91 RX-7 GXL brakes

OK, having had plenty of brake issues myself:

What have you replaced so far, just pads?  How much does the rotor have left in it?

Have you checked your vacuum system for leaks and checked all check valves for proper function?  I had a bud with an F150 that had brake issues and it was a check valve in his vacuum system.  He replaced 2 master cylinders before they figured it out. 

It's not brake bias because you'd be able to lock up either the front or rear or both, not nothing, that's not normal. 

Also found this:

1993 Mazda Rx7

Component

Service Brakes, Hydraulic:Power Assist:Vacuum:Hoses, Lines/Piping, And Fittings

Consequence of Defect

oil mist contained in the engine intake air can collect over time in the brake vacuum check valve preventing the check valve from opening at the specified pressure reducing power assist to the brakes.

Corrective Action

brake performance can be diminished increasing the risk of a vehicle accident.

Recall Notes

dealers will replace two vacuum hoses, including the check valve, with modified hoses

FD and FC brake systems are different, particularly since mine does not have ABS  (all FD's had ABS, very few FC's did)
Also as I stated earlier the rotors are also in perfectly good order.
It's feels like it just about to lock them up but doesn't.
I have no idea how to check the vacuume stuff.

P money may be able to help you, or your allstar mechanic.  My intake whistle was caused by a stuck open purge valve and leaky gas cap... Eventually threw an evap code.

guess I'll have to bust out the Haynes repair manual and see what it says

Quick ? - why is it you want the brakes to lock up?
 
 
How does the pedal feel, does it grab high or low? Once it provides feedback, does it sink quickly, then get tighter?
 
If the master cylinder was bad, typically, your pedal goes straight to the floor and there should be brake fluid running down your driver side firewall and strut tower.
 
Whats the background on the brakes? 1991 didn't have GXL models, just coupe and turboII, so are these brakes from another car that you recently swapped on?
 
If you are bringing the car to the next Auto-x at VMP, I can take a look for you.

It's not that he wants them to lock up, he wants the ability to... it means your brakes can handle the car.  If you get new sticky tires and you can't lock up your brakes due to increased grip... you're missing out on braking potential and need an upgrade - in this case, a repair of some sort.

How does that apply if your car is equipped with ABS, lol. Losing grip is not an objective you want. I know what you're trying to say though....

How does that apply if your car is equipped with ABS, lol. Losing grip is not an objective you want. I know what you're trying to say though....

-we3rx7

It applies because ABS is only activated when you lose grip so unless you can make that happen (BEFORE abs kicks in), you are not braking to your full potential.  ABS kicks in after you have exceeded your maximum ability to brake.

Quick ? - why is it you want the brakes to lock up?  How does the pedal feel, does it grab high or low? Once it provides feedback, does it sink quickly, then get tighter?  If the master cylinder was bad, typically, your pedal goes straight to the floor and there should be brake fluid running down your driver side firewall and strut tower. Whats the background on the brakes? 1991 didn't have GXL models, just coupe and turboII, so are these brakes from another car that you recently swapped on? If you are bringing the car to the next Auto-x at VMP, I can take a look for you.

-we3rx7

The pedal seems to grabbing evenly, ie the more you depress the more it grabs, but if I had to stop short for someone else in front of me i 'd wind up rear ending them
The 91 NA RX-7's are really a crap shoot on what you get parts wise as they were built with what they had on hand that day.
Anyway I say mine is GXL because explaining that the 91's only had 3 models confuses people and it has all the optional equipment you'd see on a GXL except for the electrical dampening contols and LSD.
So it has the 4 piston calipers,which are not stopping the car anywhere near as well as the single piston ones I had on my previous FC.
Can't bring the 7 down because I'm driving the Miata in that autocross.

Is the master cylinder different between the two sets of brakes (four pot vs two)?  Maybe you have a mis-sized master cylinder?

Is the master cylinder different between the two sets of brakes (four pot vs two)?  Maybe you have a mis-sized master cylinder?

-brandini

I think it's still the original, either way I find that unlikely.
Anyway th damn thin overheated again on me this morning, I'm really getting irritated with it.

What type of brake fluid are you running?

What type of brake fluid are you running?

