Power Assisted DRUMS FAQ

[visket]

Greetings -

1969 Bay Window Westy. I have heard that, other than welding a bracket on my front beam, I can get standard 71-up booster, master cylinder, check valve, etc.. to power assit my drums.

If I were to build a shopping list, *exactly* what would be on that shopping list?

Also, regarding the bracket - any dimensions or pics, or illistrations or part numbers would be greatly appreciated.

Please don't ask why I just don't bolt a '71 beam on and upgrade to disks. Please don't.

Thanks -

Mike

[tom62]

Hi Mike,
My 68 double cab has power brakes. They were on the truck when I bought it.

The brakes work great! I just replaced my master cylinder and had the booster rebuilt.

I used a 71 and up master cyl and reservoir connected to my org fill in the kickpanel.

The rod from the pedal will have to be changed.

You will have to put a port into your Intake for the vacuum, the bracket will have to be welded to the beam.

I don’t know the dimensions but here is a picture from another thread.

you may want to pm him and ask about the bracket.

http://www.thesamba.com/vw/forum/viewtopic.php?p=4167409#4167409

The original master cyl bracket may be in the way of the pedal rod and it will have to be removed. It was in the way on mine and the p.o. had cut it out.

You can use copper or steel tubing for most of the line running from the engine to the booster snd secure it with clamps.

Look at your donor bus and pull all the metal lines ect that you think you may need when you get your booster and pedal rod.

The brakes are sure are better than the brakes on my 69 single cab were.

[visket]

Sweet! Exactly what I needed.

I actually don't have a parts bus. Other than the bracket, the parts are (or, should be..) available. I'm checking the parts out at Bus Depot.

I can bend/mold the vacuum line and drill/tap my intake manifolds.

Thanks again -

Mike

[Blaubus]

you only need to tap one manifold if you have dual carbs. find the thickest part up at the top and angle it 30 degrees or so downward- if the tapping is perpendicular to the airflow, it doesnt make such good vacuum. i have tried it both ways.

also, the brake proportioning valve may not provide the proper pressures suitable for front drums. this is a safety issue so it should be mentioned. i am not saying it will be unsafe, just sayin'... read the bentley and consider the possibilities.

[Desertbusman]

If front and rear drums normally operate at the same pressure it should be good providing the MC has the same diameter piston for both front and back circuits. And actually, if the MC piston diameters are the same between the old and new one the only difference is going to be less foot pressure to stop it or lock up the brakes.
_________________
71 Superbug
71 Westy

[Air_Cooled_Nut]

[Desertbusman]

I understand what you are trying to say but it is wrong thinking. Pressure equals force divided by area. The piston diameter in the master cylinder is the same for both the front and rear circuits, so the available pressure developed is the same coming out of both MC circuits. I said available because pressure is only developed when there is resistance. The wheel cylinders are the restance. But that equal pressure acting against different diameter wheel cylinders produces different force at the shoes. Same formula P=F/A, or F=PxA. With drum brakes the front cylinders are larger diameter and produce more force to the front shoes than the smaller dia. rear cylinders do to the rear shoes. Same ratio regardless of the pressure source. The only thing the OP is doing is changing the MC which is the pressure source and adding power boost. The old one gets it's input force only from the brake pedal. The new one gets it's force from the brake pedal plus the vac boost. So the bottom line is that he will be getting the same amount of force to the front and rear as the old system did but now will just require less pedal pressure. Less pedal pressure will now give the very same braking as before. And the same balance or ratio between the front and rear as before.
The stock booster, caliper, drum system needs the proportioning valve to compensate for the way the caliper functions differently than rear brake shoes. It clamps the rotor vs. pushing a shoe against a drum. Shorter travel, twice the size piston. Totally different mechanics.
_________________
71 Superbug
71 Westy

[SGKent]

[morymob]

If stock don't do it get an aftermkt adjustable valve,install and go on a side road somewhere and do your own panic stop/trial and error adjustment. This is the way we do it on a streed rod build.

