Vacuum leak question - brake booster connection... (1 Viewer)

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Hi there. I am trying to improve vacuum as part of a smog failure and can't get above 16# and am chasing potential leaks. I have been spraying carb cleaner and the only place that drives up the RPM's or causes vacuum to increase is the manifold fitting that provides vacuum to the brake booster. See pic below. As a troubleshooting step, even though the brake booster hose and the AC idle adjust vsv hose seemed to be in decent shape, I took an inch or so off of both to be sure. No change in vacuum or RPM's with the hoses reseated. This makes me think the fitting is leaking where it screws into the manifold. Is this a normal failure point?

2EA1BFEF-D218-4831-9A98-EBED817DA856.jpeg
 

lcolon

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I usually do not even bother to put tape or sealant on that fitting. The trouble for you is going to be taking it out on a head that is installed in the truck. The small pipe coming out of the fitting will likely need to be carefully bent so that you can remove it. The coolant pipe fitting on the head interferes with this fitting in the manifold. Once you remove it, you could try some teflon tape around those threads and put it back in.
 
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I usually do not even bother to put tape or sealant on that fitting. The trouble for you is going to be taking it out on a head that is installed in the truck. The small pipe coming out of the fitting will likely need to be carefully bent so that you can remove it. The coolant pipe fitting on the head interferes with this fitting in the manifold. Once you remove it, you could try some teflon tape around those threads and put it back in.
Is Teflon tape heat resistant? Should I try to tighten the fitting as is first? It moves when I put a wrench on it...
 

lcolon

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If it is loose, try snugging it up and see if that resolves your problem. Don't go too crazy tightening it down. Teflon tape should be fine. I have used it on the coolant temp sensor on the block that probably gets as hot as the intake manifold.

Maybe someone else on here can chime in on an alternative sealant that could be appropriate.
 

lcolon

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One more comment - for a reference point - on my truck with an intake gasket leak I still had 17" of vacuum. With a new intake gasket I was at 19" of vacuum (that was also still with a couple of semi leaky valves). You may want to do a leakdown test on the cylinders if you do not get a significant improvement from addressing the leak on the fitting.
 
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One more comment - for a reference point - on my truck with an intake gasket leak I still had 17" of vacuum. With a new intake gasket I was at 19" of vacuum (that was also still with a couple of semi leaky valves). You may want to do a leakdown test on the cylinders if you do not get a significant improvement from addressing the leak on the fitting.
Thank you for the info. I will look for some teflon tape. I have never performed a leakdown test, I will look into that. The compression on this rig is frigging outstanding, best I have even seen actually. All are between 165 and 175 tested dry with the throttle open... Does that make the leakdown test unecessary?
 

OSS

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Just remove the manifold and fix it correctly. Use Permatex high temperature thread sealant. This way you can kill two birds with one stone—that pesky fitting AND the manifold gasket that's undoubtably leaking in spots. If the manifold gasket hasnt been replaced in 10 years, it's overdue. They don't last forever. They wear out.
 

lcolon

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Just remove the manifold and fix it correctly. Use Permatex high temperature thread sealant. This way you can kill two birds with one stone—that pesky fitting AND the manifold gasket that's undoubtably leaking in spots. If the manifold gasket hasnt been replaced in 10 years, it's overdue. They don't last forever. They wear out.

Actually this is the best suggestion. If you want to know what is involved in pulling the manifold I have a thread going where I did just that. If you do take it off, then I would suggest that it goes to a machine shop to have it checked for straightness and machined if necessary. PM me if you want a reference and some experiences with one of the machine shops semi-close to the bay area.
 

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