Bristol

iTrader: (1)

Hi guys. I am having issues with my 91 Z28 1LE 355 with my brakes. Long story short...new cam and intake mean low vacuum and bad brakes. Im only able to pull 10"s of vacuum at idle and the brakes suck. I have no vacuum leaks...car idles pretty smooth considering it is running a stock tune. Just a couple of questions

1)Will a tune clear up or help my vacuum issues at all?
2) How much vacuum is needed to have good braking
3)What are my other alternatives ((vacuum pump/resevoir etc))

I am at a point where I need solid answers. I dont know if I should tune the car with the vacuum issue and hope it gets resolved or do I need to resolve this before I tune. Thanks alot in advance for any help or suggestions.

Kris

IHI

iTrader: (1)

You should be fine with a vacuum canister for $35. My motor only pulled 5" warmed up in gear idleing and I had excellent pwr brakes with my vac can.

Save the electric vacuum pump as a very last resort due to high cost.

Bristol

iTrader: (1)

Thank you very much!!!

Kris

CaptPicardsZ28

I'm pulling 5" of vac and using a canister as well...

Bristol

iTrader: (1)

Thanks!! Would you mind posting a picture of where and how you mounted your setup. Thanks

Kris

CaptPicardsZ28

Here you go but I am moving it to a spot next to the brake booster where my MSD box is currently because I think my hoses are too long from the booster to the canister and i want to shorten them up.

IHI

iTrader: (1)

Same location i have mine located....think of the long hoses as extra capacity

rx7whoreboy

what the heck kind of cam you be running to get only 5" of vac?
also mr guy getting only 10" I don't think your going to get much betterif you have no vac leaks. big cam = no vacuum. best to start getting a canister. also just curious what cam you runnin

Bristol

iTrader: (1)

My name is Kris. What I was asking is if tuning would help my vacuum situation. My car is SD and as we all know a moded SD needs tuning and with my heads,cam, intake etc. I definetly need a tune. I was trying to determin if I can get away with tuning or if I needed a canister. The strange thing is...I have a Comp Cams 08-305-8 with 1.6 roller rockers and according to many tuners and even Comp themselves this cam should make 12"-15". My car idles at about 750rpm in drive, RPM drops immedietly when shifting from park to drive, used a stethoscope around all the intake seems and bolt holes and even a small propane torch with no change in rpms, and finally I capped all the vacuum ports except for the MAP line and still measured the same vacuum. I had my mechanic look at it for leaks as well as the Audi techs I work with(( one of which has over 15 years GM experience in a dealership, Players crew member, high perf. race shop etc) This guy says my rockers need about 1/4-1/2 turn of adjustment but figures that wont raise my vacuum to the point where my brakes will be 100%. Whats your thoughts? I dont understand cams and thats why Im asking for anyones thoughts. Appreciate any suggestions you may have.

Kris

rx7whoreboy

well if there was no tuning at all done I would guess that getting it tuned right at the prom might help a little bit with getting vacuum up and you might be able to get away with it.

but I would still almost assume that at even 12" your brakes aren't going to be the greatest. prolly better then what they are now at least.
and sorry kris for calling you mr. I'm bored and it's late

Bristol

iTrader: (1)

No worries. Im gonna start with the tank and do tuning right after that. At least while Im tuning Ill be able to stop LOL

Kris

CaptPicardsZ28

Thanks IHI but I thinnk if I shorten the hoses and move the canister I will have better brakes. I still dont have enough. If I use the brakes and then try to use them again right away they become real hard.

CaptPicardsZ28

My cam is running around 102 on the lobe seperation and almost 600 lift. The idle is real lopey and I like it...lol...The engine is maxed out for a 400 sbc. I havent put it on a dyno yet but it is between 500-600hp and should net me 11's in the qtr mile. I am installing a ford 9" with 4.0 gears so we will see...

JesasaurusRex

iTrader: (3)

Cant be that bad, i have 4-5" as well as IHI and i have no vac can

Difflock

Excuse the hijack, but would you humour a curious Limey?
Is the vacuum canister you refer to an extra item you can fit IN ADDITION to the brake servo (booster) where the master cylinder bolts to?

