(Not So) Modern Jeep Problems

The early closed-knuckle front axles (Dana 25 from 1941-1959, Dana 27 from 1960-1971, and FSJ Dana 44s up to 1973) don’t hold up very well to 33-35s if a locker is used. Early Dana 25s had either a Bendix or Rzeppa joint until around 1950, when Spicer-style joints were used. Regardless of the joint style, all Dana 25 and Dana 27 have small 1.16-inch, 10-spline shafts. The Dana 27 has 10 bolts holding the ring gear to the carrier verses the Dana 25’s eight bolts and a slightly beefier centersection where the tubes press in. The open-knuckle Dana 30 was used in ’72-’86 Jeeps. Dana 30s run 1.16-inch shafts, but they’re of slightly better material and have stronger 27-spline inners.

Closed-knuckle front axles used kingpin bearings instead of ball joints. The kingpins can wear out and cause death wobble and poor steering. Also, the spindle is affixed to the soft cast knuckle material with screw-in bolts. Removing the bolts and replacing them with graded button-head screws (see Jp magazine, “Disc Swap Plus,” May ‘11) makes for a much stronger attachment point and will prevent the spindle from ripping away from the knuckle with real off-road use.

Disc brakes weren’t standard on Jeeps until 1977. Drum-brake-equipped axles use a six-bolt, external-body hub (shown). With the exception of FSJ Dana 44 disc brake axles, most Jeep disc-brake-equipped axles use a five-bolt, external-body hub. Both six- and five-bolt hubs employed bolts with locking tabs to retain the locking hub dial to the hub body. With heavy use, the hub bolts work themselves loose and then the hub body explodes. Replacing the bolts with studs helps with hub body retention. If you have a drum-brake Dana 30, you can swap components from a ’60s or ’70s drum-brake Bronco Dana 44 front axle to get internal body hubs. You’ll need the Bronco stub shafts, spindles, and hubs. It’s a cheap and easy way to get internal-body hubs on a drum-brake Dana 30. We haven’t tried to see if the kingpin Dana 30 Bronco stuff will fit on a Dana 25 or Dana 27, but we think it should.

Willys pickups and Wagons used a driver-side upper kingpin with a cast-in steering arm. The steering arm exerts a lot of leverage on the bolts holding it to the soft cast-iron knuckle. Replacing the kingpin bolts with studs will help prevent the bolts loosening and damaging the knuckle, but periodically checking the fasteners can help prevent a major trail repair.

With the exception of the ’70½-’75 CJs and Jeepsters, all CJ, Willys pickups, Wagons, Jeepsters, and pre-’70 FSJs had weak two-piece rear shafts. A nut held a tapered outer portion of the rear shaft to the drive flange. If the nut loosened, the hub could walk off the shaft and sheer its Woodruff key, ending your outing. Early Dana 41 and ’49-’60 Dana 44 rear axles used 10-spline shafts while the late ’60-early ’70 Danas had 19-spline shafts. The 1970½-1975s got one-piece 30-spline shafts. You can’t put the one-piece shafts in the two-piece Dana 44 rears, but you can buy full-float conversion kits to change your 10- or 19-spline semi-float Dana 44 rear to full-float 30-spline from ATV Manufacturing. Don’t forget you’ll need to change the diff carrier. If you have a ’76-’85 CJ, you can upgrade your Model 20 two-piece shafts to one-piece with conversion shafts from a variety of manufacturers.

Technically, it’s not your drivetrain, but we’re betting you’re gonna want to steer. The early CJ steering systems were a Rube Goldberg-esque assortment of pivots and levers. The steering boxes, bellcrank, and tie rod ends all wore out. Replacement components are still available and it’s all fairly rebuild-friendly stuff. When used with the stock-height suspension the Ross cam-and-lever steering setup provides pretty good mechanical advantage to turn the wheels off-road.

Everybody wants a T-98 or T-18, but most stock three- and four-speed manual transmissions that found their way behind four- or six-cylinder Jeep powerplants weren’t too bad. At around 2.80:1-3.40:1 the First gear in most is adequate. Some exhibit poor on-road performance like jumping out of gear or grinding between gear changes, but normally that’s from wear-and-tear and no inherent design flaw. The T-90, T-14, T-15, T-150, and T-176 are but a few examples of underrated, but good transmissions. Most are easily rebuilt at home and a simple set of synchros and bearings can toss decades of life back into these cast-iron cases. Check ATV Manufacturing and Novak Conversions for top-quality rebuild kits and components.

One bad thing about wheeling vintage Jeeps is that they often suffered decades of shoddy maintenance. If you’re experiencing chatter or odd noises as you let the clutch out, you may want to check the case for cracks or missing ears. Cast iron is relatively soft stuff and worn or broken tranny mounts, motor mounts, or cracked frames can add lots of stress to fragile transmissions and T-case cases.

Gear-driven Jeep T-cases like the Spicer 18, Dana 20, and Dana 300 have an inspection cover at the bottom of the case. If you hear odd noises coming from your T-case, you can often drop the inspection cover or (on a Spicer 18) remove the PTO cover plate to inspect the gears for missing or chipped teeth. As soon as the intermediate shaft or bearings begin to wear, the gears can run cockeyed and chipped or broken teeth are often the result. Again, rebuild components for these T-cases are cheap to buy and relatively easy to install. When properly rebuilt, these iron T-cases are plenty tough for moderate-to-heavy off-road use.

Shown is a genuine Warn Overdrive, but modern versions are available from Advance Adapters and ATV Manufacturing. These overdrives are incredibly strong for their size, but most were sent to their doom from improper installation. Shown at bottom is the special drive nut (star-shaped center) and four-corner snap ring that secures the bowl gear to the transmission output shaft. After torquing the drive nut to 100-120 lb-ft, you need to install the special snap ring. Most installers booger up the drive nut or don’t get the snap ring correctly in its bore, which ultimately allows the bowl gear to back off the output shaft, destroying gear teeth as it goes.

This isn’t so much an inherent problem as it is a tip, but save everything usable. We used to keep a stash of Spicer 18 parts on hand and found at least once a year the need to visit one of these boxes for an output shaft, yoke, gear, or odd component we never thought we’d need. New replacement or used take-out parts can often be found for sale on the web, but you’ll often discover the broken part the night before a big trip, so having spares on-hand helps maintain sanity for the vintage Jeeper.

The Spicer 18 originally came equipped with a drum-style parking brake on the rear output. The trouble is, over years the driveshaft yoke studs can flex and wallow the bores of the cast iron into which they’re pressed. When you try to take the rear shaft out for a field fix, the studs often spin inside the brake drum backing plate and the shaft can’t be removed. You can either tack-weld the studs or replace them with hex-head bolts that won’t spin as the nuts are removed. Also, in this photo you can barely see the Advance Adapters chain clutch linkage. It’s way better off-road than the factory cable- or rod-type linkage and still works when the chassis is all flexed up.