I currently have the fiero store grand am brake upgrade up front with vented and cross drilled rotors. At the time i purchased the upgrade kit i also bought there big bore master cylinder but never put it on. Meanwhile i also have the bigger brake booster but still have not got that on either. Anyone have any suggestions on wether i should put on both or just one or the other? Just looking for suggestions before i do the job.

I'd say that since you got them both put them both on. But then again I haven't done all the math and what not so maybe someone else will chime in. But I don't see how doing both could hurt

Bump, anyone else have suggestions

I would put them both on. When you do the grand am brake up grade you need the bigger master cylinder do to the bigger caliper pistons and the bigger brake booster is just an added bonus. Thanks

achbaby,

The big bore master will require you push harder to achieve the same braking torque that the stock master generates, so I would not recommend changing masters. By all means install the S-10 booster and do it FIRST!

And upgrade the rears as well as mentioned before!

Larry

I guess it's one of those things where people all have different opinions. Keep the suggestions coming though, also what would the recommended upgrade be on the rear brakes? Thx guys I appreciate the help

achbaby,

Here is what theOgre has to say about the big bore master: "NOTE! The Fiero Store sells a "big bore" master cylinder (Blazer MC). Increasing the MC bore diameter REDUCES fluid pressure. It will always make the brakes weaker not stronger! When installed on an otherwise stock Fiero it will seriously reduce brake system performance. You DO NOT want this thing on a stock Fiero! (See alt MC below.)"

I STRONGLY suggest you to the Ogre's Cave (link at top of every page) and read ALL of his article on brake upgrades!

Larry

On my 86 SE, I have the Grand Am upgrade in front, the Seville/Grand Am upgrade in back, and the stock master and booster. This combination works very well.

This is actually more complicated than a lot of people realize but in short the bigger the MC piston the more the line pressure will be. This basically means that the pedal will travel less to achieve the same amount of force than a smaller bore cylinder. If you increase the size of the calipers you increase the amount of line pressure they need to apply a specific amount of force so you need a bigger MC to get that same amount of force. The booster comes into play because when the MC bore gets bigger you need more leverage to get it to move because it’s got a higher amount of line pressure. Again, it gets very complicated very fast so I’m guessing that the FS did the homework before recommending parts. I’d put both components on.

Firejo,

I believe you are mistaken. Perhaps you should also go and read the Ogre's article.

quote Originally posted by imacflier: Firejo, I believe you are mistaken. Perhaps you should also go and read the Ogre's article.

Yep, the larger bore will move more volume but will require much more force to get the same pressure as before.

Kevin

The larger bore will increase pedal effort, the large booster will reduce it.

Thx for all the feedback. What would be the cheapest route be for upgrading the rear brakes also and will the results be minimal at best?

You're going to laugh at how easy it is to do the Grand Am/Beretta upgrade to the rears. It's just change the calipers and rotors. But, you will lose the E-brake.

Fiero's need to have similarly sized caliper pistons on all fours, or just slightly bigger pistons in the front for correct bias. Anything other then that will result in spinouts, or front's locking up with little help from the rears. Anyone that tells you otherwise doesn't know how well brakes should perform.

The big bore master cylinder is an upgrade that should only be done if the piston area on the calipers is increased substantially. Weather or not the Grand Am calipers are big enough to warrant the big bore master is a controversial topic. I suggest trying your setup with the stock master first, but DO the upgraded booster for sure!

If the pedal has too much pedal stroke after you are 100% sure you have all the air out, then consider changing the master for the big bore one.

[This message has been edited by Fierobsessed (edited 05-15-2012).]

what year beretta rotors and calipers are required for the rear

1990

so 1990 rear pads. rotors and calipers. Are these also the same ones used on the grand am rear

Let me see if I can clarify what I was trying to say.
Increasing the size of the MC decreases the pedal travel for the same volume of fluid moved. If you change nothing at the wheels and then you apply the same force to stop, you do less work. Because “work = force x distance”.