Cheers,
Mark.

CaptPicardsZ28

It's an extra item. Where you put it will depend on where you have room.

Difflock

Ah, I see.
Thanks for that

Bristol

iTrader: (1)

I installed the can ((Comp Cams)) as per the instructions and I honestly dont feel any difference. Before my cam swap I could hit the brakes hard and even lock them up. Now I hit them hard...pedal feels hard but the car stops very poorly. Im gonna list things that Ive done since I had good brakes.

1) Replaced my cam 08-410-8 with an 08-305-8 and retained my Edelbrock TPI

Cars brakes immedietly sucked

2) While in the shop they installed stainlees braided brake lines

Brakes still sucked...was told the cam wasnt making enough vacuum

3) Changed intake to HSR and had poor idle
4) Pulled cam and intake...sent to machine shop...all checked out
5) Reassembled... still poor idle

Brakes still suck and am still pulling only 10"

6) Changed and regapped new plugs, and readjusted rockers

Great idle, decent road manners considering no tuning...brakes suck still and still 10"

7)Installed vacuum resevoir

No change in brake pedal feel and still crappy brakes.

8) Hunted for any vacuum leaks...found that the vacuum line for the heater vent system had a break. Replaced line. Test drove and brakes still bad but heard a loud hiss from the HC panel.

Found cracked connection and am trying to locate a new HC panel.


Guys. Where do I go next? Some guys brakes seem to be fine with 10". Mine sucks. I havent put a vacuum gauge on it yet but will after the new HC panel. Im thinking the vacuum isnt the issue. How do I check the Booster or Master? Im gonna try re bleeding again. HELP!

Kris

Bristol

iTrader: (1)

Oh. And to describe the pedal feel. Its not soft or travels to the floor. In fact it feels maybe a little too firm and at times hard and seems to travel the distance it should, or at least the distance it did when I could lock them up. If the rear end is raised the brakes dont even have enough power to stop the wheels from turning in drive. So is anyone coming to Vancouver BC for holidays anytime soon? LOL

IHI

iTrader: (1)

I know this is kinda of a dumb question, but do you have the check valve installed in the can and the hoses going to the correct port?

Manifold vacuum to the check vale on the canister and the other side going to the booster? I installed the check valve in my canister and left the factory one in the booster.

Keep digging, hopefully it's somthing dumb, since 10" is more than enough with a can to give pwr brakes.

Bristol

iTrader: (1)

Thanks for the reply. I do have it set up right. I thought I was wrong at first so I tried it the other way...even worse LOL. I then thought maybe the booster valve was bad...so I used the new one and went from manifold to booster with no change. Im gonna re bleed all the brakes really really well....must be air in there cause Im stumped.

IHI

iTrader: (1)

I can relate, on my 3rd or 4th stock rear end replacement I had one hellava time getting them to bleed properly, Tried the typical pump 3 times, hold, then had buddy crack valve...did'nt do it. Let it gravity feed for an hour...did'nt do it, stuck the vacuum bleeder on the bleeder valve and tried sucking it through...still did'nt do it. Finally borrowing a power bleeder that C clamps over the M/C with an air fitting which literally blows the fluid through the lines-so you have to be careful as not to clear the entire system of fluid LOL. but that finally did the trick.

Had troubles with air locks in cooling systems like that before also, ya try and try and think it's finally done, then comes back to haunt you.

One thing with my car, at inital start up the brake pedal is hard. It takes a few revs of the throttle to get the vacuum built up/stored, then after that it's fine. What I call "typical pedal", you can push it down a little ways with minor braking taking effect then about the half way point brakes start to really apply hardcore.

Good luck

Bristol

iTrader: (1)

Ill try the bleeding. What are symptoms of a bad master cylinder or booster? Its really quite frustrating at the moment. Not really sure where to start. I just dont wanna spend 6 days bleeding and still not know if I need to bleed more or what. I work at an Import dealership and when we do brake fluid flushes we have a big machine the pressurises the system and feeds new fluid through. Maybe Ill get a tech to do it.

