XBS

iTrader: (29)

Hey guys, I have a Rotora 8 Piston front/ 4 Piston rear brake kit on my car. I thought it had air so i bled the entire system twice. The problem i am having is that while i am driving the first time it press the brake pedal it is soft and goes down half way. If i hit it again after that it is nice and firm and doesnt go down very much before the brakes start stop. I thought it was air in the lines, but it isnt. ( i hope not after all the bleeding i did) So people are telling me the master cylinder could have gone bad.

I think someone did a swap once from a Q45? just wanted to know if that is possible and a good idea since my new brakes are much larger. Also anyone have any other ideas on what my problem could be?

I want my brakes to be nice and firm and grab high the FIRST time i hit the brakes, the second time might be too late .....

Thanks!

-George

dscheers

iTrader: (3)

If you have racing compound pads in your BBK, they'll have to warm up before they grip...

aalzuhair

iTrader: (2)

I would like to know too?

Az

Ahsmo

iTrader: (13)

Id gettem flushed professionally but thats me... especially with that kit

XBS

iTrader: (29)

professionally? like the dealer ship that fu/cks up my car everytime i take it there. sorry dude i dont trust other people to work on my car. Its not the proceedure im doing. Just looking to know if anyone else has had this problem. Thanks for the replys.

plumpzz

iTrader: (10)

Those aren't teh symptoms of a bad brake master cylinder. Have someone watch the cylinder or fluid level while you brake...

drsifu

iTrader: (6)

i have the same issue with my Stoptech 14" BBK. I replaced all four brakes and bled the system several times thinking air was in the lines.

it doesn't effect the braking power, just feels awkward at times. not quite sure what the problem is, so if you get it fixed, let us know.

Ahsmo

iTrader: (13)

Well 'professionals' have a device to keep head pressure on the brake fluid reservoir.

I didnt take mine to the stealership. I found a shop I trusted and let them do it with their fancy tricks and gadgets. I love working on my car as much as the next guy but if I dont have the tools to do something correctly, I'll let someone who does do it.

Z1 Performance

iTrader: (564)

I would highly recommend changing pads....they have alot to do with how things bite

HyperSprite

iTrader: (6)

If the caliper capacity is to large for the MC, it can cause excessive pedal travel because you need to push more fluid into them to get them to get firm on the rotor. The only fix for this is to replace the MC with a larger bore unit.

On the other hand, since your components are new I would really triple check for air. I don't know what procedure you went through to change them but if a large amount of fluid came out of the system it is possible there is air trapped in a tough to bleed position.

When I put new calipers, lines and MC on my old Mini I ended up power bleeding them because I had pushed two bottles of fluid through them and it was still soft. Once i got it done right the pedal was and still is, hard as a rock.

Chris

G_Cogis

There's 2 things possibly going on here.

The first and most obvious is the possibility of air in the system somewhere.
Brand new lines...and brand new calipers...there's allot of space for traped air.
A couple tricks:
1) (and I know this is remedial) But are the bleeder vavles pointing upward??
2) Drive the car a bit and see if the road vibration can loosen any trapped air in the new components. Re-bleed
3) Durring bleeding tap the caliper with a rubber mallet to loosen any trapped air.
or you could...
4) Flush the system and start from scratch.

Another thing could be air in the ABS unit. I have seen mechanics remove the factory calipers and let fluid run out of the line. If the resevoir ran dry durring installation you could have air in the ABS unit. Sometimes there is a way to bleed the ABS unit...sometimes flushing the system will help it out. Check with your dealer and see if there is a way to bleed the ABS.

***A bad master cylider has different symptoms than what either of you described.***

The second thing, and one that is very possible with a company like Rotora & and possibly Stop Tech, is just too much piston area within the 8-piston, 4-piston, or even both calipers. It may just require more fluid volume to move those calipers than your factory master cylinder can handle. I would never reccomend upgrading a mastercylinder on a late model car. If this is the issue the kit is just wrong and needs to be sent back to the manufacturer.

Stop Tech is less likely to have this issue due to the fact that they do pay quite a bit more attention to the piston sizes than allot of other companies out there.

How old is your kit?? Is it the old 4-piston rear or new 2-piston rear???

Stop Tech takes raw caliper bodies and machines their own piston sizes to "match" each vehicles factory brake torque. In theory their upgrade isn't an upgrade for stopping power...just heat capacity. If done correctly the pedal is usually firmer than stock since when you increase disc diameter you usually have to decrease piston area. The reason I mention this is because even though they have the ability to machine whatever piston sizes they want into the caliper bodies they buy, they're still limited on the # of piston sizes to choose from. They may have been forced to use larger pistons that what they would like to do.

I really reccomend talking to the manufacturer of the kit before anyone goes too crazy and starts modifying master cylinders or adding proportioning valves. If you can get the piston sizes from the calipers, for Rotora or the StopTech, it is pretty easy to find out if it is a volume issue or possibly air in the system.

