Bad Booster? - Team Camaro Tech
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post #1 of 13 (permalink) Old Jun 3rd, 08, 08:25 PM Thread Starter
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Alan
 
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Bad Booster?

I have done a search for diagnosing low engine vacuum because of a leaking brake vacuum booster. Many recommend using a mityvac to pump down the booster. My question is shouldn't the dial on the mityvac stay high because the check valve only allows movement from the booster to the manifold but not the other way? So theoretically, wouldn't the mityvac hold it's reading even if the booster bleeds down or is it the case that if the diaprhagm is malfunctioning, you won't even get the mityvac to pump up at all?

thanks

alan
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post #2 of 13 (permalink) Old Jun 3rd, 08, 11:21 PM
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Re: Bad Booster?

the check valve works the other direction
when the engine is off it should hold vacuum in the booster

if you think the booster is leaking run the engine for a minute
shut it off and let the car sit for a while, then pull the check valve out- if there was a sucking sound (vacuum left in the booster) then its not leaking

good luck
Jon
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post #3 of 13 (permalink) Old Jun 4th, 08, 04:55 AM
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Re: Bad Booster?

Years ago, I had a small vacuum leak. I traced it to the vacuum booster. My leak was at the rubber seal where the check valve resides.

Disconnect the vacuum hose at the valve and plug the hose. See if your problem goes away. It it goes away, you can then focus on the booster/valve.
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post #4 of 13 (permalink) Old Jun 4th, 08, 08:06 AM Thread Starter
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Re: Bad Booster?

Thanks guys, much appreciated.

alan
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post #5 of 13 (permalink) Old Jun 4th, 08, 08:25 PM Thread Starter
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Alan
 
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Re: Bad Booster?

OK, booster won't hold any vacuum, in fact, when I myself suck on the hose, it just keeps going, no resistance. So I guess I need a new booster.

1. Are all boosters the same? Heartbeat City just offers one booster. I need one for a Z28, were those different from the other small block versions? Classic Industries offers one for a 69Z with Bendix brakes (is that disc front, drum rear-that's what I need).

2. In removing the booster, I am hoping I don't have to remove the MC, I hope it can be moved a bit forward out of the way once unbolted from the booster. Also, does the rear rod from the brake pedal detach from the booster upon removal or is it fixed to the booster?

thanks guys

alan
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post #6 of 13 (permalink) Old Jun 5th, 08, 05:35 AM
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Re: Bad Booster?

1. I belive there is only one booster that the Camaro uses. Heartbeat has alwasy done well by me. Good support.

2. You can remove the booster with out removing brake lines. Just seperate the m/c from the booster by removing the 2 bolts. The m/c should be able to slide/move forward with the flex in the brake lines. However, if you find too much resistance, be safe and remove the primary brake lines at the m/c. You don't want to damage the brake lines.... just adds to the project.

2a. The rod from the booster to the brake pedal is for the most part fixed. It can be removed, but is difficult when installed in vehicle. I would recommend that you not try to separate them.

I know you self tested the booster, but keep in mind that there is a lot of surface area and volume of air to move. Your lungs may not be enough to test this. If you can, use a hand held vacuum pump, with hose adapters and try again. I'm also asuming your engine ran better with the vacuum hose to the booster removed and plugged? Hope so.
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post #7 of 13 (permalink) Old Jun 5th, 08, 07:55 AM Thread Starter
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Re: Bad Booster?

Well, initially, the vac came up to 8-10" (302) but as the car got warm, the vac fell off (booster vac line was plugged at this point). This leads me to believe the valves might be too tight so I am gonna adjust the valves to the correct lash of .030" tonight and see if that helps the lower vacuum when warm issue.

The reason I think the booster is bad is no hiss after a few minutes after shutdown when the hose is removed and I could keep sucking air (using my tongue as a flapper valve in between breaths) and no resistance at all.

alan
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post #8 of 13 (permalink) Old Jun 5th, 08, 08:33 AM
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Re: Bad Booster?

Changing a booster takes only 30 minutes.

