I just put in a new cam and am having a problem with my brakes. This is on my 91 TPI Z28. At idle the brakes dont seem to have enough vaccuum and the pedal is stiff. The car has yet to be tuned and I have searched everywhere for any vaccuum leaks with nothing. Will the problem go away with tuning and having the car run properly? What steps should I do to determine what the problem is and anything I can do to correct it? Thanks.

 

Well, first of all check your engine vacuum at idle. I installed a cam and my vac dropped to 14" and the brakes were bad around town. I installed a Crane Vacuum Reserve canister and they work much better.

Auggie

 

Your vacuum will probably be better after tuning and so will your brakes. The bigger the cam the more timing it will want at an idle to achieve the most vacuum.

Charlie

 

How large is your cam?

I have a MAF system, and I installed a relatively large cam on my 305. The brakes were intermittent at first, but after some minor tuning it smoothed out the idle enough to start pulling stronger vacuum at idle. Now it's just running pig rich at idle, so that'll be my next area to focus on.

Might also want to check to make sure you have the vacuum canister installed and hooked up, and that the check valve is working properly. That could help out quite a bit

My specific cam is a lunati grind. .471/.480" @ .050 lift, 112/108 LSA, 219/227 duration. It's set 4 deg. advanced from the factory.

 

Well, on your cam specs there the 112* = the cams lobe seperation angle and 108* = intake lobe centerline.

Auggie

 

Could very well be, I'm going off memory on the specs. Seemed to have misplaced the card for the time being

 

If your cam is too radical you WILL have a lack of vacuum problem. You can either install a Vacuum Canister or GM has a Master Cylinder with a built-in vacuum pump designed just for this problem. Off hand, I can't remember what it came on or its name. I'm sure if you called SD or Pace Performance, they could look it up for you. Some of the others in here might also know what Im talking about.

Good Luck,
Bill

 

You guys rock!!! Thanks for all the replies. I bumped my idle up just to see what happens. It seems to have worked!! I measured the vacuum at 750rpms-850rpms and I pulled 19" of vacum and the brakes felt great. This is only temporary til I can have my chip burnt. Im gonna replace the booster check valve since I dont think it was ever done and clamp the line ends of the hose from the manifold to the booster valve. My cam is 08-305-8 from comp cams and I have 1.6 Crane Gold roller rockers....the car needs a tune sooo bad but it will get one soon. My buddies computer shows the stock ECM is pinned trying to lean the car out.....I hope the tune comes soon...LOL

 

Oh. What should the vacuum be at for the brakes to function 100% ??

 

AllData didn't tell me Jack for vacuum, but according to my Vacuum Gage instructions: "A steady reading between 15 & 22 inches indicates a mechanically sound engine." I did find out however that your idle settings are: In Park, Warmed Up, Closed Loop 425rpm +-25rpms. I was looking at CompCam.com yesterday, went back to check on you cam, you'll need a vacuum can from what I saw. If you call them, they will verify if thats true or not. Considering you've just about doubled your idle to get the 19ins, I'd say it will be true.

Just my $0.02 worth
Bill

 

i had the same prob with my 406 carbed and then i installed the 2400 stall TC and that solved my prob.

 

What kind of tranny were you running?

A 91 Camaro uses a THM-700r4 which does not uses a vacuum modulator like the THM-350 or THM-400. Instead a THM-700r4 uses a Throttle Valve Cable. The throttle valve cable controls line pressures, shift points, shift feel, part throttle downshifts, and detent downshifts. The function of the cable is similar to the combined functions of a vacuum modulator and detent downshift cable.

Therefore, Intake Manifold Pressure or Vacuum doesn't come into play when dealing with a TMH-700r4. I may be wrong but, I can not see where installing a stall converter on a 700r4 will change intake manifold pressure or vacuum. And this is what powers the brake booster.

Bristol, I forgot to mention last night, the master cylinder that I was talking about with the built-in vacuum pump is called a Hydro-Boost. I found it will looking for your vacuum specs.

Bill

 

Thanks guys! Im gonna tune first and then see how it is.