Dana 300
Problems & Rebuild Cost

The Dana 300 went into the Jeep CJ-5, CJ-7, and CJ-8 Scrambler from 1980 through 1986. It replaced the Dana 20 and it is the reason so many people still swap a Dana 300 into Wranglers, Samurais, and early Broncos. It is a part-time, gear-driven case with no chain, a 2.62:1 low range, and a very simple internal layout: an input gear, an intermediate (idler) gear cluster on a fixed shaft, a rear output with a sliding range gear, and a front output with a sliding clutch.

Because there is no chain to stretch and no oil pump to fail, a Dana 300 that has been kept full of oil will usually outlive the Jeep it came in. The problems we see are almost always leaks, worn shifting parts, and bearings that were run low on oil. Here is what goes wrong, in order of how often we see it.

The Most Common Dana 300 Problems

1. Intermediate shaft O-ring leaks

The intermediate shaft is pressed through the case and sealed with O-rings at each end. After 35-plus years those O-rings are hard, and the case weeps oil from around the shaft ends. Left alone, the level drops until the needle bearings inside the intermediate gear run dry and start to gall the shaft. If your case is wet around the shaft bore, plan on a new shaft and O-rings rather than just O-rings; a grooved shaft will chew new seals up quickly.

2. Front and rear output seal leaks

Both output seals ride on the yokes. A grooved yoke will leak no matter how good the seal is, so check the seal surface with a fingernail before you buy parts. A yoke sleeve or a new yoke is cheap insurance. The rear output also has a speedometer drive gear behind the seal, so a leak back there can also take out your speedo.

3. Popping out of low range

This is the classic Dana 300 complaint. The usual causes, in order: worn or bent factory shift linkage, a broken engine or transmission mount that lets the drivetrain move away from the shifter, a weak detent spring or worn detent ball, and finally worn engagement teeth on the range gear. The factory linkage pivots on the frame and transmission and every bushing in it wears. Fix the mounts and the linkage before you open the case. Our popping out of 4-Low guide walks the full check.

4. Output bearing wear

A Dana 300 that was run low eventually shows a growl that changes with road speed, not engine speed. Rear output bearings go first because they carry the driveshaft load full time. Front output bearings usually survive unless the case sat with water in it.

5. Water intrusion

CJs get driven through water. The case breathes through a small vent, and if the vent line is missing or kinked, the case pulls water in when it cools. Milky oil means a teardown, not a fluid change, because the needle bearings will rust in weeks.

6. Shift rail and fork wear

Fork pads wear and the rails can stick from corrosion. A stiff shifter that suddenly gets loose usually means a worn fork, and a shifter that will not go into 4WD at all is often a stuck rail or a seized linkage pivot, not an internal failure.

Dana 300 Rebuild Cost

Used Dana 300 prices climbed a lot once swap demand took off, so for most owners a rebuild of the case you have is cheaper than chasing a "good used one" that will need the same bearings anyway. The case comes out of a CJ in an afternoon with basic tools, and the rebuild itself is one of the friendlier jobs in the drivetrain world: no special pullers beyond a bearing separator and a press.

Rebuild Tips From the Bench

• Replace the intermediate shaft, not just the O-rings, if there is any wear step where the needles ride.
• Count the needles before you take the intermediate gear apart. A thick grease or assembly lube holds them in place during reassembly. A dummy shaft makes it far easier.
• Check the input gear spline before you order parts. CJ cases are mostly 23-spline input, but swaps behind other transmissions often use a different input gear, and the bearing is not always the same.
• Inspect the range gear teeth for rounded or tapered engagement edges. Tapered teeth push the gear out of mesh under load and no new detent spring will cure that.
• Use the correct oil. The Dana 300 takes gear oil, not ATF. Check the fill plug spec for your case and fill to the bottom of the fill hole.

Upgrades Worth the Money

Twin-stick shifter. Replacing the factory linkage with a twin-stick setup fixes the worn linkage problem permanently and gives you front-wheel-drive low for tight turns on the trail. It is the single best Dana 300 upgrade for a Jeep that goes off-road.

4:1 low range. The stock 2.62:1 is decent, but a 4:1 kit transforms a CJ on rocks. These kits replace the reduction gearing and need a revised bottom cover plate to clear the larger gear, which is exactly what our Dana 300 cover plate for the Lomax 4:1 kit is for.

Rear output upgrade. If you are running a short rear driveshaft on a lifted CJ, a fixed yoke and CV driveshaft setup cuts vibration and ends the rear seal leaks.

For background on why gear cases like the Dana 300 hold up better than the chain cases that replaced them, read chain drive vs gear drive transfer cases.

FAQ

What years did Jeep use the Dana 300?

The Dana 300 was used in the 1980 through 1986 Jeep CJ-5, CJ-7, and CJ-8 Scrambler. It replaced the Dana 20 and was replaced by the NP207 and NP231 chain-drive cases in the Wrangler.

Is the Dana 300 gear driven or chain driven?

Gear driven. Power goes from the input gear through an intermediate gear cluster to the outputs. There is no chain, which is a big reason it is popular for swaps.

What is the Dana 300 low range ratio?

The stock low range is 2.62:1. Aftermarket 4:1 kits are available and require a revised bottom cover plate to clear the larger gear.

Why does my Dana 300 pop out of low?

Most often worn factory shift linkage or broken engine and transmission mounts. After that, check the detent spring and ball, then the range gear engagement teeth.

How much does a Dana 300 rebuild cost?

A DIY bearing and seal rebuild is typically $150 to $300 in parts. A shop rebuild usually runs $600 to $1,100 depending on what is worn.