Brake Pressure Issue

[Johannes]

IN SHORT (if you're lazy to read today):
Hard brake pedal, takes effort to stop
Stock brake system did this.
Replaced brake system to Z32 four corner, Z32 BMC, already replaced brake booster three times from a working car
Replaced non-return valve
Vacuum source good. Direction of non-return valve is proper.

Question; what would cause a hard brake pedal/takes effort to stop?
It can't be seized calipers...



Hey fellow Zilvianians. I've been having problems with my rear brake pressure.

To start with, in 2010, I had stock brake system on my coupe. I noticed that in my other S13, it had better stopping power. So I went and checked my brake pressure on the coupe and the fronts were fine. However the rear brake pressure was lower than the specifications.

So what I did was I bought a new master cylinder. Bench bled the new master cylinder and the whole system, and I was still having the same problem.

What I then did was I got another brake booster from an automatic S13 (bigger diaphragm compared to manual B.booster), and it was STILL the same.

So I was like fawk it, I then upgraded to Z32 all four corners, with Z32 b.master cylinder.

After all of this, my other S13 STILL had better stopping power. (my other 240 has the slightly bigger JDM calipers/rotors just like the Altima ones)

What I then did was I removed the whole brake hard line assembly including the tee's all the way to the back and blew it with air comp. at 120psi.
I checked for bents/damages and they seemed fine.
I then drilled out slightly bigger holes on the tee's and put it all back together.

I have also checked the non-return valve (vacuum source) and changed brake booster twice. And it's still the same.

Simply put, my rear brake pressure is lower than what it's supposed to be, and have checked, replaced, double checked, and re-bled the whole brake system

Any suggestions what might be wrong? Maybe I need to try out a new hard line assy. that goes to the back? Thanks.

[brndck]

what are you using to measure brake pressure???
also, what pads are you running?
also, what tires are you running on each car?

i'm not sure what your criteria for determining that you don't have enough pressure, but i feel like there is more going on here than what you've posted.

z32 brakes should feel noticeably superior to stock s-chassis brakes.

[Johannes]

what are you using to measure brake pressure???
also, what pads are you running?
also, what tires are you running on each car?

i'm not sure what your criteria for determining that you don't have enough pressure, but i feel like there is more going on here than what you've posted.

z32 brakes should feel noticeably superior to stock s-chassis brakes.

Hydraulic gauge w/ max. pressure of 1,000 PSI.
It's actually a brake pressure kit at our school shop.
(remove brake bleeder, and replace w/ gauge assembly to measure psi)
Fronts measured at 800-900 psi (stock brakes)
Rears measured at 150-200 psi (stock rears)

I'm running semi-metallic duralast brake pads.

225/40/18 on 9.5's all around.

Thanks for the response.
I might also try a different bypass valve on the vacuum source since that's my last option. I'm getting vacuum all the way at the end of the hose though. And gauge reads -20mmhg at idle.

Stock everything S13 w/ JDM slightly bigger calipers have;
195/60/15
Duralast brake pads as well.


EDIT:
If it helps in any way, I have S13 auto brake booster, and Z32 Master cylinder and my brake pedal is way up high and really hard to press on.
I need to push on the brake pedal harder to get my front brakes locked up.

[Johannes]

EDIT: Still having brake problems

[Johannes]

Soooo... bringing this thread back instead of making a new one.
I thought I already fixed it but after a day or so, it's still the same..

Hard brake pedal, takes some effort to stop the car.

I basically changed/removed/replaced my whole braking system and it's still the same..

Replaced:
Non-return valve (Vacuum source)
Brake booster
Upgraded to Z32 BMC
Upgraded to Z32 4 corners
SS Brake lines 4 corners
Removed hardline from BMC all the way to the rear of the car, blew it out with compressed air


Any ideas guys? The only thing I haven't replaced is the brake pedal itself.. but it shouldn't matter right?
I've also checked the brake booster pushrod specifications..

No vacuum leaks.

Possibilities?
Air in the system? (Wouldn't it make the pedal feel soggy/soft?)
Air in master cylinder?

What do you guys think?

[KiLLeR2001]

What about replacing/cleaning out the splitter for the rear brake hardline? The point where the rear line splits into two and distributes to each caliper.

[koukimonster139]

what method are you using to bleed your lines? sounds like you didnt do it right

[jr_ss]

If he didn't do it right he'd have a spongy pedal.

Have you checked/cleaned the rear bias valve? I'm not sure where it is located on S13's but that sounds like part of your issue.

