I purchased bmwguru's front bracket kit for 84-87 earlier this year. This kit utilizes 88 front calipers with c4 12" rotors. There were several posts in the original thread related to the differences in weight of the c4 calipers as opposed to the 88 calipers( https://www.fiero.nl/forum/F...4/HTML/060571-8.html ), but no answer as to whether the c4 calipers could be used instead. I have slowly acquired all the parts needed for this upgrade, except the calipers. 88 calipers are very hard to find and their cost is much more than the c4 calipers. Can anyone weigh in on the ability to use the c4 caliper instead on the 88 caliper?
Mounting bolt spacing distance is much wider with the C4 calipers vs. the 88 Fiero ones, so they will require a different bracket. Also, the C4 calipers will have an effective area 25% larger than the stock fiero calipers and cause major bias imbalance issues if you don't so something with the rear calipers. The issue will be that the rears will not have enough brake bias (fronts will be doing a higher % of the braking), and most off the shelf rear bias adjusters only work to reduce rear brake bias, not increase it.
You can buy new/rebuilt 88 Fiero calipers on ebay or from calipers online.
They proportion the brake balance completely wrong. Fieros have damn near identical caliper piston diameters on all fours on 84-87's and it actually has the same piston diameters on all 88's calipers. The end result is good proportioning all around for a slightly rear heavy car. The proportioning combination valve does trim back the rears pressure as the braking forces increase past light braking. This car is one of the few that under light braking, all four wheels are doing the exact same amount of braking.
So if you put Corvette front calipers on, your fronts become way over braked compared to the rears, resulting in early front wheel lockup and severe under utilization of the rear brakes as well, which will negate weight transfer to the front wheels, causing them to have less traction then they should, in addition to the early lockup. NOTHING about this is good for braking performance, which is the end goal of any brake upgrade.
Fiero's natural braking biases are: 1:1 on 88's 1.06:1 on 84-87's
Corvette 1.59:1
So, in a nutshell. Stay away from the Corvette brakes, they would be a serious downgrade. The rear brake calipers are smaller in every way than a Fiero's anyway.
Guru beat me to it! But hopefully we've helped steer you right.
[This message has been edited by Fierobsessed (edited 09-18-2014).]
Thanks for the info. Bmwguru didn't have all the kinks ironed out for the rear c4 rotor/ 88 caliper setup when I purchased the fronts from him. I was intending to possibly use c4 calipers on the front and rear, but the info you've provided indicates I can't do that without acquiring the brackets for c4's.
I also have the front c5/rear c4 brackets from doublec4 and 4 rotors( 12" front c4/12" rear c4 ) already drilled for 5-100mm. Obviously, the 88 calipers front and rear would be the best as far as brake bias is concerned. I guess my best bet is to find someone to buy the 84-87 front 88 caliper bracket kit/c4 rotors and obtain c5 calipers for front, 13" c5 front rotors drilled for 5-100mm, and c4 calipers for the rear.
87 Fiero Front Caliper = 48mm dia = 1,809 sq mm C5 Front Caliper = 54mm = 2,289 sq mm or 26% increase in caliper clamp load.
87 Fiero Rear Caliper = 48mm = 1,809 C4 Rear Caliper = 40mm = 1,256 sq mm or a 31% decrease in rear caliper clamp load.
So with this brake upgrade, you increase front caliper clamp load by 26% while reducing rear caliper clamp load by 31%. The 31% loss in clamp load negates almost all the mechanical advantage gained from the 12" rotor, so you effectively add a bunch of parts and rear braking will remain very close to stock (but with better fade resistance).
If you are going to go to the trouble to swap calipers, then ideally you want to see similar increases in caliper piston areas front and rear.
From what I understand, the Seville rear caliper is ~54mm. That would probably be the best bet for use with the C5 fronts. Not sure if anyone is making the brackets for the Seville upgrade( dpwood? ). The Seville calipers also require Lebaron rotors. The 88 caliper/C4 rotors front and rear would also be optimum, except for the fact that as far as I can tell no one is making the rear brackets. Both of these rear calipers use the ratcheting piston design that I would really like to get away from.
