GM designed the proportioning valve to work with equal size brakes on the Fiero.
It is balanced from the factory. To go to a larger caliper on the front and not the back just does not make good sense, even with a larger master. I still maintain, that whether you do the Lebaron or GA conversion, you should do all 4 corners. If you want to stay legal, we have ebrake conversion brackets available to use with the Seville calipers on the rear.
There is a whole lot of discussion IMHO on how to do the job cheaper and cut corners. The bottom line for me is that you do all 4 corners on a brake conversion and don't cut corners for both performance and safety.
But hey, to each his own.
Arn
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08:25 PM
82-T/A [At Work] Member
Posts: 25714 From: Florida USA Registered: Aug 2002
GM designed the proportioning valve to work with equal size brakes on the Fiero.
It is balanced from the factory. To go to a larger caliper on the front and not the back just does not make good sense, even with a larger master. I still maintain, that whether you do the Lebaron or GA conversion, you should do all 4 corners. If you want to stay legal, we have ebrake conversion brackets available to use with the Seville calipers on the rear.
There is a whole lot of discussion IMHO on how to do the job cheaper and cut corners. The bottom line for me is that you do all 4 corners on a brake conversion and don't cut corners for both performance and safety.
But hey, to each his own.
Arn
Yeah, I saw the spot-break on Jegs (link someone posted). I may end up going that route...
You forgot CG height. BTW, what is it on a Fiero? Anybody ever do the "tilt test"?
According to somewhere on the forum, it's 19.5 inches for a stock Fiero. I don't know which engine or trans, or how it was obtained. I searched for "tilt-test" results, but I've only ever seen corner scales being used on level ground.
Someone did weigh a 5-speed Fiero Formula though, and reported that the front weight was 1280 lbs, and the weight supported by the rear wheels was 1676 lbs (static).
The spot calipers wouldn't be bad, if you can find a way of mounting them.
For the record, my "super-high level" of education is merely a high school diploma.
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11:37 PM
Nov 1st, 2010
82-T/A [At Work] Member
Posts: 25714 From: Florida USA Registered: Aug 2002
According to somewhere on the forum, it's 19.5 inches for a stock Fiero. I don't know which engine or trans, or how it was obtained. I searched for "tilt-test" results, but I've only ever seen corner scales being used on level ground.
Someone did weigh a 5-speed Fiero Formula though, and reported that the front weight was 1280 lbs, and the weight supported by the rear wheels was 1676 lbs (static).
The spot calipers wouldn't be bad, if you can find a way of mounting them.
For the record, my "super-high level" of education is merely a high school diploma.
To be honest, I really don't want a larger caliper and rotor on the back because I just don't want more than proportionally stock braking force in the rear. All that I really want is just to keep the brakes proportional. It seems like the goal is to keep the piston bore to be around the same size. I might try going with the Cadillac rotor and caliper, and then use a spot caliper.
If I can't find something that's entirely decent, then I'll probably take my car somewhere (when I get it finished) and buy an adjustable proportional valve, or do some research on some stock units that GM sells for other cars, and see if there's some way to re-adjust the bias so as to shift it back towards stock somewhat. It would certainly be a much more clean install. I would get improved braking, not substantially so over stock, but it would be improved. All I have is a 3.2 anyway, so my car won't be exceptionally faster than a stock one anyway. I'll probably spend a lot of time in the Ogre Cave after work.
These responses are great because it really gives me an idea of what everyone has done. I was smart to put it in here (O/T), because I know there's a lot of head butting... (like the H272 cam vs the H260) and just figured I would hash it out here.
As for the degree... I got to where I am (computer programmer) without a degree... like you, a high school diploma. I'm in my early 30s now, and although it isn't critical at this point, I realize that in these times, and... should I ever seek to go into management or break a 6 digit salary, you pretty much need at least a bachelor's degree... unless you plan to open your own business. I graduate in Februrary... thank God... can't wait till it's over. I also read a study that said the unemployment rate for people with bachelors is only 4%, while it's over 20% for people without.
When it comes down to it... two people can have nearly the same experience, and both be charismatic and eager for a job... but the guy with the degree always ends up winning out. I think companies see it as a "rite of passage" or at the very least, that you were willing to put in the effort and stick to something through completion. Also, keeping your performance reviews from all your companies (assuming they are good) helps too!
If we didn't have discussions on that basis, what would we ever discuss?