[Johannes]

What about replacing/cleaning out the splitter for the rear brake hardline? The point where the rear line splits into two and distributes to each caliper.

I did clean it during the process of hardline removal, but didn't make the holes on the tee's bigger.

I removed the line going to both of the rear calipers and I blew the tee on the back with compressed air @ 120psi. Brake fluid was coming out on both of the brake lines.

what method are you using to bleed your lines? sounds like you didnt do it right

RL, RR, FL, FR.
Both two man bleed, and one man bleed.
Plus having air in the system would cause the pedal to feel soft/soggy.

But nonetheless, pump three/however many times, hold pedal, open bleeder, close bleeder, let go of pedal. (two man)

Fill water bottle with clean brake fluid, clear hose from bleeder screw, submerge hose in brake fluid, loosen bleeder screw, pump away until no bubbles show.

Or another way would be... loosen bleeder screw, pump pedal once and hold, close bleeder screw, let go of pedal, repeat process..

[koukimonster139]

If he didn't do it right he'd have a spongy pedal.

Have you checked/cleaned the rear bias valve? I'm not sure where it is located on S13's but that sounds like part of your issue.


true, but depending on where the air is in the system it can cause a hard or soft pedal. its still a restriction in the system that creates high return pressure.

have you checked for vac. leaks or tried a brand new booster?

[blueshark123]

I had a problem similar to this it turned out to be the brake booster threaded rod was adjusted to long i believe.

[KiLLeR2001]

RL, RR, FL, FR.


You must always do FR before FL.

I do, RR, RL, FR, FL and never had issues with trapped air.

[Johannes]

Hmm well FSM states RL, RR, FL, FR.. so I just follow it =p

Anyway.. today I removed the hardline going to the rear and the brake lines going to the caliper and blew it out with compressed air again.. Bled the system.

Test drove, still the same.

Removed BMC, bench bled it again, bled the system.. test drove and it's still the same.

It takes a lot of effort for the front wheels to lock up.

I've tried three different brake boosters and they are all the same result.
I've even tried adjusting the pushrod on the brake booster.
I've also replaced the non return valve on the vacuum hose twice......

I'm going to go ahead and put together a brake pressure gauge and see where the brake pressures are at... if they're good, then I might just need pads.

Any other suggestions guys?

[jr_ss]

You must always do FR before FL.

Sorry Steven, but you're wrong...

Hmm well FSM states RL, RR, FL, FR.. so I just follow it =p

You're doing the bleeding procedure right. The RR may appear to be further away from the MC, but in reality there is more plumbing to bleed on the RL than the RR.

Any other suggestions guys?

Like I mentioned above and apparently it was missed, have you checked your rear proportioning valve?

[Chaluska]

Is the brake pedal stiff, similarly to how stiff the brake pedal would be if the car was off?

can you verify some of the pistons are not locked up? did you buy all new calipers? or were they junkyard/used calipers?

im running a 17/16 mbc with brembo front calipers and z32 rears, and if i dont have a vacuum source hooked up to the booster, its retarted stiff, and wont bite very hard.

sounds kind of like what your describing

[Mikester]

Hey dude-

First of all, thank you for putting that stuff in bold- I didn't feel like reading the whole thread... so if what I am about to say is already listed- My bad.

Your fix: Get rid of the Z32 MC and put a 240SX MC back in if you don't want stiff pedal-feel. The Z32 MC actually puts out less pressure than the 240SX MC (pushing multiple, smaller pistons and design does not require as much pressure believe it or not... and the Z32 booster assist and/or pedal ratio is different than the 240SX's). That's why guys who don't do this complain that when they do Z32 brake swaps, the brakes are mega-responsive, but semi-mushy; and tend to lock up quickly. If this is what you desire, put a 240 MC back in and you will love it. Long sotry short: Larger bore MC = lower output pressure.

When I did my F & R R33 brakes, Z32 MC & auto-booster swap recently, I was a little taken back at the stiffness required to stop the car... so I re-accomplished the bench & plumbing bleeds to the very same end. This prompted me to do some research... Found this: Brake FACTS to help you with your Z32 brake upgrade that you should know - SR20 Forum (http://www.sr20forum.com/240sx/140434-brake-facts-help-you-your-z32-brake-upgrade-you-should-know.html) ... Should tell you everything you need to know if you still have questions.

So the end result for me? Seeing as how I just payed a pretty penny for a shiny new DIF/Tokico MC; my plan is to grin & bear it. However, I will eventually switch back to a smaller-bore MC down the road because it IS a bit scary sometimes ;)

Peace.