C4 front calipers are ~48mm which would reduce the imbalance that the C5( 54mm ) would have when using the C4 rears. C5 rears are 45mm, but do not have the ebrake.
It looks like there is no solution( maybe Brembo ) for using modern calipers that would even be close to a 1/1 ratio. I'm curious as to why there are so many vendors/individuals selling brackets for the C5 and C4 brake products that have not included this data. I would estimate that a large part of the PFF community doesn't understand or is unaware of the front/rear bias pertaining to the various caliper/rotor combinations being sold.
Also, the proportioning valve's affect hasn't been factored in to this data. I know the valve will limit the amount of braking power to the rear during panic stops, but how much does it affect stock hardware as oppose to the C4 or Seville calipers.....
Originally posted by flimbob: From what I understand, the Seville rear caliper is ~54mm. That would probably be the best bet for use with the C5 fronts.
From a hydraulic perspective, yes the C5 front (54mm) and Seville Rear (54mm) would be a good match. However, you will still alter the brake bias (less to the rear) due to running 12 3/4" rotors in front and 11 1/4" rotors in the rear just due to the leverage effect of the caliper placement. Assuming a 2" tall brake pad (centered on the caliper piston) placed with its edge at the edge of the rotor, the fronts would have 16% more mechanical advantage from rotor diameter vs. the rear.
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Originally posted by flimbob: The 88 caliper/C4 rotors front and rear would also be optimum, except for the fact that as far as I can tell no one is making the rear brackets.
To clarify... 88 Fiero calipers in front and rear with 12" rotors front and rear would keep the stock brake bias F/R while proving the same relative braking increase front/rear. 88 C4 front caliper is dual 38mm (2267 sq mm) and the 88 C4 rear caliper is a single 40mm. Using this pair on a Fiero is a very bad idea...
The key to a balanced brake upgrade for most street driven Fieros is to make sure you keep the same piston area front/rear and same rotor diameter front & rear.
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Originally posted by flimbob: C4 front calipers are ~48mm which would reduce the imbalance that the C5( 54mm ) would have when using the C4 rears. C5 rears are 45mm, but do not have the ebrake.
88 Fiero calipers are 48mm F&R, the 88 C4 front calipers are dual 38mm ones and have about the same piston area (2267 sq mm vs 2289 sq mm or within 1%) as the C5 single 54 mm caliper. So the imbalance issues would be very close to the same. Even if you go to the 84-87 C4 Corvette front calipers, they have a single 54mm piston.
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Originally posted by flimbob: It looks like there is no solution( maybe Brembo ) for using modern calipers that would even be close to a 1/1 ratio.
The Fiero is a very odd platform from a braking perspective. They use the same (or nearly the same - depending on source of info) caliper piston size front/rear and rely entirely on the combination valve to adjust the rear bias. Almost every other car made uses a much smaller caliper piston diameter in the rear for the rough bias adjustment, then just makes a small trim adjustment with the combo valve. This likely stems from the transplanting of the FWD setup to the rear, they kept the same caliper and then GM just had to make a new combo valve.
Here is the data comparing caliper hydraulic pressure front/rear on a stock 88 Fiero at various input levels. Clearly the Fiero has significantly less brake pressure in the rear at higher pedal force. I suspect that most cars with the smaller rear caliper pistons, run the rear line pressure much closer to the front line pressure.
I'm curious as to why there are so many vendors/individuals selling brackets for the C5 and C4 brake products that have not included this data. I would estimate that a large part of the PFF community doesn't understand or is unaware of the front/rear bias pertaining to the various caliper/rotor combinations being sold.
You are going to have to ask them.
I do not offer any hardware or brake kits that use the C5 or C4 corvette calipers for all the reasons listed above (all I sell are the rotors drilled to 5x100mm for those who purchased the brackets, but can't redrill the rotors). The brake kits I sell are designed to maximize braking potential front & rear while keeping the stock brake bias and parking brake function.
