All standard engines maintain (if operating properly) about -9PSI at idle, -6PSI at cruise and ~0PSI at WOT. A SC/Turbo engine is just the same, with the exception that they go to above 0 PSI at WOT and heavy acceleration, they will still stay at -9 idle and ~-6 cruise, if they didnt you would get really really bad gas mileage as the ECM would constantly be in full enrichment mode. While I have no way of confirming, I would speculate that the boosters would maintain and check in as much vacum as possible, IE the -9PSI on all models, though the larger area would take longer to evacuate, if you turn your car off and pump the brakes you can get 2-3+ full pumps out of them before they go rock hard, so I again would speculate that there would be plenty of air available, and unless you are slamming on the brakes while holding WOT you should be fine.
What I dont like about the setup is modifying the pushrod, I hesistate to change anything that could result in a catastrophic brake failure, such as that coupler's threads sheering or the rod bending or what not. I also dont really see a need as I can lock the brakes on all of my Fieros without too much effort, even with 12" vette rotors, but I guess thats the same deal as the power steering. If you think you need it, go for it.
Fundamentaly this install seems sound.
------------------ Boost is like Venereal Disease, one night of passion can result in weeks of pain (and work.) Its not always about who gets to the finish line first, its who looks good when they get there. 'Course it doesnt hurt to have both. http:\\www.myspace.com\keeptherubbersidedown
But I have a revelant question.........Does replacing the Master Cylinder with a Bigger one have an affect on the pedal? I replaced my M/C with a Bigbore and the brakes haven't been the same since! Now,...if I replaced the Booster with the aforementioned S-10 option,...would that help my "soft Pedal" problem?
A bigger M/C will definately affect your pedal feel, for the same amout of foot pressure you will get less brake line pressure . If you are still using the stock Fiero calipers you will have to push the pedal harder to get the same braking force at the rotors. I'm not sure what you mean by "soft pedal"
........What I dont like about the setup is modifying the pushrod, I hesistate to change anything that could result in a catastrophic brake failure, such as that coupler's threads sheering or the rod bending or what not. I also dont really see a need as I can lock the brakes on all of my Fieros without too much effort, even with 12" vette rotors, but I guess thats the same deal as the power steering. If you think you need it, go for it.
Fundamentaly this install seems sound.
The push rod ends up being exactly like the stock Fiero pushrod. If you had the proper tools you could take the pushrod out of the Fiero booster and put it in the S10 booster.
But I have a revelant question.........Does replacing the Master Cylinder with a Bigger one have an affect on the pedal? I replaced my M/C with a Bigbore and the brakes haven't been the same since! Now,...if I replaced the Booster with the aforementioned S-10 option,...would that help my "soft Pedal" problem?
sounds like you need to do some bleeding. the MC should have been "bench bled" before installed, then the whole system heavily bled. your pedal should be harder, not softer. in fact, thats what this whole thread is about.
Oh, ok I didnt read that far into It, I just saw the coupler dealy on the one pic
But yea Ditto the bleeding. If you have the car off, pump the brakes, once they firm up, they should go rock solid and hold by 1/2 pedal travel, if not you have air in the system or bad hoses that are flexing and expanding.
Some General comments on Boosters,,,, Im not familar with the two booster sizes.
Bigger Booster does have more Total Boost Assist ( once Vacuum levels stabilize )
Bigger Booster will take longer to reach Max Vacuum Level
Bigger Booster will typically have a lower system response ( assuming simular Booster Design )
Bigger Booster typically has more can deflection ( assuming common Can Design, you can see the can deflect under higher pedal forces)
Also the the pedal feel will be softer / mushy with a larger booster ( if the internals of the booster are the same, spring rates etc)
Larger Diameter Master will generate Less Pressure with a given input force
There may be some internal differnces or improvements in a 96 S10 booster so the feel improvement may not be size alone. modern boosters over time have improved force/travel losses,,,,,,
Booster 's have what is called a Reaction Ratio / Gain Ratio
Which is simply THE RATIO OF INPUT FORCE / OUTPUT FORCE , AT A GIVEN VACUUM LEVEL (SLOPE OF THE CURVE)
THIS IS DETMERINE BY BOOSTER DESIGN,, THERE IS AN AIR VALVE INTERNALLY TO THE BOOSTER THAT CONTROLS HOW QUICKLY BOOST IS APPLIED ( THE RATE IN WHICH ATMOSPHERIC AIR IS RELEASED INTO THE BOOSTER )
YOU CAN HAVE THE SAME SIZE BOOSTER WITH TWO DIFFERENT GAIN RATIO'S.