Mike

[jr_ss]

I rock my factory 15/16" MC and auto booster with Z32's all a round. I now have Wilwoods up front and that changes my bias slightly but nothing dramatic.

Good catch Mike, I overlooked the setup.

[Johannes]

Sooo an update..

My friend has a lifetime warranty bmc at autozone.. found a broken bmc off of a Nissan and used that as a core for it.

It's a 7/8 BMC for an S13.. bench bled it, bled the system and test drove. It does lock up a little easier but it feels about the same.. still needs a little effort for the front wheels to lock up.

Hmm.. maybe I just need better brake pads? I'm comparing my 4 corner Z32 brakes to my other stock S13 with 180sx brake calipers and stock rear brakes.. It stops much better and locks up much faster with little effort on the pedal.

I'm now wondering if this is because of tire width, and coilovers? but then I think to myself... why is my brake pedal hard when my other stock s13 feels a little mushy (no air) and easy to lock up?

My pedal basically feels rock hard and won't go down any further after it hits that rock hard feel. It goes down about 1/2 way down and turns rock hard, then after that, much more effort is needed to lock the front brakes up.

And I don't think it has anything to do with vacuum source.. I've replaced my brake booster three times from a working car, i've also replaced the check valve twice from a working car. Vacuum is on point.. 22mmHg at idle.. well I lied.. 18mmHg at idle because of cams.. no leaks whatsoever.

[KiLLeR2001]

Sorry Steven, but you're wrong...

You're doing the bleeding procedure right. The RR may appear to be further away from the MC, but in reality there is more plumbing to bleed on the RL than the RR.

I know what the FSM says. I've tried doing it that way multiple times and have had poor success. My friend also tried the FSM route and still had issues. I've probably bled the brakes on my S13 over 100 times, and with every different configuration of stock and Z32 brakes imaginable. I don't know if this applies to S14's, however.

Yes, the RL line has a longer plumbing than the RR, but the order in which you bleed the rears DOES NOT matter (in my testing).

For the fronts however, every time I did FL before FR, it took 4 times as long to bleed all the air out, or I was still left with air in the system.

The FSM says to bleed the RL first because its plumbing is longer than the RR. Understandable... But why would the FSM tell you to bleed the FL first when the FR's plumbing is longer than the FL's?

If you wanted to be super anal about the most optimal way of doing it, you would do RL, RR, FR, FL. This is of course for a USDM chassis.

This is the only part of the FSM that I cannot follow because it simply does not work for me.

[Croustibat]

I cant remember but someone (here) said the booster rod length was not adjusted correctly on his car, leading to the same phenomenon.

As far as i can say, i have a Z32 new 17/16bmc, feeding wilwood superlite 4 pots front and Z32 rear. Pedal is hard but progressive. Stomp on it and it locks all wheels (even at 100+ mph).

I did have a braking problem once ... i felt like polymatrix pads were eating through my rotors, so tried EBC yellowstuff at the front (endless on the rear).
These did such a bad job i first thought my front calipers died. The car mostly braked from the rear. In fact rear locked when the front barely slowed. That was scary, to say the least. It ruined my trackday a bit. I removed them and they joigned some other failed experiments that i keep so i remember never ever to buy that again.

So i'd say your brake pads suck, first and foremost. Change them.

Anyway i do believe the proportioning valve on Z32 bmc is around 0.4 rear. Considering the rear line splits in 2, and there are 2 independant front lines, arent your values the correct ones ?

[Johannes]

Soo an update guys, please help me out.

I made a custom pressure gauge to measure the amount of psi on each corner.
Results:
FL: 1500+ PSI (this was because the gauge can only go up to 1500 psi)
FR: 1500+ PSI ("""")
RR: 150 PSI
RL: 150 PSI

These were the pressure at the calipers. I then measured it at the T under chassis and got around 160 psi in the back..

I then measured how much pressure I'm getting AT THE MASTER CYLINDER and the result was the same... 160-180 psi..

Told my friend to came over, measured his rear master cylinder pressure and it turns out to at least 800 PSI.

Any ideas why? I've already replaced my brake booster four times. This brake booster I'm currently running ran perfectly fine from my other S-chassis. I've also measured my piston on the brake booster to see if it's within spec, and it is. No vac leak on the booster. One way valve works how it should..

I'm only left with one thing to replace.. and that's the brake pedal assembly..