I have no problem with inexperienced people asking questions. That's good; it's one way we all learn. What I do object to are the authoritative-sounding answers posted by people who have no idea what they're talking about and/or no understanding of the technical issues involved. I am doubly distressed when the topic under discussion involves health and safety. Brakes are a safety item, not a fashion accessory.
(A recent example: One PFFer cautioned another to always wear gloves while soldering electronic parts because "sodder [sic] ... can ... be ... very dangerous and poisoning.")
[This message has been edited by Marvin McInnis (edited 11-01-2010).]
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10:52 AM
82-T/A [At Work] Member
Posts: 25714 From: Florida USA Registered: Aug 2002
What I do object to are the authoritative-sounding answers posted by people who have no idea what they're talking about and/or no understanding of the technical issues involved.
That said ... it does sound like you had your mind pretty well made up before you even started this thread, and your use of "Argument" in the topic headline does nothing to dispel that notion. It's one thing for somebody to modify his own car however he chooses; it's quite another for him to blithely recommend ad hoc mods to somebody else.
Personal example: I engineered a relatively minor mod to the '88 rear brake system several years ago. I now have four years of driving experience on it without a single problem, but I still haven't posted anything about it on PFF because I want to be sure of its long-term safety and reliability before sharing it with others. Maybe soon, maybe not. I have freely provided all the information I have developed on my mod to one other PFFer via PM, but only in response to his direct request and only after I was convinced that he understood the safety issues involved.
[This message has been edited by Marvin McInnis (edited 11-01-2010).]
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10:59 AM
82-T/A [At Work] Member
Posts: 25714 From: Florida USA Registered: Aug 2002
That said ... it does sound like you had your mind pretty well made up before you even started this thread, and your use of "Argument" in the topic headline does nothing to dispel that notion. It's one thing for somebody to modify his own car however he chooses; it's quite another for him to blithely recommend ad hoc mods to somebody else.
Personal example: I engineered a relatively minor mod to the '88 rear brake system several years ago. I now have four years of driving experience on it without a single problem, but I still haven't posted anything about it on PFF because I want to be sure of its long-term safety and reliability before sharing it with others. Maybe soon, maybe not. I have freely provided all the information I have developed on my mod to one other PFFer via PM, but only in response to his direct request and only after I was convinced that he understood the safety issues involved.
What is it that I've already decided? I asked for pros and cons, and to see what other people have done, that's what I'm getting. Of course, I expected it to go all over the place, which is why I put it here in O/T.
I still really don't know what I want to do. I know that I want less brakes in the rear, which is what's stock anyway on the Fiero, and I know from my discussions on the Porsche forums (and based on what Ogre said) that you want substantially less braking in the rear because you NEVER want the rears to lock-up since it can cause the back end to fly out.
On the other hand, I also don't want to do major surgery to the rear, I want to keep it as stock as possible, BUT... I KNOW that I need vented front rotors, which was why I decided on going with Grand Am brakes.
When I had a perfectly functioning all stock braking system when the car only had 50k miles on it... the brakes would smoke. I changed the pads, even the rotors a couple of times, and still the brakes would have major brake fade. I drove like a psychopath... I mean, this was 12-15 years ago and I was just a kid... but it was not uncommon for me to come to a flying stop at a stop light with my brakes literally cooking (could see smoke rising from both front wheel wells). This essentially went away when I finally switched to cross-drilled / slotted rotors by Ocelot.
The brakes worked really well after that, but with the slightly larger displacement that I now have, and the more aggressive suspension that I have, (and the better tires that I'll have), I'm confident that my brakes will end up being overpowered somewhat. PLUS the fact that the GA upgrade was the same cost as me rebuilding everything and replacing the stock parts anyway. PLUS, I bought this stuff about 5-6 years ago anyway... so I'm just getting around to installing it now.
My options basically right now are:
1 - dial in an adjustable proportioning valve (from Summit, etc) to my liking, with stock new / rebuilt rear brakes.
2 - Go with the Cadillac rear calipers and fabricate a bracket for a spot-emergency brake.
3 - Go with the GrandAm rotors / calipers and a spot emergency brake and get an adjustable proportioning valve too.
Not sure really just yet which way I want to go... but I have time. I haven't started the car in 3 years, so it's not like I'm in any kind of rush.
The GA brakes on the front, with a stock MC doesn't provide enough VOLUME.
Going with a larger MC, with GA in the front provides the needed volume for the front, but then doesn't provide enough PRESSURE for the rear (about 1/3rd less pressure)... which of course upsets the brake-bias.
Looks like there's a couple of threads on here that show a way to increase the volume of the stock MC so that you maintain the pressure in the rear, while still providing the needed volume for the front Grand Am brakes.
