88 GT brakes. (Page 1/2)
Tallguy68 JAN 12, 02:51 PM
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).]

fieroguru JAN 12, 05:33 PM
The rear pistons are too far from the pads.

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.
theogre JAN 12, 11:39 PM
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)

The Ogre's Fiero Cave

Tallguy68 JAN 13, 02:13 AM
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.
fieroguru JAN 13, 11:22 AM
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.
Tallguy68 JAN 13, 12:26 PM
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!
ceverhart JAN 15, 02:10 PM
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.
Tallguy68 JAN 18, 12:49 PM
Thank you ceverhart!

Just got to my weekend so I’ll be doing The Ogres manual adjustment. Hopefully 🤞 that will work. If not I’ll be asking where this valve is at!
Mickey_Moose JAN 26, 04:54 PM
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.

If that makes sense.

See this post: https://www.fiero.nl/forum/...02-2-101129.html#p22

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).]

theogre JAN 26, 11:41 PM

quote
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).]