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914World.com _ 914World Garage _ Plenum Repair
Posted by: ctc911ctc Apr 15 2019, 02:35 PM
I have been chasing a vacuum problem. Found 2 likely culprits so I started a new thread.
1. BOTH plenum support columns at the top are leaky. I just tried soldering and then brazing, both did not work. I am reluctant to weld because of the gage of the material and the skill of the welder......grin
2. The control shaft in the Throttle Body is leaking as well, is there any way to fix this without milling and new sleeves inserted?
Also, as luck would have it, my son cleaned and painted the unit PRIOR to me having time to test it........
Thank you,
CTC911CTC
Posted by: 76-914 Apr 15 2019, 02:49 PM
Brazing is fine but might be easier to buy a known good one. The shaft needs to be redrilled with new bushings. The bushings are self lubricating and will be installed "in line" when done correctly. If that shaft were to bind when wide open you might be in for "the ride of your life".
I prefer the silicone rubber for those runners but you usually need to buy a 3' length at a diesel shop and it ain't cheap. It does take heat well and will out last the OEM sleeve.
Posted by: 914_teener Apr 15 2019, 02:49 PM
JB weld for the plenum. Done.
For the TB. What Kent said.
While you are there....how good is the throttle switch?
Scored.....great? Is it clean?
Posted by: worn Apr 15 2019, 05:30 PM
Also, as luck would have it, my son cleaned and painted the unit PRIOR to me having time to test it........
Luck has nothing to do with that sort of thing. I have had excellent results with silver containing filler rod when brazing reluctant steel. It comes with bright orange flux coat and is kinda spendy. Good luck.
Posted by: ctc911ctc Apr 15 2019, 06:57 PM
*********UPDATE*******
Used fast set Marine Epoxy, chemically the same as JBWeld, after a few hours I tested the plenum and it held vacuum, also I pulled the control rod out of the Throttle body, put some white Lithium Grease on the shaft.
Seems to hold..... 
After it sets firm (tomorrow) will try the pressure test.
Posted by: EdwardBlume Apr 15 2019, 07:10 PM
Just a thought, but make sure you have or need to put the plastic bolt back on your accelerator stop. A common destroyer of plenums is not having the plastic bolt and flooring it a lot. Your plenum is compromised by the cable pulling the throttle open past where the throttle goes, tweaking the plenum.
Ask me how I know.... 
Posted by: ctc911ctc Apr 15 2019, 08:24 PM
Plastic Bolt? Accelerator Stop? HHHmmm, mine is a '74 2.0 - is there one on this plenum?
Do you mean the one on the floorboard?
Just a thought, but make sure you have or need to put the plastic bolt back on your accelerator stop. A common destroyer of plenums is not having the plastic bolt and flooring it a lot. Your plenum is compromised by the cable pulling the throttle open past where the throttle goes, tweaking the plenum.
Ask me how I know....
Posted by: Mark Henry Apr 16 2019, 06:35 AM
*********UPDATE*******
Used fast set Marine Epoxy, chemically the same as JBWeld, after a few hours I tested the plenum and it held vacuum, also I pulled the control rod out of the Throttle body, put some white Lithium Grease on the shaft.
Seems to hold.....
After it sets firm (tomorrow) will try the pressure test.
I welded a surge tank to my VW bug gas tank, no matter how hard I tried I couldn't stop all the leaks.
I used a quality marine epoxy and it sealed right up. Been in use about ten years now. They make fiberglass fuel tanks, I believe all underground tanks for gas stations are fiberglass.
Posted by: mgphoto Apr 16 2019, 03:33 PM
I would find another, dangerous to weld or braze on the plenum because of residual fuel, just like a fuel tank.
Marine Tex is great stuff, used it to seal a vw gas tank. But it is not a permanent, vibration can loosen the material.
Posted by: dr914@autoatlanta.com Apr 16 2019, 04:04 PM
vacuum hose fitting for the aux air valve is pointing the wrong way
Have never seen the support tubes leaking before, if you are afraid of welding then epoxy they have some really good ones these days\
Tubes should be painted with Wurth zinc spray for the exact color and texture
I have been chasing a vacuum problem. Found 2 likely culprits so I started a new thread.
1. BOTH plenum support columns at the top are leaky. I just tried soldering and then brazing, both did not work. I am reluctant to weld because of the gage of the material and the skill of the welder......grin
2. The control shaft in the Throttle Body is leaking as well, is there any way to fix this without milling and new sleeves inserted?
Also, as luck would have it, my son cleaned and painted the unit PRIOR to me having time to test it........
Thank you,
CTC911CTC
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