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 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.
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. | 
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. |
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. | 
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. |