\Ok the car is a 91 S-chassis with a head/cam swap LS6.

I know a few others run the same or a similar cam and brakes and well I am kinda confused and just cant figure out my issue.

So its a 5.7 LS6 with ported and polished 243 heads, and a Texas Speed MS3 cam (.605/610, 238/242 at 114LSA). The brakes are z32 front a rears with a brand new OEM Nissan brake master and they have been bleh to high hell.

The issue is the brakes feel like manualish. The pedal only moves down about 2 inch's the first inch is normal then they feel like they are manual brakes. Vacuum lines were checked, then we bled the brakes and nothing they were the same. The vacuum pressure is 12psi on the meter. I then added a comp cams vacuum reserve canister thinking that I wasn't holding enough vacuum. I then replaced the used master cylinder for a brand new one, and we bled the hell out of them again and again. Still they are doing the same thing. At idle I really have to put all my force on the pedal to hold the car in place. Running and driving they feel worse the the OEM S13 brakes, I cant get the brakes to lock to save my life.

The only other thing I can think of is the booster maybe, because the calipers are new, master is new, lines are new and nothing. When bleeding with engine running the fluid come out in a nice strong stream. Perhaps the front calipers aren't good, but I don't know.

I just figured I'd ask the other LS guys with aggressive cams and z brakes. How do yours feel?

I would try the booster. If there was any brake fluid inside of the booster, ever, you can pretty much bet it's shot, as the fluid will ruin the vacuum diaphram inside the booster. That is definitely where i would try next.

And an easy way to check the calipers is... Take them off, hit the pedal, if they move... TADAAAHHH!!!!

Sorry. It's early, and i haven't had my coffee...

OutToWinPAHC wrote: At idle I really have to put all my force on the pedal to hold the car in place.

Now that's a powerful motor!!!

j/k.

I agree with wrxratd, sounds to me like a bad booster. Are you getting proper vacuum to it? Have you double checked the vacuum line to make sure it's not collapsing or crimped off anywhere? Fluid in the booster would be bad as well.

Yeah I have a gauge on the reserve.... a sold 12-14 ft of vac. Yeah I think its the booster. I am sourcing a cheap used one to test, if it work I'm gonna get a new one. I just cant see spending 150 and have it not be the issue

I was having similar brake issues. I am assuming that you have the check valve in place. I did not.

I keep reading that you need at least 18" vacuum for the power brakes on cars to work right. the big cam throws that off. I'm a noob but I keep reading this in different places. that is why some cars are running mechanical or electric vacuum pumps.

did you buy a brand new 240sx or 300zx master cylinder and did you adjust the length of the rod from the brake pedal to the booster?I have read that it needs to be adjusted when you replace master cylinder.

Its making 14 feet of vacuum, I replaced the used Z32 BMC with a new Z32 BMC. A buddy also gave me a larger auto+abs booster off his S13 front clip. Still all feels the same.

At this point I am going to rebuild the front calipers.

When bleeding the pedal feels fine, after they are bled the pedal movement is very limited. Feels almost manual. Its not the BMC, or booster, I run a vacuum reserve can so I have stored vacuum, the lines aren't collapsing, when bleeding the fluid stream is solid and strong so there is no line blockage.

are you using a vacuum bleeder? just asking because with the vacuum on ,the bleeder screw cracked and pressing the pedal it will definitely feel fine because there is no resistance from the brake fuild. If you know, this sorry,just making sure.

what about the amount of vacuum you actually have. all the vacuum pumps are either designed to come on at 15" or 18 " of vacuum because less than that is not enough. most of those pumps keep you vacuum between 18" and 22"

so it should feel manual with out enough vacuum.

if your calipers move they are probably good and if the pedal is stiff there is not air in the lines(not much anyways)

based on what you said " The pedal only moves down about 2 inch's the first inch is normal then they feel like they are manual brakes."

it sounds like you are just not making enough vacuum.

but that is just my opinion.

I am running a vacuum line off of the cold air intake and the manifold.once the motor gets spinning and the air gets sucking through the filterI bet there is enough extra vacuum that you can get the amount needed.I am running a check valve on both the intake and manifold then t fitting ,then to the canister, to brake booster. running the check valves for extra.don't want any boost in the line coming off manifold. and the closer the check valves are to the source of vacuum the better. when the sources begin to produce vacuum it still has to suck out any air in the lines so the closer the check valve the better.

I will see tomorrow if this works. can let you know.

Modified by 450SX! at 12:22 PM 6/5/2009
Modified by 450SX! at 11:43 PM 6/7/2009

so I got to drive a little yesterday and the brakes are awesome. not sure how much extra vacuum I am getting off of the cold air intake but I only have 14" of vacuum and the brake booster only stores extra vacuum does not create vacuum. so I figure that the cold air intake is helping.

have you rebuilt the calipers again and if so are your breaks working?if so kudos to you.

good luck

A caliper rebuild is in order as well as adjusting the booster some more, then I should be ok

have you resolved the brake issue yet? just curious to know what it was?