Gumby

You just described the same problem I am having.
I had worn my pads down to nothing being lazy, but after new pads the brakes wern't better. So I got new rotors. Still no change. So I got new calipers, still no change.

I have gotten lots of tip but not real answers.

Good used booster is in the mail as I type.
Someone else told me it could be a bad prop valve.
Another said air might have migrate into the master cylinder which is near impossible to get out by normal bleeding.

Ill be watching your thread close.

IHI

iTrader: (1)

A bad booster would lend itself to rock hard pedal since you have no "pwr" assist. If you have access to that brake machine, I'd get that done so you can eliminate that air problem all together.

If you just had no brakes or a caliper haging up I would mention the rubber brake lines may have swollen internally limiting fluid to the caliper, but you have braided lines and moderate pedal so that kind of eliminates that one.

M/C are cheap, usually when they fail they bleed fluid all over, but if your fluid level is staying the same that option is out also.

Bristol

iTrader: (1)

Dont wanna sound like a ***** but Im glad Im not alone. If you resolve your issue please let me know! Ill pay you as well LOL. Im gonna try the pressure bleeding machine. Its scary though cause once in a while it cracks the resevoir but Im at the end of my rope. I NEED to drive this car hard soon cause Im starting to loose interest . The only fun I get to have with her is scaring the neighbors when I start her up.

Bristol

iTrader: (1)

Could it be just a dying booster? Like its still functioning just not fully like its loosing air? Sorry to be naive...How does a booster and MC work together?

IHI

iTrader: (1)

http://auto.howstuffworks.com/power-brake.htm

Bristol

iTrader: (1)

Thanks

Gumby

I don't like the pressure bleeders either. Seams sort of back wards to try and force air out and down that will not bleed out normal.

I let mine gravity bleed for about 2 hrs. Used 1 1/2 giant bottles of brake fluid.

I think the pressure or forced bleed would work better in reverse.If normal bleeding even with a vac bleeder wont get it out. Force the fluid up and out the top which thoes hard to get air bubbles want to go anyways, up.

Bristol

iTrader: (1)

sorry to keep dragging this on but can anyone think of a way where I can temporarily boost the vacuum going into the booster to say 20" ? I figure if I can get 20"s in it would be way more than enough to make the breaks function correctly assuming vacuum is the real issue. So if I can get that amount of vacuum into the booster and hit the pedal and it still sucks then I can eliminate a vacuum issue. If its perfect then theres my problem. Any commentes? Thanks

Kris

IHI

iTrader: (1)

Would say a 12V electric vacuum pump, but dont think any junk yard pieces pull that much??

or you could just purchase the $250 unit outta Jegs and know vacuum is'n the problem and narrow it down from there, then you can go with cam of choice with no worries

Bristol

iTrader: (1)

I want to find a way to just boost the vacuum for a 1 time use, just so I can verify its a vacuum problem or not. Im thinking of maybe getting another car and running an extended vacuum line from their plenum to my booster just so I can try and see if the problem is in fact a vacuum issue.

Petes 84Z28

That should work, as long as the hose you're using doesn't collapse due to the vaccuum.

Lo-tec

Just checked the cam specs. 220/230 duration@.050" on a 114 LSA. You should have alot more vacuum than 10" with this cam, and a tune should solve that problem. You might want to do a quick tune on just the idle to get your vacuum up to see if the brakes will work.

Bristol

iTrader: (1)

So you think tuning would create more vacuum?

Gumby

Bristol

I vacuum time my V8 car. At idle I adjust the timing to pull 17-19 on the gauge. Its a bit simple but works well for me.


I will have my brake booster friday and let you know if it fixes it.

Bristol

iTrader: (1)

Gumby...Id love to here your results. Please do let me know. Hmmm. So if more timing improves vacuum and the HSR likes lots of timing maybe then a tune will infact help. Ive talked with a really really good tuner ((thanks again for your constant help)) and am told the correct way to change timing is through the ECM in its tuning but for now Im definetly gonna try that. I talked to a tech I work with and found out he was on a pit crew for the R7U which is a Canadian Players Challange Camaro race car. He worked for McGyver! LOL. But he really suspects the porportioning valve. He wants me to uses a hand held vacuum pump with gauge and boost the master to 20" and hit the brakes. I dont mind spending the money on an electric pump but the fact that lots of knowledgable people say the same thing about this cam should make 12"-15" and Im doing 10" ....thats what concerns me. I really appreciate everyones input.

