So two mechanics couldnt figure this out. My brake pedal takes *forever* to return and release the brakes. I have enough time to physically pull the pedal back with my foot and only then does the pedal release.

Both confirmed that the master cylinder is 100% operational (and a brand new same year S10 MC) and that system is fully bled, here are the details.


- This is the summit racing booster(90s S10)
- The brake pedal is returning incredibly slowly (more than 10 seconds) if depressed while the vehicle is running.
- The booster is brand new
- If the vacuum line to the booster is removed, the pedal returns instantly (just like normal)
- I replaced the vacuum pressure regulator going to the booster, it did not help
Anyone else have this issue? Any possible fixes?

Do you have vacuum to the booster ? Is the line collapsed internally?

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" 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, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite.
"THE COLUSSUS"
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" ON THE LOOSE WITHOUT THE JUICE "

I do have vacuum, otherwise the pedal wouldn’t behave normally with the line disconnected.

Vacuum source etc has little to do w/ this...

Is very likely the Control Valve in it that's you real problem.

You push the pedal.
Pedal puts that load in the booster and control valve keeping air pressure on the diaphragms. Fiero and most others are Dual Diaphragms Vac Boosters.
You hold pedal down for X time.
Then you release pressure and small spring(s) in the control valve slows or stops Air feed and allows vacuum back in on rear part.

If that valve is "bad" for any reason... This is 1 of Booster Failure modes.
Valve, pedal push rod, or both can be bad.
Make sure pedal bearing (the plastic bushings at top) and switches are not causing binding pedal. That might cause fake booster problems.

Do Not lube pedal bearings! They are installed Dry. If other have lube them, the bearing are junk and need new ones. Could use slightly bigger bushing and trim the slot area to fit.

Other more common failure is 1 of 2 diaphragms are bad and have a very heavy pedal.

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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.
(Jurassic Park)

The Ogre's Fiero Cave

I made sure that the switches and stuff were not causing it. So this means the brand new booster is bad? Bummer.

Same thing happened with the M/C..dang chineseium.

I didn’t cause it by letting the booster sit out for 6 months before install, did I?

Left out where?
If it got wet dirty etc then maybe.

Fiero OE booster have a boot etc on pedal side to keep out crap in front area because of big spacer/bracket riveted to pedal side used to fit.

Booster uses a lot of air every time you push the pedal.
Most times you won't hear it sucking because short distance of pedal, most time you push pedal slowly, road noise, and booster design.

roughly how they work...
https://www.youtube.com/watch?v=wbTUvp-tD5M

quote Originally posted by theogre: Left out where? If it got wet dirty etc then maybe. Fiero OE booster have a boot etc on pedal side to keep out crap in front area because of big spacer/bracket riveted to pedal side used to fit. Booster uses a lot of air every time you push the pedal. Most times you won't hear it sucking because short distance of pedal, most time you push pedal slowly, road noise, and booster design. roughly how they work... https://www.youtube.com/watch?v=wbTUvp-tD5M

I left it in the box for 6 months.

I might have just gotten a bad one..is there anything install wise that I could have done incorrectly to cause this?

I removed the old bracket from the fiero booster with a dremel, installed it on the new one, then installed this booster. I used Rodney Dickmans big booster install kit to hook it up to the pedal (here: http://rodneydickman.com/pr...php?products_id=350)

I just bought another booster, so I will see if that was the issue..

[This message has been edited by Threedog (edited 06-15-2020).]