How big of a cam should effect power brakes

iapexl8r · Oct 20, 2005

I have a 408 (stroked 351w) with afr 185 heads.It has crower cam p/n 15514. with 1.7 to 1 roller rockers. the advertised duration is 298 deg /304 deg, dur @.050 is 234deg/240deg Gross lift is.534"/.545".(this is with 1.6 to 1 rockers). with the 1.7 rockers lift should be around .560"/.570" this is on a 110 lobe ctr the cam was installed straight up . the brakes feel like the power booster is not working. I personally thought this cam was pretty small. but usually dont run power brakes so what do I know?? if any of you gurus have an answer if this is a cam issue or a brake issue. please let me know. the brake set up is 1987 5.0 mustang master cylinder/booster with cobra (2 piston 13") brakes up front and 86 turbo mustang disks in back. have a proportioning valve (played with it no help). the car is very fast and dangerous with the brakes the way they are now need to figure out if it is the cam before I proceed with trouble shooting the brake sys, cuz if it is the cam I will go manual brakes. thanks guys Chris

iapexl8r · Oct 20, 2005

come on some one here knows this. you guys collectivly know everything. not ment as smart a$$ coment I am continoulsy amazed at the info that comes across this board. chris

Dbeck002 · Oct 20, 2005

I am pretty sure that cam is affecting your brakes. It sounds like it's a very unstreetable cam.

Daggar · Oct 20, 2005

I don't know what your whole setup is or how efficient the heads are that you're running (though the AFR heads are pretty darned efficient) but with an LSA of 110-112 degrees you should be pulling somewhere around 12 to 14 inches of vac at idle. If I were to hazard a guess, I'd say that you are probably venting vac pressure somewhere (either a vac leak or poor performing brake booster). You'll need to get a vac gauge on it to find out if your vac is less than that for some reason.

Daggar · Oct 20, 2005

Heya... I just noticed that you're running an 87 MC and brake booster with Cobra dual piston calipers... how long have you been running that setup???

Seems to me like the small diamater of the 87 MC along with the decreased diameter of the brake pistons would make for a pretty significant lack of mechanical advantage in your braking system.

I'd also be a little concerned that the piston area in that 87 MC might not contain enough brake fluid volume to feed all 4 calipers on your front brake (I do not know for certain that it wont but the thought comes to me none the less). I don't know what the total volume of the Cobra dual disk calipers are in relation to the single on the 87+ cars but I understand that the differences are pretty good.

TheUser · Oct 20, 2005

maybe call the manufacturer and see how much vacuum your cam should pull at idle. I've read anything 10 hg vac and under at idle and you should get a vacuum canister which would provide vacuum to the booster.

iapexl8r · Oct 22, 2005

thanks for all the help.

first I will inspect all vac lines then check vac @ idle if that checks out I will be looking for a new master cyl. Any part number suggestions. chris

How big of a cam should effect power brakes

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