Leaky air distribution box

911buff · 911buff's Garage

I finally discovered my vacuum leak in the fuel injection system...the brazing around the support struts in the air distro box has broken. And there are some slight tears in the metal around the support. Can this area be repaired? Does it have to be brazed or can it be mig welded? I realize it is very thin there. Any advice? Thanks!

The cap'n · 12-03-2014, 06:51 PM

Might be helpful to better describe your problem. Like maybe tell us which engine you have. There are a ton of good used plenums out there if you choose to go that route.

The Cap'n

911buff · 911buff's Garage

It is a 2.0 with factory fuel injection. It was running rich and I could not find the leak. I am in the middle of a rebuild when I discovered the problems with the air box. Just curious if it can be welded or if it has to be brazed.

The cap'n · 12-04-2014, 06:07 AM

I have seen them repaired. Nearly impossible to weld because of the contamination from the brazing alloy used at the factory. I think I would opt for a carefully inspected used one. If you do repair yours, media blast the affected area (NOT with glass or sand - soda or dry ice would be best) before attempting repairs. It would be useful to know what alloy the factory used. I'm guessing they furnace brazed them.

The Cap'n

John Rogers · 12-04-2014, 08:24 AM

We acid cleaned the one on our 1974 2L engine and then used plumbers solder to redo some failed joints like you have. Once I did that I coated all the joints with that sealer named "GOOP" and it lasted until we sold the car, about another 6 years at least.

I would imagine these were put together either at the factory or a sub contractor but in any case back in those days Porsche had probably the worst welds in the world! I would not be surprised if they did not use a mock up to align everything?! Check out the frame on a 917 some time and you would not want to go 240 MPH in a frame like that!

The cap'n · 12-04-2014, 08:41 AM

I might add that brazing with common brass is not the way to go. Brass doesn't like vibration all that much. I would find someone who can silver solder the problem areas.

The Cap'n

TheCabinetmaker · 12-04-2014, 10:26 AM

mine leaked, brazing failed. simple solution was to take some penny's and epoxy them to the top and bottom of the support on the exterior to seal them off. painted them and they can not really be seen well. simple and effective, been running that way for maybe 10 years and no more leaks. the two supports get a penny, top and bottom.

just my 4 cents worth.

911buff · 911buff's Garage

TheCabinetMaker, you are my hero! I am all about working smarter, not harder! Simple, efficient, cost effective solutions are awesome. I was contemplating a similar fix but never thought of using pennies. Brilliant! Maybe a small Porsche badge on the exposed side...wait, that is not cost effective! I will accomplish tonight. Thanks!!!