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  #141  
Old 08-18-2011, 07:21 AM
REM REM is offline
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Even though your engine vac drops the check valve at the booster should hold the vac in the booster for at least one brake application.
Is there any way you can check the vac on the boodter side of the check valve.
I'm not sure where the check valve is. Is it in line or in the booster?
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  #142  
Old 08-18-2011, 09:21 AM
davidmij davidmij is offline
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There's actually 2 check valves. The one on the brake booster (it's a typical elbow). I also have the original 3 way one that goes to the can behind the fender. That's the line I plugged into. I also measured the vacuum by plugging straight into the manifold line. The can behind the fender holds vacuum for days. I'll take some pix and post them. But i think you get the idea.
thx, Dave J
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  #143  
Old 08-18-2011, 09:42 AM
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Checking at the line to the manifold you should get a rise and drop in vac as the manifold vac changes.
Vac in the booster should not fluctuate with manifold vac as the check valve or valves should hold it steady.
You should still have vac in the booster with the engine shut off.
Try pulling the check valve out of the booster with the engine off and see if there is vac therte.
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  #144  
Old 08-18-2011, 05:24 PM
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OK, took a day off and did a lot today.
(per Dakota Boy) I used my new Mity-Vac tool to bleed the brakes - sure makes it easy, and you know there's no air in the system when you're done. Great advise Greg, thx!
The brake booster does hold vacuum - so does the can behind the fender. Per the vacuum gauge diagnosis web site I tried a couple of things. I adjusted the idle mixture screws per the shop manual, they were only about 1/2 turn open. After adjustment they are now at 1 1/2 open.
I also tried rotating the distributor again, this time I checked the vacuum each move. After moving it a good 1/2 inch counter clockwise it brought the vacuum up to 15+. That would be about 21 at sea level. However as soon as I shift into gear it drops to about 9 (15ish at sea level). The engine RPM went up quite a bit, and the brakes improved slightly. If I stand on the pedal while coasting in neutral at 25 mph I can make the back drums skid a bit. Still no where near power brakes, and the front discs just won't lock up. That makes sense because the front discs should take way more power to operate than the rear drums. This basically says that I have no power assist happening.
(A note: if I press the gas pedal while in park and observe the vacuum gauge it drops to zero) According the diagnostic web site scenario #4 this indicates worn rings. I kind of already knew that because of all the smoke that comes from the crankcase vent and the oil cap. I think I almost asphyxiated myself today working over a running engine!

Summary, I've done, and tested everything from pedal to tire. If you read back through this thread you'll see that I've done some things two or three times. I've chased my own tail a few times too. I really think I need to get it to a good brake shop and let them figure it out. As someone here said, "it's a modern brake system and should be fixable".
My best guess to date is that the power booster doesn't work - either because it's defective somehow, or because there's not enough vacuum, especially when the car is in gear.
Feel free to let me know if you guys have any other ideas, but I'm ready to give it a rest until I can afford a mechanic. (Either that, or go "Thelma and Louise" on her)
Really appreciate all your input and help, Dave J
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  #145  
Old 08-18-2011, 06:56 PM
Astrowing Astrowing is offline
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Dave, I think you've said it. The vacuum pump (the engine) is not working well and needs to be tackled next. Otherwise, you're "spinning your wheels".
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  #146  
Old 08-18-2011, 07:18 PM
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Another thought from me: Is the vacuum hose beween motor and booster of a large enough diameter?

A long time ago I had a similar brake issue and it turned out that due to a cunning plan of mine (don't ask!) I had the hose between the two WAY too narrow in diameter.

And I almost crashed when I first went to use the brakes out on the road.
Just worth a thought...

And I guess a hose that's not designed for vacuum (collapses/sucks in) or is in someway faulty will give the same symptoms.
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  #147  
Old 08-18-2011, 09:47 PM
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Yup, that's my plan Astrowing. Some day when the engine is rebuilt (or replaced) I'll know for sure. Meanwhile there's tons of other fun stuff to do on the old bird. Maybe it's time I called a friend of mine who has an old Ford with a 430 in it. If he'll sell it I can drop it in and build the 352 at my leisure.
Scumdog, good call, but the lines are 5/16 ID, proper vacuum lines and new. All my seals are good too, I only have one line coming off the manifold and the booster and canister hold a vacuum indefinitely. I was surprised that the mity-vac used such flimsy lines, but they work.

thx again, Dave J
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  #148  
Old 08-19-2011, 02:19 PM
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Then there is still my advice, You could add a small electric vaccum pump to this whole system (after the check valve).

This could make up for your weak/worn 352cid engine...

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  #149  
Old 08-19-2011, 02:29 PM
davidmij davidmij is offline
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Yes, thx Jon.
That would be the best way to fix (test) it for sure. Trouble is the only ones I found online run $250 plus and I don't want to invest that much if I'm going to build or replace the motor one anyway.
Yo don't happen to know anywhere that sells a less expensive one do you?
thx, Dave J
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  #150  
Old 08-19-2011, 04:05 PM
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Seems like hotrodders where buying these from auto part chain stores (Autozone, O'reillys, etc) for old Chevy Camaros/Chevelles maybe??

This route sounds cheeper than $200.00 to me....

-Jon in TX.
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