Hi, Guys,

OK, this tends to be a very emotional topic. Right up there with "which engine is best" and "power steering". So let's try to keep it just on the facts.

I have owned an '87 puchased new and two '88's purchased not so new. It has been MY experience that even when at their best, the '84-'87 are simply inadequate, both in terms of pedal pressure required and in fade resistance. The '88's are considerably better, but still marginal in terms of pedal pressure, I have not seen any fade issue with the '88's.

I personally find it difficult to modulate the brakes at the limit when so much pedal pressure is required (YMMV). Accordingly I have looked into the various brake upgrades and what you get on a comparative basis (I have no means of direct measurements).

Pedal pressure is directly related to brake torque. Brake torque increases directly with brake rotor diameter and pad compound and as the square of the radius of the brake booster. It is not affected by the area or number of the brake pads (increasing the area or number of pads MAY reduce the heat transfered to the brake fluid or the maximum temperature of the pads which may in turn affect fading). Brake torque is also affected by the ratio of the area of the master cylinder to the brake cylinders. I do not have data on this so it is not included in this analysis.....if anyone can give me that data I will add it into the table that follows.

Brake torque required increases directly with the radius of the wheel/tire combination, with the area of the contact patch, and with the rubber compound. So as a larger wheel/tire package is installed the stock brake torque becomes even more inadequate (in MY opinion).

The table which follows assumes no change in the wheel/tire diameter or contact patch or in the pad compound or in the ratio of the master to wheel cylinder area. Note that increasing the booster radius combined with increasing the rotor diameter results in a multiplicative increase in brake torque. The data in the table was taken from the AutoZone website.

All that said (WHEW!), this is how brake torque varies among the various common brake upgrades. The brake torque is set at '1' for the stock brakes and the other combinations are expressed as a fraction of the stock brakes (subtract '1' from each number and multiply by '100' to get the percent increase in brake torque for each combination).

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			               84-87	  Grand Am     88	LeBaron	12" Vette	13" Viper

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Rotor Diameter(inches)		9.68	     9.68	    10.43	 11.26	 12.01	13.03

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84-87

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Rotor Weight(lbs)			13.85	     10.8	    11.25	  13.7	  20.4	    17

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Vented?			                  N	       Y	      Y	    Y	    Y	     Y

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Torque Factor			1.00	     1.00	    1.08	  1.16	  1.24           1.35

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W/ 9" S-10 Booster			1.27	     1.27	    1.36	  1.47	  1.57           1.70

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88

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Torque Factor					   1.00	  1.08	  1.15           1.25

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W/ 9" S-10 Booster					   1.27	  1.37	  1.46           1.58

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Conclusions: The single greatest increase for 84-87 is going to 13" rotors (35%), second greatest is the brake booster change (see $100 brake upgrade) at 27%. For 88's the single greatest is the brake booster (27%). Accordingly I would suggest trying the brake booster in all cases first. I was a bit surprised that even when the largest rotors are combined with the increased brake booster, the increase in brake torque is only 70% or 58% (84-87 and 88 respectively). I think this puts the lie to the idea of having video game sensitive brakes. Again, YMMV.

I solicit your comments and experience, but PLEASE, if you are merely going to say that stock brakes are just fine and I only need to fix mine, please start your own threads.

Sorry, the formatting is lost. I will email an excel spreadsheet to anyone who would like it.

Larry.

[This message has been edited by imacflier (edited 09-21-2011).]

Use the "code" tag to fix formatting for the table.

Dobey,

How do I do that? Or where is it documented so I can learn and not be so ignorant?

Larry

use [code ] without the space at the end and [/code]

quote Originally posted by imacflier: How do I do that? Or where is it documented so I can learn and not be so ignorant?

When you are writing/editing a post, on the left there is a thing that says "PFF Code is ON" which is a link. Click it, and it tells you all the tags you can use.

Dobey,

Thank you. Still haven't got, but closer!

Larry

I think you only need one block of code tags. You don't need to use it for every line you want. Just every block of text you want to preserve formatting on.

