68 Wiper and Headlight Vacuum rebuild

**Joe L.** · January 12, 2004, 08:10 PM

Re: 68 Wiper and Headlight Vacuum rebuild

Rich-----

1) "Normal" vacuum is about in the range which you describe, but it's really a function of the particular engine involved. For your engine I would expect idle vacuum at the low end of the range and, perhaps, even a bit lower than 17".

2) Vacuum source for the accessory vacuum system comes straight from manifold vacuum at a fitting in the intake manifold (between the carb and distributor).

3) I don't know if the master cylinder has to be removed to remove the vacuum tank;

4) A Mityvac-type pump is the most practical. Pumps like you describe are available, but are not usually available from automotive sources. The cost for one would likley exceed anything that you're thinking in terms of.

**Jim T.** · January 12, 2004, 08:33 PM

Re: 68 Wiper and Headlight Vacuum rebuild

Vacuum problems are sometimes a challange for sure.
The vacuum tank should have a vacuum source line coming from a fitting screwed into the intake manifold. My 68 does not have power brakes, but my 70 does, and one vacuum line from the intake fitting go to the power brake booster. Another vacuum line that has a vacuum line filter in the line followed by a vacuum check valve in the rubber vacuum line that connects to the vacuum storage tank. You can check the vacuum tank for a leak by putting a vacuum guage on the other nipple of the vacuum tank and starting the car establishing good vacuum in the tank, clamp the vacuum source line closed between the check valve and the vacuum tank. Shut the car off and check out the leak down if any.
Vacuum pumps are available, the electric type are used to pull vacuum on air conditioning systems to remove moisture.
If you car is not running you can use a donor car using several feet of vacuum line.
I believe that the vacuum storage tank can be removed straight down from its mounted location, but you have to remove the metal splash shield to do this.

**Richard D.** · January 12, 2004, 09:43 PM

Re: 68 Wiper and Headlight Vacuum rebuild

Guys, as usual, your advise is invaluable.

I will look through my Aim, and Service Manual, but, your practical advise is the best.

A guy at work, in our shop, gave me a "Venturi" attachment to hook to a standad air compressor, that gives a vacuum pump. Simple, cheap, and it actally works. Seems it can be built from some standard available stuff.

Anyway, when I get the details on this thing he had, I will pass it on.

It will be usefull to folks in my predicament.

Regards,

Rich

**Dave F.** · January 13, 2004, 07:14 AM

Vacuum System Troubleshooting manuals

Does anyone have any positive experiences with using the "commercially" available troubleshooting guides such as the ones sold by Corvette Central etc?

**Terry M.** · January 13, 2004, 11:49 AM

Re: 68 Wiper and Headlight Vacuum rebuild

Richard,
The compressed air driven vacuum pumps tend to be noisy, and that obscures the noise of vacuum leaks. I have had success with the vacuum pumps designed for air conditioning work, but those are not inexpensive. As others have suggested another car, especially if it can be located on the other side of a wall, and about 25 feet of hose, is probably the least expensive option. In any of these cases a vacuum gauge is indispensable.
If you are into testing your luck, often the check valve right at the beginning of the system is faulty. This is a gray cast circular valve with one pipe facing the engine, and two pipes (one larger than the other) on the other end. This valve will be the second item in the system from the intake manifold. The first is a white filter. I believe the check valve, and maybe the filter, are still available from Chevrolet. The check valve, once removed, can be checked with vacuum from your mouth. One should be able to draw and hold a vacuum on the side with two pipes. Cover one with a finger and suck on the other.
The larger of the two check valve outlet pipes goes to the vacuum reservoir and the smaller goes to the control circuit. In testing for system integrity one can isolate the two parts of the system at this valve. I would strongly urge you to test the vacuum canister before removing it. If you have tested it and know it is faulty, only then go through the trouble of removing it.

**Jack H.** · January 13, 2004, 01:11 PM

Re: Vacuum System Troubleshooting manuals

Yep, they work, BUT you have to put them in context. They give a generic description of the Shark vac system. There were differences over time (wiper door eliminated after '72, Etc.) and none of the books I've seen go model year by model year.

So, you read, understand the 'big picture' of how the vac system works, then begin troubleshooting as they suggest walking through your system from the intake manifold outward looking for vac drops of +2 psi or more along each adjacent leg of the system and being careful to understand when/where there are parallel paths in the system. At a parallel path junction, test each leg independently by plugging the opposite side of the parallel path, then going back and reversing the process.

Last, NEVER assume there's only ONE problem! The likelihood is high that there are problems in more than one place and you have to find and fix ALL of the little devils....

**Richard D.** · January 13, 2004, 05:25 PM

Re: 68 Wiper and Headlight Vacuum rebuild

Thanks Terry.

I purchased new valve and filter, checked them, and they were OK.

Hooked up that vacuum device I mentioned (air compressor run), and it worked like a charm.

Unfortunately, the storage tank had a number of cracks in it from a previous front left fender hit, and was never replaced or repaired by the prior owner -go figure.

Good news is, is that the front headlight cannisters seem to be OK after testing them with the vacuum source.

Getting the tank out is a bear. For a 68, it looks like you need to remove the brake master assm., which is not easy.

I had my shop cut a line up the fenderwell (about an inch and a half from the seam where it's bonded to the fender, about 6 - 8 inches in length) then drop the bottom access panel, bend the fender in (the cut upward along the portion where it mates to the fender acted to create a bendable "flap" in the fender well), and the tank came out.

A real bear, but it's easier to cosmetically fix the cut on the fenderwell, vs. pulling the whole brake assm. out (at least for me).

I have a friend that can weld the splits on the tank and test it for leakage.

It's original to the car, and they don't make that configuration anymore.

Pretty bad design for the tank, and I understand the replacement tank is a smaller "coffee can" type of tank, that can slip in without all this other work.

Anyway, thought I'd pass that along as I move through my adventures in vacuum land.

Regards,

Rich

**Terry M.** · January 13, 2004, 06:49 PM

WOW!! Thanks for the update *NM*

**Richard D.** · January 13, 2004, 07:55 PM

Re: WOW!! Thanks for the update

Terry:

As soon as I get the rest of the specs on how to put this vacuum source device together from my engineer at work, I will get some digital shots together along with the part pieces numbers and email them to anyone who needs it (any shark guys who need to go through this crazy excercise).

You can hook it to your compressor, put a long hose on it to keep it away from your car, and go to town. At least you'll be able to hear where the leaks are coming from without starting your engine, in which case you can't hear anything.

It should be relatively cheap (maybe $30.00 or so) to make with readily available type stuff from Home Depot and a hardware store.

Regards,

Rich

**Terry M.** · January 14, 2004, 02:09 AM

It would make a nice tech tip for The Restorer *NM*

68 Wiper and Headlight Vacuum rebuild

68 Wiper and Headlight Vacuum rebuild

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment