Vacuum Booster/Brake Question CJ7

[tthstrm179]

1978 CJ7 , AMC 304 , 71,000 original miles, part time kit in the QuadraTrac .

Recently I spent over $700.00 trying to fix a low brake pedal that was/is somewhat soft and wont lock up the brakes. Started with wheel cylinders, calipers, moved to lines, changed the proportioning valve, and had the booster rebuilt. Same problem existed.

In an act of frustration I took it for a smog check in order to sell it. I live it a county where smog is only required when buying/selling.

The jeep failed with high tailpipe emission, however, the evap system was fine. Tech said that the levels were high and could be from timing, and that the EGR and ported vacuum valve should be checked.

I found 0 vacuum at the ported vacuum from all of the three ports on a hot motor, 17"-19" from the manifold, and about 14" at the power brake booster.

I plan on replacing the ported vacuum tomorrow, however, I noticed that one its three lines shares splits and goes into the same manifold vacuum as the brake booster hose.

So my question is: Is the ported manifold defective, and also, how can I increase vacuum to the power brake booster?

I should add that the smog shop tried to adjust my carburetor to lean it out, and now the Jeep runs like too boot. Timing is set at stock 5 btdc as shown on spec sticker.

Thoughts????

 

[tarry99]

1978 CJ7 , AMC 304 , 71,000 original miles, part time kit in the QuadraTrac .

Recently I spent over $700.00 trying to fix a low brake pedal that was/is somewhat soft and wont lock up the brakes. Started with wheel cylinders, calipers, moved to lines, changed the proportioning valve, and had the booster rebuilt. Same problem existed.

In an act of frustration I took it for a smog check in order to sell it. I live it a county where smog is only required when buying/selling.

The jeep failed with high tailpipe emission, however, the evap system was fine. Tech said that the levels were high and could be from timing, and that the EGR and ported vacuum valve should be checked.

I found 0 vacuum at the ported vacuum from all of the three ports on a hot motor, 17"-19" from the manifold, and about 14" at the power brake booster.

I plan on replacing the ported vacuum tomorrow, however, I noticed that one its three lines shares splits and goes into the same manifold vacuum as the brake booster hose.

So my question is: Is the ported manifold defective, and also, how can I increase vacuum to the power brake booster?

I should add that the smog shop tried to adjust my carburetor to lean it out, and now the Jeep runs like too boot. Timing is set at stock 5 btdc as shown on spec sticker.

Thoughts????

You need a minimum of about 19 inches of vacuum for the brake system......Vacuum is all about cylinder leakage and piston to valve timing.......a worn out motor , rings and leaking valves will not have very good vacuum.

I would go around that motor and check for vacuum leaks......at the carb, under the carb. at the intake manifold gaskets. You should also run a compression test and a leak down test on all cylinders to assess condition. You never mentioned what sized booster you have.......a dual chambered 8 inch will hold more than a single 9 inch.....and helps in low vacuum motors or when you live or operate the vehicle at High altitude.

 

[tthstrm179]

Thank you for your answer. I have only had the Jeep for about a year and it passed smog with no problem when I bought it. It does not burn oil and seems to run well so I am hoping that this is not a work motor/cam issue. Have not done a compression check.

Does anyone know if the ported vacuum switch can draw vacuum away? The idle vacuum seems fine but the brake vacuum is not.

Any suspicion on the catalytic converter? I have read that a clogged one may reduce vacuum.

Thanks in advance.

 

[IOPort51]

I understand you are speaking Californian so please excuse my failure to translate. I do not understand "replace ported vacuum".

I would think that the booster would be on manifold vacuum

 

[mtnwhlr]

I do not understand "replace ported vacuum".

I would think that the booster would be on manifold vacuum

Me either, Ported vacuum are the ports above the throttle plate on the carb. Your brakes should be hooked to nonported vacuum which are the ports on your carb that are below the throttle plate.

 

[007]

My brakes are off a port on the manifold in front of the carb.

Sent from my iPad using Tapatalk

 

[ThisGuyUKnow]

Me either, Ported vacuum are the ports above the throttle plate on the carb. Your brakes should be hooked to nonported vacuum which are the ports on your carb that are below the throttle plate.

? ? ? I thought ported vacuum ports are vacuum ports that only open up when the manifold reaches operation temperature or when the vacuum is higher like during wot, I didn't think it referred to their location on the carb.

 

[mtnwhlr]

? ? ? I thought ported vacuum ports are vacuum ports that only open up when the manifold reaches operation temperature or when the vacuum is higher like during wot, I didn't think it referred to their location on the carb.

No manifold vac is the same no matter what the temp of the engine is. Ported vac is only at the carb above the throttle plate that is why your vac advance for the dissy hooks to a port on the upper part of the carb.