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Brake Booster Test with Mityvac
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busman78
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PostPosted: Sun Apr 18, 2010 1:43 pm    Post subject: Brake Booster Test with Mityvac Reply with quote

Purchased a Mityvac, discovered that all the plastic hose connections to the metal tube and at the booster were leaking, replace all of that line with DOT booster line. Now my question is, when I evacuate the entire line including the booster with the Mityvac from the end of the hose that would attach to the intake how long should a vacuum be holding? I have brough it up to 17hg, and that takes a lot of pumping with the vac tool, it holds for a few minutes then slowly drops to 15hg, after 40 minutes there is still 5hg holding, is that a leak or normal?
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busdaddy
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PostPosted: Sun Apr 18, 2010 2:04 pm    Post subject: Reply with quote

That's a leak, a small one, but still a leak, it should hold a vacuum for weeks or months.
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WestyPop
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PostPosted: Sun Apr 18, 2010 2:05 pm    Post subject: Reply with quote

Sounds like something is leaking. Good commentary here... http://www.thesamba.com/vw/forum/viewtopic.php?p=3626103

I'd have to agree with the assessment by SGKent "... I would replace a booster that doesn't hold vacuum for at least over night (assuming the valve and hoses are good and not leaking.)"

Such a booster is definitely on its way out, and could leave you, or another driver of your bus, seemingly without braking power at the most inopportune moment. Don't buy a booster from a place that forces you to buy its 'rebuilt' master cylinder with the booster, as a package. Those MCs are usually crap.

Your call.
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busman78
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PostPosted: Sun Apr 18, 2010 2:29 pm    Post subject: Reply with quote

Cool, thanks, I have a spare I can send to H&R for rebuild then swap out on return.
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SGKent Premium Member
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PostPosted: Sun Apr 18, 2010 4:29 pm    Post subject: Reply with quote

Quote:
it should hold a vacuum for weeks or months.


keep looking at your connections. Our bus sat in a field for 10 months and still had a vacuum.
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busman78
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PostPosted: Sun Apr 18, 2010 4:41 pm    Post subject: Reply with quote

Good idea, I may vac pump just the can and let it sit, and then do the lines if the can holds.
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patayres
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PostPosted: Mon Apr 19, 2010 8:29 am    Post subject: Reply with quote

Have you tested how the Mityvac itself holds vacuum? I've had one go bad and it caused me to chase leaks that didn't exist.
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busman78
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PostPosted: Mon Apr 19, 2010 8:36 am    Post subject: Reply with quote

No, but a good idea. Will do.

Update: Tested the tester and it bleeds out at about the same rate as it did while testing the entire booster system. Bummer. Need to make a phone call to Mityvac.
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busman78
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PostPosted: Sun Apr 25, 2010 11:38 am    Post subject: Reply with quote

Update: Got the replacement Mityvac Friday, tested it and it holds vac, Yes! Tested the bus from the line at the engine all the way to the booster including the can. 15hg held for over forty minutes with no drop. even hit the brakes, lost about 4hg and vac held held steady.

Really is a cool tool.
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SGKent Premium Member
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PostPosted: Sun Apr 25, 2010 12:41 pm    Post subject: Reply with quote

busman78 wrote:
Update: Got the replacement Mityvac Friday, tested it and it holds vac, Yes! Tested the bus from the line at the engine all the way to the booster including the can. 15hg held for over forty minutes with no drop. even hit the brakes, lost about 4hg and vac held held steady.

Really is a cool tool.


Awesome! Great job and glad it was just the tool. Great suggestion by patayres to test the tool.
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busman78
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PostPosted: Sun Apr 25, 2010 2:11 pm    Post subject: Reply with quote

You bet, last thing I would of thought of is a new tool not working, not only was Lincoln (maker of Mityvac) helpful, but the company I bought it from had the replacement sent the day before I returned the broken one and they paid for the return shipping.
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patayres
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PostPosted: Mon Apr 26, 2010 9:21 am    Post subject: Reply with quote

Nice. Glad you got it figured out.
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