IF YOUR NOTICING AN IMPROVED ABILITY TO LOCK UP THE BRAKES,, MY GUESS IS THAT THE REACTION RATIO OR GAIN RATIO IS HIGHER FOR THE 96S10 BOOSTER. AND YOU COULD GET AWAY WITH A HIGHER RATIO SINCE THE VOLUME OF THE BOOSTER IS LARGER (SO IT TAKES LONGER TO DEPLET VACUUM ).
and thanks kcfiero, I knew it had to be more complex than just simple diaphragm size.
So -9PSI is all the vacuum we have? On the internet I'm seeing GM boosters listed as either 8" or 9" in diameter (there may be more, this is just one web site). If the fiero is an 8" that sounds like ~50 lbs of assist and if the s10 is 9" that sounds like ~64 lbs of assist. So it's going to remove ~14 lbs of foot effort and that sounds worthwhile. It also sounds a little low, so I'm still scratching my head on that one... I always imagined engines producing more vacuum than that.
But, the naysayer in me would still be happier if Phil could measure the vacuum inside his s10 booster so I could compare it to the stock one. I know you posted 18" of merc on the engine, but I'm not sure off the top of my head what that refers to in PSI, and I would love to see the same number show up inside the booster itself...
Of course, maybe kcfiero can shed one more piece of light on this: The check valve. Is it just a one way valve that grabs the most vacuum it can from the engine? Or is it a limiting one way valve that will limit the amount of vacuum in the canister?
My guess, now that I've perused the internet for a length of time and we've got some numbers on the vacuum engines produce, is that it's just a one way valve that gets as much as vacuum as it can. I can't see putting a limiter on there if the engine itself only produces -9PSI. That's not much at all...
Exactly how was the bracket connected to the booster? Was I reading correct you said 4 rivets?
My first concern at the moment is long term strength of the bracket. It was built to have the 4 rivets. There is a chance that long term the bracket may not hold up if you have only two connection points and nothing to reinforce.
My next concern whenever I see this sort of thread...
A "larger" brake booster can help brake performance. I'm not arguing that.
The issue is that many people that might do this, and see a performance increase, are compairing apples to oranges. IE compairing a defective OE part to a new or better condition used part. This happens allot when people compair OE rubber suspension parts to polyurethane aftermarket parts.
I'll mostly skip over the chronic caliper problems that most people have and never actually fix. Fiero brakes for most driving are not bad design, even with all solid rotors. Yes there are times where the brakes require upgrades but allot of people that are doing this on otherwise stock or lightly modified cars could be simply hiding major system malfunctions. Malfunctions that left hidden will simply get worse until there are no brakes at all.
My last item is this...
The Fiero brake pedal is a 4:1 lever. At least one of the links above might make you think it is a 3:1 lever, which it is not. 100 pounds on the pedal is 400 pounds on the MC/Booster rod. It is very easy to put over 1000 pounds of force onto that rod. A strong person might even make a solid ton or more.
Any modification to the brake rod MUST be able to handle that load or it will fail. Likely with no warning at all and at the worst possible time.
IE... Epoxy is not a viable solution. I'm not sure anything less than welding, likely with some splinting on the weld, is safe.
The rod can and likely does flex some under high load. A modification that can't deal with that will eventually snap like a twig.
The correct fix is to see if the Fiero brake rod can be transfered to the alternate booster. These rods are usually held by some snap ring etc that is fairly easily removed. It's been a long time since I had to replace a booster so my mind is a bit fuzy on details.