[KiLLeR2001]

I'm gonna have to go with clogged rear lines. Maybe there is gunk stuck the the inner walls of the hardlines. I know this is going to sound drastic but I would replace the entire rear hardline. If that doesn't fix it, time to cast the car off of a cliff and never speak of it again.

[G5SR20240]

Do you have a catalytic converter on your car? If so it may be a bit clogged, a clogged cat could effect the brake booster in a weird way. Try pulling your cat if you have it and drive it

[Johannes]

I'm gonna have to go with clogged rear lines. Maybe there is gunk stuck the the inner walls of the hardlines. I know this is going to sound drastic but I would replace the entire rear hardline. If that doesn't fix it, time to cast the car off of a cliff and never speak of it again.

The thing though is that I measured it at the master cylinder (fitting closest towards the car) so it bypasses all the hardline. I'm only getting like 170 psi at most. :-/

[KiLLeR2001]

How many different master cylinders have you tried?

[Croustibat]

Soo an update guys, please help me out.

I made a custom pressure gauge to measure the amount of psi on each corner.
Results:
FL: 1500+ PSI (this was because the gauge can only go up to 1500 psi)
FR: 1500+ PSI ("""")
RR: 150 PSI
RL: 150 PSI

These were the pressure at the calipers. I then measured it at the T under chassis and got around 160 psi in the back..

I then measured how much pressure I'm getting AT THE MASTER CYLINDER and the result was the same... 160-180 psi..

Told my friend to came over, measured his rear master cylinder pressure and it turns out to at least 800 PSI.

Any ideas why? I've already replaced my brake booster four times. This brake booster I'm currently running ran perfectly fine from my other S-chassis. I've also measured my piston on the brake booster to see if it's within spec, and it is. No vac leak on the booster. One way valve works how it should..

I'm only left with one thing to replace.. and that's the brake pedal assembly..


Looks like your BMC has an internal leak ... or your ABS pump if you still have it. If you do, bin it, they are known to do that. I removed mine because of that. May i ask how you made your gauge ? I need to check mine too, i fear my front system may leak pressure a bit.

[Mikester]

I'm gonna have to go with clogged rear lines. Maybe there is gunk stuck the the inner walls of the hardlines. I know this is going to sound drastic but I would replace the entire rear hardline. If that doesn't fix it, time to cast the car off of a cliff and never speak of it again.

He can pull the rear lines and blast them out with compressed air... but it sounds to me like a leak somewhere else in the system.

Do you have a catalytic converter on your car? If so it may be a bit clogged, a clogged cat could effect the brake booster in a weird way. Try pulling your cat if you have it and drive it

Brake booster has nothing to do with the amount of pressure being distributed between the front & rear brakes... That's all integral to the MC.

However, the brake system is not unlike the fuel system. A leak at one of the rear calipers or anywhere else for that matter will result in a pressure drop across the whole system as the fluid being displaced is going to flow out the path of least resistance; and like the fuel system, the pressure drop will be 'felt' everywhere as it is a closed system. Before assuming there is something wrong with the MC, check every other connection in the rear brake system between the MC and rear caliper pistons before tearing into a brand new master cyl. I wager there is a small leak somewhere.

Also, it could be as simple as air in the system somewhere in the rear lines... Again, there will be a lack of pressure across the whole [rear] system if this is the case.

Hope this helps.

Mike

[Johannes]

Looks like your BMC has an internal leak ... or your ABS pump if you still have it. If you do, bin it, they are known to do that. I removed mine because of that. May i ask how you made your gauge ? I need to check mine too, i fear my front system may leak pressure a bit.

I've changed my m.c. at least three times now because of low rear pressure brakes. And every time I change them, I do bench bleed them first to get rid of air bubbles in the MC.

Previously, I was running Z32 Master Cylinder from a working Z32. I thought the proportions in the Tokico BMC were off so I bought a brand new master cylinder (S13 BMC), bench bled it, and I'm still having a low rear brake pressure at the master cylinder.

Materials;
**1/4 NPT Gauge that goes up to 2,000 psi
**1/4 NPT female to 1/8 NPT male
**1/8 NPT female to 10x1.00mm (this is the thread pitch for Z32 bleeder screw, and the rest of the system.)
OPTIONALI had an extra OEM Z32 rubber line that had the female (connect male side from gauge 10x1.00mm) and the male side that had double flare, and this is what I connected to my MC to prevent high pressure leak.

He can pull the rear lines and blast them out with compressed air... but it sounds to me like a leak somewhere else in the system.



