j9fd3s

iTrader: (3)

so ive noticed the average FC has a really mushy brake pedal. ive had 4-5 different fc's and they all have mushy brakes.

ive tried bleeding em, putting braided lines on, rebuilding calipers, new master cylinders

nothing seems to work.

is there something else i'm missing? out of adjustment? or should the pedal just feel like crap?

OC_

Yup. theres one other thing your missing.
Have you tried different pads?

This is somthing I found on the race track. I was wondering how my pedal could feel so mushy after a few laps when im sure im not boiling the fluid and have SS lines. Then i remembered somthing i heard a while back about different pad compounds giving a different pedal feel. If you can believe it, the pad compound actually flexes! espsecially when it gets really hot!

I even replaced the master cyl just like you because i thought that was the problem. Then, for the longest time, i thought the pushrod that operates the mastercylidner was not properly adjusted. I spent so much time adjsuting the length of that pushrod and never got good results. Now i realise that my shitty pads are the problem.

I have sat in some other RX-7's that had hawk HP+ pads. Those cars did not have the mushy feeling that my car had. I think im going to go with those.

Black91n/a

Another thing to consider is a brake master cylinder brace and/or using the TII booster and MC. That MC is slightly bigger and will give a shorter and stiffer pedal.

I built myself a brace out of a ~3" piece of 2" square steel tube and a long bolt. The tube is bolted to the strut tower and then a long bolt attached to it and the head is butted up against the MC (pre-load it). Get a friend to push hard on the pedal as you watch the firewall, it flexes quite a bit and the brace helps to minimise this, improving feel.

I've used HP+'s and wouldn't really reccomend them. They're not a full racing pad so they won't stand up to sustained track abuse if you're going fast, and as a street pad they're noisy and dusty. Sort of the worst of both worlds, not exactly the best combination. They did get me through my first few driving schools when I was slow, the car was on street tires on a track that's easy on brakes, but I doubt they'd be any good to me now that I'm better and am using race tires. Something like the HPS would be better for the street, and if you're going to the track get real race pads like the Hawk Blues or Blacks or the Porterfield R4 that I use and like. Street pads are fine for autocross 99% of the time.

j9fd3s

iTrader: (3)

yeah, hawks are a no no on the street, thats not brake dust, its metal shavings, it ruins the wheels really fast

micah

I had a couple FC's with mushy brakes too... In both cases it was the booster. Luckily my current car had a good booster when I got it. Brakes like a champ.

laserkei

iTrader: (3)

I have the same problem with the spongy brakes. I'll take the advice black21n/a.

t04tii

Has anyone ever removed the booster and put a much larger master cylinder on? I have seen this on one car (my old roomies 240) and loved the feel. You could feel EXACTLY when you were pushing the brakes to hard and about to lock the tires. Obviously braking effort goes up, but a bigger diameter M.C. helps. Kind of like PS vs Manual rack. More effort, but much better feedback to the driver.

alexdimen

iTrader: (13)

Pads are not going to change pedal feel... brake fade and response, yes, but pedal feel is not effected.

YES X 1 MILLION

I had persistent shitty brakes forever. Nothing cleaned it up... until I put in a rebuilt booster.

I had replaced my MC, SS lines, rebuilt calipers, even tried different pads and rotors.

The thing about a bad booster is that it's nearly impossible to diagnose sometimes. It can hold good vacuum and still be your culprit. You may even go as far as pulling off the MC, running the car and watching it actuate the pushrod like it should and it's still not working properly under load.

After my pedal felt good after a new booster, I put in a Wilwood proportioning valve and I love my single piston brakes now.

OH, and never use used brake parts.

fastrotaries

I've also replaced old crappy looking brake shims...mine were rusty and having replaced everything but the calipers, MC and booster, the feel and response went way up. I didn't really think that shims would make that big difference, but apparently it does.