I field calls on a weekly basis where people are looking for a C4 or C5 kit front/rear and I try my best to educate them on what happens using those parts, but some people just have to have Corvette brake parts so they say it stops as good as a C4 or C5 Vette... or something along those lines. I would rather have the car stop that fast, with proper balance, for the least amount of $$$ and work... this is the premise for all my brake kits.
Most people don't fully understand brake systems to understand how changing specific parts will impact the balance of the system. If you don't understand it yourself and your vendor can't explain in detail how his/her kit improves braking potential in the front & rear and how bias is impacted, then my recommendation is to not buy it.
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Originally posted by flimbob: Also, the proportioning valve's affect hasn't been factored in to this data. I know the valve will limit the amount of braking power to the rear during panic stops, but how much does it affect stock hardware as oppose to the C4 or Seville calipers.....
The proportioning valve limits pressure before it gets to the caliper, so its behavior will be nearly the same regardless of the calipers used... I say "nearly" because the combo valve has a spring where above a certain input pressure, the rear brake line pressure will gain at a slower rate vs. the front. As you install larger rotors (with proper calipers), the pedal pressure needed to stop the car under normal conditions will become less and and increased number of typical stops while commuting might stay well below the knee pressure (which gives higher rear brake bias). The other area where there "could" be a small impact is the volume of fluid flow through the combo valve if you use calipers with larger pistons, more fluid will have to flow to compress them. But for normal discussions, the combo valve's impact can be assumed constant as the calipers are changed.
I will say that the stock Fiero combo valve is the problem when trying to swap newer caliper setups. So if you absolutely had to have C5 brakes front & rear (calipers & rotors), you might want to look into swapping the C5 master and combo valve as well, so you swap the entire hydraulic system (except ABS) from the C5 to the Fiero. In theory, this would keep the bias the same as the C5 (50/50 weight distribution), but likely would still have too little rear brake bias for the Fiero (but not near as little as keeping the stock Fiero combo valve). I haven't a clue if you could make all the C5 parts work with the Fiero parts (fitment, pedal travel, pedal leverage, etc), but that is probably the path that needs explored more (and it won't be by me).
[This message has been edited by fieroguru (edited 09-21-2014).]
...Clearly the Fiero has significantly less brake pressure in the rear at higher pedal force...
In real world panic braking, I have found this to likely be the case. I think I even mentioned this in another thread or communication. If anything, I would prefer a little more braking power to the rear, within reason. (Still want the fronts to lock first, but with a little more rear bias.)
A bit off topic but, if nothing else, it makes me want to go with wider front tires next time. (I currently have 215/45s front, and 235/45s rear. When I chose those sizes, I was shooting for the same rolling diameter as a stock Formula, and not paying much attention to anything else.)
I'm looking at 12" C4 rotors all around but stock 88 calipers in back and C4 calipers up front. I don't want balanced brakes, when you hit them the weight transfers to the front. So, that would be bad. There's also the fact that I'm getting new wheels and I'm going with a taller wider wheel in the back and that should give the car a de facto front weight bias. Not when it's on a set of scales mind you, but in a practical real world way.
[This message has been edited by Internet-man (edited 01-16-2022).]
I just checked and here locally, I can get front and rear calipers from Napa and O'reilly.......they are approx' $32-45 each for the fronts and $65-80 for the rears. They are not impossible to find! I have installed the 88 rear subframe and am in the process of rebuilding my front end- along with installing 88 calipers and 12" vette discs- I bought the adapter brackets from Sluppy123- He is also starting to manufacture Aluminum billet hubs that have the proper offset with the added vette disc thickness- His work is exceptional!
I run the C4 calipers front and rear on my Chump race Fiero with an adjustable proportioning valve. I typically brake at around 1.1-1.2 gs, higher than street cars so I need to be able to dial back the rears because of the extra weight transfer. With essentially the same parts front and rear, my car has sufficient range to set the brake balance for conditions ranging from standing water to a dry and rubbered (sticky) race track.
It was pretty easy to fab a bracket to install the front calipers but the rear was a little more involved and of course you end up with no emergency/park brake. I use RDX rotors on the front and Jetta rotors on the back with Hawk blue pads. All just fine for a race car but not advisable for a street car.
