2Lucky2tha7

iTrader: (3)

Ok, I'll get right to it:
If I stomp on the pedal and hold it really hard at anything over 5 mph, it will slow down, but is absolutely impossible to lock them up. When I'm stomping on the pedal, it's about halfway down, but does not go to the floor, no matter how hard I push it. To give an idea, it's basically braking about as hard as a stock 12A will accelerate.
So, with that in mind, this is the status of the brake system:
-The rear wheel cylinders are fine, as well as the front calipers.
-The front calipers and rear wheel cylinders were actually replaced at the same time as the brake booster
-Everything bleeds out just fine (when bleeding the lines)
-The rear shoes and front pads are relatively new
-The rear shoes are adjusted
-The air has been bled out of the master cylinder
-There are no leaks anywhere
-The brake booster has only about 5k miles on it (about 8 years from sitting)
--->the booster also works fine with the car running.
-The pedal does NOT "fall" to the floor at all when holding it....not even slightly
-The lines have been bled thoroughly
This is my current assumption:
It's a 79 with rear drum brakes and a front brake setup from an 84. However, the rear wheels are 15x9's and the fronts are 15x8. Also, the brake booster is for a 79 model, and it has the earlier style (80 - 83 I believe) axle drum brakes that had a smaller diameter than the 84 and 85 rear axle. I'm wondering if the large wheels are too much for the brake system.
Also, does anyone know if the 1980 style brake booster is any better than the one for a '79? There are 2 different part numbers for the '79 and '80 model. The design was again changed for 81 - 83 and is much different than the '79 model, and is too wide to fit. The same goes for the master cylinders as well.

Opinions/ ideas?
P.S: it's actually the red rx7 in my avatar

2cute

first question is when did the problem start? was it when you put the wheels on? was it when you changed something in the brake setup?

AsianImage

Something else must be wrong. The RX7 brakes amazingly are pretty good for A LOT of applications. I know dudes who use to run full street port, bridge port motors on stock brakes. So something else has to be wrong.

Scott1982

You should be able to lock them up (front and rear) with good condition stock brakes. My brakes were poor (and braking sucked) even after new calipers (rotors and pads looked fine). I replaced pads with the cheapest pads from Advance and I went from not feeling the front working (although they looked fine) to locking the wheels pretty easily. You may have some glaze on the pads/rotor?

I am assuming that you know that the calipers are good, the pads are decent and the fluid has no air in it and is fresh and sliders are well lubricated. These are the simplest brakes of any car I have worked on - they are pleasure to work on and replace! I am running 15" wheels with 205 tires.

Scott

justint5387

iTrader: (1)

What tires do you have? Tires has a lot to do with slowing down

2Lucky2tha7

iTrader: (3)

well, it's actually worse now than it was before. This was all done to the last car originally (the black one in my avatar). Even after doing all of that, it was still pretty crappy, but after transferring everything over to the red one (after the parts sat for about a year and a half), the problem is much worse now than it was before. All the parts are the same too.

2Lucky2tha7

iTrader: (3)

Well, the fronts are 225/50-15 Dunlop SP9000's and the rears are 245/50-15 Dunlop SP8000's.
I'm actually going outside now to check over everything once more and see if I can't find the problem.
I'm actually thinking of replacing the master cylinder, as well as possibly the front calipers and rotors, but I'm not going to jump into that just yet....let me see if I can't find a problem

maxvol

iTrader: (2)

from your little pic I have the same Kit on my SA

orion84gsl

iTrader: (5)

Well for starters, I'm not sure if what you are experiencing is acually a "problem". You in no case ever need to lock your brakes up. That just causes skidding, generally into something. Also if your brake pedal goes to the floor under braking, it means either theres air in the lines (which you've ruled out) or the lines are flexing too much. So we know theres nothing wrong with your lines, because it won't go to the floor. What your brakes need to do is slow the car safely and consistently. The first thing that comes to mind is that your tires are providing more frictional force against the road than your pads are against the rotors. Meaning your tires are doing their job. With larger/wider/grippier tires your brakes don't have to work as hard to slow the vehicle down. If your car feels unsafe, than you should probably consider upgrading your pads, change to a higher DOT fluid and changing out the stock lines for stainless steel lines. Unless your pushing out monster HP numbers the stock brake size will do just fine.

