My brake pedal on my 87GT is spongy even after a thorough bleed ( and some time running) and its probably time to change the master cylinder. I would like to use the S-10 master cylinder to go with my S-10. Looks like it will bolt on and uses the same size brake line fittings. This is a larger bore master cylinder and w the S-10 booster figure that the higher capacity May provide better braking action. Anyone try this? If so what were the results?
------------------ " 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" 87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H " ON THE LOOSE WITHOUT THE JUICE "
[This message has been edited by Dennis LaGrua (edited 09-18-2020).]
A larger bore will lower the line pressure. Pline=Fin/Amc With the same pedal force your line pressure will drop. As your line pressure drops the force your pads apply to the rotors will drop, since: Fpad=Pline*Acal
I had a larger bore MC, but with bigger calipers than stock.
I like the feel that the bigger bore MC gives; it gives a stiffer pedal that feels more expensive. Less cheap and flexible.
More pedal force is needed to stop the car, but that brings the braking feel towards the sports-car end of the spectrum, and away from the one-touch lock the tires CUV feel.
After such a modification, make sure that you or whatever other probable driver (spouse?) has the necessary leg strength to threshold brake the car.
Hey Dennis, I have tried that master cylinder and booster combo. I have larger calipers on all four corners and it works great. Very nice brake feel. Cheers
Hey Dennis, I have tried that master cylinder and booster combo. I have larger calipers on all four corners and it works great. Very nice brake feel. Cheers
My Fiero has standard calipers. While I feel that the far lower cost S-10 master cylinder would work nicely, I just played it safe and ordered a new AC Delco unit. ($130 from Summit Racing Equipment) I believe that the Fiero MC bore is .944" while the 2000 S-10 pickup /BLazer is 1" -nearly identical. That would result in about the same braking pressure. The advantage is that the S-10 Master cylinders are about 1/4 the price of the Fieros.
Good move! I tried this change you were thinking of doing... It Does NOT work after the change you would need to almost STAND on the brakes to make the car stop. Went back to the original size for the car and all is well. A change to the larger brake booster would be a better choice.
Using a larger master with stock fiero calipers is a very bad idea... it is a brake downgrade as it will result in lower line pressure = lower clamp force = lower braking force.
Most who have done it with OK to favorable results did it in combination with calipers with a larger piston area. They still have the same lower line pressure (result of the larger master bore) but this lower pressure over a larger than stock caliper piston area allows the caliper clamp force to be the same or higher than stock.
Never mix and match brake components unless you have done the math to know the results you should expect.
Originally posted by pmbrunelle: ...assuming that braking_force/pedal_force is the metric you wish to maximize.
There's a range of workable gains; I wouldn't set the factory gain as a hard lower bound.
I am merely stating that if you swap in a large master assuming all other things being equal the car will stop better with the same pedal effort, you will be woefully disappointed. The car will either take longer to stop or require more pedal effort to stop the same.
During my quest for superior braking performance, i tossed a S10 master in my fiero because my buddy had a autozone warranty for them. I can still easily lock up all 4 at any speed, and I get a little better modulation now. I'd say it was an upgrade although it did slightly increase my pedal effort and shorten my throw which makes for a little better heal toe braking.
Originally posted by fieroguru: I am merely stating that if you swap in a large master assuming all other things being equal the car will stop better with the same pedal effort, you will be woefully disappointed. The car will either take longer to stop or require more pedal effort to stop the same.
Yes, is Basic Hydraulic 101. "Big MC" puts out Higher Volume and Lower PSI vs Fiero Factory Installed MC And will to this w/ stock And any "upgrades."
You install "big MC" to address Bigger Pistons that need More Fluid Volume on GA and other "Upgrade." Not to give you a big boost in line pressure.
------------------ 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)
All I know is that I have 2 88s, One previous owner installed the S-10 Booster and slotted rotors, the other is completely bone stock except for the new pads and rotors I put on it. The one with the S-10 booster locks the wheels up with ease. The stock system takes a LOT of effort to do the same.
[This message has been edited by 0z (edited 09-24-2020).]
All I know is that I have 2 88s, One previous owner installed the S-10 Booster and slotted rotors, the other is completely bone stock except for the new pads and rotors I put on it. The one with the S-10 booster looks the wheels up with ease.
Does your car have the S-10 Booster with the S-10 MC?
Like Ogre says, larger bore = lower line pressure which means you have to use higher brake pedal effort to get the same pressure as you get with the OEM MC and brake booster. The S-10 Booster provides a good bit of additional "oompf" with the original master cylinder. Using it and a S-10 master cylinder may help with the pedal effort. Maybe Ogre has an opinion about use to the S-10 booster / MC combination on Brake upgrades.
BTW, I've got and S-10 Booster and Wagner TQ pads on my one of my '86 GTs and it stops a lot faster than the one with the stock booster.
Originally posted by 0z: All I know is that I have 2 88s, One previous owner installed the S-10 Booster and slotted rotors, the other is completely bone stock except for the new pads and rotors I put on it. The one with the S-10 booster looks the wheels up with ease. The stock system takes a LOT of effort to do the same.
Very Likely something is wrong w/ you "all stock" car. Any Vacuum booster can have 1 or more problem affecting brake performance on top of whatever else maybe wrong and w/o a clue saying use big booster means bloody little.
No-one should compare non-ABS to ABS. ABS systems often way over boost the brakes to the point that even small kids can push the brake and let ABS box to handle wheel skid problems. Problem is many ABS systems still have problem even on Dry Pavement like ABS "trips" when brake and turn and even at low speeds.
Just a heads up . After all the discussion I decided to play it safe and just replace the master cylinder with a stock part. I went with a new AC Delco unit and I purchased it from Summit Racing Equipment, a reputable dealer, so I'd get the real Delco part and not the counterfeits that are sold on eBay. I paid a premium price $130 shipped but when it comes to brakes whats your life worth?. The best part is that this master cylinder is Made in the USA and its stamped right on the bottom of the unit. If you decide to buy this master cylinder it is sturdy cast iron not aluminum. Installation was a 30 minute job. Pedal is no longer spongy but I will again bleed the calipers to insure best braking action..
[This message has been edited by Dennis LaGrua (edited 09-26-2020).]