------------------ 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. (Jurasic Park)
given: 25.4 mm to the inch , 760 mm of merc is one atmosphere, 1 atmosphere is 14.7 psi (every square foot at sea level has a column of air weighing a shade over a ton sitting on it) the conversion goes like : (18 in Hg) x (25.4 mm / in) x (1atm / 760mm Hg) x (14.7 psi / atm) = 8.84 psi vaccuum.
doesn't sound like a lot, but 8 or 9 psi vacuum means almost 60% of the air molecules have been sucked out of a given volume. -14.7 psi (gauge) is a complete vaccuum, or 0 psi (absolute)
[This message has been edited by D B Cooper (edited 04-05-2006).]
The Fiero bracket has 4 riviets holding it to the booster can - when removed the bracket attaches to the 4 bolts on the new booster. Unfortunately the pushrod is attached to the booster by a clip on the inside of the booster so in order to remove the rod you would have to take the booster apart Here is a shot of a stock Jimmy booster
The bracket just bolts onto the back side of the booster. The pushrod in the Fiero is the same diameter as the S10/jimmy only about 2" longer
as far as idle vaccum for STOCK N/A cars goes, *MOST* produce between 18-22" Hg (30" being a "perfect" vaccum) how that relates to negative PSI/atmospheric, i'm not sure. but if atmo at sea level is 14.7psi and that becomes our referance of 0, then i can see -9psi being a viable number for STOCK N/A engines. the higher the number, the better the idle quality, which is what manufactures gow for as far as driveability is concerned. *MOST* boosters need a MINIMUM of 14" Hg to opperate with satisfactory results, and *MOST* N/A engines produce < 24" Hg during decel (throtle closed). within the time you release foot from gas and apply brakes, the engine (depending on RPM) will have drawn enough volume of air (@ < 24" hg) to have emptied the booster (in this case the 9" Jimmy booster) at LEAST 10 times if not more (using 2.8L as reference for volume and giving the jimmy booster a volume of 2.6L). so if you're worried about refersh rate of the booster, you'll never notice it, EVER.
now if your engine dies and you need to brake, here's where the larger booster becomes an asset: depletion time goes up (this is a good thing). as volume of booster goes up, so does the number of available pedal pumps that are in reserve.
Thanks Phil etc. but by a, "Soft Pedal" I do mean it takes more pressure to stop. I had all brake work performed by an expert mechanix and he couldn't figure it out! So.... bottom line, is this S-10 Booster exchange what I need to make my "Big Bore" M/C work? (Fiero Store Big-Bore M/C)
why did you up size your master cylinder? did you change calipers..
a larger Master will yield lower line pressure for the same pedal force.
What Master cylinder did you use... ( Some are Diagnal Split others are Front Rear, I believe the fiero is front rear split but could be mistaken) if Split is worng it could cause a low pressure issue in the front brakes.
The best way to make up for this is to increase the mechanical pedal ratio...... ( but not the easiest )
If you have a mushy feel,,, a larger booster may make it even mushier (not sure if thats a word).
Boosters are designed with a input vs output slope..... which varies for each vehicle application. This slope can be chosen by the OEM somewhat independent of size.
If all things are equal internally to the booster All the larger size allows you to do is, you can hold the gain ratio slope longer before you run out of boost ( therefore reaching a higer total boost prior to runout),, but typically drivers dont reach the upper edges of this during typical braking.
If Phil has noticed an improvement with this booster Im guessing that this booster has a higher gain ratio... which would make the brakes feel more "snatchy" usually larger boosters can get away with highr gain ratio since they have more volume to work with( but its not always the case)
If I have time at work I will see if I can dig up perfromance plots of each booster....
for the problem you are arguing about is easily solved, people with big cams, blowers, etc have been using them for years. there called an electric vacume pump... something like this:
I can't answer for Quickstar, but we have the Blazer M/C on our Finale.
I was very well aware of what would happen when I put it on. We autocross the car and I don't care for the (what I think is) the long stroke of the brake pedal on the stock Fiero system. Yes, the pressure requirements on the pedal from your foot go up, but because of that you can modulate your brakes better on an autocross course (or I should say that *I* can). It also shortens up the stroke of the pedal quite a bit.
I changed mine for two very specific reasons. I WANTED higher brake pedal force and I WANTED a shorter throw on the pedal. That's why I did it. If someone doesn't know, or want, both of those two things, they should leave the stock setup alone.