Also note that with larger diameter pistons the line pressure needed to get the same braking force will be proportionately less, skewing the car towards rear brake bias with the stock proportioning valve. I did the same pressure test with the stock proportioning valve and came up with about the same numbers as seen in Fieroguru's post. Do a little figuring based on piston diameters and you'll see how the balance changes with the bigger pistons. Have a look at this and you can see a specific location of the "knee" of the propotioning valve:
The "knee" serves to approximate the curve needed for ideal brake balance; close but always on the conservative side. Lowering the line pressure needed to get a specific braking force will shift the curve downwards which needs to be accompanied by a shift downwards of the knee as well to maintain safe and balanced braking. That's why an adjustable (and properly adjusted!) proportioning valve becomes necessary when changing piston sizes.
The easiest is to use the stock calipers with bigger rotors and better brake pads; that'll give a street car all it'll ever need for braking. Unless you're planning on running the car hard at the track and know enough to re-engineer a braking package safely, stay with stock or proven combinations.
[This message has been edited by mender (edited 04-12-2016).]
Sounds like you need to get your stock brakes working properly before you run over someone.
What about what I said makes it sound like my brakes aren't working? They work fine but they could work better in the way that everything about every car could work better, which is why we modify them. Going from 88 Fiero front and rear calipers to single piston C4 fronts and 88 Fiero rears means an increase of front piston surface area of 6%. Obviously it's not a huge change but it seems like it would be a tweak in the right direction. Because Nobody Ever Puts the same size calipers front and rear. Corvettes have a 50/50 weight distribution and they have way larger fronts. Mid engine Ferrari's have larger fronts. Fek, Porsche has larger calipers in the 911's front and it's not even mid engine. 996s have 48mm front pistons,42mm rear pistons with no bias valve.
Originally posted by Internet-man: Going from 88 Fiero front and rear calipers to single piston C4 fronts and 88 Fiero rears means an increase of front piston surface area of 6%. Obviously it's not a huge change but it seems like it would be a tweak in the right direction. Because Nobody Ever Puts the same size calipers front and rear. Corvettes have a 50/50 weight distribution and they have way larger fronts. Mid engine Ferrari's have larger fronts. Fek, Porsche has larger calipers in the 911's front and it's not even mid engine. 996s have 48mm front pistons,42mm rear pistons with no bias valve.
88's use a 48mm piston front/rear and the early C4s (85) with the single piston are 54mm which is a 26% increase in piston area. What caliper where you using to get the 6% number?
Most cars do the gross brake bias front/rear with brake caliper piston area differences - front piston area is almost always more than the rear. Then they make fine adjustments with their proportioning valve.
The Fiero is an oddball where the gross brake bias is done with line pressure differences front/rear while using the same caliper piston areas. So the gross and fine adjustments happen in the combination valve. The end result is still more braking in the front/less in the rear, but mixing and matching components from cars with completely different designs is risky unless you know the specs and do the math.
We are talking about C4 calipers. 84-87 Fronts were single 54mm pistons (2289 sq-mm). 88+ went to dual 38mm pistons (2267 sq-mm).
Stock 88 Fiero is 48mm (1809 sq-mm)
going from 48mm to 54 mm is a 6 mm increase not a 6 percent, my bad. what can I say? It was like 2:AM.
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Originally posted by fieroguru: Most cars do the gross brake bias front/rear with brake caliper piston area differences - front piston area is almost always more than the rear. Then they make fine adjustments with their proportioning valve.
The Fiero is an oddball where the gross brake bias is done with line pressure differences front/rear while using the same caliper piston areas. So the gross and fine adjustments happen in the combination valve. The end result is still more braking in the front/less in the rear, but mixing and matching components from cars with completely different designs is risky unless you know the specs and do the math.
I still want to figure it out. Maybe after I get out of school I will do the hard work of the maths and designing the bracket since no one else wants to.
[This message has been edited by Internet-man (edited 11-09-2017).]
