• JP Magazine
  • Dirt Sports + Off-Road
  • 4-Wheel & Off-Road
  • Four Wheeler

Rebuilding an NV4500 Manual Transmission

Posted in How To: Transmission Drivetrain on August 1, 2006 Comment (0)
Share this
Rebuilding an NV4500 Manual Transmission

The NV4500 five-speed transmission in our high-mileage diesel-powered '95 Chevy 2500 pickup was exhibiting some bad behavior. Part of the problem was that the clutch wasn't releasing completely when the clutch pedal was depressed. This made selecting First Gear a grinding challenge. Eventually, the main driver of this rig quit using the clutch during standard gearshifts because it wasn't disengaging anyway. Another problem was that as the transmission began to age, it began to leak. In a pinch, someone ignored the requirement of Castrol Syntorq LT synthetic oil (or equivalent) and fed it petroleum-based oil. Things quickly went from bad to worse as the synchronizer rings objected to the wrong oil. It wasn't long before the trans was becoming very hard to live with.

Since we're not manual-transmission rebuild experts, we took the truck to someone who is. Larry's Automotive is located on the outskirts of Rock City, Illinois. The owner, Rick Jacobson, has been wrenching on trucks and cars since he was 12 years old, so he knows his stuff. His knowledge is vast and varied, and his resume includes a couple of years fabricating and wrenching for noted off-road racer Scott Taylor. Jacobson and his team of technicians not only have a working knowledge of vehicles (including heavy trucks) from end to end, they also know the intricate workings of both automatic and manual transmissions. Best of all, Jacobson is a 'wheeler, so he's intimately familiar with how we use our rigs.

Jacobson and his crew removed our crusty trans and then they totally disassembled it and gave us the tally of what bad things were lurking inside. The list of parts we needed was lengthy. Normally, they'd just order the parts and complete the rebuild in a few days, but we wanted to utilize specific companies, so we hit the phone.

Here's our Larry's Automotive-rebuilt trans ready to reinstall in our Chevy pickup. The folks at RSG note that one of the important things to remember about the NV4500 is that it requires Castrol Syntorq LT synthetic oil (or equivalent--RSG has an equivalent that they sell under their own brand name) due to the synchronizer material and design, as well as the large amount of gear teeth in mesh in this unit. Using standard gear oil will cause the NV4500 to shift poorly and eventually fail. Here's our Larry's Automotive-rebuilt trans ready to reinstall in our Chevy pickup. The folks at RSG note that one of the important things to remember about the NV4500 is that it requires Castrol Syntorq LT synthetic oil (or equivalent--RSG has an equivalent that they sell under their own brand name) due to the synchronizer material and design, as well as the large amount of gear teeth in mesh in this unit. Using standard gear oil will cause the NV4500 to shift poorly and eventually fail.

The first place we called was Rockland Standard Gear. RSG, as they're called, has been in business for more than 25 years, and they're one of the largest suppliers of manual transmission and transfer-case parts in the country. Here's some mind-boggling facts: They are the only aftermarket company ever selected to rebuild transmissions for ZF; they are one of five Master distributors for Borg-Warner transfer-case parts; they are one of 10 Elite distributors for Tremec; and they are a major distributor for New Venture Gear. Needless to say, we knew they could handle our NV4500 needs.

Since the clutch in our Chevy was original, our second call was to Centerforce. The company has been around since the early '80s and was started by Bill Hays, the founder of Hays' Clutches in the 1950s. Bill Hays designed and patented the Centerforce Weighted Clutch System, which increases pressure-plate clamping force while maintaining easy pedal effort. Further, his new design solved the sticking-over-center problem of diaphragm clutches. Centerforce offers a full range of clutches and flywheels for a number of applications.

What follows is a synopsis of the major items addressed by the team at Larry's Automotive. It'll give you a good idea of what you can expect if you plan on having your NV4500 rebuilt.