Also, can you point at the math/information you used to come up with your analysis?

I think stock 84-87 brakes are adequate. I thought they were okay with mid-grade summer tires. As you mentioned, it's YMMV. I don't doubt you prefer/benefit from more gain. I like a hard pedal.

You should concern yourself with pedal force, not pedal pressure.

Don't use the outside diameter of the rotor for the brake torque calculation. Use the center of the piston.

I can't find it anymore, but EBC brakes used to have coefficient of friction as a function of pressure for their different pad compounds published on their website. It varied somewhat. I like manufacturers that publish information. You're right though, the actual amount of change in brake torque after something such as clipping the corner of a pad as required for the LeBaron brake mod with rotated calipers is way overblown by people.

As far as brake boosters go, diaphragm area*manifold vacuum determines the maximum assisting force possible, not the gain. That said, the gain is probably related to the maximum assisting force, so the comparison of working area to estimate gain is probably okay. If the booster is dual diaphragm, take that into account also.

Dobey,

Had Adobe update crash my computer in the midst of my reply so I lost the links <sigh>

So: the Sliding Friction Equation is simply Friction = (Coefficient of friction between the two surfaces) x (Normal force applied). Therefore pad area can be ignored.

The Torque Equation is simply Torque= Force x Lever Length.

I see PMBrunelle already addressed the issue of the booster areas and I concur. Thank you PMB.

I do have an error in that I used the radius of the rotors in my calculation and I properly should have used the average of the maximum distance from the center to the outer edge of the pad with the distance to the inner edge of the pad, but this is a comparison not a hard force calculation.

If you have an email addy in your profile, I have sent you a copy of the spreadsheet.

Thanks for your help and comments.

Larry

perfect timing to post this. I'm toying with the idea of upgrading soon. Just got 18s and I suspect I will be feeling the difference in my brake response. Only other real comparison is how much each changes the offset. Could really make or break someone with aftermarket wheels. For me the extra would help. I had to compromise and go a bit further in then I wanted, but swapping brakes could equalize everything.

just a thought to help people use the comparison info

quote Originally posted by imacflier: So: the Sliding Friction Equation is simply Friction = (Coefficient of friction between the two surfaces) x (Normal force applied). Therefore pad area can be ignored.

Because the coefficient of friction in brake pads is a function of unit pressure, and unit pressure is a function of pad area, it really shouldn't be ignored. That said, ebc seems to have taken down their information (won't be buying from them), and the only information that came with my vanilla parts-store pads was something along the lines of:

"Made in China"
"Premium Quality"

So I'd just call it a day and assume a constant coefficient of friction, maybe 0.4.

which one is more beneficial to cost?

(more stop per $)

[This message has been edited by americasfuture2k (edited 09-21-2011).]

Depends how you define "stop".

84-87 brake is very good IF:
restore Brake system work done with qualified brake tech. And Many "pro's" auto tech are not qualified at Fiero brakes.
restore Brake system work done with very good parts.

lacking either, likely both, then brake system suffers big time, and not just Fiero.

Example:
most just use low grade pads.
some use "race" pads for street use. Many race pads need more heat to work.

But Fiero brakes suck they think...

List of example for bad fixes is long, longer, then your arm.

next...
You likely need more math....
You assume front/rear bias is 0? Some, GA 4 wheel, is...
Fiero and GA/Seville is bias to front. Is both cases Bias is hydraulic function.
Some bigger rotor setups are bias to front. Some bias are hydraulic, mechanical, or both.

Bias matters. Too much/little bias, or worse bias to back, will affect brake performance. Bias to back will cause car to spin out.

I think Setting rotors total outside diam is wrong for math. Rotors working diam to use in math is center on working area of rotor. (Need inside and outside diameter of working area and find center of that...) Some setup uses rotor w/ same total outside diam but smaller working area in back, functionally (often physical) changing rotor and bias.

