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November 2010 Techline

Posted in How To: Tech Qa on November 1, 2010
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'70s GM K-Truck Aspiration Woes
Q I'm inquiring about the age-old problem of carbureted vehicles dying on steep hills. I have a '77 Chevrolet K5 Blazer with the Carter AFB sitting on top of a 350, and I was recently wheelin' up a steep and winding trail when my truck died. I had heard about this happening, but it had never happened to me personally. I would like to know what I can do to my truck to get it to the top of the hill. What are the expensive and less-expensive options I have, and what are the advantages and disadvantages of each option? I have to get to the top of that hill!
Jon Crawford
Mesa, AZ

A Having an engine die when going up a steep hill is not fun. Even less so when you have to back down without power steering and power brakes.

As you found out, the Carter AFB is not one of the better carburetors for off-road use. It was, and still is, a fairly popular street performance carburetor. I wonder why this is on your engine and not the original Rochester four-barrel Quadrajet that all 1977 350 V-8s came with. The Rochester four-barrel is what's commonly referred to as a "spread-bore" design, with a large amount of difference in size between the primary and secondary throttle bores. The AFB is what is referred to as a "square-bore" carb, in that all four throttle bores are approximately the same size. If I remember right, the bolt pattern is different, so that means you also must have an aftermarket intake manifold; but then again, as I think about it, they may have dual bolt-pattern holes.

So let's start with making your AFB a bit better. The first thing you need to do is figure out why the engine died. Was it from too much fuel or too little? If it blew black smoke out of the tailpipe when you got the motor restarted, that's a pretty good indication that the motor died from too much fuel. There are a couple of things that you can do. Make sure that the fuel pump pressure is between 3.5 and 5 psi. Yes, you're going to need some type of a fuel pump pressure tester to do this. I suggest you obtain some type of a repair manual and read how to do this. You may want to do an Internet search under something like "AFB carburetors" for information, too. Used bookstores are a good source, as is your public library.

Excessive fuel pump pressure can force the float's needle off the seat and cause too much fuel to enter. You also need to check the float level. This will give you a chance to check the condition of the needle and seat assembly. If there is any question as to its seating ability, then replace it. If the float is set too high or the fuel pressure is too high, then when the vehicle is on a steep hill, the fuel can flow back through the vent tube and flood the engine. You might even want to slightly lower the fuel level. We're talking increments of 1/16 inch here. The float is kind of a pain to adjust due the metering rod design.

Could it be that you actually ran out of fuel when on the steep hill? Either from the fuel being a bit too low and the pick-up tube uncovered, or the fuel pressure from the pump too low? In this case, the engine should have restarted without the black smoke.

If none of those measures help, then I really suggest you sell the AFB for what ever you can get for it to some street rodder and go back to the original-style Quadrajet. These are quite common on any of the '70s GM vehicles, so it doesn't have to come from another pickup. Just match the cubic inches of the motor as a general guideline. There may be some minor differences in throttle linkage. Keep in mind that the carb is not the easiest to rebuild and there are several updates that need to be made, so again I'd suggest taking a look on the Internet for these tips or using a rebuilt unit. They work quite well off-road, and in fact I use one on my own 4x4, as it works almost as good as a fuel injection unit. (Keep in mind that I said almost as good.) I believe the fuel pressure for it should be somewhere around 7 psi.

As an alternative, Holley's Truck Avenger, the 670cfm version (p/n 0-93679), is an excellent off-road carb if you want to buy something brand-new. I have used one, and can say I have been impressed with its performance. You will need a new intake manifold with the proper bolt pattern or an adapter. You will also need to make some changes to the fuel lines and linkage.

Jeep Quadra-Trac: How It Works
Q I bought a '73 Jeep Wagoneer with what is called a "Quadra-Trac" transfer case. All I know is that it is a full-time system. Luckily, the owner's manual was in the vehicle, so at least I understand how to use it. Are you familiar with it? Can you explain more to me about how it works?
Tom Burns
San Diego, CA

A Sometimes, short questions like this take up a lot of space to answer, so here it is. It was made by Borg-Warner, and for its time was way ahead of anything else on the market. There were two models: A two-speed 'case with a 2.57:1 low-range gear which was referred to as the Model 1339, and a single-speed case, the Model 1305. It was used in full-size Jeeps such as your Wagoneer from 1973 to 1979, and in CJ-7s from 1976 to 1979. The two-piece aluminum case uses drive sprockets and a drive chain very similar to present day transfer cases. Within the case is what's referred to as an "unloading" cone-clutch limited-slip differential from which power to both front and rear is transferred.

