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TECH TIPS: Fuel tanks, engines & clutches

Steve Turchet answers readers' questions about a leaky gas tank, Cummins JT engines and clutch failure on a jeep. 

The gas tank on my 1968 M715 is leaking badly and looks like it’s falling apart. Do you know of any company that sells replacement tanks for this truck?

Five-quarter fuel tanks are known for rusting and leaking, but you have many options. If you want to keep your truck stock, you could contact various advertisers in this magazine who offer M715 parts to see if they have an NOS or a good used tank.

Depending upon the condition of your present tank, you could investigate various means of repair, including coatings touted as being able to seal leaking or rusted tanks. You could also search through truck wrecking yards to possibly find a tank that could be modified to fit. Or, if money is no object, you could have a tank custom built.

My grandfather is a Vietnam vet who was drafted. He was not gung-ho about what he calls the “Bungle In The Jungle”, but he has always liked old military vehicles and I have, too.

We have two Jeeps on our ranch, a Willys MB and a Willys M38. They are not restored but they are painted olive drab and mostly stock. I have a chance to buy a Kaiser Jeep M715 pickup. It has been re-powered with a Cummins JT 6-cylinder diesel engine and a Clark 5-speed transmission with overdrive 5th gear. It is an old conversion that was done in the 1970s and was done by a professional truck mechanic.

Except for this, the truck is stock and looks very nice. The truck seems to run and drive very well but I’m worried because the engine is very loud and smokes a lot. The truck will run on the road at 60 mph in 5th gear, and has a lot of power off the road, but you need earmuffs to drive it! The guy says this is normal for this engine and the engine is in good shape. Have you had any experience with Cummins JT engines? —Phil

As the cyber-kids say, “OMG!” When I think of all the diesel engines that could have been put in that truck, and someone chose a Cummins JT! In the trucking industry during the early 1950s, the JT was known for three things ... noise, smoke, and lack of power.

Like the GM 6-71, the Cummins JT could be heard and identified a mile away by its sound. In fact, if one wanted a diesel that “sounds like a diesel” (and also an engine four times its size) the JT would be an excellent choice.

While the power issue shouldn’t be a problem in an M715—in fact I’d dive carefully in low range to avoid snapping axles or drive shafts­—there isn’t much you can do to muffle a JT’s iron bellow, except maybe to pad the engine compartment and hood with fireproof sound-absorbing material.

As to the smoke—assuming it's not blue, which indicates that an engine is burning its lubricating oil—you would just have to live with it. Other than these faults, the JT isn’t a bad engine, and its bum rap in the power department was mostly due to its being installed in trucks and other applications that were simply too large for what it could put out.

As I say to most folks who ask if they should buy a certain MV: bottom line, “if you like it the truck, buy it.”

I answer every letter I get. However, it may take several weeks for MVM to forward a snail-mail letter to me. If you want a quick reply to a Tech Tips question, it’s best to use e-mail.

I was driving my 1944 Willys MB last week. When I came to a stop sign and stepped on the clutch the pedal went to the floor and stayed there. No clutch. I crawled under and checked the linkage but nothing looked broken. But the clutch wouldn’t work and I had the jeep towed home. What’s wrong?—Barry McFarlane

I had this happen on a CJ3A, but managed to drive it home without any clutch, though with considerable grinding of gears when shifting. It is hard to “match revs” from a stoplight!

I suspect your clutch release fork has failed — a fairly common occurrence on older model jeeps. The clutch fork is a steel stamping and pivots on a ball and socket point within the bell-housing. It is quite common for the socket on the clutch fork to fatigue and wear through since no provision was made to lubricate it.

While all one needs is a new clutch fork to fix the problem (available from many of our advertisers) it’s not a simple repair since one must pull the engine to replace the fork. You could also weld or braze your old fork, but you run the risk of another failure if the job isn’t done right. Put a healthy dab of grease in the socket of your new or repaired fork.

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