walk closer to the rotor and closes the gap, but still allows the pad to retract a preset distance when everything is released. The shaft basically ratchets the inner piston out.
Someone also posted a thread of a complete teardown of the piston and using a f-body seal on the internal piston, but I can't find that thread right now.
[This message has been edited by Mickey_Moose (edited 01-26-2023).]
Originally posted by Mickey_Moose: If it does not self adjust (the gap closes up) then it is s a problem with the inner piston not functioning properly - I suspect the shaft for the inner piston it is not allow to rotate freely inside the inner piston when the parking brake lever is retracted. The inside of the piston and the shaft for the parking brake are a worm gear type assembly that allows the inner piston to walk closer to the rotor and closes the gap, but still allows the pad to retract a preset distance when everything is released. The shaft basically ratchets the inner piston out.
Lt Blue is about Correct. The rest not so much...
P-brake Screw Threads are cut so act as a Cam to activate and deactivate the P-brake function. This actually seems to work. The Driver Using the P-brake has very little or Nothing to do w/ self adjusting!
Problem here is inner and outer pistons have binding/frozen and the Hydraulic section won't self adjust as covered in my Cave, Rear Piston notes This needs the P-brake screw threads to work too but those threads isn't the problem. Note that the patent image is Not actual size of many parts. Actual Inner Spring has only a few mm to work before has coil crash. (Somewhere here are pics showing this. Not searching right now.)
Worse, When the pistons are "Frozen" and Hydro is used then the screw and tube (Orange part in cave page) compresses inner spring "to death" and often blows out the back (Big Brown part in cave page) of the piston set. Then people may push the piston in doing brake job and in turn compress the back cover and weaken the cover so easier and easier to blow out again.
Again. Any Manual method to adjust is crap and won't help except maybe a very short term. Including the cave and GM TSB is based on. And cave said If it "Helps" the calipers are "Dead."
"Just use the P-brake," "Follow GM doc's," and more is 100% Wrong this time. P-brakes was never made to be an "adjusting tool" no matter what GM said after the Brake Recall covering Fiero and several other model lines. Those BS statements that NHTSA allowed that directly contradicted FMVSS 571.105 require all hyrdo brake to be self adjusting without driver actions. This "Recall" and many others give carmakers the easy and cheapest fix for whatever problem. This is Why only Manual Transmission cars had this Recall because GM and NHTSA thought the Auto Trans Park Pawl is enough to hind this problem.
Complicated rear disks and problems with them happen to GM Porsche and others are part of Why Rim Size for Tires are now 16" 17" and bigger so can easily fit Disk-Drum rear brakes in many vehicles now. Simple Disk for Hydro Brakes same as Front w/ Drum for P-brake and no need for auto adjust parts that fail use in other w/ Full Rear Disk and Drum brakes. Many Full Drums, Front or Rear axles, try to self adjust every time you back up by a cable and arm ratcheting a screw that have 50+ years of problems. (howstuffworks and other had good animation but in Flash now dead even if found on archive.org etc.)
[This message has been edited by theogre (edited 01-27-2023).]
1) Go look at your rear calipers. Are the brake pads in contact with the rotors? 2) If so, then your problem is probably elsewhere: master/slave or air somewhere. 3) If the pads are not contacting, it's telling me your rebuilts are garbage. No rebuilders I know of rebuild the internal piston, not the Fiero store, not calipers online, especially not the local auto store. They change the other seals but not the piston seals since they can't get that seal anymore. You likely wasted your money since they didn't rebuild the piston which is the biggest problem area for 88 rears.
I don't believe new rear pistons available anymore.
I have seen 88 rear piston rebuild kits with the new piston seal for sale on ebay a year or so ago, but they weren't cheap. Not sure if they're still on there.
As an update, I did The Ogres adjustment over my weekend and been test driving around my neighborhood to test. I’ve got a pretty good little circle that I can do a test that includes freeway and in city and be only a mile or two from a safe port.
So far, the car stops and the parking brake works. Yeah! But….. the brakes don’t lock up. It stops good, and within a safe distance, but I would expect wheels to lock if I stomp hard? I want to put a few more miles testing, then I’ll jack it up again and see what it all looks like, get the missus to pump the brakes, see how they’re working.
The gist I’m getting from all of the rebuild and parts posts is that if the calipers don’t function properly, we’re kind of screwed. So if turns out the calipers are shot, and there are no parts available there’s one more question. One that might need its own thread?