***please excuse any spelling or grammer issues...I am on my lap top in the car and don't feel like using spell check***

XBS

iTrader: (29)

Ok let me put some more information out there.

I bought the Kit Used. So the parts have over 6k on them

I bled them when i first put them on. Then 2 weeks later because of this issue.

I installed the brake system and did once caliper at a time, did not let the lines run dry.

I can acquire a tool to pressurize the master cylinder resvoir to do some more bleeding.

Also what is this "power bleeding" you mention?

I want to try again next weekend so need all advice I can get. Thank you.

-George ( appreciates all the feedback he is recieving )

aalzuhair

iTrader: (2)

Thanks good info ....

GaryM05

If it's not air in the lines, then it could be pad knockback (aka hub flex):

http://www.stoptech.com/tech_info/wp_knockback.shtml

That has similar characteristics to what you're describing (and it doesn't just happen on the track).

G_Cogis

They can easily check to see if it is indeed pad knockback by doing a series of stops in a straight line without any turns. Possibly on the freeway. Give some time in between stops to allow everything to settle.

I personally haven't heard of any cases of noticeable knock back on the 350Z.
Has anyone else???

Ahsmo

iTrader: (13)

Also what is this "power bleeding" you mention?

is the same thing as:

"I can acquire a tool to pressurize the master cylinder resvoir to do some more bleeding."


I think.

XBS

iTrader: (29)

This is the power bleeding im talking about:

http://www.motiveproducts.com/02bleeders.html

Should attempt one last time to do the following:

Bleed master cylinder first by pressurizing then crack the lines open at the MC

Then start bleeding the brakes starting at the farthest from the caliper,

with this power bleeder i should get any air that is left out, i would also be tapping the calipers with a rubber hammer to make sure its all out.

Also what was this about bleeding the brakes with the engine running?

Thanks for the input.

-George

barthelb

I have the 14" stoptech BBk up front and have no issues. My pedal is firm and consistent, even when they get hot, it still grabs and doesn't get mushy. I had my lines replaced with the Steel braided lines and Motul brake fluid. I had mine done at Zcargarage in San Jose and i haven't had an issue. They are really knowledgeable about the whole car and many products for it.

Dan@StopTech

Hey everybody, I'll consider Gary Cogis' bringing up StopTech's name an invitation to join in. For those of you who don't know Gary, his job title is "Sales Director for Race Technologies." That company is the distributor of all Brembo's GT kits in the U.S.

Matt Weiss, StopTech's Technical Support Manager, took the time to write up some helpful technical information this morning that will hopefully more fully address George's original questions and how to solve/troubleshoot them:

While bleeding brakes, assuring than any trapped air is out of the calipers by tapping them with a rubber mallet can work very well. Due to the orientation of some calipers, it may be necessary to loosen the caliper and turn it so the bleeders are facing straight up as shown on Page 21 of our Installation Manual for the 350Z. I have had many instances of just a small burp of trapped air making a huge difference at the pedal.

Pad knockback could also be an issue, especially on a 350Z with larger rotors and oversize pistons. There is some inherent flex in the 350Z suspension where the hub and rotor can move in relation to the fixed caliper. It is only a very slight movement, but enough to be felt in some instances. Original-equipment 350Z Track models with opposed-piston, fixed calipers have reported pedal issues during track use. Non-Track models with sliding calipers are not as prone to pedal issues due to knock back, because the slider accommodates the rotor movement very well and the smaller stock rotor diameter is not so pronounced in movement. Other platforms, such as the WRX, can also have hub flex or wheel bearing deflection issues. A larger rotor diameter means more relative movement at the rotor's edge pushing back the pads. Larger pistons aggravate the issue as pushing on the pads and pistons results in more fluid displacement.

What was initially described by George: The problem i am having is that while i am driving the first time it press the brake pedal it is soft and goes down half way. If i hit it again after that it is nice and firm and doesnt go down very much before the brakes start stop. Could be pad knock back, but there are a few things to look into to narrow it down.

Is your pedal only going halfway down once and then staying at its normal height as you drive for awhile? Might it come on now and again during the course of driving; such as after coming off a curving freeway off ramp?

Gary’s gave this advice: They can easily check to see if it is indeed pad knockback by doing a series of stops in a straight line without any turns. Possibly on the freeway. Give some time in between stops to allow everything to settle.
This would not reveal any knock back issue as lateral force on the hub is needed to induce knockback. Driving in a straight line won’t show knockback. Doing a series of turns without touching the brake pedal, then seeing if pedal travel is long after the cornering maneuvers would be more revealing. If the first maneuver of the day is backing out of a parking space or driveway and turning hard in reverse, that can also exaggerate knock back and make the first application of brakes have a long pedal; my Mustang does this every morning. Sometimes it’s impractical to get enough side load to reveal such an issue by reasonable street driving, but close attention to the exactly how the pedal is acting could confirm knockback.

