Replacement third-speed mainshaft gear for the NV4500 five-speed, for rebuilds where third is chipped, pitted, or jumping out under load.
Third gear jumping out on a hard pull, or a grind going into third that new synchro rings did not cure, is one of the most common NV4500 complaints on Dodge Ram 2500 and 3500 Cummins trucks and on Chevrolet and GMC heavy-duty pickups. This is the mainshaft third-speed gear for that five-speed, Motive Gear NV23712R, the same 29-tooth gear supplier catalogs list under number 23712.
The NV4500 is a constant-mesh box: every forward gear on the mainshaft is always turning with its mate on the countershaft, and a gear only drives the output when the synchronizer sleeve slides over its dog teeth and locks it to the shaft. Third gear rides on the mainshaft next to the 3-4 synchronizer hub and is driven by the countershaft third gear. When you pull the lever into third, the 3-4 sleeve engages the clutch teeth machined on this gear. That means the gear carries two wear surfaces that matter: the helical drive teeth and the dog (clutch) teeth the sleeve locks onto.
Jumping out of gear happens when the dog teeth on the gear and sleeve wear from square to tapered. Every time the driveline loads and unloads, that taper pushes the sleeve back off the gear. Synchro rings only help the shift; they cannot hold a worn engagement, which is why rings alone often fail to fix it.
With the case split, look at the clutch teeth on the gear under good light. Rounded or ramped tooth ends, or a shiny wear step on one side, mean the gear and usually the sleeve need replacing. Then count the teeth. This gear has 29 teeth and is the version for 5.61:1 first-gear boxes. Early GM trucks with the 6.34:1 low first gear use a different 28-tooth third gear, and mixing them is not possible because the countershaft gear has to match. Our manual transmission repair cost guide helps decide between a rebuild and a swap, and the NV4500 rebuild cost breakdown shows what usually gets replaced alongside.
The listing covers Dodge Ram 2500 and 3500 from 1992 to 2005 and Chevrolet and GMC 2500 and 3500 from 1992 to 2001. Supplier catalogs describe the 29-tooth 23712 gear as fitting all Dodge NV4500 boxes and GM units with the 5.61 ratio. If your GM truck is an early 6.34-ratio box, it needs the 28-tooth gear instead. Count the teeth on your old gear, check the first-gear ratio on the case tag, or send us your year and VIN and we will confirm before it ships. More NV4500 parts are on our manual transmission hard parts page.
| Part Number | |
| Brand | |
| Position | |
| Transmission | |
| Fitment | |
| Exterior | |
| Package Dimensions | |
| Warranty |
Doing this repair right usually means replacing these at the same time. Same transmission, ships together.
This NV23712R is the 29-tooth gear for 5.61-ratio boxes, which covers all Dodge NV4500s. Early GM trucks with a 6.34 low first gear use a 28-tooth gear. Count the teeth on your old gear or send us your year and VIN.
Usually not. Popping out comes from tapered dog teeth on the gear and sleeve. Rings help the shift but cannot hold a worn engagement, so the gear and often the 3-4 sleeve need replacing.
The third-gear needle bearing, the thrust washer, the synchro rings and the 3-4 sleeve if its teeth are worn. Inspect the mainshaft journal too.
No. Third gear lives on the mainshaft between the 3-4 hub and the countershaft, so the transmission has to come out and the mainshaft has to be removed.
Dodge NV4500s take a 75W-85 GL-4 manual transmission lubricant; GM NV4500s take Synchromesh-type fluid. Avoid GL-5 hypoid gear oil.
