Real Fiero Tech

My new calipers have a total piston area of about 3.97 sq in per caliper, compared to a stock area of ~2.84 sq in per caliper, this necessitates a master cylinder change, the brakes currently work, but don't have very good feedback.

So far, I'm aware of only one direct fit option, the S-10 master, which is about 40% larger, according to oreilly's website which should bring me back up to about stock MC/caliper area ratio. That being said, I don't really trust their website, I have found too many wrong values on it in the past.

Can anyone confirm the stock master is 1", that's the summit value, which like oreilly, I don't really trust.

Are you guys aware of any other direct fit MC, or one that requires only minor modification or adapting to fit? In the meantime, I'll start taking measurements and see what I can find.

On my old Fiero brake setup, up front I had single-piston 2.25" floating calipers (so 3.97 sq in), and I found that it worked fine with the 1.125" quick take-up Blazer MC.

Hard enough to be easy to modulate (not too easy/squishy), but not so hard as to require too much leg force.

I usually look at Rockauto to determine bore sizes.

I personally measured my calipers, but I didn't verify the MC.

pmbrunelle wrote: ↑Sun Jan 31, 2021 6:20 pm On my old Fiero brake setup, up front I had single-piston 2.25" floating calipers (so 3.97 sq in), and I found that it worked fine with the 1.125" quick take-up Blazer MC.

Hard enough to be easy to modulate (not too easy/squishy), but not so hard as to require too much leg force.

I usually look at Rockauto to determine bore sizes.

I personally measured my calipers, but I didn't verify the MC.

10-4, I might just pick one of those up and see how it feels. Thanks for the response.

Is 3.97 in2 the piston area of C5 Corvette calipers?

I know I have a larger MC on The Mule, but I don't remember the original application.

The Dark Side of Will wrote: ↑Mon Feb 01, 2021 9:44 am Is 3.97 in2 the piston area of C5 Corvette calipers?

I know I have a larger MC on The Mule, but I don't remember the original application.

according to the info I found online, I didn't take measurements though.

I posted this info in my build thread, so if you're following that, you've already seen it.

in my hunt for a larger master cylinder to match my C5 'vette fronts on all four, I found the GMT-400 trucks use a master with a similar bolt pattern and fitting locations to the stock Fiero. it's not quite a bolt in affair, but it's also pretty easy, the hardest part is getting the inverted flare right, with minimal OE tubing removed, the stock lines can be reused.

Here's the new master alongside an S10 blazer master:



The new master is off of a 1996 chevy C3500hd and has a 1.57" bore, it physically bolts in place fine, but the reservoir is HUGE, so I pried it off and installed a stock fiero reservoir. The reservoir removes by simply pulling it off, not fasteners hold it on. The lines connect in the same position, but, the fittings are not the same size. I fixed this by cutting the lines just behind the flare, and removing the OE tube nuts, which I replaced with nuts of the correct size, then I flared the line and bolted everything back together.

where I cut the flares:





use a double flare kit, it looks like this:




The parts list:

New MC:

https://www.summitracing.com/parts/aaz-13-2754

1/4" tube nuts:

https://www.summitracing.com/parts/sum-220115

3/16" tube nuts:

https://www.summitracing.com/parts/sum-220137

now, lets talk results. with the S10 MC, the pedal feel was crap, and the travel was very long. Using the C3500HD MC I have a firm pedal, but the travel is very short, honestly I think it might be too short, so if I have a reason to crack the system open again, I'll probably install a 3/4 ton master to replace the 1 ton, it's 1.25" instead of 1.57" and should be a direct bolt in now that the I have the 1 ton master installed.

3/4 ton MC:

https://www.summitracing.com/parts/dhb-m390257

after all this nonsense, I finally drove the car for the first time in ages. because my fuel sender works, and it showed empty, I figured it would be a good idea to stop and fill it up at which point I found out the O ring on top of my fuel tank is shot, or not sealing, as the pump clicked off, and I heard the splash of the fuel hitting the ground...thankfully it was a very small amount of fuel, probably only a 1/2 cup or so, but it was enough to let me know I need to drop the tank and fix it. the part I'm still unsure of, is if my car has an 85 sender still, or an 87+, I don't remember which I installed when I put the tank in 7 years ago, and I don't know how to tell the difference, if it's still the 85 sender, that would explain the leak, as both senders are different.

Have you thought about building a master cylinder brace for a harder brake pedal? The Fiero firewall (well, not really firewall, since there's no engine in front) seems pretty flexible.

Example:
https://www.fastwrx.com/products/radium ... e-fr-s-brz

pmbrunelle wrote: ↑Wed Apr 14, 2021 7:39 pm Have you thought about building a master cylinder brace for a harder brake pedal? The Fiero firewall (well, not really firewall, since there's no engine in front) seems pretty flexible.

Example:
https://www.fastwrx.com/products/radium ... e-fr-s-brz

Yes. I have been, while bleeding the brakes I observed a significant amount of flex, and have been trying to find an acceptable solution. Yhe problem is finding something suitable to brace off of, the sheet metal on the other side isn't much stiffer than the "firewall". I was considering making something that bolts to the front subframe, as it would be significantly more rigid, on the filpside the master would have more leverage on the brace mounted down low, so it will take a more substantial brace. I haven't put a ton of thought into it yet, and honestly, it will probably have to wait until after I move.

pmbrunelle wrote: ↑Wed Apr 14, 2021 7:39 pm Have you thought about building a master cylinder brace for a harder brake pedal? The Fiero firewall (well, not really firewall, since there's no engine in front) seems pretty flexible.

Example:
https://www.fastwrx.com/products/radium ... e-fr-s-brz

Like Eric said, the Fiero doesn't really have anything convenient to brace the MC against.

I started working on a Firewall reinforcement plate... I'll get back to that once I get The Mule back on the road.

Of course I haven't been looking forward to that, as R&Ring the pedal box is a huge PITA and the car has to be laid up while doing fit/futz. However, once the engine has returned home, I'll move the car back to my dad's place to complete reassembly, build the harness and put the finishing touches on some ancillaries.