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  what is the maximum thickness of rotor acceptable for a stock 88 fiero rear caliper?

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what is the maximum thickness of rotor acceptable for a stock 88 fiero rear caliper? by m0sh_man
Started on: 01-09-2015 11:48 AM
Replies: 11 (409 views)
Last post by: m0sh_man on 01-11-2015 06:24 PM
m0sh_man
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Report this Post01-09-2015 11:48 AM Click Here to See the Profile for m0sh_manClick Here to Email m0sh_manSend a Private Message to m0sh_manEdit/Delete MessageReply w/QuoteDirect Link to This Post
ive got an 88 rear cradle under my 84 fiero, id like to upgrade the rear brakes to have a little more effort, im wondering what the thickest a rotor can be before it will no longer work int he stock 88 rear caliper. Id like to find something thats already 5x100 bolt pattern if possible.

on the fronts im looking at several options also, but the front brakes will lock up already and the rears will not so im thinking i need a little more rear braking force for right now compared to front.

thanks in advance if you have the answer.

matthew
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Report this Post01-09-2015 01:46 PM Click Here to See the Profile for fieroguruSend a Private Message to fieroguruEdit/Delete MessageReply w/QuoteDirect Link to This Post
Maximum thickness really depends on the thickness of the pads, some pad manufacturers use thicker pads to improve life.

Stock is 19mm, the C4 setup that is used all the time is 20mm.

You can go slightly wider by adding a shim between the bridge and the caliper.
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Report this Post01-10-2015 10:56 AM Click Here to See the Profile for tsharkSend a Private Message to tsharkEdit/Delete MessageReply w/QuoteDirect Link to This Post
The rear brakes locking up under braking is a bad thing. The back end could come around. Most of the braking is done in the front.

You could use the proportioning valve to adjust for the desired bias, however. Be very careful.

I also suspect that thicker rotors wouldn't help, anyway. When they were installed, the brakes would be adjusted for the thicker pads. As your brakes wear, they don't go away as the rotors/pads get thinner; they adjust. More fluid stays in the caliper, and the pistons keep the pads pushed out further. You retain a consistent pedal right up to the wear out point.

Also, you have to be careful about heat in the brakes. I don't know much about this, but you could develop overheating/warping under heavy braking. There has to be a way to dissipate the heat. With more mass and less air space, I would carefully consider this potential issue.

Then there's the rotating weight. Again, I know little about this, but was once given a lecture about this and unsprung weight. My takeway was that these two things are bad. The lecture was good, and I had a good understanding, that seems to have stayed behind in the same room as the lecture took place. I still don't understand unsprung weight, so this paragraph may be of no value.

Finally, I would think that thicker pads would be a better idea than thicker rotors, anyway, as long as the mounts could contain the extra leverage.

[This message has been edited by tshark (edited 01-10-2015).]

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Patrick
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Report this Post01-10-2015 02:59 PM Click Here to See the Profile for PatrickClick Here to Email PatrickSend a Private Message to PatrickEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by m0sh_man:

on the fronts im looking at several options also, but the front brakes will lock up already and the rears will not so im thinking i need a little more rear braking force for right now compared to front.


If I had your concerns about my brakes (which I don't), this is the route I'd go... Direct Swap Adjustable Brake Proportioning Valve Adapter
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Report this Post01-10-2015 03:19 PM Click Here to See the Profile for tsharkSend a Private Message to tsharkEdit/Delete MessageReply w/QuoteDirect Link to This Post
Yes, that. If he still makes them.
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Patrick
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Report this Post01-10-2015 04:15 PM Click Here to See the Profile for PatrickClick Here to Email PatrickSend a Private Message to PatrickEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by tshark:

Yes, that. If he still makes them.


I was surprised to see that the fella who makes these valves hasn't posted in that thread since last October, even though there seems to be a lot of interest in his product.

 
quote
Originally posted by aaron88 on 10-07-2014 08:52 PM:

Sorry for the wait folks, and thanks for the reminder. I'm setting aside some shop time as we speak...

The backlog is as follows:
Five 19mm
Eight 21mm
Six (unconfirmed size)

So that's 19 on back order, I will get them out as fast as I can now that I have a few spare moments a couple times a week.

[This message has been edited by Patrick (edited 01-10-2015).]

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Report this Post01-10-2015 05:20 PM Click Here to See the Profile for tsharkSend a Private Message to tsharkEdit/Delete MessageReply w/QuoteDirect Link to This Post
Yes, I wanted to buy a few, in case I wanted some later, because these vendors seem to quietly vanish.
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m0sh_man
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Report this Post01-11-2015 01:09 AM Click Here to See the Profile for m0sh_manClick Here to Email m0sh_manSend a Private Message to m0sh_manEdit/Delete MessageReply w/QuoteDirect Link to This Post
i dont need a thicker rotor, im just looking at brake rotors in general and would need to know if it would even work, i found the WRX rotors are around 12 inches, but they are 25MM thick so i dont think they would fit in the 88 caliper.

im also considering the 11.3" Chrysler lebaron brake rotors, but if i can go 12-13" that would be better. I have a 3800 series II supercharged engine, and i want the car to be able to stop well without locking up the fronts, ive NEVER had a fiero that i felt had good brakes. and ive had atleast 15 daily driven fiero's and parted out 30 or so. in my 15 years of owning fieros.