------------------
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 Ogre's Fiero Cave (It's also at the top and bottom of every forum page...)

theogre,

Of course bias is significant, just as is heat capacity for fade resistance. But I carefully defined what I was comparing and felt those topics were beyond the scope of what I wanted to address in this thread.

Yes, the correct radius should be the mean distance of the pad from the rotor center, as PMBrunnele pointed this out and I concurred with him about 5 posts back. This is a measurement which will vary with each bracket implementation and is a relatively minor factor in my calculation.

No, I do not agree that the '84-''87 has/is EVER been good. It was marginal at best right off the showroom floor....at least mine was.

After I get my '88 upgrade done (12" vette if I can fit them inside of stock lace wheels, else Lebaron rotors, plus the booster upgrade), I expect to do another thread on bias and how to adjust it. I believe that there is too much front bias, btw.

A general thanks to all who have responded: nice job on keeping pretty much to facts and experience!

Larry

i thought stock brakes did its job pretty well. iv locked all 4 tires once during a sudden scary stop.

Actually I see the Grand AM upgrade to offer the greatest advantage.

It loses 3 pounds per wheel of un-sprung rotating mass. Guys will spend $900.00 each on rims to lose 3 pounds per wheel.

If anyone is doing fiero racing this is just what they need to see.

this chart i think does a great job to help people make up their minds about how they might want to modify their brakes .i have a lebaron style upgrade with front lebaron rotors on the front of my car instead of using 4 rear rotors .the rear lebaron rotors that most people are using incorporate a drum for the parking brake .the front rotors dont have the drum and are a pound lighter each .they come in different diameters too , so i had to order in some to get the right ones .willwood part# 120-7197 gets you an all aluminum racing caliper designed to replace the GM metric caliper that most of us lebaron swappers are using on the front .saves about another pound per wheel .as far as being able to lock up your tires with stock brakes , means you have poor tires and small diameter wheels .the stock brakes were designed to work with the original 13" diam wheels and skinny tires of the 2m4 .then the v6 came along , car weight increases and the brakes stayed the same .i put the wheels and tires from my 86 gt on my 85 2m4 and the brakes were barely adequate , couldnt get a chirp out of them .

timgray,

Actually it is not really all that straightforward. The Grand Am conversion requires machining and retaining the original hub. I am not at all sure that simply comparing the weights of the rotors is appropriate. Now the rotors SHOULD be lower in weight than stock since they are vented....but THREE pounds. I simply do not have the data to do more than a straight published rotor weight comparison.

Good thought, though....thank you.

Larry

quote Originally posted by timgray: Actually I see the Grand AM upgrade to offer the greatest advantage. It loses 3 pounds per wheel of un-sprung rotating mass. Guys will spend $900.00 each on rims to lose 3 pounds per wheel. If anyone is doing fiero racing this is just what they need to see.

While we generally don't like mass, a rotor wouldn't be generally considered an "upgrade"(in terms of fade resistance) if if were lighter. Mass is a necessary evil with brakes - the energy of the moving car has to heat up something. And see Larry's comment about the hubs.

Also note the calipers used with that swap are iron, not aluminium like the stockers. It's an overall weight adder.

quote Originally posted by imacflier: Actually it is not really all that straightforward. The Grand Am conversion requires machining and retaining the original hub. I am not at all sure that simply comparing the weights of the rotors is appropriate. Now the rotors SHOULD be lower in weight than stock since they are vented....but THREE pounds. I simply do not have the data to do more than a straight published rotor weight comparison.

At least in my case, the machining to turn the rotors into hubs was pretty simple. Only the braking surface was removed. So just measure the volume of the braking surface, multiply by the density of cast iron, subtract that value from the published weight, and presto, we know how heavy a hub is.

quote Originally posted by timgray: Actually I see the Grand AM upgrade to offer the greatest advantage. It loses 3 pounds per wheel of un-sprung rotating mass.

HUH?

On my Fiero (87 SE), the Grand Am brake upgrade added 8 lb per wheel in front, and 4 lb per wheel in the rear (24 lb total). The weight gain in the rear was lesser, because the parking brake hardware was deleted.

