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Late Model NV3550 Transmission Rebuild - Jp Magazine

Pete Trasborg Brand Manager, Jp

We knew something was wrong, but not how to fix it. We had lost Reverse in our ’01 Wrangler’s NV3550 and the forward gears were hard to shift. So, we stopped driving the Jeep and started looking for answers. Then Reverse came back on out of the blue, and we were really confused. We knew from the clutch pedal travel that we were getting down to the end of the clutch’s life, but with more than 142,000 miles on the original clutch and lots of off-road abuse, that was to be expected. Our B&M shifter was getting kind of loose and it was getting hard to find the gears. And, occasionally, when we did find the gears and put it in Reverse, it would kick back out.

five Speed Overhaul Part 1 jeep In Shop Photo 39838960

Normally when we start having transmission issues, we start looking for a better tranny that whatever we have. We looked at an NV4500, but it’s just too big and heavy for this Jeep. We also looked at Rockland Standard Gear’s Terminator bolt-in NV3550 replacement. But in the end our curiosity got the better of us, and we decided to dive into our NV3550 to see what was wrong.

We first attacked the problem ourselves trying to fix it by addressing easy stuff, and quickly learned we weren’t going to have any luck doing so at home. We are no strangers to transmission rebuilds and clutch swaps, but we didn’t just want to throw a ton of money at it possibly replacing things we didn’t have to. So, we got some expert advice and troubleshooting tips from professionals before finally figuring out the problem wasn’t just in the clutch or the shifter, but inside the transmission itself. To finally get the transmission back to good working order, we took a trip farther down the rabbit hole than we originally planned, but in the end we got ’er dun. We picked up a lot of cool information—not only about the NV3550 in particular, but also about clutches and transmissions and assembly procedures in general. In order to bring all the info to you, we split the story up into two parts. Tune in next time when we’ll reassemble the tranny and put it back in the Jeep.

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Our transmission has always been difficult to shift and Trasborg just kind of figured that was normal. However, after Hazel drove it, the orders came down from on high, “Something is wrong, figure out what it is and fix it.” We drained the tranny fluid and didn’t see any chunks or silver and gold, so we figured the synchros were OK and the bearings were probably good. We then pulled the B&M shifter off and found that after so many miles of pushing a bad transmission, the shifter was a bit worse for the wear.

We like the short throw of the B&M shifter. We figure that had it not been for internal problems with the transmission, it would have lasted way longer, so we ordered another one. In the 11 years since we installed the old one, B&M modified the design a bit. The base of the new shifter has the same CNC-machined and anodized aluminum, but the stainless steel stick was changed. B&M tells us they changed the location and angle of the bend between our old shifter (top) and the new one (bottom) for better floor pan and console clearance. With our 1-inch-lift motor mounts and Tummy Tucker skid, our old shifter was indeed hitting the console. The new one doesn’t.

The new shifter didn’t entirely solve the problem, and we started thinking the hard shifting and occasional grinding might be clutch related. We took the Jeep to Jeeps R Us in Laguna Niguel, California. It was quickly determined there was no air in the clutch lines which pointed to internal transmission problems. An easy way to test this is to pull the shifter off the tranny, press the clutch, and try to shift it with a large screwdriver or prybar. With the tranny still very hard to shift, we stopped lying to ourselves and admitted it was time for the transmission professionals.

We took the Jeep to Orange County Transmission. After a test drive, the problem was deemed internal, with the shift rail the prime suspect. The company doesn’t like aftermarket rebuild kits, as they are often missing parts or don’t quite fit right. We got a genuine factory rebuild kit thanks to a good parts guy at our dealership who tracked down the elusive PN R0035503AA Mopar rebuild kit. It includes all the internal wear items as well as seals. Armed with that part number you should have no problem finding a rebuild kit of your own.

We ordered a clutch kit from Spec clutches that included a throwout bearing, pilot bearing, flywheel, pressure plate, clutch disc, and new flywheel, and new pressure plate hardware. We noticed the clutch assembly arrived bolted to the new flywheel, which we had never seen before. Dave Dibs at Orange County Transmissions pointed out that the assembly was balanced. He says on average one out of five clutches that he sees are about 8 grams out of balance and that causes first-order vibrations. He suggests balancing clutches to flywheels for everything he works on, even Jeeps.

Once the transmission was out, we were able to see that our pilot bearing was fried, and from the looks of things, had been for a while. Dibs opened Orange County Transmissions over 30 years ago and that experience told him that what you see here is a pilot bearing that died about 10,000 miles ago. We prefer pilot bearings to pilot bushings as we feel they last longer in a dirty environment. So, we were happy to see that the Spec kit included an actual bearing and not just a bushing.

If you are thinking about building a metal work table for your home shop, you might want to steal this idea. Orange County Transmission’s work tables are �-inch-thick steel and feature built-in drainage. By slightly angling the table towards the drain and angling the drain slightly to a hose that dumps to a 5-gallon bucket, they are able to open any nasty, sludge-filled thing and not worry about what is in it.

Once the front half of the transmission is pulled away, you will need to use a drift to remove the shifter mount. The shift rail passes through a cast-in section of the rear half of the transmission and the assembly won’t come out with the shifter cup roll pin still in the rail.

When you pull the rear seal out of the case, you want to be very careful not to damage the aluminum housing or the transmission won’t seal after putting it back together. Dibs uses this slide hammer. On the seal end, the slide hammer screws into the rubber of the seal. You can make something similar at home using a screw and some rope. Don’t worry if the screw pulls out of the seal a few times, it happens even with the high-end tool. Be careful not to screw too deep into the seal, as there is a bearing behind it that has to come out the front of the transmission.

If you are like us, and have no friends, you are screwed when you get to this part. One guys needs to hold the mainshaft and countershaft while the other guy gently taps on the mainshaft to get the whole assembly out of the case. When we say whole assembly, we mean mainshaft and gears, countershaft and gears, and shift rail and shift forks.

Dibs was able to tell that the Spec clutch was balanced by the machining on the back of the flywheel (arrows). We like heavy flywheels because the extra inertia makes wheeling in rocks easier, so we were alarmed that the new flywheel was lighter than the factory one. The Spec flywheel is 23.5 pounds and the factory flywheel 27.5 pounds. Then we realized that the Spec clutch disc and pressure plate weighs 22.5 pounds and the stock only 18.5 pounds. That means the overall package is the same weight as the factory setup was, just with more beef in the pressure plate assembly.

As soon as the assembly was out of the case, it was apparent what the problem was. That chunk of aluminum (arrow) is half of a shift fork. The other half was still attached to the shift rail. We figured it was the Reverse fork, and we were half right. Turns out it is the Fifth gear and Reverse shift fork. If we were doing this on our own, this would have put a big damper on things. Fortunately, Dibs knew exactly what other parts needed to be checked, and where to get replacements. More on the fix next time.

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Late Model NV3550 Transmission Rebuild - Jp Magazine

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