Black91n/a

Actually a bigger MC causes the pedal effort to go UP and the travel goes down. Braking power is a function of line pressure, and it takes more force to get the same pressure on a larger area of the larger MC.

The TII's have a slightly bigger MC, and I've read that the 929 MC can fit on the S5 TII booster and is larger still.

I don't know about removing the booster, you'd need to make some sort of adapter to make up the gap, or maybe just gut it or something?

chuckrx

funny, i actually believe that the rx braking is better than any comperable brands as far as feel, reliability and fade (stock vs stock) However that does not mean there is not room for improvement. First, upgrade to a better pad; secon, completely change brake fluid, then try some upgraded materials/design in rotors. I run solid magnesium rears and cross-drilled fronts(i don't care about debates, and I check them often); axis semi-metalic pads (great feel and fade resist, but a little loud and wearing), and, I cant remember the name, but it was German-made blue race fluid. You could increase diameter and pistons and I am sure some on here have some elaborite mods

Black91n/a

I call BS on the magnesium rotors. The only materials I've ever heard of being used on brake rotors are as follows: iron, steel, ceramic and carbon.

A properly working FC brake system is a very good one though with quite good stopping power, fade resistance and feel. It takes a lot before it's overtaxed and truly in need of upgrades to bigger rotors and calipers.

yeti

iTrader: (1)

Just a question.. Would putting clamps wrapped around the master cylinder and reservour help or hurt things?

Fault Bucket

Can you share a pic? I'm not quite visualizing what you're describing...

Black91n/a

Unfortunately I don't have a pic, and the car's hundreds of miles away.

Basically the piece of stock is vertical with one wall bolted to the strut tower so that it's immediately in front of the MC, then on the side facing the MC there's a long bolt that butts up against the MC.

I did a quick drawing on this picture, hopefully it helps.

Fault Bucket

Ahh....makes sense now. Thanks.

turboeric

That must be exciting. Hard stop from high speed, rotor glows red for a short time before bursting into flames. Car burns to the ground... Too exciting for me - I'll stick to iron thanks.

arghx

iTrader: (3)

this is a little-known trick...

You may find a little help by adjusting the brake-booster pushrod.

Unbolt the Master Cylinder from the firewall and move it to the side. You do not need to remove any brake lines, at least I didn't on my N/A. there is enough flex in the lines so you shouldn't have to remove the lines and subsequently bleed the system or anything (although if you haven't bled it in a while, do so). When you move it aside you should see a little pushrod thing sticking out (you may have to reach in there to get it). Hold one end with a vicegrip and loosen the pushrod with a deep 7mm socket SLIGHTLY to lengthen it. This will make the brake pedal "catch" higher.

Beware though. If you lengthen it too much, the brakes will drag. Lengthen it a few turns, bolt the cylinder back up, and test the car. You may notice a little difference and have to do it again two or three times. When I bought my 88 GTU I had to put the pedal to the floor to stop the car. Stainless lines and an adjusted pushrod made a huge difference.

alexdimen

iTrader: (13)

That's not such a good idea. You're supposed to remove the master cylinder, measure the depth of the pushrod hole from the mounting flange, then apply vaccum to the booster and adjust it to have a small amount of clearance.

With that said, the only time you should adjust the clearance is when the booster is being replaced. Otherwise, it comes set correctly from the factory.

If you use vice grips to adjust it, don't scrape the shaft... it has to make a seal with the booster and will be a vac leak.

arghx

iTrader: (3)

Our cars are twenty years old. Do you really think everything is still at factory spec? Your more precise method would be a better way to do it though. A couple other people on here have done it with good results. I'm not the guy who came up with it, I searched through threads. it's been years since I messed with it but I never had any subsequent vacuum leak problems or anything.

Anyway, it's something to try and it takes 20-30 minutes to do max. Btw You are not adjusting it with a vice grip, you are holding one end with the vice grip so it doesn't turn. the adjusting is done by the deep 7mm socket. And of course you need to be careful not to scuff anything up.