DivinDriver

iTrader: (15)

How many feet does it take to stop from, say, 25mph? Is that distance shorter or longer than another car takes?

If it's taking longer distances to stop, then my guess would be the pads are polluted with oil or something.

If it's stopping shorter than an average car, then it's likely as Orion has said; your tires simply have more roadgrip than your pads have diskgrip.

Considering the light weight of the -7, and the size of your tires, it should stop a lot shorter than an 'average car' from the same speed. And as Orion said, locking your brakes actually increases stopping distance and loses control - - that's why anti-lock brakes were invented.

Average stopping distance from 25mph on dry pavement for a passenger car is 62 feet. You should be able to beat that handily. If not, you've got a malfunction. If you're stopping a lot shorter, you're just at the frictional limit of your stock brakes.

2Lucky2tha7

iTrader: (3)

Well, I unbolted and separated the master cylinder from the brake booster about an inch or 2 to check it and I did however find that there is a very slight amount of brake fluid on the master cylinder piston. It was more or so a little wet, but it hadn't collected inside the brake booster or even dripped out between the booster and MC. Either way, I'm going to replace the MC by monday.
The front pads are Metal Masters (PBR if I remember correctly). The rear are organic shoes (only kind available). I'm going to consider stainless lines at this point as well.

As for the stopping, I guess I shouldn't have stated that I can't lock them up, but rather that I can't come to a sudden stop. (I completely agree with Orion). The stopping distance is definitely much longer than any car I have ever driven. If I cruise around and stop at a stop sign normally by not braking at the last second, it's fine. However, if I want to stop any quicker than that, it's basically not possible.
I don't think I can compare it to my '91, but if I were to, well then my 2nd gen, from about 45mph will come to a sudden stop in about 1/3 of the distance that's needed for the 1st gen.
I am going to check the drum brakes tomorrow as well just in case. Also, the pads and shoes were absolutely clean, and as usual, I used a good amount of brake clean before reinstalling the pads and shoes.

note:
when backing down the driveway, I have to hold the pedal harder than usual to keep it from rolling, and if I use the e-brake in that same spot, I have to pull it pretty hard in order for it to keep from drifting.

Thanks for all the replies!! I know this will get figured out sooner or later

1badFB

iTrader: (1)

I run 17" Falken Azenis RT-615 in 215 front /245 rear on my GSL-SE. I can lock it up and it prety much stops on a dime. If I really heat up the brakes I get some brake fade, but nothing even remotely worrysome. I was a little worried from what I had heard here on the forum about bigger heavier wheels, but after putting some good miles on em, I wouldnt say there was much (if any) difference stepping up from my old 15s.

I ran 15" kosei K1s with G force KDWs on a GS model with drums in the back and also on a GSL rear end. Never had any problems braking with larger wheels.

From my experience there is a difference between the GS and the GSL-SE's brakes, but aftermarket wheels should be acceptable regardless of the stock braking system unless theres an underlying problem.

elwood

iTrader: (1)

I don't know what's wrong with your braking system, but there's definitely a problem. Your brakes should produce enough torque to lock up your wheels at any speed, under any conditions -- it's a regulatory requirement. The fact that you upgraded your rubber means the brakes have to generate slightly more torque to lock them up, but that difference shouldn't even make them sweat.

There's a lot of misunderstanding out there concerning brakes, and one of the biggest ones is that upgrading your brakes will make your car stop in a shorter distance. In general, your OEM brakes have correct front/rear balance (bias) and enough power (torque) to lock up your wheels at any time (see above), so making them more powerful doesn't help -- the tires are the weak link. If you want to improve braking distance, stickier tires are what you need.

Now in your case, if you can't even get your tires to lock, you need more brake. This is very unusual, and it isn't very safe. Sorry I can't be of more assistance in root-causing your problem, but I didn't want you to think that your condition is normal or OK.

BTW -- I'm running the same brand of tire in a slightly smaller size (205/50 F and 225/50 R), and I can lock them up easily.

trochoid

iTrader: (6)

When I upgraded the widebody to the same tire sizes, along with a complete redo/replacement of the braking system, except the master and booster, my stopping distance came down dramatically. I can rarely lock up the tires due to their size though. I have since gone to ReSpeed's big brake kit in the front, will do the rear eventually.

