Fiero brakes

General Fiero Maintenance including oil changes, air filters, suspension refreshes, restorations, painting, etc.

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kmelcher
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Fiero brakes

Post by kmelcher »

This has probably been discussed multiple times, but I am at my wits end and may be out of parts that need replaced. I am trying to get the best performance out of my fiero brake system. I have just performed a complete replacing job, beretta from calipers and rotors (parted old hubs to fit the rotors) on the front, new capilers and discs on the rear (stock fiero), new stainless steel braided brake lines, and 94 chevy 1500 master cylinder 1.25 bore. All seems to work ok, but I still do not get a good stop. I define this by being able to lock up the wheels. No matter how hard or fast I press. I had a fellow gear head recommend that the brake rod may be too short with the new master, but when I measured the travel, it moves about 1.5 inches and that seems to be the max travel of the master cylinder. I purchased a new master cylinder, but have not tried it yet. Any recommendations?
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Emc209i
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Re: Fiero brakes

Post by Emc209i »

The stock rear calipers are the reason you're still not performing. Being the engine's in the back, your rear brakes are hugely responsible for stopping the car, unlike other front engined cars. The stock discs back their are an absolute joke.

I'd look into using the upgrade caliper that came with the ebrake function (Seville wasn't it?). I'd stay away from '88 calipers if you can, they're a pain to source these days and expensive. The Seville calipers require a special ebrake cable from the Pontiac 6000 on the passenger side I think.

I've always played with the '88s, which actually had a decent system originally. My last car was an '86 and the brakes were a complete joke. I went to Berreta fronts, '88 rear end, and the S10 booster. Holy hell what a sensitive and powerful system compared to what it was. The stock pedal effort reminded me of a truck. With the S10 booster and the Beretta/88 brakes, I had to be careful not to throw passengers forward in their seats, much like newer cars have sensitive pedals. If I didn't have an '88 cradle to work with, I'd have used the Seville calipers on the back.
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Series8217
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Re: Fiero brakes

Post by Series8217 »

Sorry for my ignorance of pre-88 Fieros, but what's the purpose of the larger bore master cylinder? Assuming you don't actually need the extra volume, that's just going to decrease brake pressure for the same pedal effort..
The Dark Side of Will
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Re: Fiero brakes

Post by The Dark Side of Will »

The stock Fiero brakes are a joke.
In order to lock the wheels up, you need to have a lot of brake torque available. In order to do this with the tiny stock rotors, you need very high line pressure. However, the stock booster will not apply enough force to generate that pressure without extreme force on the pedal.
Switching to the larger bore master cylinder makes this WORSE rather than better.

The Beretta calipers do have larger pistons than the Fiero calipers, but the difference is not such that you want to use the largest possible master cylinder with them, which is what you've done. You should have kept the stock master cylinder.

My recommendation, based on the system you have now, is to go to the 11.25" brake setup. Those rotors and calipers will fit under stock 15" wheels and are the system the car should have been built with originally.

http://www.fiero.com/forum/Archives/Arch ... 48271.html
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Emc209i
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Re: Fiero brakes

Post by Emc209i »

Going to the 11.25" means that he can't use any of the brake hardware he's just purchased. While I agree that the 11.25" setup is a better performing setup than Beretta, if he gets the vented Beretta rotors and ebrake equipped Seville calipers on the back, his car should come in line and far outperform the stock setup, without requiring he start over from scratch.

Going back to the stock master might be a good idea. Back when I was reading about the Beretta setup, those who were recommending the larger bore master were doing so not to decrease hydraulic leverage (that's what it does), but because they claimed they could modulate the brakes better in corners when racing. I didn't like that line of reasoning, so I kept the stock master.
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Re: Fiero brakes

Post by The Dark Side of Will »

He's done the hard part, which is to have the stock rotors parted down to hubs. The Beretta calipers are ~$15 reman... I don't see it as a big loss. These days I count a <$100 mistake as basically free. (Not that I have a lot of money... I just make more expensive mistakes than I used to)
kmelcher
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Re: Fiero brakes

Post by kmelcher »

I will go back this evening with the stock master, but I am having a little trouble following the argument that the larger bore master is the issue. The berets calipers are a larger bore and this should require more fluid for the same linear movement, this the larger master, agreed? Pressure will be achieved once the brakes come against an imovable object and an incompressible fluid. What about brake pads? How much difference could that make?
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Re: Fiero brakes

Post by The Dark Side of Will »

Say for the sake of argument that 150# of force on the brake pedal results in 1500 psi of line pressure with the stock master cylinder. I don't recall the piston dimension right off, but if it's 1" vs. the 1.25" bore you have now, the same 150# pedal force will only result in 960 psi of line pressure.

Fieroguru did an analysis on Pfiffle of the line pressure vs. pedal load relationship for the Fiero brake system. He found that at high pedal loads, assistance from the booster drops off dramatically. This is a double whammy for stock diameter rotors. In order to lock the wheels with stock rotors, you MUST achieve very high line pressures, however, the stock booster can't apply enough force to create that pressure. You need to keep the master cylinder bore small in order for the load the booster can create to generate enough line pressure to lock the wheels.

Rodney Dickman does (or did?) sell an uprated booster to address the problem of running the stock booster out of its linear range.

My preferred solution is still 11.25" brakes, as this gives you the brake torque you want without high line pressures.
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Emc209i
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Re: Fiero brakes

Post by Emc209i »

The booster he's selling is the S10 booster. The difference in assist is substantial.

The larger bore master will move more fluid, but offer less hydraulic pressure, as Will pointed out. Someone was saying they had more modulation in the pedal because of this lesser hydraulic advantage. I never bought it.
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Re: Fiero brakes

Post by The Dark Side of Will »

Emc209i wrote: Someone was saying they had more modulation in the pedal because of this lesser hydraulic advantage. I never bought it.
Yeah, that's crazy talk.

I thought that the S10 booster had to be modified with a different length banjo fitting.
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Series8217
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Re: Fiero brakes

Post by Series8217 »

The Dark Side of Will wrote: Rodney Dickman does (or did?) sell an uprated booster to address the problem of running the stock booster out of its linear range.
He cancelled that project due to flaky product testers (a few members of Old Europe) and liability concerns.

It was an S10 booster with a properly installed longer pushrod (no extension).
Emc209i wrote:The booster he's selling is the S10 booster. The difference in assist is substantial.
sardonyx now sells reman S10 boosters with the Fiero pushrod and bracket installed in it. Basically the same thing Rodney was going to sell except reman instead of new.
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Emc209i
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Re: Fiero brakes

Post by Emc209i »

I got mine at the yard for $10. I cut the S10 booster rod and Fiero booster rod, threaded both ends, and attached the Fiero end to the S10 rod with a union. I've got a set of C4 double piston calipers on the shelf at home. No idea if I'll be able to use the booster with that much braking power when I'm done.

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kmelcher
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Re: Fiero brakes

Post by kmelcher »

New update. After my garage looked like a brake master factory (3 in total), I installed the 94 blazer (1 1/8) bore. Bled the brakes and rolled it out. They felt much better from the beginning. I got them to lock up and they did stop well. Still a little spongy and I think I am now looking for a used s10 booster. (In for a penny, in for a pound?). I will keep you posted. Thank you for the help.
finallall
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Re: Fiero brakes

Post by finallall »

You can do it without cutting the banjo. Was browsing and came up on this guide: http://www.gtfieros.com/phpBB3/viewtopi ... ster#p4086
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