Early Bay Single cab - air in brake lines

[sheldonk]

I use the samba as a resource all the time, but this is my first post. There are quite a few threads about bleeding early bay bus brakes, but my issue has me stymied. I replaced all rear drum brakes and installed new front calipers on my 71 single cab. I have original steel lines and soft lines. I can bleed the brakes with my pressure bleeder and my brake system also holds pressure for 24 hours. The brake pedal is nice and firm - until - I start the bus and start to drive it. Then the brakes become spongy and the pedal travels almost to the floor. It takes many pumps to stop the bus. I am guessing air is entering the system, but why only after I start the bus and drive it. I am hoping someone with more experience than I can point me in the right direction. I also have a new master cylinder (original reservoir and tubing) and a new brake booster. Many thanks, sheldon

[lil-jinx]

the extra travel could be from the increased pressure from the brake booster,if you have indeed bled all the air from the system,and the brakes are properly adjusted ,what's left is a weak rubber line expanding under pressure ,or maybe one of the brake push rods is out of adjustment the one from the pedal to the booster or the one at the master cylinder,or the master cylinder could be at fault,
rear brake adjustment would be my first step,
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https://www.thesamba.com/vw/forum/viewtopic.php?t=620186
https://www.thesamba.com/vw/forum/viewtopic.php?t=668799
1974 Bay Westfalia. she likes to be called Ethel.
1968 Dune Buggy sold dec 2024

1974 parts bus
A smart man learns from his mistakes,a very smart man learns from other's mistakes.

[SGKent]

best guess is bad master cylinder even if it is new or low brake fluid.
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[airschooled]

…does your new booster have a blue aluminum hex nut in front of the rubber boot? :/
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[kreemoweet]

My guesses:

1) Bus not level when bleeding, air pocket trapped somewhere.

2) "original" soft lines?! Those would be VERY suspect, might be "ballooning" under pressure.
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[sheldonk]

Thanks Everyone, yes I think the brake booster has the blue aluminum hex nut in front of the rubber boot. I will replace the soft lines this week-end, bleed the brakes and cross my fingers. Many thanks for all the advice.

[Wildthings]

If you replaced the booster and/or the master you need to adjust the rod between the two.

[lil-jinx]

before replacing the lines,check them first,have someone or something hold the brake on and take a look/feel of the lines,try to identify the problem before throwing parts at it.
_________________
https://www.thesamba.com/vw/forum/viewtopic.php?t=620186
https://www.thesamba.com/vw/forum/viewtopic.php?t=668799
1974 Bay Westfalia. she likes to be called Ethel.
1968 Dune Buggy sold dec 2024

1974 parts bus
A smart man learns from his mistakes,a very smart man learns from other's mistakes.

[sheldonk]

Many thanks, I will do both and appreciated the advice. I will post the results when I have brakes in my single cab again ...

[sheldonk]

Hi Everyone,

Thanks so much for the advice. I removed the brake booster and the adjusting rod was very loose and did not inspire confidence, so I ordered a new one without the blue hex nut, installed it; bled the brakes and miracle of miracles ... I can stop. After a full year of replacing the master cylinder, soft lines, all new drum brakes and uncountable attempts at bleeding air out the system, the issue was the brake booster. Thanks again!