IHI

iTrader: (1)

I know with carbs you can manipulate the vac signal slightly by changing idle mixture.

Kinda dumb ?, but are you sure the intake is COMPLETELY sealed. I had a intake gasket fail once and I lost alot of brakes, also had the silicone fail on the rear of my block where the intake sits and lost brakes.

Bristol

iTrader: (1)

I am pretty sure. I guess its possible though. Ill double check using a stethoscope around the seams and bolts. I just thought that the vacuum gauge would show an erratic readings and the fact my car idles relatively smoothly at like 600rpm or something in the ball park. I assumed a vacuum leak would make the car idle higher.

MurcoRS

Ok, guys
For a booster to operate at 100% it needs to see at least 18" of vacuum. Normal air pressure at sea-level requires 14" to make it work at all! Even with a cannister there is no way your booster is operating properly on only 10" of vacuum.

IHI

iTrader: (1)

Not initally, but the canister stores vacuum. My car had 5" at idle, after letting it warm up, or driving around the guage on the canister would go upwards of 30".

TurboGM1

Ok here's a dumb tag along to this thread. My brakes suck and are getting worse. Bleed them, fluids good, vacum lines are good, evry sensor other than the ICM has been changed, it needs to get timed as I have nothing to plug into the computer to do this with and by hand is ok but it just isn't getting right, it comes close though and is running much better (for the most part). But now I can't stop!!!!! I already have a can at the front of my car as pictured above on this thread, except mine has a larger almost gas cap sized piece that the hose goes into on it at the top and a small line out. My brake gets harder to push down at times, or goes to the floor and then back up. When the car is running good (as good as it's gotten so far while working on it) the brakes are good. But when the idle goes off and jumps around especially when it goes high (1500) the pedal getrs harder to push and it feels like it's not getting any action out of the pads. My thought at first was a master cylinder, but why would it opnly happen when I'm hard on the brakes or when the idle is high? Otherwise it's fine. If I already have this canister, could it be bad? Am I looking at something else? Is it the booster or the master? My Camaro has the 2.8 MPFI. I read this whole thread seeing common things with my problem. Just hoping for a clearer answer before I take the wheels off again this weekend. Thanks

Gumby

Well Bristol I got my brake booster but will need to find some more tipe to even start getting mine out. There is a brace bar for the brake pedal that is right in the way. Thinking I need to drop the colum and all to even get at the top bolt for the brace. Its gonna suck.

But I am pretty sure it is the booster though. I had the brake rod unhooked and pushing on it by hand the one in the car makes a giant wosh when pushed. While when I charged the new one and pushed the rod by hand. It didnt make 1/4 of the noise.

Bristol

iTrader: (1)

Thanks for the update! Im gonna tinker with mine on the weekend. Need to find another strong running car to steal vacuum from. If the brake pedal improves drastically then I know its vacuum related.

V6#22

The above posts are correct about needing 18" of vacuum for *normal* operation. Even at only 14" the brakes will be hard from lack of booster pressure.

When all else fails- go to a hydro boost. Its the hot new ticket even new car manufacturers are going to.

Bristol

iTrader: (1)

Got a link to it?

V6#22

Never worry about Vacuum brake problems again-

http://www.hydratechbraking.com/products/universal/

Bristol

iTrader: (1)

I took a short video of my car ideling and in drive showing the vacuum gauge. Then showing the rpms in park and drive. Anyone know where to host it or can anyone tell me if the gauge shows something likwe a vacuum leak?

MurcoRS

To check a booster on the car - Engine off, pump the brake pedal until all boost is gone (3-5 pumps), and while keeping your foot on the pedal start the engine. The pedal should drop 2-3" if the vacuum diaphragm is good.
Next, with the engine running, apply the brake pedal again, keep it down, and shut off the engine. It should stay down for at least 30 seconds. If it does not, you have a bad booster control valve.
Simple as that.