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What Were OEMs Thinking When They Sourced These Parts?

Posted in How To: Tech Qa on April 7, 2017
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Photographers: 4 Wheel & Off-Road Staff

This story started with a trip to our local parts store to borrow a compression tester from the fleet of rental tools there. While looking at the laminated tool card we saw the listing for a spark plug remover for Ford three-piece spark plugs. You know it’s a bad design when a part requires its own tool! Particularly for a wear item like a spark plug. That got us thinking about some of the other designs and components that the OEMs have gotten wrong over the years. They are typically easy to spot because the aftermarket will have generated a solution for them (slip yoke eliminator, anyone?). Here are our picks of the greatest misses. Have your own list of things that make you say, “How did this get made?” Send it to us at editor@4wor.com.

Christian Hazel, Editor

JK Driveshafts

These seems great in theory but deliver a big bag of suck in the real world. The JK Wrangler comes equipped with CV-style front and rear drivelines in lieu of good old-fashioned U-jointed shafts. In practice, the constant velocity joints operate more smoothly than a conventional U-jointed driveshaft due to the elliptical path a standard U-joint travels. However, once the boots crack or get torn, the vulnerable CV assemblies inside are quick to corrode and then explode.

Quadratrac Transfer Case

Truth be told, when they are new they are actually a very good transfer case. However, the overly complicated vacuum actuation units, plumbing, and analog switches often suffer from leaks or poor performance. A cable shifter would’ve been more reliable and faster. Also, the chain design stretches out in heavy FSJs, especially behind the 401 engine. If the chain stretched far enough, it would jump cogs on the output shaft sprockets or, worse, rub a hole through the case material. Nowadays only cheap Chinese-made chains that stretch super-quick are available . . . unless you luck into a stash of good American-made Morse chains—although BJ’s Off-Road now has its own chains made in the USA.

3.8L Exhaust Manifolds

Putting a minivan V-6 with questionable rod bearing reliability in a 5,500-pound, four-door Wrangler notwithstanding, JK Wranglers really worked the little 3.8L V-6s hard. And if you added slightly larger tires or some weight it got even worse. A hard-working, modern fuel-injected engine creates a lot of exhaust heat. And the paper-thin cast iron exhaust manifolds found on the JK 3.8L V-6 cracked severely and frequently. A heavy-duty, thicker cast manifold never materialized either in factory or aftermarket forms, no matter how many Jeep or aftermarket exhaust manufacturers we spoke to about the problem. The only real solution was somewhat ill-fitting tubular headers that tended to fry vulnerable spark plug wires and fry the ignition control module on the driver-side valve cover.

Unit Bearings

In theory they were a cost-saving idea. Since just about all Dodge 1/2- and 3/4-ton 4x4 pickups and SUVs came with the full-time NP203 transfer case in the 1970s, why bother with the added expense and hassle of outfitting the Dana 44 with locking hubs? In their place, Dodge fitted crappy unit bearings with a meager 5-on-4 1/2 or eight-lug bolt pattern. The unit bearing assemblies had small bearings placed very close to each other, so leverage from larger tires, heavy front bumpers or high load weights, and regular old wear and tear shortened their lifespan dramatically compared with the regular widely spaced Dana 44 hub assemblies on Chevy, Jeep, and Ford trucks of the era. Dodge finally came to its senses and went back to a standard Dana 44 hub with a big 1/2-ton, 5-on 5 1/2 bolt pattern in 1981, but over the years plenty of other manufacturers have used sealed, nonserviceable unit bearings with plastic races and closely spaced bearings.

Ammeters

You hear that? Tick, tick, tick. It’s the time bomb lurking inside the dash of your 1970s truck. The factory ammeter is a fuse that’s been lit at the factory, and there is no telling how long it’ll burn before it blows the whole electrical system from the dash to the alternator. High resistance in the ammeter windings increases with age and causes excess heat buildup. Those in the know bust open the dash and simply connect the ammeter leads to one another to bypass the problem. Jeep recognized the problem and revised the harness and gauge design in 1979 to help alleviate the problem, but Dodge and others also have ammeters that pose a potential fireball.

Verne Simons, Technical Editor

GM IFS steering

Since the solid front axle died at GM in 1991, IFS has been the design of choice for all the General’s 4x4s. The design of this IFS is very similar between the compact S-10s, Tahoes, and Silverados all the way up to the 1-ton 3500 trucks and Suburbans. While the size of some of the components varied to meet the demands of the larger, heavier trucks (like differentials and half-shaft size), the steering has always left something to be desired. Issues are blamed on odd steering geometry and more, but at the end of the day the real problem is in GM's failure-prone and tiny tie rods. Add in larger tires and lower gearing and these tiny parts strike fear into the heart of anyone who sees a late-model Bowtie vehicle near the entrance to any off-road trail.

Vacuum Axle Disconnect

At some point in the 1980s, an engineer was tasked with getting rid of manual locking hubs while keeping the front end from spinning to improve fuel mileage. The problem is people are lazy. While locking hubs are durable and functional, folks can’t be bothered to get out and unlock them. The unfortunate solution is the widely used and equally loathed vacuum-operated central axle disconnect system. The idea is that when the vehicle is in 2WD a vacuum switch slides a collar to disengage a two-piece axleshaft. Sound complicated? It is. Both front U-joints still turn, and the side gears of the differential still turn, but if there is enough drag on it the front driveshaft shouldn't turn—and voila! A modicum of less drag equals slightly better fuel economy. Bring back locking hubs!

