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distributor without a vaacum advance?


alanhaley

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My daughter and I are putting an old '51 dodge pickup on the road. The serial number plate was lost so I dont know the exact model but it has a flathead six in it. We are converting it over to a 12 volt and when installing a new capacitor I noticed that there is no vaacum advance. How can this be? Is it possible that some previous owner cobbled up a distributer from some other application and installed it here?

Sucking air in north Maine

Alan

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Many industrial engines did not have a vacuum advance. Not required on an engine that runs at a set (governed) speed. Someone may have installed an industrial engine in your vehicle. The engine serial number may tell you what the engine is. You can easily install a distributor with a vacuum advance. Just make sure the distributor is the correct length for your engine. Not sure if you have a long or short block engine.

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Alan,

A few cues to give you an idea what model you have;

1/2 ton trucks have a 108" wheel base

3/4 ton trucks have a 116" wheel base

1 ton trucks have a 126" wheel base

I'm guessing it's a pickup, so I"ll stop there.

The vehicle serial number is stamped into the left frame rail, just above and ahead of the front axle. You may have to clean up the frame in that area with a stiff wire brush or sanding disc/paint stripper. With that number go to http://www.t137.com/registry/help/decode.php and type in your serial number. It'll tell you what model you have.

The engine also has a model and serial number. It is stampped into the block, at the front left side up near the top. Look just below the head to block seam, above the generator/alternator location. The truck engines started with a T. The engine in my '50 truck is a T172. If you have a '51 it would be T306 for a 1/2 ton, T308 for a 3/4 ton and T310 for a 1 ton. These numbers are followed by the serial number. If your engine begins with anything other than a T it may be an industrial engine, like Don says, or a car engine. But if it had been a car engine it should still have the vaccume advance. There are distributors out there for our trucks, or if you're converting to 12v maybe you'd consider a confersion to electronic ignition. There are distributors available for that too.

Good Luck,

Merle

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As Don Coatney pointed out, most industrial application gasoline engines typically do not use vacuum advance units. Anything with a governor will generally not have a vacuum advance, like farm tractors, heavy trucks, etc. Typically these distributors do have centrifugal advance units, just not the vacuum type. The purpose of the vacuum unit is to improve economy on vehicles that move in traffic at varying speeds. If you used a non-vac advance distributor in a B1B, the only difference you might note is a little less fuel economy, IMHO.:)

Having stood on my stump and said all that, I'm sure someone out there will probably be able to point to an exception or two. Go figger . . . . . .

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Thanks for your help everyone. I dont feel quite so nervious about the truck right now. My daughter put a lot of time and money into this on my advice that it was a good deal and I sure dont want to find out that it was a lemon. I cant see the serial number on the frame but the truck number indicates that it is a one ton. I thought the springs and brake drums looked awfully large.

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Above the generator or alternator there is a casting boss on the block just below the cylinder head. This area will have a number stamped into it. Post this number along with the part number from the data plate on the distributor.

It was very common for these engines and vehicles to have had engines swapped between models when the original went bad. Rather than rebuilding it it was easier and quicker to find a doner from any number of sources, and plopping it in and runnig that one till it died. Very common in the days of non detergent oil, not very effective oil and air filters, and driving on dirt roads that these engines were down and out at 50000 miles so swaps were common.

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Just finished reading in my new issue of Auto Restorer a letter about running without a vacuum advance, where the writer estimates this practice costs the operator about 20 percent fuel mileage in the wrong direction. He goes on to remember using dual-point distributors in early day street rod applications that typically used centrifugal-only advance. He mentioned one Ford that gave only 4 mpg with such a setup.

Vacuum advance units are typically found only on passanger and light truck units, and are really used to save fuel in stop-and-go driving conditions. The writer went on to speak about adjustable vacuum advances, where the advance curve can indeed be controlled with a set screw inside the vacuum port. To my best knowledge, no such animal is available for our older MoPar applications.

Wouldn't it be fun to adapt an adjustable advance unit to a flattie distributor and do some tests with different vacuum advance curves to see how economy and drivability are affected. Why, if someone came up with an easy retrofit for a later model adjustable advance unit, it might be both better and cheaper than the 65-75 dollar pirce range we are all now paying for sealed, non-adjustable advance units.

Anybody have an idea on where to start finding such an animal? I know a few of you have parts backgrounds. Can anyone offer some retrofit help/ideas?

Thanks:)

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Dave;

I am running dual points in my distributor. It is possible to alter the vacuum advance curve in our distributors by adding/removing shims in the spting chamber. I have not changed my curve sence I initially set it up per book specifications. I might try what you suggest. What direction would you recommend?

dual_points_1.jpg

vacpump.jpg

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Don,

Where'dya get that neat vacuum advance? You are right - it looks like it domes apart, so certainly should be adjustable. As to which direction to go, I am not the best person to give expert quarter mile advice here. I can tell you that when I was a Ford Div. Service Rep back in the glorious HiPo days, V8 engines liked to have all the advance - centrifugal and vacuum applied by about 2500 rpm for quarter mile performance. Of course they ran right up to 7 or 8 grand rpm-wise.

One of the reps I worked with at Teterboro, NJ held the national Class G super stock record for three years with a 1968 427 Fairlane. He sold it tp a doctor's son who raced it the first night out and shelled a differential. Then they put in a welded diff- an axle broke half way down the strip and he did a 90 degree into the stands at WOT. Killed himself and two others at an NHRA strip in NJ, if memory serves.

Methinks what you will want in an advance curve would best be laid out with the aid of a dyno. Lacking that goodie, guess the best recipe will depend on what you want - good mpg or (gulp) beating that red rascal in blue sky country . . . . . .:) :)

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  • 10 years later...

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