I had what I presume were Grand Am brakes all around so I replaced the rear calipers and pads with stock Fieros so I could have a parking brake and pass inspection. Bled all 4 twice but still barely have brakes. It will stop but I can’t slam on the brakes and stopping distance is probably dangerous . Please help !!!

You sure you bleed the system? Have you checked for vacuum leaks on your booster?

I have a hand pump that I use to bleed my brakes, it works but you would be suprised how much air can get into a system.

You have to bleed driver rear, passenger rear, passenger front and driver front in that order. Somebody bled brakes with their parking brake on the other day and that does not work at all. If you have a firm pedal then you will not have max braking until the pads bed in.

[This message has been edited by wftb (edited 04-30-2018).]

So you have GA front, Fiero rear?

Therein lies your problem.....

I haven’t checked for booster leak. Not sure how to do that , but Olejoedad says having GA fronts and Fiero backs is a problem. Any idea why that combo won’t work ?

Do you have new hoses?

Probably because the larger front brakes to the rears isn't proportioned correctly with mismatched parts, the car may become unstable in a high speed braking senereo and loss of control may result. This is just a guess, others with more knowledge may want to chime in on this.

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"Discord"
Red 1988 GT under restoration!

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It could be due to a mismatch in the size of the caliper pistons between front and rear calipers, the volume of fluid needed to move all four pistons, the proportioning between the front/rear brakes.

In your case, however, you actually decreased the size of the rear caliper pistons, so my initial thoughts may be off track.

How were your brakes before swapping to the Fiero rear calipers?
Are you still using the stock Fiero master cylinder?
Did you adjust the ebrake levers to come in contact with the rotor when you installed the rear calipers?

If you problem started after you swapped to the stock rear calipers, you did not bleed the system properly.

After checking out vacuum hoses ,I found one near the cruise canister that had a huge crack. Fixed that and the brakes seem 100% better and idle is so much better. Could the vac leak have been the brake problem ?

quote Originally posted by olejoedad: Did you adjust the ebrake levers to come in contact with the rotor when you installed the rear calipers?

Yeah, my guess is that the parking brakes weren't adjusted properly for each rear caliper prior to the bleeding procedure.

[EDIT] You posted while I was posting.

quote Originally posted by Blmkso: Could the vac leak have been the brake problem ?

I suppose so, but IMO if you were pressing the brake pedal hard enough (even without vacuum assist), you still should've been able to stop the car fine.

quote Originally posted by Blmkso: Bled all 4 twice but still barely have brakes.

[This message has been edited by Patrick (edited 04-30-2018).]

Patrick , when you say adjust ebrake till contact with rotor , do you mean when adjusting the pads , they should actually touch the rotor or the ebrake caliper arm touches the caliper ?

quote Originally posted by Blmkso: After checking out vacuum hoses ,I found one near the cruise canister that had a huge crack. Fixed that and the brakes seem 100% better and idle is so much better. Could the vac leak have been the brake problem ?

Yes, see below.

quote Originally posted by Patrick: I suppose so, but IMO if you were pressing the brake pedal hard enough (even without vacuum assist), you still should've been able to stop the car fine.

Back in 2012 I did some data collection using an air cylinder to apply consistent brake pedal pressure and measured the brake line pressure with and w/o vacuum assist. https://www.fiero.nl/cgi-bin...1747&style=printable

The applied pedal force at 60 psi air pressure was about 100 lbs.
W/o vacuum assist the line pressure was 475 psi
With vacuum assist, the line pressure was 1475, or 3 times higher.

So to overcome the loss of vacuum assist, you would need to apply 3 times the force at the brake pedal...

Blmkso
If your sure you bleed the brakes... Caution: See my Cave, Bleeding MC notes
you read old post and likely PM but did you read my cave?

See my Cave, Brake Upgrade
In short...
GA front brakes and big MC Will make OE rear brake very weak.
Big MC w/ All OE Fiero brakes Will make the brake very weak.
Either can/will cause very long brake distances.
In first the rears to very little to nothing to stop the car. Second case all wheels do less to stop.
"booster upgrade" might hide this to your foot but you still have same problem(s).

If the PO messed up or switch the Combination Valve to screw w/ Prop Valve then expect more problems. But often won't make the brake very weak unless they really screwed up. Look for tool marks or mods on prop valve section etc.

If you replace MC too and now you have "low pedal" problem then likely Rear piston(s) have not self adjusted.
Many rebuild units can be bad right out of box and won't self adjust. If true then return it/them.
Read entire brake section start w/ Rear Brakes

Brake Booster problems will make a hard to a very hard pedal.
If you can't push the pedal easy then have vacuum problems and/or booster failure.
Vacuum can be plugged anywhere in the line. You should easily blow into the line w/o engine on. (87/88 Does Not use a booster vacuum filter in the engine bay so one less problem.)
Vacuum leaks should cause high idle but not always. See my Cave, Vac Leaks
Booster is 2 stage type w/ 2 diaphragms and common to have 1 fail and not the other cause a harder pedal. Total fail is close or same as pedal effort w/ engine off. IE total fail often need two feet to push the pedal and even then very hard to stop.

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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.
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The Ogre's Fiero Cave

[This message has been edited by theogre (edited 05-01-2018).]