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Discussion Starter #1
My eBeetle ( 65 T1 ) has a delay in the brakes from when the pedal is depressed from what seems like the booster cutting in, my electric vac pump is putting out 25 hg so plenty of suck. It has a dual circuit m/c from a latter bus ( 24mm bore ) T3 drums on the rear and vented GM rotors on the front with floating calipers. Ive done all the math on hydraulic ratios and pedal leverage and ive got a 30: 1 overall pedal leverage ratio. The booster is the remote type that is mounted up front and the vac pump in the rear to keep the noise down.
The delay is only a split second but annoying.
 

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If the brakes are spongy feeling, they may need more bleeding-off of trapped air. Sometimes in custom brake systems, an air trap is built-in and an additional bleed point needs to be added where the air collects .

If the drum brakes have a leading shoe(one sometimes with a longer, bigger friction surface), it should be mounted towards the front of the vehicle. This gives more servo action when the brakes are applied going forward. If the leading shoe is mounted to the back of the vehicle, less servo action is generated(anti-servo?) Mounting the brake backing plates on the wrong side might also cause this to happen.

Also, in a safe manner, try normal stopping with the parking brake slightly applied. If this cures the problem, the brake shoes may need to be adjusted tighter(closer) to the drums.

If these don't fix the problem, try mounting the vacuum pump closer to the booster/vacuum reservoir. You could also mount an auxiliary vacuum reservoir close to the booster.

Maybe the braking actions are not very well balanced and you need a proportioning valve, usually to send more pressure to the front brakes.
 

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Discussion Starter #3
No they're not spongy, the pedal feels good, its just the slight delay. I've bleed them multiple times, the booster doesn't have a bleed nipple so I've been cracking the line fittings while the system is under pressure. The rear drums are single leading shoe, Type 3 VW which have wider shoes than the Bug.
Yeah I might try moving the vac pump to the front or the booster to the rear so they're closer together and still keep the reserve reservoir. Something I didn't mention is because its a dual circuit system and my booster is designed for a single circuit system, i only have the booster plumbed into the front circuit, drums don't really need a booster as they're self energizing.
 

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It's a 65 Beetle ?

Why do you need a booster? - I'm sure they did not have one as standard

Brake boosters and power steering only came into fashion in the 80's - they are not needed for a light weight car
 

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Discussion Starter #5
Its quite heavy now with the lead acid batteries, with the booster the brakes were only average, Im thinking of going to a smaller m/c to give a better hydraulic ratio and try it without the booster.
 

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Discussion Starter #6
Its quite heavy now with the lead acid batteries, without the booster the brakes were only average, Im thinking of going to a smaller m/c to give a better hydraulic ratio and try it without the booster.
 

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You didn't mention it, so you don't have it - you need a vacuum reservoir, preferably close to the booster and with a fat hose going between them. A check valve from the pump would also be a good idea.
 

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Discussion Starter #8
No they're not spongy, the pedal feels good, its just the slight delay. I've bleed them multiple times, the booster doesn't have a bleed nipple so I've been cracking the line fittings while the system is under pressure. The rear drums are single leading shoe, Type 3 VW which have wider shoes than the Bug.
Yeah I might try moving the vac pump to the front or the booster to the rear so they're closer together and still keep the reserve reservoir. Something I didn't mention is because its a dual circuit system and my booster is designed for a single circuit system, i only have the booster plumbed into the front circuit, drums don't really need a booster as they're self energizing.
I did mention here about the reserve reservoir, and yes i have a non return valve close to the booster
 

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The reservoir, not the pump, needs to be closest to the booster, and you should run a larger dia. hose/pipe between the booster and reservoir, IMO.
 

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Did the master cilinder you are using come from a 4-disc car?
And are you now using it on a front disc and rear drum setup?
Then you need to add a 10 psi residual valve to the rear.
It ensures the rear brake pads do not go all the way back and stay close to the drum. Otherwise you will have a lot of brake pedal travel before it starts braking.

At least that was the solution in my case when I had the this issue.

More details in:
https://www.oudevolvo.nl/english/2019/01/22/testing-tesla-ibooster-power-brakes/
 
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