-we3rx7

as far as I know, your basic DOT 3, when I bled them a few months ago the fluid looked good with no junk or discoloration

I think it's still the original, either way I find that unlikely.Anyway th damn thin overheated again on me this morning, I'm really getting irritated with it.

-niburu

 
water wetter from autozone works wonders, dropped my coolant about 15 degrees and it still stay well within tolerance driving hard, you may want to consider a lower temp thermostat. I know the FC's were notorious for overheating. those two may be a viable option before the needed addition of a koyo rad. also make sure your front under tray leading from the bottom of the bumper to the radiator is buttoned up well, this helps divert air to the rad.
 
as for your brakes, i read that you mentioned no ballooning, so i am assuming you have braided lines. also, the FC and FD were VERY flighty at best in thier order of bleeding the brakes, deviation from plan leads to minor "squish". but if you still have firm pedal feel, and the pedal stops before hitting the floor it could just be the pads, or a vac leak. an easy way to tell if your brake booster isnt getting enough pressure is, kinda tricky, is to "heel/toe". you start on a SECLUDED road, go about 60mph, slam on the brakes, half way through slowing down, still slammed on the pedal rev your engine some, to about 5k. if your brake pedal dips in more and you slow down more it could be a clogged vac line, or brake booster vaccume leak. sometimes the large diaphram can go bad.

water wetter from autozone works wonders, dropped my coolant about 15 degrees and it still stay well within tolerance driving hard, you may want to consider a lower temp thermostat. I know the FC's were notorious for overheating. those two may be a viable option before the needed addition of a koyo rad. also make sure your front under tray leading from the bottom of the bumper to the radiator is buttoned up well, this helps divert air to the rad.

-the main cooling issue been found, it is due to a dead e-fan, I'm getting a clutch and fan from Saavedro
-The car already has a Koyo Racing radiator (3 pass), the PO incorrectly thought the e-fan would be better than the stocker
-the undertray is missing, known issue, I'm going to make one out of sheet metal if ever get the time, I'd like to make a cover for the hood latch area too while I'm at it

as for your brakes, i read that you mentioned no ballooning, so i am assuming you have braided lines. also, the FC and FD were VERY flighty at best in thier order of bleeding the brakes, deviation from plan leads to minor "squish". but if you still have firm pedal feel, and the pedal stops before hitting the floor it could just be the pads, or a vac leak. an easy way to tell if your brake booster isnt getting enough pressure is, kinda tricky, is to "heel/toe". you start on a SECLUDED road, go about 60mph, slam on the brakes, half way through slowing down, still slammed on the pedal rev your engine some, to about 5k. if your brake pedal dips in more and you slow down more it could be a clogged vac line, or brake booster vaccume leak. sometimes the large diaphram can go bad.

-standard brake lines, they are fairly new, the brake fluid looks like new, the pads are new
-the pedal feels fine till you get near the end where the brakes should bite and start locking the wheels and the they just don't do it - like the piston were only extending 90% of the way out
you can pump the brakes, you can jam the pedal down as far as it will go, it's just missing that last 10%

 -the undertray is missing, known issue, I'm going to make one out of sheet metal if ever get the time, I'd like to make a cover for the hood latch area too while I'm at it.

-niburu

I'm missing the undertray on my vert as well as many of the original parts in the hood latch area. Do you think that is a cooling issue (the hood latch area)? On my other vert I can see all of the plastic trays in there, I'm just not sure if they have anything to do with directing air flow.

I'm missing the undertray on my vert as well as many of the original parts in the hood latch area. Do you think that is a cooling issue (the hood latch area)? On my other vert I can see all of the plastic trays in there, I'm just not sure if they have anything to do with directing air flow.

-vr8

the undertray and hood latch plastics definetly affect cooling
the undertray is the more important as it  keeps air from getting pushed under the car by the rad itself - though I know plenty of people that have run without with no adverse affect
I do have a Koyo rad that about twice as thick as the stock unit though so it really needs the air forced over it
the overheat i had the other morning was while the car was idling in the driveway, which it had  never done before because the e-fan had been working - till now
the stock unit is much more reliable and pulls much more cfms of air than an e-fan ever could