Davidmij - Disc Brake Conversion & Rim Problems

[davidmij]

It's all coming back to me now - I remember doing this when I was kid and we used to work on our cars. I remember adjusting the points with a match book cover once too somewhere. Anyway, I'll check it out tomorrow afternoon golfing.
Thanks a ton for the quick easy try.
Cheers to world south of the equator!

[davidmij]

I tried it both ways and it made no diff in the braking. It seems to idle best (highest) right where it is. I'll try the vacuum gauge (while driving) next weekend.
i wish there was a way to add a electrical or mechanical vacuum pump just as a test. I haven't looked yet but I'll bet they are expensive.

thx gents

[davidmij]

OK, I bought a vacuum gauge/pump and hooked it up where my canister normally goes. After running the engine for 15 minutes I checked it at idle and it read 13.5. That's about 19.5 if I were at sea level, so it's good.(It idles fairly high) Also, the needle flickers very rapidly a full 2 inches hg vac while parked. Then I put the car in reverse - it immediately dropped to about 7.5 - that would be about 13.5 at sea level. I took it for a spin, in drive at various rpm's it stayed between 7.5 and 9. If I shift into neutral while rolling it jumped to almost 15 and the needle quit flickering, (that's 21 at sea level) Remember, my engine is old and tired.
I'm guessing this is my problem, the engine is too beat up to maintain decent vacuum under load. I think I read somewhere that the flickering needle tells me something about the rings, valves, or gaskets, I'll have to look up what it means on line.
Any thoughts etc. from you guys?

[Guest]

Here's the link to the vacuum guage diagnosis

I'd say it's a bad valve/valves
Try adjusting the mixtures as per 15 first

http://www.secondchancegarage.com/public/186.cfm

[davidmij]

Thx Richard, that's the exact same web site (or link) I had seen a while back while "googleing".
Yeah, none of them really fit my senario, but my idle is quite high, and I did take the carb apart when I first got the car because it had a stuck float and was over-flowing. I tried not to adjust any settings on the carb, but I did use a rebuild kit and change out as many parts as I could without tearing it down too far.
I'll try adjusting the mixture screws tomorrow - it's dark here now.
Thx a ton, Dave J

[REM]

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?

[davidmij]

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

[REM]

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.

[davidmij]

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

[Astrowing]

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".

[scumdog]

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.

[davidmij]

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

[tbird430]

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...

[davidmij]

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

[tbird430]

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.