Those numbers are approximate, since I used a bathroom scale. But the brake upgrade definitely did not reduce weight.

[This message has been edited by Blacktree (edited 09-22-2011).]

quote Originally posted by theogre: 84-87 brake is very good IF: restore Brake system work done with qualified brake tech. And Many "pro's" auto tech are not qualified at Fiero brakes. restore Brake system work done with very good parts.

Just to add my two cents....We had a new Fiero, back in the day, and the brakes were okay but never considered great. Even then people made comments about how sub-standard they were. Compared to brakes today, they are simply aweful.

quote Originally posted by Blacktree: HUH? On my Fiero (87 SE), the Grand Am brake upgrade added 8 lb per wheel in front, and 4 lb per wheel in the rear (24 lb total). The weight gain in the rear was lesser, because the parking brake hardware was deleted. Those numbers are approximate, since I used a bathroom scale. But the brake upgrade definitely did not reduce weight.

That is what his data says. Fiero rotors are 3 pounds heavier than GA rotors. So that means his data is wrong then. All the rotor weights need to be redone with the required hub.

timgray,

Come now, I clearly sourced my data from the Autozone site, and the weight of a modified hub is not avaliable anywhere that I am aware of. It is great to understand any distortion in interpreting the table I provided, but the data is not wrong.

Larry

quote Originally posted by imacflier: timgray, Come now, I clearly sourced my data from the Autozone site, and the weight of a modified hub is not avaliable anywhere that I am aware of. It is great to understand any distortion in interpreting the table I provided, but the data is not wrong. Larry

If you have to add a hub to use any of these other calipers, then the weight of that hub MUST be included. Just ask someone to weigh one and add it to your figures.

It's the only way to make all the weight numbers accurate, otherwise it's comparing apples and oranges. I made an assumption based on your data and was told by several people that it is wrong.

So who is right? is a Grand AM rotor 3 pounds lighter than a Fiero rotor or is it not counting the hub weight which would make ALL the other options significantly heavier? I really want to know. I am certain that others looked at your table and jumped to the same conclusion.

quote Originally posted by timgray: That is what his data says. Fiero rotors are 3 pounds heavier than GA rotors. So that means his data is wrong then. All the rotor weights need to be redone with the required hub.

The data isn't necessarily wrong, you just need to look at it carefully. Rotor weight is rotor weight, and hub weight is hub weight.

Adding the two together and calling it rotor weight (when it's really two parts) would be confusing.

quote Originally posted by timgray: is a Grand AM rotor 3 pounds lighter than a Fiero rotor or is it not counting the hub weight which would make ALL the other options significantly heavier? I really want to know. I am certain that others looked at your table and jumped to the same conclusion.

Stock brakes are the lightest "mainstream" option.

[This message has been edited by pmbrunelle (edited 09-24-2011).]

When I did my brake conversion I weighed all the parts including the modified hubs. This conversion was on an 85GT and consisted of 12" vette rotors, 88 fiero calipers, modifed 85 front hubs, and the caliper adapter brackets/centering rings.

I do not remember the exact weight but I do remember it being just under 3lbs heavier on each corner. I remember this because it was the basis for my wheel choice.

Most brake complaints are from guys with poorly maintained systems with poorly chosen pads.

If either the 87 or 88 systems are in top shape, using a good street pad from Hawk or Porterfield R4-S, you won't have any issues with them. The Grand Am conversion is silly - losing a possibly important part of the safety system(a handbrake) for no real benefit is...dumb. If you really don't like the braking effort, then you will have to trade off effort for increased travel, which can be easily done with a master cylinder swap.

BillS,

Well we sure made it a long way before this particular canard arose....as it always seems to do. As I asked in my original post: please start your own thread!

Larry

quote Originally posted by imacflier: Come now, I clearly sourced my data from the Autozone site, and the weight of a modified hub is not avaliable anywhere that I am aware of. It is great to understand any distortion in interpreting the table I provided, but the data is not wrong.