Not yet, I am getting ready to pull my headers for ceramic coating, and I am going to powdercoat the calipers too. So I am going to rebuild them when they are back from powder. My issue now is running warm. Upgrading fans, cooling panel, and oil cooler

I'm running warm too. , just replaced my fans 2 12" permacools(3300cfm each), built shroud for one that is pusher and the other is puller, stupid fan controller stopped working so I sent a signal through the temp sender from ignition source and have it return to the a/c override, fans are on all the time now (once the sender becomes a closed circuit) , drilled little holes in the stat so air can pass and not get trapped, added a filler neck in upper radiator hose, raised my reservoir 2 inches so it was high enough to function. mine is fine while sitting idling in garage for 15 minutes (180 degrees) but when driving it will get to about 210 to 215 after 20 minutes of city traffic. then slowly starts creeping up. on freeways I am great or any other road where i am not stopping and going and waiting at lights.

not sure what is wrong now. I am running lean when my secondaries open slowly ( know hot to fix just not sure that is enough to make it overheat) besides my turbo being about a half inch from the radiator.haha. i might want another layer of heat shield on there.

hope you get yours running cool.

Modified by 450SX! at 2:39 AM 6/26/2009
Modified by 450SX! at 1:08 AM 6/30/2009

Yeah I just got the same fans they 3300cfm fans. I am also going to space the hood and add an oil cooler. If that dont get me down to 210 traffic I am going to have to bite the bullet and run an electric water pump.

the electric is a good idea. unfortunately I ate a whole magazine already. does not seem like they have inlets for the heater hose return line. how does your heater hose run ?do you have heat?

I had it out tonight and had the heat running...... never broke 200 degrees.... which is awesome. But not so good for summer lol.

I am adding the oil cooler with a 180 degree oil temp tstat.

But for spring/ summer I came up with something. I ordered a Chevy Surburban heater core, and motorcycle radiator fan. I am going to mount it under the bumper behind one of the openings. Kinda like a second radiator. That paired with an oil cooler should drop my in traffic / hard running temps from 225 to 195 I hope...... coolant is a 160 Tstat.

I had it out tonight and had the heat running...... never broke 200 degrees.... which is awesome. But not so good for summer lol.

I am adding the oil cooler with a 180 degree oil temp tstat.

But for spring/ summer I came up with something. I ordered a Chevy Surburban heater core, and motorcycle radiator fan. I am going to mount it under the bumper behind one of the openings. Kinda like a second radiator. That paired with an oil cooler should drop my in traffic / hard running temps from 225 to 195 I hope...... coolant is a 160 Tstat.

that is cool, I looked into the oil coolers after you mentioned them. not as expensive as i thought.

I added a bleader/ drain valve to my heater line, and changed the rubber on my upper radiator hose because they were too big and I was trying to squeeze them down with the clamps. now that I bled the system a little better and got rid of the leaks the car was idling at 150 for a while then went up to 160. about 5-10 minutes to hit 160. fans turn on as soon as the temp senderbecomes an open circuit(150).

what clutch MC are you using? I am having a problem with my wilwood.leaking from the bore.

clutch....... dont have one of those on this lol

Oh this is what I am using for the Oil T-Stat. The LS series oil Tstat is bolt on to the block. It bolts to where the oil pressure sender is. So its a sender unit with a built in T-Stat for 149 bucks.

http://www.racerpartswholesale...ostat

was wondering why you had a auto booster.

what are you idling at?

trying to figure out if I can work in a oil cooler.the port above the oil filter on my block is plugged. the block was used an when rebuilt for some reason they plugged it. I am running oil pressure and oil feed to turbo off the back of the block.

OutToWinPAHC wrote:I had it out tonight and had the heat running...... never broke 200 degrees.... which is awesome. But not so good for summer lol.

I am adding the oil cooler with a 180 degree oil temp tstat.

But for spring/ summer I came up with something. I ordered a Chevy Surburban heater core, and motorcycle radiator fan. I am going to mount it under the bumper behind one of the openings. Kinda like a second radiator. That paired with an oil cooler should drop my in traffic / hard running temps from 225 to 195 I hope...... coolant is a 160 Tstat.

That's weird, I had mine running in 100 degree weather in traffic and it never broke 205, with a 185 degree thermostat. I've read that if your cooling system is sufficient, there is never a need for an oil cooler unless you're tracking the car and just beating on it for extended periods. For the street, it's really not necessary (given your cooling system is up to the task).

On topic, I have the same cam as you, an auto booster, 26mm Z32 brakes up front only and I have the same crappy brake feeling and they are easy to lock up. It has to be the cam...that's my best guess.

I rather have the oil cooler and extra radiator surface space. The waterpump is not OEm, its an aftermarket parts store brand.... If I break 210 again I am going to upgrade the water pump.

do you know what your oil temp is getting up to.

Stays about 5-10 under water temp until it get warm then its about the same temp