I'm running the GA brakes out back with the rest of my system being stock and I don't have any issues(on dry pavement, wet pavement is another matter entirely) with wheel lockup or loss of control, and I've had more than my fair share of emergency braking situations. At highway speeds it sheds speed like no-bodies business, and when I first did the upgrade I went out to an abandoned parking lot that's got enough room for me to hit 70+ and stomped the brakes multiple times in various maneuvers with no degradation in brake performance, no wheel lockup and no loss of control.
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03:52 PM
PFF
System Bot
RandomTask Member
Posts: 4547 From: Alexandria, VA Registered: Apr 2005
I'm running the GA brakes out back with the rest of my system being stock and I don't have any issues(on dry pavement, wet pavement is another matter entirely) with wheel lockup or loss of control, and I've had more than my fair share of emergency braking situations. At highway speeds it sheds speed like no-bodies business, and when I first did the upgrade I went out to an abandoned parking lot that's got enough room for me to hit 70+ and stomped the brakes multiple times in various maneuvers with no degradation in brake performance, no wheel lockup and no loss of control.
Yeah, if I'm reading it correctly, Ogre's article essentially says that so long as the tolerances on the Grand Am brakes are within ideal spec, then you would NOT run out of fluid volume that would cause the brakes to bottom out and not gain any additional braking force.
In my case, I have the Blazer master cyl... so that comes with some issues. I have more than enough volume and pressure for the front, but not enough pressure for the rear brakes to really function at their best.
EDIT: to say that if the pads start taking some significant wear, the article states that the stock MC wouldn't have the volume to properly make the front caliper pistons fully compress... IE: your brakes would begin hitting the floor like they did for David Couldhardt in one of his races with Mercedes McLaren a couple of years ago. (don't know why I thought of that)
GA front, Seville rear, blazer MC is close to OE system in balance (Bias F/R ratio). Allot closer that All GA caliper... See balance section in brake math Excel sheet
82-T/A You system move to: Row 6 front Row 12 rear Row 32 balance
Do Not use OE MC under any condition with GA caliper.
Problem is rear caliper never stay in adjustment most time. As so as rear gets too much clearance, you have no rear brake. update info on that page...
------------------ 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)
GA front, Seville rear, blazer MC is close to OE system in balance (Bias F/R ratio). Allot closer that All GA caliper... See balance section in brake math Excel sheet
82-T/A You system move to: Row 6 front Row 12 rear Row 32 balance
Do Not use OE MC under any condition with GA caliper.
Problem is rear caliper never stay in adjustment most time. As so as rear as too much clearance, you have no rear brake. update info on that page...
Hey Ogre, thanks for the response. Where is there a Row32? You don't show any charts or tables on your page that have that many rows on them. Also, the rear doesn't have a column 12, but if it does, it says "Warning! Table does not account for effect of the proportioning valve!"
Download Link near the bottom... "Where else should I read?"
OE balance/bias is Row 30 and the GA-Seville is Row 38
------------------ 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 way I see it, you have a few good options for the back:
1. 1988 rear cradle and brakes (plus you get the good suspension). Yes, the 1988 piston is far smaller than the GA piston, but it acts on a larger diameter rotor. Note that piston bore AND rotor diameter affect overall brake torque as a function of hydraulic pressure.
2. Cadillac rear calipers on GA rotors. I have Cadillac calipers acting on LeBaron rotors, and the parking brake is is good.
3. GA rotors, GA calipers, mechanical spot calipers for parking brake. I have evaluated this option on my own 84-87 Fiero and didn't deem it realistic in terms of mounting, although you may be more creative when it comes to mounting than I am. Also note that the spot calipers don't have a reputation for having much clamping force, so when using them on tiny rotors, they'll be relatively ineffective compared to their usual ~12" rotor supercar big brake applications, but your mileage may vary..
There was misinformation posted earlier in the thread... Boosters have nothing to do with brake balance.
As far as adjustable proportioning valves go, they should be seen as a fine-tuning tool for an already well-designed brake system, not a band-aid for grossly mismatched brake parts.
[This message has been edited by pmbrunelle (edited 11-02-2010).]
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10:32 AM
82-T/A [At Work] Member
Posts: 25714 From: Florida USA Registered: Aug 2002
The way I see it, you have a few good options for the back:
1. 1988 rear cradle and brakes (plus you get the good suspension). Yes, the 1988 piston is far smaller than the GA piston, but it acts on a larger diameter rotor. Note that piston bore AND rotor diameter affect overall brake torque as a function of hydraulic pressure.