John Stricker
quote
Originally posted by kcfiero85:
sorry didnt notice that you said fiero store big bore,,, so the split should be ok....
if you didnt go with larger calipers than you should not upsize the Master cylinder.
- Larger caliper pistions genterate more torque at the wheel with lower pressure, (require more volume) due to the larger surface area of the pistons.
- Stock Calipers (smaller) need the pressure of a smaller master cylinder to generate adequate Torque at the wheel.
I get it... I couldn't see parts of the other pictures very well.
It's been ages since I had a booster from anything apart. Stinks about the clip being burried too deep. The booster can be taken apart but I would not recomend people try that. You need special tools and odds are if you tried reusing parts the thing wouldn't last long if it worked at all when you got it back together. I don't think anyone sells booster parts to the public or even to shops much anymore. It's one of those things that isn't terribly complicated but you have to know exactly what you are doing or you get a big lump. (Hopefully it gets bricked before someone tries to drive with it.)
for the problem you are arguing about is easily solved, people with big cams, blowers, etc have been using them for years. there called an electric vacume pump... something like this:
This is very interesting. I didn't realize things like this even existed. This could be an upgrade for us all on it's own. By taking out the vacuum line running all the way down the car it can free up some room for other things like cables for a battery relocation, etc....
I think I'd hestate running the battery cables in the interior of the car, but that's just me. The brake vacuum line runs inside the car on top of the center console.
There was discussion on booster size vs. which engine, the V6 and the 4 both take the same booster part number from GM on the 96 S10 so apparently GM doesn't think it's much of a factor. As kcfiero pointed out, besides the area, the gain ratio is important and it is, in effect, a controlled leak. Unless you design these things the only way to know if it helps or hurts is to just bolt one on and try it, as Phil did. In his case, he felt an increase in power assist so the gain ratio had to be greater than the stock Fiero booster.
All that said, you can get a pretty good idea on how things are going to work by looking at how they are sized on the vehicles and their intended use. A huge booster off of an '80's era Caddy, for instance, wouldn't real be an appropriate alternative. Although the designs vary, often they are subtle variances as long as you stay in the same size/weight/brake type arena with what you have now. Barring any earth shattering technological developments, we are dealing with physics here, and the laws of physics haven't changed much in quite a while.
John Stricker
quote
Originally posted by fierogt88:
This is very interesting. I didn't realize things like this even existed. This could be an upgrade for us all on it's own. By taking out the vacuum line running all the way down the car it can free up some room for other things like cables for a battery relocation, etc....
this article does look interesting... since i have an engine out of an S10.. im sure it will work vaccum wise
------------------ GT just waiting for the conversion
84 Fiero Turbo Vortec 4300 Phantom GT L35 block, Syclone Intake and ECM with Moates adapter 50lb injectors, 3 bar map sens, T04B H3 Turbo
www.cardomain.com/id/vortecfiero Murphy's Constant Matter will be damaged in direct proportion to its value Murphy's Law of Thermodynamics Things get worse under pressure. Arthur C. Clarke "Any significantly advanced technology is indistinguishable from magic"
Just some input on the concerns of some folks about vaccum problems- I just did this conversion on my wife's 88 Duke at a tech session today and it works perfectly. I even left about 20 FT of rubber on the street by locking up the brakes at 35 MPH. I had done some test runs earlier in the week and I couldn't lock them up at 30. Granted I had to apply a GOOD force to the pedal but now I can lock them up if I want to. If a Duke can work the system so can any motor.
Here is proof of Phil's skid marks. I was there too. Before the swap, Phil was saying that he couldn't get the brakes to lock up at 30 MPH. After the swap they certainly worked real good from the cloud of smoke and rubber marks he left.
[This message has been edited by avengador1 (edited 04-23-2006).]