I’d first suggest tilting the caliper as described in our instructions to get any trapped air out, then work to see if knockback is an issue on your car.

-Matt Weiss
***********************************

As for Gary's comments about StopTech products, it is ironic that he would bring up our name as a company that may possibly have too much piston area, as correct piston area and brake balance have always been our primary selling point. The decision to pursue this path was made on day one at StopTech, for many of the reasons Gary suggests are important: correct pedal feel, compatibility with all other vehicle systems, etc.

Gary is correct; we take our squeeze-forged caliper bodies and machine them to the piston sizes we determine as best for each platform. We do all machining, not just piston bores, in Torrance, CA.

Today, StopTech can choose between two-, four- and six-piston calipers, with pistons ranging from 28mm to 44mm in 2mm increments. With that array of combinations, we don’t have to make compromises. In reality, there have been applications we simply did not produce a kit for because we could not provide a proper balance. Better to not make a sale than provide something we KNOW is not correct. But we don't just "match" the torque output of the OE systems. When we build a brake system for a new platform, we go to test. We often find that moving the balance a few percent toward the back or front will take feet off the stopping distance and still meet our other test criteria. A brake company that doesn't track test its individual products before selling them can't know that.

Gary later wrote “In theory their upgrade isn't an upgrade for stopping power...just heat capacity.”

What is stopping power? Though is sounds like a simple concept, it is not a term commonly used in the braking industry. Some people might think it means when you press on the brake pedal a little bit, you slow down a whole lot. That's something brake engineers call "gain." It's literally analogous to turning up the volume on your stereo: it's the same tune, just louder.

StopTech, if we were to use the term "stopping power," would say it's the shortest braking distance, whether on the first stop on the street, or cutting fractions of seconds off your lap time, corner after corner, lap after lap. Maybe even for 24 or 25 hours.

The shortest stopping distance comes from using all the available grip from your tires to slow the car. That is what balance is all about, and that's what StopTech is looking at when we go testing.

If you increase gain (piston size/rotor diameter, or torque output in this discussion) while keeping balance the same, you will reach the point of maximum deceleration with less brake pedal force, so it may feel like your brakes are more powerful, but you won't do anything to shorten actual stopping distance. Is that a good thing? It depends on your driving style, but too much gain will end up as a loss of feeling and feedback, meaning less ability to modulate the brakes under threshold braking conditions. Early ABS intervention is one probable symptom. If you increase gain unevenly, by increasing the torque output disproportionately at each end of the vehicle, you will reduce the maximum deceleration that can be achieved, in spite of the "volume" being turned way up.

StopTech brake upgrades result in very little, if any, change to a vehicle's original relationship between brake pedal force and vehicle deceleration. That's one area where factory brake systems are typically very good. To say we're an upgrade for "just heat capacity" is silly. Of course that's the number one performance reason to buy either StopTech's products or those sold by Gary's company. More “stopping power” is not on our list of features, nor do we want it to be. I don't think anything more needs to be said on that point.

I hope this clears the air a little.

Dan Barnes
Marketing Manager
StopTech

Dan@StopTech

RE: pressure bleeders

I'm putting this in a separate post, as it's unrelated to the content in the rest of my previous message.

In our experience, the simplest, most reliable way to bleed brakes is the traditional way. It has the downfall that it takes two people. There are a variety of products available designed to make the process a one-person job. Some work very well, others don't.

When it comes to systems that pressurize the fluid in the master cylinder, it is absolutely critical to separate the fluid from any volume of compressed air (the small amount above the fluid in the reservoir is probably ok, but still imperfect). There are pressure bleeders that accomplish this by putting a diaphragm between the air and the fluid inside the pressurized canister. This is what you want. You don't want a pressure bleeder that pressurizes air directly on top of, and in contact with, the brake fluid.

Pressurizing any gas above a liquid tends to cause the gas to be absorbed into the liquid. Brake fluid with air absorbed into it will feel ok at low temperatures, but the air molecules tend to take up more space when they get warm, making the mixture more compressible. You'll bleed the brakes over and over at the track, and forever have a pedal that feels firm in the pits but gets spongy on the second or third lap. There will be no visible bubbles, because the problem is millions of individual little air molecules hiding out in the spaces between the big brake fluid molecules. The air molecules don't find each other and form a bubble that you can see.

The solution is just flushing the system completely with new fluid, in the traditional way.

What I described is something that happened with a StopTech customer earlier this spring. He just couldn't get his new brakes to feel right, and basically wasted a track day because of it. We saw the equipment he was using to bleed the brakes, helped him flush the system with new fluid in the traditional way, and bam, perfect brakes.

I hope this helps someone.

-Dan