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ChevyTech · 07-17-2009, 10:31 PM

If it is the original 1991 transmission it is referred to as NVG 5LM60
NVG= New Venture Gear

People will call your transmission a NV3500 which it is not.

The 5LM60 has 4 internal shift rails is much more difficult to work on then the NV3500 which has a single internal shift rail.

The 1991 transmissions were superior to the 1988 to 1990 design but are very complicaed to repair

There are four design levels of this unit. It started as a 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.

There is no way I would suggest opening your transmission. 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 pressing them together during reassembly.

A large holding fixture (special tool) is used to hold everything in position when assembling the transmission.

It is almost always less expensive to replace these transmissions then it is to rebuild them. Even in parts prices alone.

07-17-2009, 10:31 PM	#2
ChevyTech Registered User Join Date: May 2004 Location: Minnesota Posts: 4,620	Re: 1991 Sillverado 5 Speed trans problem If it is the original 1991 transmission it is referred to as NVG 5LM60 NVG= New Venture Gear People will call your transmission a NV3500 which it is not. The 5LM60 has 4 internal shift rails is much more difficult to work on then the NV3500 which has a single internal shift rail. The 1991 transmissions were superior to the 1988 to 1990 design but are very complicaed to repair There are four design levels of this unit. It started as a 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. There is no way I would suggest opening your transmission. 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 pressing them together during reassembly. A large holding fixture (special tool) is used to hold everything in position when assembling the transmission. It is almost always less expensive to replace these transmissions then it is to rebuild them. Even in parts prices alone.