brake booster problems 71 vw bus

[jed81]

I have a 71 vw bus. I recently put a rebuilt brake booster as well as new vacuum lines and a master cylinder.I used the strongest vacuum lines i could find for them. my problem now is everytime i start my bus the brakes lock up and I cant even move. I am new to VWs please help!!!

[Desertbusman]

New to VW's and have you gotten the service manual yet? You need it for the work you did plus any other tasks you do. And aalso welcome to the Samba. But offhand it sounds like the pushrod from the brake arm to the booster might be way out of adjustment.
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71 Westy

[jed81]

i have 2 books. Ive been reading the hell out of em when i work on my bus but, they dont say much about the booster. from reading other posts i was thinking it was the same thing.

[VDubTech]

[Desertbusman]

You might have books that arn't specifically for Bay window busses. Such as the How to Keep your VW Alive book by Muir. That one just has sort of general information for all VWs and little specific for late busses. It's more of a general get aquainted laugh at the pictures type of book. The Bentley service manual for '68-'79 busses (the green one) is the one you need. The adjustable pushrod should not be exerting pressure on the booster when the pedal is fully retracted. That's probably your problem but get the right manual because there are other things involved. BTW, congrats on a '71. That's the good one.
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71 Westy

[Wildthings]

As others have said the push rod between the master and booster is probably adjusted incorrectly. Dirt in the master or lines can also act as a check valve causing the brakes to lock up, as can old internally failing brake hoses.

[aeromech]

Well you've done some of the work to rebuild your brake system but you still might have either bad front calipers which can freeze and lock the wheels as well as you might have bad rubber brake lines that have failed internally not allowing the brake pressure to return and the calipers to release. Let me ask you this... if you jacked the front off the ground, would the front wheels spin? Then, if you started the bus would they lock up or do they only lock up after you hit the brakes once?
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[jed81]

They lock up imediatly when starting the bus. the brake pedal also pulls to the floor on its own with out touching it. If i pull the check valve and block the vacuum line going to the booster i get some brakes witout using the booster at all

[germansupplyscott]

is the one-way valve installed?
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[aeromech]

you do have the vacuum line connected correctly to the BACK side of the booster drum, right?
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[jed81]

Everything is hooked up propoerly as far as vacuum lines. the check valve is the same thing as the oneway valve.

[busdaddy]

OK so the next thing to check is pedal freeplay (pushrod adjustment), when you push the pedal gently with a single finger is there a little tiny bit of movement before the load changes?

If there is indeed a tiny bit of play the only thing left is the booster, crap in the atmosphere valve will activate it even with no pedal application, send it to HR or find another working used one.
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[jed81]

I dont know if this helps out at all, but i put new brake pads up front, shoes and wheel cylinders(brazilian) in the back, new mastercylinder (brazilian). USED brake booster) and all new vacuum lines. the bus was sitting for 23 years prior to my ownership. been a long proccess with the restoration but this is my final step.



IS THE PUSHROD THE ROD THAT CONECTS THE BRAKE PEDAL TO THE BOOSTER?

[busdaddy]

A pad change could cause this, but it would only matter if the brakes didn't change if the engine was running or not, if Aeromech's test with spinning the wheels running or shut off exposes different circumstances the booster is likely to blame.
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[jed81]

Like i said earlyer if i bypass the booster by turning the check valve backwards, or pluging the vacuum line out of the mannifold the brakes stop somewhat, just off of the master cylinder with no booster. no locking of the brakes or anything. brakes lock up only when the check valve is the right dirrection and vacuum is going to the booster.


Probably bad booster in your best opinion?

[Desertbusman]

From what you have said it doesn't seem like it could be anything other than pushrod adjustment problem or bad booster.
Since you have done all the other brake system work go thru it all again once you get the service manual to refer to.
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[Wildthings]

I have heard of these symptoms for a bad booster. Some orifice must get plugged, or something, that keeps the boost on full even with no pedal effort.

[jed81]

Only one way to find out if the booster is bad. tommorow im gonna buy a rebuilt one and return the used one i bought to the vw dissmantling yard i got it from and start over with a new fresh rebuilt booster.
Ill let you all know how it goes. Thankyou everyone for all the help.

THIS WEBSITE IS GREAT!!!!!

[keifernet]

[Jody '71]

Could it be the air connection on the front of the booster is clogged up?
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