Gearboxes Through The Years
Over the years Jeep has offered some great transmissions that we wouldn’t hesitate to swap into anything. But along the way there have also been some horrible choices that just left us scratching our heads and wondering what in the world they were thinking when they decided to put that transmission in that Jeep.
Some of the poor choices were just epically bad, like the infamous Puke Goat (aka Peugeot), whereas some of them might have been OK transmissions, but just didn’t work well with other drivetrain options. Some would keep us from buying the Jeep that had them between its framerails, and some we’d just run it till it died.
So, follow along as we talk about why we hate them, what you can find them in, break down the gear ratios, and tell you how to identify them.
The AX5 is a five-speed manual transmission with overdrive that first showed up in the ’84 Cherokee behind the 2.5L four-cylinder. It was found only behind the four-cylinder and even behind that engine it had problems. Higher-mileage units are known for kicking out of gear. A common problem with this transmission almost regardless of mileage is the loss of the Overdrive gear. It is finicky about what gear oil you put in it and is known for losing syncros if you put in the original factory-spec oil. If you kill one you are better off swapping an AX15 into your Jeep than replacing or rebuilding the AX5.
Found in: ’84-’01 Cherokee; ’87-’04 Wrangler
Identify by: Two aluminum case halves (front and back) with steel plate in middle and 21-spline output.
Gear ratios: 3.92; 2.33; 1.44; 1.00; 0.85; 4.74 (Reverse)
This transmission has a special place in our hearts. Commonly known as the Peugeot BA 10/5, we’ve sold Jeeps in the past that had this transmission in them and we’ve not bought Jeeps because we didn’t want to swap it out. Maybe the French can keep this thing together, but we never could. Grinding, gears spit out through the case, loss of gears, and kicking out of gears are but some of the issues we’ve had and heard about with this transmission. Top that off with a less-than-wonderful internal hydraulic throwout bearing, and you are better off just tossing this thing in the nearest trash bin and swapping in just about anything else.
Found in: ’87-’89 XJ and MJ; ’87-’90 Wrangler
Identify by: Left and right clamshell-style case halves
Gear ratios: 3.39; 2.33; 1.44; 1.00; 0.79; 3.76 (Reverse)
When the NSG370 was first put in Wranglers for the ’05 model year, we were psyched. We were excited to lose that huge gap between Third, Fourth, and Fifth gears. We even got a Rubicon to test drive to Moab that year, and the next year we swapped one into an MJ. That said, today this transmission walks the walk of shame. We just haven’t had good luck keeping them alive, and they’re not as durable as the AX15s and NV3550s they replaced. Kicking out of First gear, losing gears, making noise, and so forth are pretty common. And we hear similar stories from friends and readers with these transmissions.
Found in: ’05-to-current Wranglers
Identify by: Integral bellhousing, the only six-speed behind six-cylinders.
Gear ratios: 4.46; 2.61; 1.72; 1.25; 1.00; 0.84; 4.06 (Reverse)
The SR4 was used behind both the four- and six-cylinder engines. It is not a strong transmission and has no Overdrive gear so we wouldn’t be in a big hurry to swap it into anything. It did live behind V-8s in cars, but in a Jeep it leaves a little to be desired. Bigger tires and more torque down low can cause problems for it in the Jeep. However, we wouldn’t pull it out until it started dying, which it would soon enough. Most often you will start having problems finding gears thanks to the offset shifter setup. Sometimes you will go for Fourth and find Second, sometimes going for First lands you in Reverse. You can pull the shifter housing and try to clean it, or adjust it but parts are getting harder to find.
Found in: ’80-’82 CJs
Identify by: An 11-bolt top cover in front, separate shifter cover to rear, all-aluminum case, 23-spline output.
Gear ratios: Four-cylinder: 4.07; 2.39; 1.49; 1.0; 3.95 (Reverse). Six-cylinder: 3.50; 2.21; 1.43; 1.00; 3.39 (Reverse)
T-4 and T-5
The T-4 and T-5 replaced the SR4 and were found behind both four- and six-cylinder engines. The T-4 is a four-speed while the T-5 is a five-speed. The T-5 is basically a slightly improved version of the SR4 with an Overdrive gear. It has tapered roller bearings on the input and output shafts but that rear-mounted shifter location gave it many of the same issues the SR4 eventually had. And while the First gear looks good on paper, the reality is that many of these Jeeps had differential gears in the 2.xx:1 ranges and that low First gear was needed just to get moving. Problems getting it into Reverse or downshifting after it’s in Fifth for a while are but a couple of the shifter-related issues.