[tom62]

I'll jump in again.
I have power drum brakes on my truck.
<<<<I have owned the truck for a year now.
The truck is my daily driver. I drive about 40 miles a day.
There is NO proportioning valve in the system.
It stops great on dry or wet roads without any rear wheel lockup.
All 4 wheels will lock if you try hard and the truck stops straight.
I am not an expert but in comparison to the 69 single cab the brakes on my 68 double cab are far superior.
I will not go back to standard brakes.
I would make this modification to any other drum brake bus that I will ever own.


This is my personal experience and opinion.

[Batan]

Depending where you live, the dry/wet performance of proportioning might not be enough. One needs to test it on snow and ice.
I will be following this thread closely as I too have drums and the 71 beam I believe does not fit in my bus (manufactured in late 6.
_________________
'69 Riviera Bay
'03 20th Anniversary GTI
'74 Super Beetle
Badzak Creative – Still and Motion Pictures

[aeromech]

DBM,
That's the best post I believe I've ever read from you. Good job man!
_________________
Lead Mechanic: San Diego Air and Space Museum
Licensed Airframe and Powerplant Mechanic
Licensed Pilot (Single engine Land)
Boeing 727,737-200-300-400,757,767
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DC9/MD80
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VW type 1 1962,63,65,69,72
VW Type 2 1971 (3 ea.) 1978, 1969
VW Jetta
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Capable of leaping tall buildings in a single bound

[Desertbusman]

Sorry, but a couple of you guys evidently are lost somewhere in the clouds .

If a stock '68-'70 has no need for a proportioning valve then the OP has no need for one either. He is not doing anything to change the brake system at the 4 wheels. All he is doing is adding power assist to the source that supplies brake fluid to the 4 wheels.
Likewise if you think he might need a proportioning valve you are also saying that every stock '68-'70 needs one also.

Somehow you must be thinking that a proportioning valve has to do with having a brake booster, wrong. It only has to do with a system that has 2 different types of actual brakes, calipers and drums.


P.S. Thanks AM
_________________
71 Superbug
71 Westy

[aeromech]

I'm currently working on a 1968 bus and the owner would sure like to have power brakes but I was reluctant to jump in because all I was considering was changing to front disk brakes plus all the other booster, etc. Now, the job seems much simpler if all I have to do is weld a bracket and mount the booster, etc. Looks like a piece of cake.

_________________
Lead Mechanic: San Diego Air and Space Museum
Licensed Airframe and Powerplant Mechanic
Licensed Pilot (Single engine Land)
Boeing 727,737-200-300-400,757,767
Airbus A319,320,321
DC9/MD80
BAe146
Fokker F28/F100
VW type 1 1962,63,65,69,72
VW Type 2 1971 (3 ea.) 1978, 1969
VW Jetta
VW Passat
Capable of leaping tall buildings in a single bound

[Batan]

DB, you are right about that. I guess the feel during the "knife's edge" of ice braking would change, but everything else would stay the same.
_________________
'69 Riviera Bay
'03 20th Anniversary GTI
'74 Super Beetle
Badzak Creative – Still and Motion Pictures

[tom62]

[Batan]

[aeromech]

[Jeff Geisen]

... to make the cable clear, get yourself a pulley and attach it to something under there to move that brake cable a bit. If you have the bracket and booster in under there the hard part is already finished.
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I Corinthians 4: 1 thru 5

‘63 ragtop - ‘68 single cab

[aeromech]

I've got the mounting plate fabricated but not welded into place yet. I'm just wondering if I should weld a fairlead onto the side of the booster to offset the cable? The cable should have enough length to it for the added distance. Another idea would be to install a fairlead between the upper and lower beams that would slightly change the cable direction around the booster. Maybe something like a 1/2 round stock welded top and bottom with a pipe on the outside to serve as a roller?
_________________
Lead Mechanic: San Diego Air and Space Museum
Licensed Airframe and Powerplant Mechanic
Licensed Pilot (Single engine Land)
Boeing 727,737-200-300-400,757,767
Airbus A319,320,321
DC9/MD80
BAe146
Fokker F28/F100
VW type 1 1962,63,65,69,72
VW Type 2 1971 (3 ea.) 1978, 1969
VW Jetta
VW Passat
Capable of leaping tall buildings in a single bound