What are the options to get functioning rear brakes? I have read that people have put front calipers on the rear out of frustration, but as this is a 5-speed, I kind of need that parking brake.
⚠️ Warning: Do Not put Front calipers on the Rear Axle. This is 100% Illegal in most states and many other countries. Including most US States w/o inspections or poor inspection that doesn't actually look/test for missing/bad P-brake parts. Driving a vehicle w/ "Cheater Fixes" and other Illegal Mods Can and often does go very bad after a wreck and you get sued etc.
As to "Locking the wheels" while braking... Fronts can/will lock up depending on road surface, tires, and more things. Rears almost Never lock on most pavement types. Can lock on wet roads, sand and other dirt on roads, etc. but harder to lock even then unless you Drive Too Fast for Road Conditions also Illegal w/ big Fines and Points.
GM and most others will try to never lock the rears because can easily spin out and worse. That's All vehicles without ABS, TrackCon or other computer controlled braking. And even before Nader "Unsafe at any Speed" crap book.
Is a function of the Proportion Valve (Often part of Combination Valve for cars.) and brake bias covered in my Cave, Brake Upgrade But 88 Fiero is "unique" in bad ways because have near 0 to No System Bias except the prop valve. Meaning if the Prop Valve fails then is a "ticking time bomb" waiting to spin out w/o warning because Rear Brakes Will Lock at "Random." Nearly all DOT Legal vehicles from car makers have Bias built into them with Front brakes made way different to the Rear so Prop valve often does nothing for most braking.
Back to the e-brake. In order to understand how the e-brake works, one has to understand how the master cylinder works. There are effectively three pistons in the master cylinder; the front brake piston, the rear brake main piston and the rear brake quick take-up piston. The front brake piston is farthest forward, the rear brake main piston is in the middle and the quick take-up piston is in the rear. The first two are in the small diameter of the bore and the quick take-up is in the large diameter of the bore. The front brake piston has a spring and the rear brake main piston has a spring. The front piston spring is weaker than the rear brake piston spring. The rear brake main piston telescopes over the front brake piston. The front brake piston and rear brake main piston have cup seals that seal in one direction but can pass fluid in the other direction similar to a check valve. The quick take-up piston has an rear o-ring that seals in both directions.
When the brake pedal is applied the brake booster presses on the end of the piston causing piston to move forward. The front brake spring compresses and fluid is compressed to start applying the front brakes. There is initially little compression of the rear brake main cylinder spring and therefore little pressure is applied to the rear brake lines. After sufficient pressure builds in the front brake system then the rear main cylinder spring compresses and the rear brake main piston starts applying pressure. The fact that the springs have different are spring rates, I think creates some front/rear brake bias.
Now to the quick take-up piston. This piston communicates with the rear part of the brake reservoir on the master cylinder. There is a small black plastic device in the bottom of the reservoir held in by a circ clip. The best way to think about this device is that it is both a spring loaded pressure control valve ( I cut one apart and there is a spring) in parallel with a check valve. When the master cylinder piston moves forward, fluid flow up through this device and the pressure is controlled to a few psi. Fluid flows past the rear cup seal of the rear brake main piston and a few psi of pressure is applied to the rear brake lines. The geyser of fluid in the rear reservoir that happens when the brake pedal is pushed is the excess fluid being relieved by pressure control valve to regulate the pressure on the rear brake lines. If the calipers are in good shape this is sufficient pressure for the brake pads to lightly contact the rotors. When the master cylinder piston retracts, fluid flows from the back reservoir (the device now acts as a check valve) to fill the space created by the retracting piston. Light pressure is held on the rear brake lines because there is no way for fluid to get past the cup seals for the rear brake main piston. I know this is true because the pressure control valve got plugged or by some other means became blocked. So when the pedal was pushed lots of pressure was applied to the rear brakes and there was no way to relieve it. There was virtually no free play in the pedal. The pedal force was very hard. The car felt like there were no front brakes. The rear brake were locked on and I warped the rear rotors and had a caliper catch fire from a fluid leak in a 7 mile drive. Upon checking there was no geyser in the master cylinder rear reservoir when the pedal was pushed. Replacing the master cylinder solved the problem.