Found in: ’82-’86 CJs
Identify by: 13-51 casting number (T-4); 13-52 casting number (T-5); 10-bolt top cover with rear-mounted and separate shifter cover, aluminum case
Gear ratios: 4.03; 2.37; 1.50; 1.00; (0.86 T-5 only); 3.76 (Reverse)
While the three-speed T-14 isn’t really in league with some of these other duds, it makes the list because of the way it was set up. The high First gear means a lot of clutch slip is required with even slightly bigger tires on a stock-height Jeep. Add to that the lackluster low range, and wheeling a Jeep with one of these transmissions can be difficult. It is considered a light-duty transmission so we would be leery of running it with huge tires or in a heavier Jeep. Bearing and synchro wear are not uncommon, resulting in grinding and popping out of gear. That said, while we’ve never killed one, we also wouldn’t swap this into anything.
Found in: ’67-’75 CJ-5, CJ-6, C-101, and C-104 with six-cylinders.
Identify by: Cast-in nubs on side of case that were for side-shifter car applications, six-bolt cast iron top cover.
Gear ratios: 3.10; 1.61; 1.00; 3.10 (Reverse)
While a solid little package, the three-speed T-150 was introduced at a time when Jeep was going to constantly higher and higher axle gears in an effort to meet CAFE standards. At the same time, engine output was going down due to increasingly stringent emissions controls. The two factors worked together to make the 2.99 First gear only moderately bearable with the factory-sized tires. At a time when 32-inch tires were possible on a stock-height Jeep and other vehicles were enjoying four-speed transmissions, this one didn’t last long. We wouldn’t swap it into anything if it would cost us money. In the long run, unless you are running super-high axle gears, it might be cheaper in burned clutches to just swap this one out for a four-speed.
Found in: ’76-’79 CJs
Identify by: eight-bolt cast-iron top cover, aluminum input bearing retainer, casting numbers 2603983 or 2603347.
Gear ratios: 2.99; 1.75; 1.00; 3.17 (Reverse)
While the three-speed T-86 might have been an improvement over the T-90 it replaced, it was put in heavier Jeeps with more powerful engines and really didn’t hold a candle to the T-14 that came shortly after its introduction. The only way the 2.79:1 First gear worked was because most Jeeps of the era had 3.73, 4.27, 4.88, or 5.38 gears in the differentials and relatively small tires. Of course, that meant spinning the heck out of the engine to put the Jeep on a highway and that can lead to all other kinds of issues. Basically if you’ve got one of these in your old Jeep with really low axle gears and it is working for you, keep it. If you decide you want to go faster than 50 mph on the highway, you’ll want to regear your axles—but then the pitiful non-synchronized First gear in this transmission will mean lots of clutch slipping to get the Jeep to move even in low range.
Found in: ’65-’67 CJs
Identify by: eight-bolt cast-iron top cover, T-86 or T-86AA cast into the side.
Gear ratios: 2.79; 1.68; 1.00; 3.79 (Reverse)
By and large, the automatic transmissions Jeep installed at the factory were decent units. And, if you keep water out of them and change the fluid most of them will last a very long time. However, the one glaring exception to that is the 42RLE. The torque converter is too loose to work well while wheeling, and the pump pickup gets uncovered and sucks air if the vehicle is attempting a steep climb, which can result in an inability to move under its own power. Even with moderately larger tires, it hunts between Third and Fourth gears on the highway—and it just isn’t that durable. We popped ours with barely 100,000 on it in an LJ. Once it made its way into the JK. We’ve gotten questions from lots of readers with similar experiences to ours.
Found in: ’03-’11 six-cylinder Wrangler; ’02-’13 six-cylinder gas Liberty
Identify by: Barcode on Bellhousing or PK number on rear flange.
Gear ratios: 2.84; 1.57; 1.00; 0.69; 2.21 (Reverse)