Push/Pull Steering

We love solid-axle 4x4s because of their simplicity and reliability. Generally their steering systems are also simple and reliable, but that is not always the case. GM, Dodge, IH, and Toyota all had solid-axle 4x4s with push/pull steering that, when compared to crossover steering, leaves something to be desired in a truck that gets used heavily off-road. That is to say that the steering box is connected to the axles’ outer knuckle using a short drag link that runs parallel to the driver-side framerail. The shortness of the drag link is really where the problem lies. As the suspension cycles, a short drag link sees greater changes in angularity and the distance between the pitman arm and steering arm on the knuckle can change quickly. That can cause the tires to turn in an unexpected way. Add suspension modifications and flex the truck out and this problem is amplified.

Slip Yoke Transfer Case Output

The best transfer cases are those made with cast iron gears and cases with fixed outputs. Unfortunately in this day and age those transfer cases are few and far between. Most modern transfer cases use aluminum housings and have adopted the slip yoke output at least on the rear output, and sometimes also on the front output. Moving the slip from the driveline to the transfer case is a cost-saving measure carried over from 2WD vehicles. On a 4WD though, they present a problem, particularly after the vehicle is lifted or modified with additional wheel travel. Perhaps the worst aspect of a slip yoke is that should the rear driveline break, all of the fluid will drain out of the transfer case unless you happen to have a plug handy. Or a Gatorade bottle cap, which works almost perfectly.

Aluminum Differential Housings

On more than one occasion we have seen an aluminum front differential housings fail, even in stock vehicles. The use of aluminum is another way that OEMs improve fuel economy through lighter components. While lighter than iron, aluminum is also more malleable and deflects enough to allow the pinion to part ways from the ring gear. Generally this is accompanied by a spectacular pop! and the rapid bleeding out of gear oil. Larger tires and locking differentials exacerbate the stresses on aluminum differential housings, making failure even more likely. For those reasons we look for 4x4s that have steel or iron front differential housings, and they are out there.

Harry Wagner, Freelancer

Transfer Case Pump Rub

The New Process transfer cases used in 1998-2007 GM trucks have a magnesium rear housing and an aluminum pump. Since the pump rides on the mainshaft it moves within the housing, wearing through the softer magnesium. If left unchecked for long enough a hole can wear through the housing and the fluid may leak out, potentially burning up the entire transfer case. While the aftermarket offers an inexpensive fix, you have to drop the transfer case and disassemble it to perform the installation.

47RE Transmission

TorqueFlight transmissions are completely reliable in the cars that they were originally designed for. The four-speed automatics have even been used in V-8 Jeeps without issue. But put them in a 7,000-pound truck and add an engine that is capable of making gobs of torque by just turning a few screws and you have a problem. So take whatever money you saved by hot-rodding your 12-valve Cummins engine on the cheap and spend it on a billet torque converter and upgraded internals for your transmission.

6.0L Diesel

International has built some legendary engines, but this was not one of them. The head bolts are undersized, and there are not enough of them to keep the heads from lifting off the block with the high cylinder pressure of the diesel engine. Add in emissions components like poorly engineered EGR coolers and the fact that you have to lift the cab from the chassis to remove the heads from the engine and you can see how easy it is to have $20,0000 wrapped up into your $10,000 truck. As prices of earlier 7.3L-equipped trucks keep rising, fixing a 6.0L becomes a more economical alternative.

Track Bar With TRE

Through 2006, coil-sprung Jeeps (and 2002 Dodge trucks) used a track bar with a tie-rod end at the frame end. Death wobble can have many causes, but one of the leading issues is when this tie-rod end wears out. Plus, it is difficult to diagnose. Fortunately later models came with a bushing at the frame end, and that bushing is easy to swap out for a higher-durometer polyurethane or even solid Delrin spacer. There are also brackets on the market to retrofit these new-style track bars onto older coil-sprung vehicles.

3-Piece Spark Plugs

This is the one that prompted the entire story. Ford three-valve Triton engines used long, three-piece spark plugs to reach the combustion chambers in the overhead cam engine. The problem is that carbon in the combustion chamber fuses the lower portion of the plug to the head, and it does not want to come out with the rest of the plug. Additionally, the plug threads are not cut very deeply into the cylinder heads, and under certain high-pressure conditions (like towing or hauling under a big load) the plugs could shoot right out of the heads, hitting the underside of the hood with a thunk. Ford replaced the three-piece plugs with one-piece plugs in 2008. Unfortunately it will not retrofit to the 2004-2007 heads, but Champion does make one-piece plugs for the earlier heads.

Honorable Mention

Dana 35 rear axle
Jeep CJ model 20 rear axle
GM 2.8L V-6 engine
Peugeot BA-10 transmission
Toyota 3.0L V-6 engine
JK front axlehousing
Land Rover 24-spline axles
Dodge Ram ball joints
Sealed automatic transmissions (no dipstick)

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