But wait till you have your replacement booster ready.
1- Remove the 2 nuts on the master and push forward.
2- Remove 4 booster nuts at firewall.
3- Pull retaining pin attaching the booster rod to to pedal bracket. (under dash) Don't lose the special clip.
4- slide booster out.

Important...
Set the 2 boosters side by side - set the height of the Y-retaining bracket the same as the old one and tighten.

Install in reverse - but do the pin last - make sure it lines up at the pedal before tightening anything.
Easy.

It helps if you have another guy (or girl) to help you guide everything into place.
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post #9 of 13 (permalink) Old Jun 5th, 08, 05:39 PM
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Re: Bad Booster?

As far as the "leaky" booster goes, make sure that there is some free play at the brake pedal. If the "pushrod" between the booster and the pedal is adjusted too long, it can keep the vac relief valve on the booster from completely seating, which would be like a small leak. Better yet, before you pull the booster completely, just remove the pin that connects the pedal to the brake pushrod (so the brake pedal is REALLY loose) and double check if it'll hold vacuum.

Assuming the booster is dead, I see 2 separate boosters listed per Rock Auto -- one for 67/68 (Bendix) and one for 69 (Delco). Not sure if they're different enough to really matter or if they'll both fit either model, but it "looks" like the input rod to the booster might be a bit longer on the 67-68 version. FWIW, the one listed for '69 fits my '69 just fine.

When you get around to installing the new booster -- pay some attention to the pushrod adjustment for the rid between the booster and the master cyl (short thing that sticks out of the front of the booster). You'll want a little play here so that the M/C fully releases when you're off the brakes. If it binds/is too tight, the brakes will tend to not fully release.
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post #10 of 13 (permalink) Old Jun 5th, 08, 08:30 PM Thread Starter
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Re: Bad Booster?

Well, I was looking at my MC-booster setup tonight when it dawned on me that my MC doesn't have bleeder nipples on it. Just 2 ports which route metal lines to the square gizmo right under the MC. Something tells me that along it's life, someone slammed in a MC when the factory one failed. Is there a difference between master cylinders(cup diameter, bleeders on the MC)? It is for a 69Z 302.

thanks
alan
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post #11 of 13 (permalink) Old Jun 5th, 08, 08:52 PM
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Re: Bad Booster?

Quote:
Originally Posted by alanrw View Post
Well, I was looking at my MC-booster setup tonight when it dawned on me that my MC doesn't have bleeder nipples on it. Just 2 ports which route metal lines to the square gizmo right under the MC. Something tells me that along it's life, someone slammed in a MC when the factory one failed. Is there a difference between master cylinders(cup diameter, bleeders on the MC)? It is for a 69Z 302.

thanks
alan
There is a difference in bore diameter. I believe the power brake bore on the master is 1" were the non power brake master is 1 1/8". The square "gizmo" I think you are talking about is pretty much a metering block ... it just passes fluid and there are no moving parts in that. But you should also have a proportioning valve under the master behind that block.
But these shouldn't effect your booster vacuum. The power booster is pretty much just a tin can with a big bladder in it.
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post #12 of 13 (permalink) Old Jun 5th, 08, 09:21 PM
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Re: Bad Booster?

If you're going to pull vaccuum on the booster, do so without the check valve (the valve itself is easy enough to check) . It'll take quite a bit on a hand-pump mity-vac to build enough vac in a booster. And that's a lot of volume to pull by mouth, not a good test on a booster.

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post #13 of 13 (permalink) Old Jun 6th, 08, 07:31 AM Thread Starter
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Re: Bad Booster?

Quote:
Originally Posted by RamAirDave View Post
If you're going to pull vaccuum on the booster, do so without the check valve (the valve itself is easy enough to check) . It'll take quite a bit on a hand-pump mity-vac to build enough vac in a booster. And that's a lot of volume to pull by mouth, not a good test on a booster.

Dave, assuming the bore on the MC is correct (1 1/8" I believe for a vac assist disc-drum setup) is there any difference between a MC with bleeder nipples and one without? In other words are they the same from a functional standpoint?

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