mgmuscari

Background: My '89 GT has been sitting for a year while I completed building a 347 stroker and swapped it in.

Here are the specs on the engine:

- 347ci dart block
- Twisted Wedge 170 heads, intake & exhaust CNC ported to flow 312cfm on intake side (about like the TW205's)
- Track Heat upper & lower intake, not ported (yet)
- Comp Cams XE274HR hyd. roller cam

I had the engine running a few weeks ago, but it immediately stalled out due to sucking tons of oil through the PCV valve into the intake. Some of the vacuum lines flooded with oil in the process. Long story short, it had turned out that I had left out the lifter oil galley plug in the block due to a misunderstanding on my part about the oil galley plugs (DERP). All the oil meant for the lifters was flooding the lifter valley instead of getting into the top of the engine. Luckily I still had good pressure to the main & cam bearings, and all that seems good. I ended up burning one rocker arm that I replaced and now all is good.

The only problem I have now (besides trying to put together a decent tune in 95-100+ degree heat) is that the power brake booster is not working at all.

I am pulling between 50 and 60 kPa of vacuum at idle (still ironing out some surge issues related to VE and spark tables). This is about 12-15" of mercury. This seems like a reasonable number to me. I have heard that the stock engine pulls 14-18". I don't have a lot of experience with this, but I assume my power brakes should be working in this case. I can only assume there's something wrong with the booster, or I have a bad vacuum leak somewhere in the system.

I have checked all of the vacuum hoses and fastened them with hose clamps - no leaks there. All of the fittings and plugs in the manifold are securely fitted with teflon tape, so there should be no issues there. The lower and upper intakes are both sealed with gas-safe non-hardening Permatex gasket maker. I can hear a whistle at idle that seems to originate from my throttle body, which is a 70mm BBK unit that people seem to complain about frequently w.r.t whistling. It used to whistle when I gave it moderate pedal on my old engine. I am fairly confident at this point that I'm not dealing with a vacuum leak in my vacuum hoses or in my manifold gaskets. I tried putting some oil on the manifold gaskets to see if it sucked it in, and it didn't. I also pulled the filler neck out of the valve cover and put my hand over the hole to check for a noticeable vacuum, and didn't find any. It also didn't have any effect on the idle.

What should I be checking at this point? Is there any way to clear oil out of the brake booster if it got some in it when my PCV valve was sucking oil? Am I just not drawing enough vacuum to operate it?

mattdel

Booster wouldn't be able to suck in oil. Make sure the check valve is installed correctly and operating.

mgmuscari

I pulled the hose off the vacuum tree and sucked on it and was able to pull as much air through it as I wanted to with slight resistance. If I blow on it, the check valve closes. I assume that if it was holding vacuum, I wouldn't be able to keep sucking on it like that. Does this mean that I have a vac leak in the booster? Why would it fail after sitting for a year without being operated? Bad check valve grommet?

Still can't exactly identify where that whistle is coming from... it's not one of the vacuum hoses, and even spraying some brakleen around the intake didn't cause any change in the idle so it's not an external vac leak... if it's inside the intake from the lifter valley, it's not sucking much air, because I can't feel any suction when I put my hand over the filler tube hole. It really, really sounds like the throttle body but I can't be sure. I can also hear the whistle loudly near the air filter.

mattdel

Intake tubes are known to whistle especially on modded motors. The swirl inside of the intake will cause a slight whistle. Only way to correct it would be to file the sharp corners in the system. Then again it very well could be a leak of sorts, so definitely don't ignore it until you're sure it's internal to the tubing and not external.

As far as the check valve, it should be strictly a 1 way valve. Given your description it sounds like its working properly. I'd mess with it a bit, take the vac line off and cap it and see what the brakes do then.

It is possible the seals in the master dried up a bit and you're leaking brake fluid into the booster, this is the most common cause of booster failure(and the reason that companies won't warranty a booster without a master replacement). One of the most common signs of this is the paint on the booster becomes bubbled and malformed directly underneath where the master bolts up.

mgmuscari

Thanks, I'll take a close look for that. Like I said, I'm pulling a solid 12-15" of vacuum, so I assume it would be working if the booster and master are good. There's plenty of fluid in the master. How hard is it to pull the booster if it needs to be replaced? Do I need to pulle the dash?

mattdel

Nah it's pretty simple. You just unhook the rod from the brake pedal and undo the bolts holding it to the firewall. Plenty of room under there.