Therefore increases in MC results in increases in Mechanical Advantage.

However, we aren’t talking about nothing having changed at the wheels. There are now larger calipers which have a larger diameter piston.

Look at it this way, if you increase the size of the caliper bore, you have to push more fluid to get it to move the same distance as the smaller caliper did. There are two ways to move more fluid. One, push the MC further or two increase the MC’s size. If you don’t increase the size of the MC then you will have to do more “work” to get the same stopping force.

Having a great amount of respect for Ogre, I can’t figure out the statement “Increasing the MC bore diameter REDUCES fluid pressure.”. You will however note that he starts that section with “Upgrade MC with OE calipers” and that’s not what we are talking about here. With that in mind, I would completely agree that you should never increase the MC size with stock calipers. But I don’t see how it decreases pressure. With that said, pressure isn’t the issue here. Fluid volume and mechanical advantage is and if you increase the size of the caliper’s you should increase the size of the MC.

Sorry, no its grand am front brakes on all four corners of the Fiero. Forgot to mention that.

firejo24,

Rather than divert this thread from the OP's original question I have sent you a PM.

Larry

Both for good measure but either way you will be playing with the pin shortening or lengthening to get it right with the peddle.

quote Originally posted by firejo24: Let me see if I can clarify what I was trying to say. Increasing the size of the MC decreases the pedal travel for the same volume of fluid moved. If you change nothing at the wheels and then you apply the same force to stop, you do less work. Because “work = force x distance”. Therefore increases in MC results in increases in Mechanical Advantage.

Wrong. Think of using a lever to lift a weight. The longer the lever is on your side of the fulcrum, the better the mechanical advantage (you can lift more weight with less effort). In the braking system, the longer the pedal travel at the master, the better the mechanical advantage. Therefore, getting a larger master cylinder piston, which reduces pedal travel, also reduces mechanical advantage.

Now, changing directions a little.... One of the reasons why the pedal travel is so long on a stock 84-87 Fiero brake system has nothing to do with mechanical advantage. It's because of sloppiness in the system. The combination of plastic pistons, aluminum calipers, and a faulty e-brake system adds quite a bit to pedal travel. In the lever analogy, it's like using a spring for the fulcrum. You have to push the lever down enough to compress the spring before any lifting begins. So if you eliminate those three items I mentioned, you can put bigger pistons on the wheels and leave the master cylinder alone. You'll get a better braking system without increase in pedal travel. That's what I got in my 86 SE, when I changed to the Grand Am system on the front, and the Grand Am/Seville system on the back, while leaving the master cylinder stock.

What’s missing (TopNotch) is the fact that the calipers (slave cylinders) have in replaced with larger diameter calipers. The bigger they get the more force they apply with the same amount of input pressure. The short of it is that if the calipers get bigger the MC should get bigger. There’s a pretty good explanation here:
I will concede that the output pressure from the MC will decrease if the bore size increases but I’m looking at more than just the MC (I’m just not very good at explaining it).

wow thx guys for all the output, even with so many opinions on this topic it still gives me a much better understanding than what i previously had.

Is this for a daily driver? Just leave the rears alone then. With the Grand Am fronts, bigger booster, plus ss braided hoses you should be able to lock up the wheels as is (panic stop, etc). The benefit of the vented rotors is less fade for extended hard braking as in long downhill slopes with a trailer or road racing. Just my .02

I personally don't recommend Grand Am calipers on the rear. The Seville calipers give you better brake balance (with Grand Am calipers on the front), and an e-brake. If you have Grand Am calipers on the rear, your rear will lock up before the front, which is not good.

quote Originally posted by Fierobsessed: Fiero's need to have similarly sized caliper pistons on all fours, or just slightly bigger pistons in the front for correct bias.

this statement is true as long as the original calipers (or identically sized replacements) and prop valve are retained. Assuming tires are good enough, going to bigger brakes means a different weight distribution under (hard) braking which requires a different bias.