Our input shaft (left) was showing significant wear at the point where the pilot bearing contacted the shaft, so we installed a new shaft from RSG. Jacobson always inspects the entire shaft for any signs of wear. Surprisingly, the gear on the other end (which is actually Fourth Gear) was in pretty good shape. Our input shaft (left) was showing significant wear at the point where the pilot bearing contacted the shaft, so we installed a new shaft from RSG. Jacobson always inspects the entire shaft for any signs of wear. Surprisingly, the gear on the other end (which is actually Fourth Gear) was in pretty good shape.
On the left you can see our old synchro ring for the Third to Fourth gearshift, pictured next to the new RSG synchro ring. All synchro rings are a common wear item on manual transmissions. When these wear, they basically lose friction and the result is grinding when shifting. All of our synchros were toast, so they were replaced with new units from RSG. The NV4500 uses two kinds of synchros: multi-piece and single-piece. On the left you can see our old synchro ring for the Third to Fourth gearshift, pictured next to the new RSG synchro ring. All synchro rings are a common wear item on manual transmissions. When these wear, they basically lose friction and the result is grinding when shifting. All of our synchros were toast, so they were replaced with new units from RSG. The NV4500 uses two kinds of synchros: multi-piece and single-piece.
This is our Second Gear (left) pictured next to our new RSG Second Gear. Jacobson found that the drive ring on the First to Second Gear single-piece synchro was worn into the teeth on Second Gear. Also, where the shift collar engages into the teeth of the gear, the teeth were chipped. This was most likely due to forcing the unit into gear before the synchro had caught up to the gear. This is our Second Gear (left) pictured next to our new RSG Second Gear. Jacobson found that the drive ring on the First to Second Gear single-piece synchro was worn into the teeth on Second Gear. Also, where the shift collar engages into the teeth of the gear, the teeth were chipped. This was most likely due to forcing the unit into gear before the synchro had caught up to the gear.
Here you can see Fifth Gear. Our old one is on the left and the new RSG unit is on the right. Ours clearly showed wear from pulling heavy loads. The hard surface was worn off the teeth and the inside splines also showed wear. Here you can see Fifth Gear. Our old one is on the left and the new RSG unit is on the right. Ours clearly showed wear from pulling heavy loads. The hard surface was worn off the teeth and the inside splines also showed wear.
On the left you can see an example of a tapered roller bearing that we removed from our trans. These are critical components that must be inspected, but they don't always need to be replaced. All of our bearings, with the exception of the caged needle bearings, showed gray areas indicating wear, as well as pitting. New tapered roller bearings were included in RSG's Bearing and Seal kit. On the left you can see an example of a tapered roller bearing that we removed from our trans. These are critical components that must be inspected, but they don't always need to be replaced. All of our bearings, with the exception of the caged needle bearings, showed gray areas indicating wear, as well as pitting. New tapered roller bearings were included in RSG's Bearing and Seal kit.
RSG sent us a remanufactured shift tower (right). Our shift forks showed a lot of wear, which often results in them not engaging the shift collar far enough into the gear. This can cause the trans to pop out of gear. Jacobson normally inspects the shift tower for a variety of wear items that can make a trans operate poorly. RSG sent us a remanufactured shift tower (right). Our shift forks showed a lot of wear, which often results in them not engaging the shift collar far enough into the gear. This can cause the trans to pop out of gear. Jacobson normally inspects the shift tower for a variety of wear items that can make a trans operate poorly.
This is the front bearing retainer, which holds the front main bearing in, and it's what the throwout bearing rides on. After a thorough inspection, Jacobson gave ours a clean bill of health. This is the front bearing retainer, which holds the front main bearing in, and it's what the throwout bearing rides on. After a thorough inspection, Jacobson gave ours a clean bill of health.
After inspecting the bearing surfaces, splines, and Fifth Gear nut retaining threads, Jacobson also found that our mainshaft was in great shape. After inspecting the bearing surfaces, splines, and Fifth Gear nut retaining threads, Jacobson also found that our mainshaft was in great shape.
As we started reassembling our trans, Jacobson pointed out that all new items such as snap rings are included in the RSG small parts kit and they must be installed. Here you can see the shaft with First and Second Gear and other components installed. Jacobson is installing the pin that locks in a thrust washer. Part of its duties include keeping Second Gear from turning against Third Gear. There are three pins like this in the NV4500. As we started reassembling our trans, Jacobson pointed out that all new items such as snap rings are included in the RSG small parts kit and they must be installed. Here you can see the shaft with First and Second Gear and other components installed. Jacobson is installing the pin that locks in a thrust washer. Part of its duties include keeping Second Gear from turning against Third Gear. There are three pins like this in the NV4500.
Here you can see the mainshaft with everything mocked up but without the bearings pressed on in their finished position. During reassembly, Jacobson says it's important to ensure that the synchros and slide collars aren't installed backwards. All transmissions, especially the NV3500, will have all kinds of issues if these parts are reassembled incorrectly. Here you can see the mainshaft with everything mocked up but without the bearings pressed on in their finished position. During reassembly, Jacobson says it's important to ensure that the synchros and slide collars aren't installed backwards. All transmissions, especially the NV3500, will have all kinds of issues if these parts are reassembled incorrectly.