THANKS PHIL!!! I just completed this mod to my 85 based GT40 Kit. I already had the Berreta brakes and Blaser M/C. Even with those up-grades I could not lock the brakes. Now I can with a lot less effort. The install on my kit was a bit difficult, since the new body work makes it hard to get to the bolts, but it was all worth it. I picked up a booster for $50.00. The only other thing i needed was 4- 10MX1.5 nuts to bolt the Fiero bracket to the new booster. I also cut the excess bolt thread off and tack welded the 4 nuts. (I couldn't find lock nuts) There have been several, comments hear about details, formulas, etc., but the proof is in the results! This is the best $50.00 I have spent on my brakes! Thanks again to Phil for a great mod! Kevin
------------------ 85 Fiero-based ASPP GT-40 MarkII. 3800 S/C, Auto, Held suspension all around with 2" drop spindles and sport fr. end. RCC bump-steer correction. Mr. Mike's interior.
For anyone interested here is a side by side picture of the orinal power booster and the S-10 one. You can see how much larger the newer one is. Phil told me he also painted it black to match the look of the original as they are silver in color when you get one.
[This message has been edited by avengador1 (edited 01-16-2009).]
THANKS PHIL!!! I just completed this mod to my 85 based GT40 Kit. I already had the Berreta brakes and Blaser M/C. Even with those up-grades I could not lock the brakes. Now I can with a lot less effort. The install on my kit was a bit difficult, since the new body work makes it hard to get to the bolts, but it was all worth it. I picked up a booster for $50.00. The only other thing i needed was 4- 10MX1.5 nuts to bolt the Fiero bracket to the new booster. I also cut the excess bolt thread off and tack welded the 4 nuts. (I couldn't find lock nuts) There have been several, comments hear about details, formulas, etc., but the proof is in the results! This is the best $50.00 I have spent on my brakes! Thanks again to Phil for a great mod! Kevin
Very glad to hear that is also as effective on a pre 88s as it is on the 88s
[This message has been edited by Phil (edited 04-24-2006).]
Bump to let more people see this. The more I drive with this mod the more I like it! Kevin
------------------ 85 Fiero-based ASPP GT-40 MarkII. 3800 S/C, Auto, Held suspension all around with 2" drop spindles and sport fr. end. RCC bump-steer correction. Mr. Mike's interior.
I would be very interested to know if anybody with a pre 88 and an otherwise stock brake setup has tried this. If you are adventurous and would like - just show up at my house with a pre 88 and bring along an S-10 booster with the 4 nuts and lock washers to fit the studs and I'll do the conversion for ya. Should only take a few hours.
Is this too far out... if you are doing the Corvette brake conversion, with the Corvette Master Cylinder, would a Corvette booster be the way to go? (providing it fits?) The Hot Rodding magazines list several companies that specialize in brake components.
BTW, I can lock up the brakes on my Duke-equipped SE at pretty much any speed I choose. I mean, I just stop if it's less than 20 MPH, but I can lock them at 30 MPH. Granted, I've got all new components except for the hard brake lines themselves, and I'm using stainless braided hose but that's it.
So there have been no reported problems with this upgrade?
Since getting a new car, and just recently driving my Fiero I am alerted to how poor the brakes are performing. I have turbocharged engine and can get moving but just dont feel safe about stopping. In retrospect the Fiero brakes have always been poor. This looks like it could help.
Again any problems?
I priced a new 96 S10 brake booster to be around $90. Should take no less than a morning to install.
When I built my Fiero trike, I put a little (1" ?) VW master cylinder in it. With no power assist, and back brakes only, braking was barely adequate. I tried a larger master cylinder ( I don't remember the size, but larger) and I couldn't stop at all. I put the VW master back in and the Bereta upgrade. Perfect, can lock them up if needed. The only time you want to go to a larger master is if the volume is needed for larger volume calipers. As for the thread, I love it. I'll be making this mod to my 87 GT. I'm giving Phil a +.
[This message has been edited by triker (edited 06-21-2006).]
I know that, I guess I didn't make it clear that I was refering to some of the other posts about master cylinder size. I'll be looking for a Blazer vacuum booster for my "other" Fiero.
I am very interested in this modification. I have the Grand AM/Blazer front brake mod on my 86 Fiero and cannot exert enough force to lock up the brakes. Can you give us a measurement on the length of the rod and the source/size/thread pitch for the threaded coupler you used. Also, did you need to use a die to form threads on the rod or are the threads already there? Finally, how do you get the bolts into the booster to attach the bracket from the fiero booster?
Thanks, Mike
[This message has been edited by NewGT (edited 06-23-2006).]
