need help- nv3500 build

[jamon8]

I have a nv3500 in my truck and I think that the 3-4 syncro is going bad and I want to rebuild

I have no idea what to buy and what to replace to build this tranny

anyone have any good advise

[ChevyTech]

There are four design levels of this transmission.

Due to the changes in these transmissions many parts are not interchangeable.

On the early units, when the bearing on the input shaft fails, one of the most common complaints is that it makes it hard to get into 4th gear.

What year tranny do you have?

[jamon8]

it came out of a 89 1/2 ton

it is starting to get hard to put it in 3rd as well

also the trans seems to whine in all gears. this might be normal

[ChevyTech]

The transmission whine is another bad sign as these transmissions are fairly quiet.

Your 1989 (if it has the origional tranny) is an early transmission with first type of input bearing design.

NOTE: this transmission should not have 80W-90 fluid it. 80W-90 is to thick and will cause problems.

There are two designs for the input shaft, input shaft bearings and main shaft bearings. The first design, which documentation will show as 1988-1990, had a ball bearing and a roller bearing behind it. The second design only has a ball bearing but it was a much larger bearing. The first design bearings were more prone to fail. They were failing when these trucks were under warranty with very low miles on them.


This site, with illustrations, is about the bearing difference:
http://www.transonline.com/transDige...ndards2_1.html


The input shafts are different so you can’t put the better bearing in the earlier trans. Also if you take apart the main shaft, many of the parts cannot be reused, and you need an oven and melt sticks to heat the parts to the correct temp for reassembly.

There is a selective shim by the front bearing that controls the main shaft end play. When you replace the bearing you must check the end play. If there is negative end play it would be very hard on the bearings. The bearings on the back end of the main shaft are the same design as the input bearings. The second design has the better bearings on both ends.


If you do decide to work on your transmission Take note:
There are four design levels of this unit. It started in 1988 as an HM290 found in GM trucks, and was re-designated 5LM60 with early and late designs. Hm290 and 5LM60 units each have 4 shift rails. The unit was completely redesigned as a 3500 with a single shift rail. Due to all the design variations it is critical to positively identify which model trans you are working on in order to get the right parts.

I have seen these truck hauled to the junk yard rather fixing this transmission due to the high cost.

This is not an easy transmission to work on. I would suggest most people don’t attempt to open it.

[edman87]

I rebuilt mine in my 91 a few years ago, a pain to say the least. I had no choice because I broke many teeth off the input shaft and about 15 or so off the custer gear and it was making all kinds of noise.
The entire gear and shaft assy slides out as a whole basically. If you have no idea what you are doing, take it to someone. It is nothing like building an older trans. It takes 2 people to hold together and re-install the setup. There is also a rear bearing retainer that is bolted through the rear and the bearing is pressed onto the shaft. This is a very difficult part to handle!