The 20 lb weight for the C4 12" rotor upgrade is indeed wrong, that is the weight for the 13" rotors that were also available for the C4's. The rotors used for the 88 Fiero 12" rotor upgrade is part # 55011 and weighs in at 14.65 lbs.

..I agree with Tim Gray,,The best bang for the buck is to install the grand am calipers on the rear,,I was originally against this because I often use the hand brake..
I installed the grand Am calipers on the rear with the cheapest pads i could find so as to have the bias not so heavy on the rear,,WOW !! what a difference ,,I did have a problem when testing the brakes I spun the car around on a wet road .this was caused by a sticking caliper I have since found out..
I love having an emergency brake,,but the increase in stopping power is amazing,phenomenal & cheap, frugal,a bargain, PLUS easy to install,,even I could do it & Im a senile, angry,fumble fingered old cripple
..You can install the Grand Am calipers on the rear & later you can use them on the front ,,but this takes a lot more work,machining & expertise.These brakes provided the emergency stopping power I needed when I almost past a cheap,college DDD sorority Bikini car wash

NO MATH needed !!The grand Am calipers put the STOP in the fiero,I have done a lot of work & experinmentation on fiero brakes.. The grand Am option works outstanding & is the least expensive option SIMPLE,a direct swap on the rear
You can get rebuilt calipers from ROCK auto with no core charge,,I recomend duralast rotors from autozone..
to upgrade a stock system use the carbomet from the fiero store,,or the wagner thermoquiets on the front ,, the carbomets should be installed on clean rotors , mildly roughed up with sandpaper,ect.....the rotors should be cleaned up GOOD,,
Old rotors often have brake material stuck to them .
The thermoquiets are one of the best all around pads on the market,,they are available from ROCK auto at a good price..

I have tried 3 mid level pads ,none provided improved braking on the stock brakes,,you have to go with top quality Pads & flush the system

Thats pretty close to what I've always read...

13.5 for rear rotors.
http://info.rockauto.com/ge...Centric/12062041.jpg

14lbs for front.
http://info.rockauto.com/ge...Centric/12062040.jpg

quote Originally posted by timgray: If you have to add a hub to use any of these other calipers, then the weight of that hub MUST be included. Just ask someone to weigh one and add it to your figures.

Don't forget the weight of the calipers. The Grand Am calipers are iron, whereas the stock Fiero ones are aluminum. I don't know the exact numbers, but the weight difference was noticeable.

I'm also willing to bet the data from imacflier compares a front Fiero rotor/hub assembly vs a Grand Am rotor. The Grand Am rotor should be a little heavier than the '84-87 Fiero rear rotor.

I guess the moral of the story here is not to get hung-up on the weights of individual components. When I compared the weights of the two braking systems, I threw the whole set of brake hardware in a cardboard box, and weighed it as a whole (I did the front and rear separately). Everything that got replaced or modified was tossed in the box. That includes the front caliper brackets, modified front hubs, and the parking brake hardware that was deleted.

[This message has been edited by Blacktree (edited 09-24-2011).]

quote Originally posted by wftb: this chart i think does a great job to help people make up their minds about how they might want to modify their brakes .i have a lebaron style upgrade with front lebaron rotors on the front of my car instead of using 4 rear rotors .the rear lebaron rotors that most people are using incorporate a drum for the parking brake .the front rotors dont have the drum and are a pound lighter each .they come in different diameters too , so i had to order in some to get the right ones .willwood part# 120-7197 gets you an all aluminum racing caliper designed to replace the GM metric caliper that most of us lebaron swappers are using on the front .saves about another pound per wheel .as far as being able to lock up your tires with stock brakes , means you have poor tires and small diameter wheels .the stock brakes were designed to work with the original 13" diam wheels and skinny tires of the 2m4 .then the v6 came along , car weight increases and the brakes stayed the same .i put the wheels and tires from my 86 gt on my 85 2m4 and the brakes were barely adequate , couldnt get a chirp out of them .

