Loss of Brakes

Is this a problem with air in the lines? (Then again maybe not with the symptoms that you describe.)

How lopy is the cam in your car? I am assuming that you have a vacuum assist on your brakes. The more lope of the motor (i.e. the wilder the cam), the less vacuum these babies like to make. If this is the problem, then you may need a vacuum resevoir to supplement your brake system needs. These resevoirs were common on GM cars from the 60's and 70's with cruise control, when cruise control operated off from vacuum. Also, if your brakes operate off from the vacuum, and you have a valve between the intake manifold and the booster, it may be a faulty valve, or a break in the vacuum line.

quote:

a break in the vacuum line

Yup, that is where I would be looking.

Especially if you have a vacuum advance on your distributor.

Did the problem go away with the AC turned off?

Larry

if it worked last year and if this happened suddenly, then a vacuum leak sounds about right. probably a bad vacuum hose to the brake booster.

listen carefully as the engine runs, is there a sucking sound as you trace the vacuum line, (no, not from your wallet as you fill the gas tank) especially around the flexible hoses, this should not be anything major.

nazgul

If this is a new problem, it sounds like a vacuum leak. Spray carb cleaner around the manifold and vacuum hoses while the engine is at idle. When the spray of cleaner hits the area with the leak, the motor will lose rpm and try to die. this will show you where the leak is.

Thanks guys. Yes I believe the cam is kind of radical, engine sounds like a popcorn machine on steroids. I only seem to lack brakes when I kick on the AC and idel drops, if that means anything? It just seems odd that idel drops almost 700 RPM when kicking in the AC as well...seems like a lot to me.

quote:

I only seem to lack brakes when I kick on the AC and idle drops, if that means anything?

The increased load from the AC compressor can be expected to lower rpm of the engine. How much is normal? Varies with a lot of variables.

Your engine vacuum is related to engine rpm, so you may have a connection in that manner.

One easy, cheap part that can affect vacuum is your PCV (valve). Pull it off and see if it freely rattles; replace it if is isn't.

Larry

I do not know anything about 5S cars, but is there such a thing on the carb end that pumps up the throttle when the A/C is turned on? There is such a thing on some big block 1970 Mopar stuff with factory A/C. A shot in the dark .....

Otherwise, I also know for a fact that my 1966 Jag has a vacuum resevoir for just such an occasion. I found a resevoir for cruise control for a GM vehicle -- same idea. Here it is:

Vacuum Resevoir

Do all of the easy stuff first -- then go on to the crazy stuff that I have listed here.

Could it be the booster itself ?

A vacuum gauge is a valuable diagnostics tool for general engine condition, and can be installed temporally or permanently. The gauges are inexpensive and should be part of any Cleveland owners tool box. Monitor your vacuum by tapping a vacuum line from the intake and operate the A/C.
There are 2 engine load increases when A/C is turned on, torque load from the A/C compressor and approx. 30 amp load from the alternator. A solenoid/dash pot device mounted on carb. can increase idle on demand. Connect it in parallel to the compressor clutch. You may have to fabricate your own bracket.

Is there some sort of vacuum pump available to test for the integrity of vacuum lines/devices e.g. booster?

Yes. The most common one that I knew off the top of my head was this hand operated one -- I'm sure there are others that operate off from compressed air making a venturi, but here is the one that I found online:

Vacuum Pump MITYVAC