The quick take-up feature of the master cylinder should make the rear brakes self-adjusting. However if the caliper pistons have a tough time moving in the bore then the light pressure applied by the quick take-up cylinder may not get them to move. Then is becomes necessary to manually adjust the emergency brake by taking the lever off and rotating the screw. Pumping the pedal should get the rear pads in light contact with the rotors. If that doesn't happen something is wrong.
Also the rear brake system has to be hydraulically tight for the emergency brakes to work. When the emergency brake lever is rotated the pads will push on the rotor. At the same time the caliper piston is trying to push fluid back to the master cylinder. If there is any air in the line, the air will be compressed and the emergency brake will not hold. If the cup seals for the rear brake main piston in the master cylinder leak, then the e-brake will not hold.
------------------ formerly known as sanderson 1984 Quad 4 1886 SE 2.8L 1988 4.9L Cadillac 1988 3800 Supercharged
Originally posted by sanderson231: In order to understand how the e-brake works, one has to understand how the master cylinder works.
No you don't and rest of that has problems. Mainly you had two or more problems and while Iffy/bad MC can affect the rest, the failure of rear self adjust isn't related.
1. Quick Take-up section affect Both circuits Before each contact and clamps the rotors. Has little to do w/ auto adjust the calipers on either axle. It Can't add Fluid Volume to the Fronts but pushes that section faster when Not @ Working Pressure. 2. The MC rear "geyser" is overflow for QT section. W/o the valve releasing QT Pressure when the function is done, you have a very hard pedal, so hard you often can't stop the car. See my Cave, Quick Take-up notes with pictures of QT "check valve."
QT MC was originally design for Front Disk w/ High Clearance Calipers. "Minor" changes to Main Seal to allow it to Distort more under hydro load to pull pistons more to give better MPG. (Because Even Tiny Fractions of 1 MPG can affect CAFE Points from US Gov that helps or hurts GM and others Bottom Line to the tune of Hundreds of Millions to Billions of $.) GM used QT MC "backwards" to help "Fiero Type" rears to work "better."
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The quick take-up feature of the master cylinder should make the rear brakes self-adjusting.
Maybe but often Not. 4 ref: Front self adjust anytime a piston is push out more then main seal distorts then seal only return to rest and only return the piston a tiny bit. Can happen during QT but needs Full Hydro Pressure to Fully self adjust.
Rear self adjust as shown in Cave and often happens After QT is Done and just Before Main Hydro is @ Full Pressure to stop the car. WHEN the two pistons fail to do this then have big problems that can cause warp rotors to brake failure and even fires. Manually Adjust the Rears, even if they seem to work for now, will cause same problems.
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Also the rear brake system has to be hydraulically tight for the emergency brakes to work. When the emergency brake lever is rotated the pads will push on the rotor. At the same time the caliper piston is trying to push fluid back to the master cylinder. If there is any air in the line, the air will be compressed and the emergency brake will not hold. If the cup seals for the rear brake main piston in the master cylinder leak, then the e-brake will not hold.
No. While you push the pedal to help you when applying the P-brakes per Owners Manual in Fiero and some w/ same rear brakes... The P-brakes Do Not use Hydro to Work nor does it put any pressure in hydro side. In Fiero, Equalizer holes built into working bore of MC and QT "Check" Valve stops this from happening.
The screw and "nut" (Orange) pushes Both pistons into the pads by Total Mechanical action via the tapper between inner and outer pistons.
No vehicle is allowed to use Hydro as part or all of P-brake function as directed in FMVSS 571.105 and 571.135 for newer cars, after ~ 95 model year. GM w/ NHTSA "Blessing" made false statements for a brake recall that blame owners for don't using P-brake to adjust the system etc just made more problem in the end.
While DOT FMVSS only test P-brake as P-brakes for a Parked Vehicle... If Fiero and many other hand or foot operated P-brake works, You can use them as "Emergency Brakes" to Stop a car if the Hydro has completely failed. Will take a lot longer like shown in many owners manuals but will stop you. Unlike nearly all Electric P-brakes on new cars that won't activate when vehicle is moving, have electric problems, etc.
Is Also Why can't use "Line Locks" as P-brakes because Hydro Parts Will Leak down enough pressure to let a car move and often hit things or people. This is 100% Illegal in many places and even if "legal" for given State, many Car Insurance Co can void the policy for this crap and/or expect to get sued after a wreck.
[This message has been edited by theogre (edited 02-02-2023).]