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Report this Post01-11-2015 07:31 AM Click Here to See the Profile for fieroguruSend a Private Message to fieroguruEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by tshark:
The rear brakes locking up under braking is a bad thing. The back end could come around. Most of the braking is done in the front.


He isn't wanting to lock the rear up, just have them contribute more to the overall braking. Stock brake bias on the 88's is between 57-64% to the front depending on pedal input pressure. While the fronts can benefit from weight transfer while braking and do more braking, a Fiero will not see as much weight on the front wheels (increases available traction) as say a camaro will, because about 53% of the stock weight is already on the rear. You can better optimize the brakes by finding the point the rears lock up first & back off slightly to ensure the fronts lock up first - ideally on a wet road.

However, you must be very careful. You MUST run the same brand and model tires front/rear. If you mix/match tires like put an all season tire up front and a summer only tire in the rear, then in the summer you probably will not ever be able to lock the rears up even if you increase the rear bias, but as temps drop, the rears will lose their grip much, much faster and make a situation where the rears will lock up before the fronts... just because the tire characteristics change with temps. So use the same brake/model tires so the front and rear will change together.


 
quote
Originally posted by tshark:
I also suspect that thicker rotors wouldn't help, anyway.


He is just wanting the info, so as he looks at rotor options, he can quickly narrow down the list that will "fit".
Rotor depth also plays a role as on the 88's you need a deeper rotor so there is room for the caliper bracket.


 
quote
Originally posted by tshark:
Also, you have to be careful about heat in the brakes. I don't know much about this, but you could develop overheating/warping under heavy braking.

This is why high performance groups are wanting the rear brakes to do more. Even with larger rotors, you can overheat the fronts with the stock brake bias under racing conditions. If the rears can safely contribute more, the fronts will do less braking and have to dissipate less heat.

 
quote
Originally posted by tshark:
Then there's the rotating weight. Again, I know little about this, but was once given a lecture about this and unsprung weight. My takeway was that these two things are bad.


Lighter for both is certainly better, but there are compromises and tradeoffs as power (and chassis weight) goes up. Outside of competitive racing, most won't notice the difference of adding 3-6 lbs per corner to have better braking. Most add twice that when they change out the stock wheels/tires.

 
quote
Originally posted by tshark:
Finally, I would think that thicker pads would be a better idea than thicker rotors, anyway, as long as the mounts could contain the extra leverage.


The pads generate the heat, the rotors must dissipate the heat or you will get into brake fade.

Thicker pad allows them to use a more aggressive compound (wears faster) and still have decent life (more pad material thickness to wear down) or use the same low wear compound and offer a lifetime warranty.

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Report this Post01-11-2015 08:36 AM Click Here to See the Profile for tsharkSend a Private Message to tsharkEdit/Delete MessageReply w/QuoteDirect Link to This Post
Thanks, fieroguru. Frankly, I was surprised you didn't address any of those things before I posted.
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Report this Post01-11-2015 09:06 AM Click Here to See the Profile for BloozberrySend a Private Message to BloozberryEdit/Delete MessageReply w/QuoteDirect Link to This Post
If you know what the brake pad thickness is, then subtracting the total pad thickness from the known distance between the brake pad mounting surfaces on the caliper will give you the maximum rotor thickness. I don't know what pad thickness you intend to use but from my measurements, the distance between the outboard pad mounting surface and the face of the fully compressed piston is 48 mm. A picture ways a thousand words so:



Edit to add: front and rear are the same.

[This message has been edited by Bloozberry (edited 01-11-2015).]

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m0sh_man
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Report this Post01-11-2015 06:24 PM Click Here to See the Profile for m0sh_manClick Here to Email m0sh_manSend a Private Message to m0sh_manEdit/Delete MessageReply w/QuoteDirect Link to This Post
thanks for all this knowledge guys, its been great to learn.

keep in mind my car is a 1984, but with 1988 rear cradle and brake setup, the rears have NEVER locked up, but the passenger front always seems to be the one to lock up first when braking hard.

as of right now the cars been sitting for 2-3 years and the brakes are kinda rusty, but still working properly, but they have never worked like they should have. i just want to put on some larger rotors to fill out the 17" rims, and also help with braking, but id prefer using the stock 1988 rear fiero brake calipers and i can do pretty much any calipers on the fronts just move them outward as most kits do.

who is still selling brackets to put larger brakes on fieros and then there is the problem of getting them for 84-87 front and 88 rear (so a split set)

matthew
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