How do I test my brake booster?

bug-nuts · Posted: Sat Feb 21, 2009 3:12 pm Post subject: How do I test my brake booster?

1978 bus. The vacuum line running to the brake booster is capped off at the booster. I assume there is a problem with the booster, but this bus has quite a few creative fixes to problems that maybe didn't even exist. I've read my Bentley and 3 pages of posts, but nothing that addresses testing the booster without the bus running. Can I pull a vacuum and see if it holds? How much vacuum? etc. If I need to send it to Texas for a rebuild, I'd prefer to do it now instead of waiting tell the bus is running and then have to.

Thanks
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Whoever smelt it, dealt it.

1973 Thing
1978 Westy
1998 Beetle

tom62 · Posted: Sat Feb 21, 2009 8:14 pm Post subject:

While the bus is down I would pull the booster off and send it off.
I don't know of a sure way to check without a running engine.
100 bucks plus shipping, not worth taking a chance in my opinion.

H & R Automotive Parts
10328 Oakwood Dr
Dallas, TX 75217
972-286-5516

Don't forget to Check your master cyl and make sure it's not leaking fluid into the booster as that will kill it for sure.

Tom
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certified VW nut since 1971
68 Double Cab
Yep I'm from Florida! and have you noticed most of the idiots used to live in other states?

I don't think of it as a hobby, I Just like the ride.

Wildthings · Samba Member Joined: March 13, 2005 Posts: 19875

The normal failure for a booster is for it to leak vacuum. Just sucking on the hose would tell you a bit, using a vacuum pump would be better as you could actually see if it made the brake pedal easier to depress.

Do you have some kind of aftermarket carb set up on your engine? Way to often people leave the booster disconnected instead of figuring out how to hook it up to an aftermarket fuel system.

SGKent · Posted: Sun Feb 22, 2009 11:56 am Post subject:

simple booster tests. Understand that all the booster does is use vacuum from the engine to assist you push the brakes down when they sense you are beginning to push on the pedal. As long as they assist, don't leak and hold a vacuum for a few pushes when the engine is off, they are usually Ok. This assumes no one has tampered with the freeplay etc.

Start the bus. Step on the brakes with the parking brake off. Notice how they feel.

Step on them again. Listen to the motor. Does it just mis-fire once or not at all each time you step on the brakes? If Ok then proceed, if the bus starts running rough and and misfiring as long as you hold the brakes down the booster is bad.

Put the parking brakes on (or block the wheels) and again step on the brakes and feel them. Take your foot off the brakes and turn the bus motor off. Count to 10. Step on the brakes again. They should feel the same as they did before. If you step on them three or four times the vacuum will bleed off and then they should get really hard because there is no vacuum left to assist. If there is no change noticed after stepping on the brakes multiple times then booster was never working and is bad. If this is the case start the car and just make sure you don't feel them get easier to push when the engine is running. If they were good when the engine was running but they get hard on the first push after you turned off your engine then test the vacuum valve. The booster should hold two to five assists. If the valve is good then the booster is bad. If the valve is bad replace it and retest again. Our 1977 booster held vacuum for almost a year.

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.)
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Steve aka Merlin the Wrench

formerly Steve's Racing and Engine Blueprinting. Wrenching since 1967.

bdamico on GF wrote

tom62 · Posted: Sun Feb 22, 2009 6:36 pm Post subject:

Good tests but he said the bus wasn't running.
_________________
certified VW nut since 1971
68 Double Cab
Yep I'm from Florida! and have you noticed most of the idiots used to live in other states?

I don't think of it as a hobby, I Just like the ride.

Desertbusman · Posted: Mon Feb 23, 2009 4:38 am Post subject:

If you've got a friend with another bus use his vacuum. Grab some old 1/2" garden hose and stick one end on you're booster and the other end on his intake manifold. Then try your brakes. I understand your dilema but keep in mind that of all the many people that have had Ron in Texas do their booster have had it back within a week of sending it to him. I didn't ask him for any special handling or even ask him how long he takes but he return shipped it the day after he received it.
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The best thing that anyone can do for their Bay is get the Volkswagen of America Official Service Manual published by Robert Bentley. Without it the bus is pretty much doomed.

bug-nuts · Posted: Mon Feb 23, 2009 6:34 am Post subject:

Thanks for the help guys.
Wildthings: Yes it has an aftermarket carb, Weber progressive, but the vacuum hose and check valve were reinstalled on the intake manifold. The hose is disconnected and plugged with a bolt right at the booster. Does anyone know what amount of vacuum the booster sees? I do have access to a vacuum generator but I need to know how much to pull.

Desertbusman: If I had friends I wouldn't need you guys. Just kidding, But no I live in a small town with little VW activity so most of my work is learn on your own. I will say for guys, like me, without the help of clubs or local gurus this forum is invaluable.
_________________
Whoever smelt it, dealt it.

1973 Thing
1978 Westy
1998 Beetle

Wildthings · Samba Member Joined: March 13, 2005 Posts: 19875

darrol weaver · Posted: Wed Nov 16, 2011 2:16 pm Post subject: brake booster

does anyone have the address and phone number for Ron in Texas? I too have having booster problems. can these things be bought rebuilt? if so from who? is it better to simply have Ron do the rebuild? thanks

SGKent · Posted: Wed Nov 16, 2011 2:21 pm Post subject: Re: brake booster

bugger101 · Posted: Wed Nov 16, 2011 2:26 pm Post subject: Re: brake booster

muffler bearing · Posted: Sat Apr 28, 2012 11:14 pm Post subject:

My rpms shoot upnwhen I press the brakes. Is that normal? Weber 2 barrel with he vac hose connected to the correct port
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" A poor ride is better than a proud walk"
56 Beetle
72 Westfalia (Driving project)
Yes, I do have a Bentley.

busdaddy · Posted: Sun Apr 29, 2012 8:24 am Post subject:

If they return to normal even as you hold the pedal then yes, if they remain higher when the pedal is held you have problems inside the booster.
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Rust NEVER sleeps and stock never goes out of style.

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muffler bearing · Posted: Sun Apr 29, 2012 9:17 am Post subject:

The rpms kinda stay up.
_________________
" A poor ride is better than a proud walk"
56 Beetle
72 Westfalia (Driving project)
Yes, I do have a Bentley.

busdaddy · Posted: Sun Apr 29, 2012 9:34 am Post subject:

Wrenchman12 · Posted: Sun Apr 29, 2012 10:51 am Post subject:

When i bought my bus nearly 15yrs ago it had a single Weber carb on it and the booster had been disconnected.. I have been driving it for yrs without the booster hooked up. I recently drilled out my manifold to recieve the 1/2" hose and hooked the booster back up.. Booster has been working great..(not rebuilt) I was suprised how much easier it is to press the brakes... Well worth figuring out what you need to do to get it working.. I wish I hadn't waited so long. Plenty of information on here to figure everything out. Don't foget the one way valve in the hose from the carb to the booster... it did take a little motor memory adjustment for my leg to get use to just tapping the brakes instead of slamming them!
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73 Riviera Camper
64 Splitty project
69 "good vibrations" bus http://www.thesamba.com/vw/forum/viewtopic.php?t=491468&highlight=

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