2. Cadillac rear calipers on GA rotors. I have Cadillac calipers acting on LeBaron rotors, and the parking brake is is good.
3. GA rotors, GA calipers, mechanical spot calipers for parking brake. I have evaluated this option on my own 84-87 Fiero and didn't deem it realistic in terms of mounting, although you may be more creative when it comes to mounting than I am. Also note that the spot calipers don't have a reputation for having much clamping force, so when using them on tiny rotors, they'll be relatively ineffective compared to their usual ~12" rotor supercar big brake applications, but your mileage may vary..
There was misinformation posted earlier in the thread... Boosters have nothing to do with brake balance.
As far as adjustable proportioning valves go, they should be seen as a fine-tuning tool for an already well-designed brake system, not a band-aid for grossly mismatched brake parts.
Yeah, I'm really considering the 88 upgrade... just don't know what all is required of it. I know I have to make adjustments to the top of the shock towers... in the 88 suspension, do they still use tie-rods to keep the steering knuckle in place? Or is it not even a steering knuckle anymore?
Based on all the info I get from Ogre's Cave... the ONLY problem with my swap (as it is) from what I can tell, is the decrease in line pressure to the rear brakes... which decreases the overall braking force to the rear brakes. SO... if there is a way to simply increase the rear brake pressure... then I would be OK, and it would be within spec. I don't believe there's anything i can simply clamp in-place of the rear brake line to do this? Either that... is there any way to bore out the piston on the stock caliper? I don't know how feasible that even is...
I have some time to think about it, because I still have to finish putting together the entire front components first (radiator, hoses, A/C stuff... etc...)
There are no rear tie-rods in 88. The knuckle was a brand-new part made specifically for the Fiero's rear suspension. Due to the strut tower changes, you can't use normal springs (which would interfere with the strut tower) Coilovers become required. Because of their smaller diameter, this avoids interference issues. There is a lot of information on the topic to be found with the search function. Details on differences in the strut mounting geometry can be found in the 1988 and 1986 service manuals, both of which are available online. Service manuals include some critical dimensions which must be maintained when straightening a car that's been in an accident.
The thing with your only problem is that it's quite a big problem... In short, there aren't any easy ways of increasing rear line pressure that are safe for a street car.
There isn't enough material in the factory rear caliper to bore it out, and then you have the challenges of finding a piston that will work...
On the front however, if you're friends with a machinist who has time to help you figure the details, you could press in a sleeve in the GA caliper in order to use the smaller Fiero piston. This is fairly realistic.
It may be possible to shave the front pads thinner and use the Fiero caliper directly on the GA rotor. I have never measured the difference in thickness between the GA and Fiero rotor, nor do I know how much pad material can be shaven. You may have to change pads far too often with this setup. I don't know, I haven't evaluated this.
All in all, the Cadillac rears are far more simple and bolt-on than attempting caliper modifications. It's already been engineered. You don't have to work out the bugs.
I don't know why you would machine to use the Fiero caliper on the front when the GA calipers are so cheap. Of course I don't have the OE rear calipers.
The way I see it, you have a few good options for the back:
1. 1988 rear cradle and brakes (plus you get the good suspension). Yes, the 1988 piston is far smaller than the GA piston, but it acts on a larger diameter rotor. Note that piston bore AND rotor diameter affect overall brake torque as a function of hydraulic pressure.
3. GA rotors, GA calipers, mechanical spot calipers for parking brake. I have evaluated this option on my own 84-87 Fiero and didn't deem it realistic in terms of mounting, although you may be more creative when it comes to mounting than I am. Also note that the spot calipers don't have a reputation for having much clamping force, so when using them on tiny rotors, they'll be relatively ineffective compared to their usual ~12" rotor supercar big brake applications, but your mileage may vary..
There was misinformation posted earlier in the thread... Boosters have nothing to do with brake balance.
As far as adjustable proportioning valves go, they should be seen as a fine-tuning tool for an already well-designed brake system, not a band-aid for grossly mismatched brake parts.
1. No... 88 rears has same problem as earlier year. match with Blazer MC, loose line pressure, and reduce caliper output. Basic Hydraulic rule.... Increase source (MC) area then increase volume but reduces pressure for a given input force.
3. Yes... Spot caliper rely heavily on diameter of rotor. Big rotor = better braking.
Agree on prop valve Sort Of...
