Power brake vacuum problem,help...

V-8 · #1 (**permalink**) 07-07-2005, 09:49 AM

Hi Guys;
My power brakes doesn't work properly at low rpms. Because of that i can't drive my car in the city traffic. First i had bought a vacuum can but it couldn't solve the problem. Now while i was looking http://store.summitracing.com/defaul...h.asp&x=30&y=7 to this unit , i remember that i'm using http://store.summitracing.com/defaul...h.asp&x=50&y=8 so if i do an inlet to the vacuum side of the vacuum pump to the booster and close the intake manifold vacuum side.It will be ok?it will be enough for my power brakes? I wish i can explane what i want to do... THANKS

nevermind65 · #2 (**permalink**) 07-08-2005, 04:04 PM

You must have a pretty horrendous cam to supply such little vacuum? Are you sure there isn't another problem somewhere?

Is the check valve working correctly? Have you pulled a vacuum on the booster independently to see if it holds? Is the cam degreed properly and/or initial timing set correctly?

Personally, I would look at another booster if you are determined to have power brakes instead of hooking up a vacuum pump. I had a truck with 5" of vacuum at idle and the power brakes worked fine with 4 wheel disks. I used a small diameter booster out of a 1 ton truck. Hit the pedal too hard and you would either lock them up or go through the windshield.

nevermind65 · #3 (**permalink**) 07-09-2005, 04:51 PM

Here's a better bet. Buy a hydroboost unit from a newer Mustang Cobra and remove the vacuum booster altogether.

V-8 · #4 (**permalink**) 07-10-2005, 12:37 PM

I haven't got P/S

V-8 · #5 (**permalink**) 07-10-2005, 12:44 PM

Quote:

Originally posted by nevermind65

You must have a pretty horrendous cam to supply such little vacuum? Are you sure there isn't another problem somewhere?

Is the check valve working correctly? Have you pulled a vacuum on the booster independently to see if it holds? Is the cam degreed properly and/or initial timing set correctly?

Personally, I would look at another booster if you are determined to have power brakes instead of hooking up a vacuum pump. I had a truck with 5" of vacuum at idle and the power brakes worked fine with 4 wheel disks. I used a small diameter booster out of a 1 ton truck. Hit the pedal too hard and you would either lock them up or go through the windshield.

Yes the cam shaft is too big mech roller comp cams 240-246 and 608-614 lift. We checked every think and valve also. The problem is there is no vacuum in the idle. At the high rpms it is ok...

nevermind65 · #6 (**permalink**) 07-11-2005, 02:43 PM

You don't necessarily need p/s. The Cobra set-up had a separate pump used exclusively for the hydroboost. If you were looking at hooking up a vacuum pump, this should be about the same and you'll never have to worry about vacuum again.

Why not just change the cam if it's too big? Sounds like it is causing more headaches than what's it's worth.

Excaliber · #7 (**permalink**) 07-11-2005, 03:31 PM

Why not just change the cam? Eh eh,,, well THATS what I was going to do when my old cam failed. But nooooooo, I couldn't stop there. Next thing you know I've stareing at a bare block and a complete rebuild.

...just got carried away I guess.

nevermind65 · #8 (**permalink**) 07-11-2005, 04:02 PM

I know exactly what you mean. I just traded a Lil Red Express truck I've had for 12 years for a Cobra Kit car. The Lil Red started out as needing "just a paint job". $15k later, and I was done.

I can see after 1 week I'm already headed down that path with the Cobra.

Considering he has such a huge cam, my assumption is somebody must have already torn the engine down and rebuilt it. You can't get that much lift out of factory heads with no modifications, and to run that big of a cam without about 10-11:1 compression, the car would be a slug. But hey...you never know!

V-8 · #9 (**permalink**) 07-11-2005, 04:42 PM

Quote:

Originally posted by nevermind65

I know exactly what you mean. I just traded a Lil Red Express truck I've had for 12 years for a Cobra Kit car. The Lil Red started out as needing "just a paint job". $15k later, and I was done.

I can see after 1 week I'm already headed down that path with the Cobra.

Considering he has such a huge cam, my assumption is somebody must have already torn the engine down and rebuilt it. You can't get that much lift out of factory heads with no modifications, and to run that big of a cam without about 10-11:1 compression, the car would be a slug. But hey...you never know!

spects:
*408w full 4340 forged steel, 6.250 rods, JE forged- alm. pistons
*TFS twisted wedge alm. heads full ported & polished and reshaped comb. chambers
*full ported & polished EDELBROCK Victor jr. intake
*12.5:1 comp ratio
*MSD pro-billet dist-MSD 6a-MSD 50000 volt coil (blue)
*23 total advance , 98 octan pump gas
*...

V-8 · #10 (**permalink**) 07-11-2005, 04:54 PM

Quote:

Originally posted by nevermind65

You don't necessarily need p/s. The Cobra set-up had a separate pump used exclusively for the hydroboost. If you were looking at hooking up a vacuum pump, this should be about the same and you'll never have to worry about vacuum again.

Why not just change the cam if it's too big? Sounds like it is causing more headaches than what's it's worth.

Hehe may be when we rebuilt my engine again, we will run with a hydraulic cam. But now, no.
Ok, if my project won't work i will buy an electric vacuum pump. But first of all i want to try my project. What is your ideas about my project?