Inside the limited slip, which is not unlike some present-day rear locking differentials, are some clutch plates preloaded by what are referred to as Belleville springs. When excessive torque loads are applied, such as going around a corner or differences in traction are encountered, they will slip, thus allowing a smooth transition of power. When one axle has less traction than the other, power will be applied to the axle with the most traction.

Under situations where you want to lock out this transfer of power, front to rear, it can be easily done by using the emergency lock switch. This switch, I believe, is found in the glove compartment and is vacuum-operated. These had a high failure rate, so I am sure yours does not work being that it is some 37 years old now. Jeep did make a conversion kit to allow manual shifting, but this kit is long out of stock. With a bit of ingenuity, I am sure one could make his own. It does nothing more than lock out the clutch action, providing a direct power path to each axle.

Like any part-time system, when "locked," it should not be operated on a dry or hard-surface road.

The big drawback of the Quadra-Trac is that when driven on straight roads for long distances without any reason for the clutch packs to release, the clutch packs would build up a varnish and had a tendency to stick. When you did turn, the clutchpacks would then release with enough intensity to cause a banging noise that the hollow driveshafts enhanced. This was commonly referred to as a "slip-stick" situation. Sometimes it's necessary to find a big empty parking lot and do several figure-eights in both directions that will force the clutches to slip to relieve this problem.

For whatever reason, drivechains only last about 60,000 miles before they need replacement. This is most likely caused by the occasional shock-loading of the clutch pack when it has a hard release. You will definitely know when the chain needs replacing-it will actually jump on the drive gear.

Another problem, which also often leads to increasing the slip-stick problem, is the fact that this case takes a special fluid. No, most likely you can't order it from your local Jeep dealer; the parts department probably doesn't even have a clue about it. A company called Crown Automotive does manufacture the proper fluid, and it can be purchased through specially shops that deal with Jeep vehicles.

I believe that Novak Conversions (435/753-2513, has the fluid, as well as rebuilding kits for the case. They also offer a kit to swap it over to a Spicer 18 transfer case. The Jeep 18 is the only transfer case to use here as both front and rear drive outputs are in line with each other. Some people have used the Jeep Dana 20 transfer case, but this puts the rear driveshaft at an angle that could lead to excessive vibration. Mile Marker (800/886-8647, still makes special kit to eliminate the clutch pack.

Disc Brake Conversion for Dana 70
Q I'm looking to make my Dana 70 HD dually into a full-floater disc-brake rearend. I know that the RVs and U-Hauls have them, but don't know how to acquire the parts to do it or where to buy them.
Scott Drenske

A Not a problem. Several companies offer a disc-brake conversion kit for the 70. One of the nicer conversions uses a special formed adapter plate of 3/8-inch steel, and front rotors and calipers from a Chevy 3/4-ton pick up. It's advertised as for a GM 14-bolt application, but I understand that it will also fit the Dana 70 HD. Take a look at

Rx for Wrangler Rust
Q I have an '89 Jeep Wrangler with a rust problem. Being that I live in Michigan, I am sure that you know what I'm talking about. The body rust I can live with, but the frame has some problems that I'm sure need attention. At the rear, where the end of the spring mounts, the frame is pretty much rusted out. Other than buying a new frame, is there any way I can have a shop weld in new patch plates, or something else I can do to fix this potentially dangerous situation?
Wayne Dolle
Ann Arbor, MI

A It's just not in Michigan that rust in this area occurs. It's a pretty common problem with all YJs that are used in snowy, muddy areas. It seems that this is a great place for junk to collect and hold moisture. Fortunately, there is a company, Auto Rust Technicians (800/407-7024,, that makes repair kits for not only this problem but others. You should also look at the front shackle mounts, as they're also subject to rust out. Auto Rust Technicians also make repair kits for 1967-86 Jeep CJ-5s and CJ-7s that experience that same problem, as well as for the Wagoneer's rear frame member, where the skidplate mounts.

Where To Write
Address all correspondence to: Techline Four Wheeler, 831 S. Douglas St., El Segundo, CA 90245. You can also reach us by e-mail at; be sure to type the words "Tech Line" in the subject line. All submissions become the property of Four Wheeler, and we reserve the right to edit them for length, accuracy, and clarity. The editorial department also can be reached through the Web site at Due to the volume of mail, electronic and otherwise, we cannot respond to every reader, but we do read everything.

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