You've caught my interest! I have a grand am swap in progress at the moment but I've been having mounting issues+ I realize that I want something bigger so I'll be reinstalling stock brakes and selling that. Anyways, I'll look into those Lebaron front rotors+ the aluminim calipers- I wonder how expensive that setup is.

I agree with most of the opinions expressed about the stock brakes- 87GT on stock size tires with new calipers, rubber hoses, pads, and rotors (pads and rotors being Delco replacements); lock up is impossible in dry conditions.

quote Originally posted by BillS: If either the 87 or 88 systems are in top shape, using a good street pad from Hawk or Porterfield R4-S, you won't have any issues with them. The Grand Am conversion is silly - losing a possibly important part of the safety system(a handbrake) for no real benefit is...dumb. If you really don't like the braking effort, then you will have to trade off effort for increased travel, which can be easily done with a master cylinder swap.

On my 86 and 87 I switched over to Porterfield R4-S pads, slotted rotors, SS lines and high temp fluid and no more brake fade. But now that I'll be putting 17" wheels with wider tires, I think I will need more of an to upgrade. Currently leaning towards Willwood calipers, R4-S pads and 12" or 13"rotors up front. We have an end mill and can make any brackets needed. BTW: What should the rotor difference be front to rear? None 13"/13", 13"/12", 13"/11" etc?

[This message has been edited by Francis T (edited 11-11-2011).]

Francis,

I think that is a great question! Different rotor sizes will change the front/rear bias on your car. Since your brake wheel cylinders are the same size (for '88's for sure, and I believe for earlier) your current bias is set by the combination valve. Many people, including myself, think there is too much front bias. This is safest since it ensures that the fronts will always lock up before the rears. It also gives up some braking from the rear wheels. Since there is a significant rear weight bias, and most people have larger tires on the rears, I believe we need less front bias. One way of obtaining it is to put smaller rotors on the rears.

The rub is just how MUCH should the bias be changed....and I do not have a good answer to that question. If you make a mistake, then your rears will lock first and you have a very dangerous situation! Changing brake cylinder diameter does the same thing. In my opinion you should not use different sized rotors front and rear....just too difficult to get the right bias.

It is also my opinion (a controversial one) that if you add an adjustible regulator to the FRONTS, you could reduce the torque on the fronts to get the balance you want, which I define as nearly simultaneous lockup for both front and rear, and do so in very small steps with lots of testing with each adjustment. YMMV, of course.

Larry

I have the Grand Am/Seville setup with a Blazer booster. My car was the first to have the Seville rear brakes and was the "experiment".

I can tell you the bias is pretty much perfect. The car stops like a much newer car.

I can occasionally break loose a front tire, normally in a downhill hard stop, but, it is more a chirp than a slide.

On the flat and in the rain, no problems and no bad habits.

I agree that a stock system when new, with braided lines, and premium pads can perform adequately. It just isn't as good as the upgraded system I have.

You have to drive both to see the difference.

As for the weight, we aren't on a race track. A total of 12 lbs for street use is not critical in any way.

Arn

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84-87 front rotor weight is 13.85?
13.85 spec = Rotor and hub & lugs...

Need to part off hub/etc so... Most of weight for 84-7 is hub area. So You can't use shipping/etc weight for unsprung weight comparison.

Need to compare weight after cutting off rotors... All pieces/trimming leftover after making a hub to new GA/etc rotors.

For guess weight... use rear rotor - 1# (maybe .5# maybe 2#) to be around front leftover rotor.
az says rear is 9.5 - 1 = 8.5 leftover front rotor. So....

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                         84-87	GA	88	LeB	Vette	Viper
Rotor Weight(lbs)          8.5	10.8	11.25	13.7	20.4	17
Caliper Weight             4.0	7.5	etc 

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GA gains 5.8# for 1 front wheel (2.3 rotor + 3.5 caliper) vs OE 84-7 Fiero

Autozone says on caliper "100% new boot, seal & bleeder screw, pistons always match the OEM part, featuring anti-seize components, 100% tested."
OE Fiero spec is phenolic piston... Add .5-1# for steel piston.