2Lucky2tha7

iTrader: (3)

what pads/ or shoes do you guys run? I also know that they made 2 different drums for the rear axles. 79 - 80 and 81 - 85. If I remember correctly, the earlier ones had a smaller diameter, and I'm not sure what year the axle is from, and it's a limited slip rear drum setup. The drums also appear to be smaller than the later years IIRC.
Just a little extra info, that's all.

dj55b

iTrader: (2)

Get some Hawk Pads for the front. One my car before I had the hawks on it would just glide and pretty hard to stop. Hawk pads i can lock up the tires at pretty much any speed. I have Disk brake from and back though but still since most of the car's braking power is done through the front brakes I would adress those first. Another thing that wouldn't hurt doing is rebleeding the front brakes just to make sure you have no air bubbles in there.

trochoid

iTrader: (6)

Just viewed your photo album. I think I've finally found someone who went to as extensive of a rehab and took more pics than I did, lol. Since you have this much work in the car, I would swap the rear axle and front struts for ones off of an S3 and install Billy's big brake kit, front and rear.

The first thing I noticed when I went to the larger tires and wheels is how much heavier the car felt. It didn't feel as light and nimble, but holds the corners so much better.

rx7kidd315

I run 225 50/15's on my 83 with drums in the back and I have no issues either. I'm running the falken azenis and I autocross it quite a bit. I def. don't think its your tires or wheels. It has to be something else.

rotor vs. piston

Ditto on all, has to be your system not the wheels. I ran/run 16x8... thought they're about the same weight as stock GSL-SE wheels the braking system on the 7 should be more than up for a few pounds of increase rolling mass.

I would look at the bias... ...

boostedHULK

iTrader: (1)

what did you use to check your booster? my car sat for a year and a half and the diaphram wasn't sealing well anymore, my brake andclutch mcs were also bad, so i wouldn't hesitate to replace both your booster and mc.

Siraniko

iTrader: (13)

you can always adjust the push-rod (brake booster to master cylinder). Took me months to figure out why my 73 RX-3's brake calipers were locking out even after I replaced them all along with the master cylinder and proportining valve. The brake booster rebuilder **** up and adjusted it without me knowing.

2Lucky2tha7

iTrader: (3)

I adjusted the push rod today to 0.5 mm spacing, because I measured it at 1.2 +/-mm or so. I bench bled the new MC and installed it earlier, and although there is most likely a tiny air bubble in each line that bolts to it, the pedal feels pretty stiff. I'll need help from someone tomorrow to bleed the system. Anyway, I took it out and it felt noticeably better, and if I really stomp on the pedal hard, it will slow down much better than last time. But, there's still a problem, and at this point I'm pretty definite that it's the drum brakes. It's a 79 - 80 rear axle with the external adjusters, and although I adjusted them as the manual stated, it doesn't seem to be doing it's job. I've also yanked the e-brake very hard and left it there for a second while cruising around 35 mph, and it felt like it was hardly doing a thing back there, and I mean hardly. If I do this on any other car, I atleast feel something going on. I guess I'm just gonna go ahead and buy another set of brake shoes and see what happens.
BTW, as for changing out the rear end for a GSL or GSL-SE disc brake setup, that will have to wait until next year because the summer is almost over and the car needs to be driven, not sitting, lol.
Also, I checked the PB booster last night by cruising around 55mph and shut the car off, then I hit the brakes, and on the 2nd push, it did next to nothing and felt like I had no brakes at all. So yeah, the booster works

flight_of_pain

question was answered already lol. way to use the refresh button, go me!


isaac

2Lucky2tha7

iTrader: (3)

quick question:
my choices for shoes are: Raybestos (organic professional grade), Beck/Arnley, or Bendix. All the others are the typical Duralast, Prostop, WearEver, and Carquest $15 stuff which I won't consider. I'm curious about opinions on any of these.

DriveFast7

iTrader: (1)

http://porterfield-brakes.com/produc...productID=3988
http://porterfield-brakes.com/produc...productID=3374
R4-S FTW!!!

Adjust those rear shoes tighter.