Surprisingly, our countershaft was in good shape. We just installed a new bearing and overdrive synchro ring. This shaft carries a load in all gears except Fourth Gear (Fourth Gear is the 1.00:1 gear, so it doesn't route power through the countershaft). Surprisingly, our countershaft was in good shape. We just installed a new bearing and overdrive synchro ring. This shaft carries a load in all gears except Fourth Gear (Fourth Gear is the 1.00:1 gear, so it doesn't route power through the countershaft).
It's important to correctly install the rear bearing retainer (shown), because it also holds the reverse idler gearshaft in place. If the reverse idler gearshaft is incorrectly installed, you can bend the bearing retainer and even possibly crack the transmission case. It's important to correctly install the rear bearing retainer (shown), because it also holds the reverse idler gearshaft in place. If the reverse idler gearshaft is incorrectly installed, you can bend the bearing retainer and even possibly crack the transmission case.
These shims go between the rear bearing retainer and the bearing to provide proper endplay for the mainshaft (the countershaft also uses shims to set endplay). After installing new bearings, the endplay may change, so endplay must be measured with a dial indicator. New shims are included in the RSG small parts kit. These shims go between the rear bearing retainer and the bearing to provide proper endplay for the mainshaft (the countershaft also uses shims to set endplay). After installing new bearings, the endplay may change, so endplay must be measured with a dial indicator. New shims are included in the RSG small parts kit.
Here you can see our dual mass flywheel after it was resurfaced. Before it was sent out, Jacobson gave it a thorough inspection that included looking for heat cracks and inspecting the springs to make sure they were intact and in good shape. Overall, our flywheel was in good shape, especially considering the high mileage and abuse it has endured. Here you can see our dual mass flywheel after it was resurfaced. Before it was sent out, Jacobson gave it a thorough inspection that included looking for heat cracks and inspecting the springs to make sure they were intact and in good shape. Overall, our flywheel was in good shape, especially considering the high mileage and abuse it has endured.
With almost 100,000 miles on the odometer, it came as no surprise that out factory clutch was shot, so we installed a new Centerforce Dual Friction clutch assembly. This bad boy generates up to a 90 percent increase in holding capacity over the stock clutch. Even with this vastly increased holding capacity, it provides smooth engagement and light pedal pressure. Centerforce also sent a clutch pilot tool and a clutch release (throwout) bearing. With almost 100,000 miles on the odometer, it came as no surprise that out factory clutch was shot, so we installed a new Centerforce Dual Friction clutch assembly. This bad boy generates up to a 90 percent increase in holding capacity over the stock clutch. Even with this vastly increased holding capacity, it provides smooth engagement and light pedal pressure. Centerforce also sent a clutch pilot tool and a clutch release (throwout) bearing.
The technicians at Larry's Automotive did battle with our pilot bearing in an effort to remove it from the engine block. Part of the problem was that the input shaft had severely worn the pilot bearing, so there was little for the puller to latch onto. This is a common issue with high-mileage manual-transmission vehicles. The technicians at Larry's Automotive did battle with our pilot bearing in an effort to remove it from the engine block. Part of the problem was that the input shaft had severely worn the pilot bearing, so there was little for the puller to latch onto. This is a common issue with high-mileage manual-transmission vehicles.
Fluid leakage and a dragging clutch forced us to install a new clutch slave. The leakage problem was solved, but not the dragging. Jacobson and his crew ended up lengthening the stock clutch linkage by about 0.25 inch to effectively raise the clutch pedal from the floor when depressed. This allowed the clutch to totally disengage. Fluid leakage and a dragging clutch forced us to install a new clutch slave. The leakage problem was solved, but not the dragging. Jacobson and his crew ended up lengthening the stock clutch linkage by about 0.25 inch to effectively raise the clutch pedal from the floor when depressed. This allowed the clutch to totally disengage.
A busy shop and our tight deadlines meant we had to install the trans A busy shop and our tight deadlines meant we had to install the trans "old-school" without the truck on a hoist. First, the clutch and bellhousing were installed, then the trans, and then the transfer case and driveshafts. Our first drive revealed a perfect shifting transmission, and thanks to the creativity of the guys at Larry's Automotive, we no longer have a dragging clutch.

Fifth Gear And The Dodge NV4500.
Having problems with Fifth Gear in your Dodge NV4500? There is a fix. According to the folks at Rockland Standard Gear, the Dodge NV4500 had a design defect in the splines on the mainshaft Fifth Gear. The splines were not long enough and they were manufactured with an incorrect angle. This caused a slight creep of the Fifth Gear on the mainshaft due to throttle changes, which resulted in many of the units having the Fifth Gear loosen its retaining nut. This allowed the gear to move out of position on the mainshaft and cease to function. If you have a Dodge NV4500 with this problem, you have options. One is to purchase the kit that RSG offers. It includes a gear and mainshaft that utilize split-ring washers under a locknut to retain the gear under thrust loads. It also has redesigned full-length splines on the gear and corrected spline angles.

Related Articles

Comments

Connect With Us

Newsletter Sign Up

Subscribe to the Magazine

Sponsored Content