I have a 88gt with the s10 booster. I have a had a issue with this s10 setup ever since I put it on a few years back. The system doesn't seems to have enough vacuum or power to run the brakes. The car also got rebuilt calipers all the way around at the same time and a new 88gt master cyl.
It has vacuum at the booster and I have even bought a vacuum tank for cars with big cams and have it plumbed in line. Nothing seems to help the pedal feels pressure like it has vacuum and then goes a little past that right after hitting the brakes. You really have to stand on it to get the brakes to hit hard enough to stop it.
I have had the system bled countless times thinking that was it but it never helped. this summer I swapped out the Booster again and had it bled on a machine at a brake shop. Same damn result.
I wonder if the adjustable rod should be adjusted further into the master cyl booster assembly. Any Ideas? There isn't any slop in the pedal . It just seems it doesn't have any braking force into you are already to the floor standing on it.
Is there any difference in running with the vacuum hose connected to the booster, and running with it removed (and plugged, for the sake of the engine)?
Are you still running 28 year old rubber brake lines at the calipers? has the master cylinder been rebuilt. not much else left if the caliper are free moving.
Is it the S-10 master cylinder as well, or has only the booster been swapped?
The S-10 master has a larger bore and would result in lower line pressures with the same amount of pedal travel, explaining your lack of braking power.
The Fiero bore is 15/16", and the S-10 bore is somewhere around 1.25." Just to give you an idea. Could explain your issue.
Did you get used booster? Any Dual Diaphragm can fail 1 diaphragm cause heavy pedal problems.
Booster w/ iffy check valve for vac line is a problem too.
The rest is brake system problems. Could be have bad rear pistons, etc.
------------------ 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)
Did the brakes work well before you changed the booster? If you wish an all new installation use Rodney Dickman's connector and this new brake booster that he recommends; http://www.summitracing.com/parts/tff-2232nb
------------------ " THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, HP Tuners VCM Suite. "THE COLUSSUS" 87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H " ON THE LOOSE WITHOUT THE JUICE "
To confirm you have a good vacuum supply buy and run a rubber vacuum hose from the engine brake booster port directly to the brake booster. Tie wrap it under the car temporary. If it then works well then you have a problem in the steel tube.
------------------ Rodney Dickman
Fiero Parts And Acc's Web Page: All new web page!:www.rodneydickman.com Rodney Dickman's Fiero accessories 7604 Treeview Drive Caledonia, WI 53108 Phone/Fax (262) 835-9575
Hook up a vac gauge to the booster line to see exactly what the vac is at. Do you hear a constant hiss from inside when you push on the brakes, not just when you first push it down but when you hold it down? And as orge said, did you use the same check valve on both boosters?