Again... OE prop valve does nothing in normal braking on most cars. Only a panic stop will activate the porp valve with line pressure 800-900PSI and above. All Bias given is hydraulic and mechanical advantage for most car/truck. In OE Fiero case, Hydraulic only will give you Bias.
Advantage OE prop solution is no valve to blow up. Car has "natural" bias without a valve to die.
"Why using a valve only in panic stop?"
Think ABS only older... Rear line pressure in high but traction in low. Easier to spin on panic stop when no valve... Remember my earlier post. Weight shift to front in braking. In panic stop, weight in back is low, very low...
Many truck and van calls ABS is actually just a adjustable valve in rear brake circuit...
"But my car as X weight in front and Y in back..."
Car has two weights... Static Weight. Car is not moving... Think curb weight. Dynamic Weight. Car is moving, stopping, accelerate, etc. Weight can shift front, back, sideways, etc. This is weight the brake system and suspension sees.
Fiero weight is 50/50 (aprox) normally but in panic stop weight shift to 80/20 (front/rear) or more... In FWD car, panic stop weight shift to 90/10 plus...
Anyone using an aftermarket prop valve to make-up for bad design is waiting for time bomb to blowup, like most with GA in rear only...
------------------ 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)
Why is this thead in the OT forum? It belongs in the Technical or General Fiero Chat forums.
When I search for such information, I never look in the OT forum for it. When this thread is done, the information might as well have been lost to most users.
88 rear brakes are not nearly as bad as 84-87 rear.
88: 1.889 in piston diameter 2.80 in^2 piston area
10.43" rotor diameter. Lets say effective radius is 0.75" from outer edge of rotor: 4.46 in approx effective radius
4.46 in * 2.80 in^2 = 12.5 in^3
84-87: 1.772 in piston diameter 2.47 in^2 piston area
9.68" rotor diameter. Lets say effective radius is 0.75" from outer edge of rotor: 4.09 in approx effective radius
4.09 in * 2.47 in^2 = 10.1 in^3
Whatever master cylinder you use, it doesn't affect brake biasing. What is important is the proportion of brake torque per unit of hydraulic pressure between the front and rear.
[This message has been edited by pmbrunelle (edited 11-02-2010).]
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02:00 PM
Dec 16th, 2010
82-T/A [At Work] Member
Posts: 25714 From: Florida USA Registered: Aug 2002
Ok, so... since I'm getting closer to this part of my rebuild on my car, this is what I've ultimately decided to do.
Rather than fiddle with an adjustable proportioning valve (simply because I have neither the time, nor the place to really test one out legally), I've decided that I'm going to go with the Cadillac brakes for the rear.
I have a couple of questions if you guys don't mind.
1 - I know the ratio isn't perfect, but it's close enough. Will I still get my benefit of having ever so slightly less rear brakes, but having it STILL be within the "safety zone" of ensuring that the brake bias is still appropriate?
2 - What years Seville do I need to get the brakes from? I am assuming these are REAR brakes from a Seville, correct?
3 - What all do I need to do to get the emergency brake working. Can I use ALL the factory emergency brake hardware? I would suppose that since this post didn't turn out as argumentative and Trash-Can-Esq as I had originally anticipated it would be (which is why I as the OP originally posted it here), this might be a good post to move to the TECHNICAL section. You know... if you want.
82 T/A,, Use Wagner Thermoquiets pads on the 84 to 87 front brake pads,,you do not need the grand Am units ! have spread the word on this for 3 years if your rotors are half way decent.& the calipers don,t leak,,all you need are the thermoquiet front brake pads. this is the BEST upgrade for the average Fiero owner leave the Grand Am upgrade for more experienced ,,on the stock calipers,,use thermoquiet pads,, also to improve braking on other cars you own,, also forget the EBS, the hawk,& the others,use thermoquiets umless you are going to race The thermoquiets give good all around braking performance the thermoquiets are $55.00 for the front pads ,,buy them when they have rebate,, get $10 to $15 back,, you can spend it on booze or drugs .. very often the rotors have pad residue,dirt grease imbedded in rotor, clean this crap off with brake cleaner,, sometimes it is so heavy and you must sand it off make sure your flexable hose are in good condition. do the thermoquiets on front first ,, then the rear if really needed.. If inexperience with brake work ,,If you do any work on rear brakes take your time,have at least one extra new brake pad retainer($3.00,fIERO STORE)use top quality pads
Thermoquiets are ok for unvented rotors. The Fiero stock system is cr*p and you can patch a cheap brake system all day and it won't be as good as a properly designed vented rotor system. But hey, to each his own