Brake booster has nothing to do with the amount of pressure being distributed between the front & rear brakes... That's all integral to the MC.

However, the brake system is not unlike the fuel system. A leak at one of the rear calipers or anywhere else for that matter will result in a pressure drop across the whole system as the fluid being displaced is going to flow out the path of least resistance; and like the fuel system, the pressure drop will be 'felt' everywhere as it is a closed system. Before assuming there is something wrong with the MC, check every other connection in the rear brake system between the MC and rear caliper pistons before tearing into a brand new master cyl. I wager there is a small leak somewhere.

Also, it could be as simple as air in the system somewhere in the rear lines... Again, there will be a lack of pressure across the whole [rear] system if this is the case.

Hope this helps.

Mike

Hi Mike, thanks for your response.
I checked the pressure at the master cylinder to basically bypass the whole system that goes to the back of the car (hardlines) and came up to 170 psi at the master cylinder.


Again, these were the same results I've had on my past two master cylinders...

Could a bent brake pedal affect this?

[KoukiMonsta]

I've changed my m.c. at least three times now because of low rear pressure brakes. And every time I change them, I do bench bleed them first to get rid of air bubbles in the MC.

Previously, I was running Z32 Master Cylinder from a working Z32. I thought the proportions in the Tokico BMC were off so I bought a brand new master cylinder (S13 BMC), bench bled it, and I'm still having a low rear brake pressure at the master cylinder.

Materials;
**1/4 NPT Gauge that goes up to 2,000 psi
**1/4 NPT female to 1/8 NPT male
**1/8 NPT female to 10x1.00mm (this is the thread pitch for Z32 bleeder screw, and the rest of the system.)
OPTIONALI had an extra OEM Z32 rubber line that had the female (connect male side from gauge 10x1.00mm) and the male side that had double flare, and this is what I connected to my MC to prevent high pressure leak.



Hi Mike, thanks for your response.
I checked the pressure at the master cylinder to basically bypass the whole system that goes to the back of the car (hardlines) and came up to 170 psi at the master cylinder.


Again, these were the same results I've had on my past two master cylinders...

Could a bent brake pedal affect this?

Been reading this a couple days, Mike always has good advice so kept my mouth shut.

But now I am leaning towards something BESIDES master/booster/lines/calipers being the cause - you have swapped multiple items and haven't seen any change.

Bent pedal....ehh mayb, what about improper adjustment if the push rod? Honestly don't even know what the procedure for that is.

[KiLLeR2001]

Yeah I'd start looking into the brake pedal and linkage, and would start adjusting the push rod out little by little until you get the desired result.

[Mikester]

So I went back to the top and re-read this thread.

Johannes,

Since I posted on May 7th, I learned something when I purged all of my fluid & put fresh stuff in. Except this time, the brake pedal feel; as well as the response was a night & day difference.

What I did differently:

Instead of bleeding w/a Mity Vac, I had a guy in the car pumping/holding the pedal. Also, I went several more iterations at each caliper after seeing no bubbles- guess what? After 5-6 times of seeing no air, there was air AGAIN that was still stuck further up the lines.

All said and done, the pedal no longer felt 'too stiff'; and the car stops like a million bucks WITH the DIF/Tokico Z32 MC. In order to do it, the rears take a while. Any air still stuck in the rear section of the system, there will be a pressure drop across the WHOLE rear system. The reason that the pedal will be overly stiff vs. mushy is that the majority of the braking is in the front and they are likely to be properly bled... If there was air in the FRONT, the pedal would probably be mushy as hell.

Anyway, I now think that the rears are not fully bled.

Also- not to insult anyone's skills; but I assume that the rear bleeder ports are at the top of the calipers and not the bottoms- yea? As you are probably well-aware, the system will never bleed with the ports at the bottom (calipers on backwards).

[Nissan2nr22]

Same issue here

[Nissan2nr22]

My issue was brake pads

[di-devol]

My issue was brake pads

What do you mean, your issue was pads?

[Nissan2nr22]

The pads looked good but when I compared them to a new set of pads they were actually very low maybe half worn . The piston was showing I could only tell with the wheel off. Once I changed the pads all around my brake pedal feel came back to normal, s15 with bm50 big booster and 30mm fronts and rear 2 pots

[Izzyidk]

damn this thread is me. I've had a super stiff pedal for 3 years. Changed masters, boosters, calipers, lines. Changing my master again Tuesday and I will do pads at the same time. Hope this changes it