Manual brakes (booster elimination) (Page 1/2)
Craig71188 NOV 25, 08:13 AM
A search turned up no reference, but has anyone eliminated the brake booster and gone to a manual brake set up? I know how to do the math for bore sizing, etc., but just looking for anyone that has done it and their driving impressions. This is for a dedicated race car. Removing the booster would allow a non-custom sized fuel cell to be placed in the front trunk - and save a little more weight to boot.

Playing with sizing will affect pedal travel and feel, but again, just wondering if someone else has done this and their impressions (and their choice of master cylinder bore size).
Dennis LaGrua NOV 25, 10:37 AM
I would not recommend removing the brake booster and make an attempt to redesign the system. You might succeed and you might not . Since brakes are a critical part of staying alive doing a mass conversion may not give you the results that you are looking for. Additionally if you ever have an accident the insurance company may decline to pay on an incident with a car with a radically redesigned brake system.
theogre NOV 25, 11:51 AM
Very likely No because This is Not just an MC issue but often Pedal and other problem(s). Might could do it but not easy. Yes, If you drive on the street at all then could have big legal problems and car insurance can void your policy after a wreck.

First, Smaller MC w/ stock system can have same problem as "GA upgrade" w/ OE MC. See my Cave, Brake Upgrade

Some Older cars, 60-70s cars, had non-boosted manual brakes as standard and PB as an expensive option.
And often had not only Different MC but different pedal parts too and many times not easy to switch in PB later.

Many had different pedal and mounting parts and mount was often welded dash frame element(s). Was done to add pedal leverage by moving top and MC pivots. You can move top pivot up and MC pivot down the arm so actual foot pedal is same height for either system. Typical PB pedal is ~ 4:1 vs MB pedal is ~ 4.25:1 to 5:1. Even change 4:1 to 4.25:1 makes a big difference in pedal effort to MC input pressure.

Others had some or all above changes and slaves in drum brakes w/ different bore size, different shoe specs, etc. to make a car will stop right w/ either setup.

Disk brakes, even Front Disk Only, Stop all of that and made PB required on nearly all cars after late 70's. PB often was needed just to stop w/ disk brakes to meet FMVSS rules.
You could get say Ford Pinto and other light cars w/ manual brake on front disk but became rare very soon. PB only on many heavier cars like "Station Wagons" w/ front disk. (Side Benefit, Also make it easier to make cars w/ one setup as reduces inventory etc.)

Not sure what you're trying to fit...
Race only car is likely to dump spare tire and mod or remove plastic tire wall so likely a "Cube" shape cell should fit w/o a lot of work... Need to support and/or move brake line to R-side caliper.
Problem tho is next to Radiator and fuel likely get warm to hot fast if race is long. Hot liquid can cause several problems and heat up F-pump too isn't a good thing. May not pass track safety inspections for this issue as hot fuel will pressurize the cell and/or "leak" a lot of fumes. Or rules may require heat shields etc. for a cell near the rad.

Note: Pressurize the tank/cell for any reason often causes problems for system pressure as acts as block return line from fuel regulator. Vacuum in a tank for low fuel etc can cause similar problems.
Is why Fiero and other tanks breath thru the EVAP canister 24/7. New cars often self test EVAP system (and why many trip DTC for a loose cap after filling) but still equalize thru EVAP can/filter somewhere in the car.

------------------
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

Craig71188 NOV 25, 02:03 PM
As mentioned in the OP, race use only. This is a car that will likely come in at about 2200 lbs dry. Pedal linkage is free so changing lever ratio is not a problem. Corvette had 4 wheel disc available w/o power assist from '65-'76. Insulation / venting / ducting in front trunk is all doable to minimize heat transfer to fuel cell. This will be a return less system, so no issue with fuel heating via pump/engine and an inline cooler is easily done with the long run back to the engine.

22 gallon cell just fits w/o mods to the frame, secondary option is to mount it in the front passenger foot well area, but this requires a lot more bulkhead construction.

May have to get a couple of master cylinders and take with us when we go to test - just looking to see if anyone had been there already. Yes, I have driven/raced other sedans / formula cars / sports races w/o power brakes. It takes careful selection of components and friction material choices, but also offers a better "feel" to modulate braking.
theogre NOV 25, 09:22 PM
You could have a Trailer Queen for track use but most others want to drive on street too is why no-one else tried this and why "warnings" above so they will see months to years later.

Track Only cars Could try many brake mods if rules allow whatever changes, even 2 MC systems in some Wilwood etc setups but Would cost more and need more work but likely takes a lot of space.

Same reason 4 wheel GA "upgrade" was "made" by a race team for a Trailer Queen car but Even for a TQ car has most problems on cave page. Some people use the crap on the street cars and ignore many warnings. Worse TFS Sell this crap to the dumb public making more problems...
Gone a very long time ago is Original site saying why and who, only several "knockoff" sites poorly telling how can be done. Many old sites are gone and only a few got backup thru archive.org.

Assuming you run standard Fiero brake plumbing... front MC goes to Front brakes. OE front piston doesn't have much "overhead" to work w/ a very small leak. Smaller bore w/ OE calipers can easily squeeze the bore dry w/o a leak and front brakes can get Less line pressure when that happens. Rear piston on Quick Take-up MC can hind this issue. See my Cave, Quick Take-up notes The GA "upgrade" needs Bigger MC to make Fluid Volume for the fronts brakes for same reason.

Pump and reg in tank/cell could have same problem w/ tank pressure or vacuum. Most regs expect standard 1 bar atmosphere = 0 Psi in any return line even if very short and dump fuel directly in the tank or return port is very near the tank. Note that One line to engine is also many new cars to help comply w/ USEPA and other countries EVAP rules because doesn't have hot return fuel heating the tank and 1 less line may leak fumes. Reg is in the tank or very near it.
So even w/o EVAP rules apply to you, still need a tank vent to atmosphere and prevent a hot tank barfing fumes.
Craig71188 NOV 26, 08:12 AM
Correct - no EVAP rules/ Yes, venting is still critical for the reasons you mention, PLUS, at least -6 line needed just to allow for rapid fueling.
DimeMachine NOV 26, 10:51 AM
This should be an interesting thread- curious to see what you end up with. Please share your progress!

[This message has been edited by DimeMachine (edited 11-27-2020).]

Johns 4.9 NOV 26, 11:50 AM
I have manual brakes on my Fiero. Dual master cylinder and pedal assembly by Wilwood. Also has brake bias adjustment in cockpit. Great set up for the track!
DimeMachine NOV 26, 01:39 PM
Nice!
Johns 4.9 NOV 26, 01:42 PM
Thank you, DimeMachine.
Cheers