power brake booster questions

[40cpe]

I was checking spark plugs today and the #4 and #8 plugs are showing a lean condition, very white. I've recently replaced the intake gaskets when I resealed the valve chamber cover, so I'm confident that it is OK. I do have a 7" power booster for the brakes connected to the top of the intake manifold behind the carburetor. I'm wondering about the possibility of the booster leaking. The brakes work good, with the exception of there is no reserve if the engine stops. There is no external vacuum reserve.

How can I check the booster? Should it hold a vacuum if I pump it down with a MityVac? The engine is a 272" Y block and holds about 17-18 vacuum. The possibility of a vacuum leak just hit me tonight and I would like to troubleshoot it tomorrow. I think I'll start by plugging the booster fitting and see if the engine vac goes up, and trying to pull a vacuum on the booster. What are your thoughts?

[40cpe]

I just went to the shop and pulled a 20" vacuum on the booster and it took 35 seconds for it to drop to 15". I wouldn't think that would be a serious vacuum leak. I put a wrench on the manifold bolts and none were loose. Tomorrow I'll warm it up and pull the plug wires on those cylinders and check for RPM drop

[KULTULZ]

Originally Posted by 40cpe

I just went to the shop and pulled a 20" vacuum on the booster and it took 35 seconds for it to drop to 15". I wouldn't think that would be a serious vacuum leak. I put a wrench on the manifold bolts and none were loose. Tomorrow I'll warm it up and pull the plug wires on those cylinders and check for RPM drop

If the booster draws outside air (leakage) and/or the vacuum source (hose - fitting - check valve) is not sound, the fuel mixture will be leaned out and what cylinder(s) are involved depends on the vacuum source location you have chosen.

[dmsfrr]

Originally Posted by 40cpe

I just went to the shop and pulled a 20" vacuum on the booster and it took 35 seconds for it to drop to 15". . .

I guess that's not too bad, but should it be dropping at all?

Is the intake manifold an ECZ-B, or something else?
Look for vacuum leaks with a spray of starting fluid, WD-40, etc.
Are there other vacuum lines to the fuel pump/wipers & heater? Check those too.
The fitting in the intake manifold may be cracked, or there can be leaks in odd places.

[40cpe]

Thanks for the "odd places" suggestion and example. The manifold is an ECZ-A. I tested the booster at the engine end of the hose, so that only leaves the fitting and threads suspect in this vacuum circuit. The only other vacuum connection on the engine is the distributor vacuum at the base of the carburetor.

[KULTULZ]

Sponsored Links (Register now to hide all advertisements)

You have drilled and tapped a vacuum source as shown-

You have an ECZ-A 4V intake with a later carb (with adapter I assume). Is that source for the booster only? I also assume you have a 57 dist. Is it's vacuum source ported or manifold? Where is two-stage fuel pump vacuum assist (if you have one) plumbed? Is there anywhere on the intake that you can take a manifold vacuum reading?


Cam we get an overall engine photo?

[40cpe]

Yes, 1959 distributor. Manifold vacuum. No 2 stage pump, electric wipers. Manifold vacuum is 17-18 inches measures at a tee in vacuum advance line.

[40cpe]

KULTULZ mentioned a drilled/tapped vacuum source. I looked up a picture of an ECZ-A manifold and, sure enough, no fitting in that location. I found a plug in the rear of the carburetor and moved the brake vacuum to a fitting I installed there. Engine vacuum is a steady 19 at 600 RPM, though about 14-15 at 400 rpm. I keep the idle RPM at 600 so as not to kill it with the AC on. I guess I'll drive it a while and recheck the plugs. Thanks for the interest and suggestions.

[KULTULZ]

Originally Posted by 40cpe

KULTULZ mentioned a drilled/tapped vacuum source. I looked up a picture of an ECZ-A manifold and, sure enough, no fitting in that location.

I found a plug in the rear of the carburetor and moved the brake vacuum to a fitting I installed there. Engine vacuum is a steady 19 at 600 RPM, though about 14-15 at 400 rpm.

I keep the idle RPM at 600 so as not to kill it with the AC on. I guess I'll drive it a while and recheck the plugs. Thanks for the interest and suggestions.

There you go. The EDELBROCK has that provision.

IMO, it is better to source the booster vacuum at or close to the manifold carb plenum instead of runner(s). The same for a PCV system.

Please check #4 and #8 plugs in a few weeks and see if they are receiving more fuel.

There are also solution(s) to speed the engine with the AC on.

[KULTULZ]

Originally Posted by 40cpe

Manifold vacuum is 17-18 inches measures at a tee in vacuum advance line.

Is the gauge hand steady or fluctuates? Stock cam?

[40cpe]

Stock cam. It is rock steady at 19 at the 600 rpm idle. It fluctuates slowly 13-15 at really low idle (400)

[KULTULZ]

Originally Posted by 40cpe

Stock cam. It is rock steady at 19 at the 600 rpm idle. It fluctuates slowly 13-15 at really low idle (400)

Sounds good to me. The varying at low idle is due to it's wanting to stall.

Is it an AT? What curb idle do you have it set at, 600 to 650 RPM in DR?

How far down does the AC drag it down?

[40cpe]

It is a 5 speed. I'm not sure how much the AC drags it down, but it is like a normal idle.

I have an idle-up solenoid but it is driven infrequently so I haven't bothered. It really needs to be at about 700 with the AC running if it is to be used a lot.

[KULTULZ]

Originally Posted by 40cpe

It is a 5 speed. I'm not sure how much the AC drags it down, but it is like a normal idle.

I have an idle-up solenoid but it is driven infrequently so I haven't bothered. It really needs to be at about 700 with the AC running if it is to be used a lot.

You are ahead of me again ...

OH!

Nice looking install...