1991 Sillverado 5 Speed trans problem

[Free88]

Today while driving on the highway something went crazy with the trany. I went to down shift from 4th to second for a stoplight and the gear shift just seemed to float wherever it wanted. It took some time to find 1st gear to pull away from the stop light. After finding the correct gear and making sure of the position of the gearshift handle I went to shift to second and slid into 4th. After some playing around i was able to get it shift again but when I went to back up it would not go into reverse. After a lot of pulling an pushing on the gear shift I got it into reverse and backed in. There seems to be way to much travel in the shift handle. Is this a sign of a worn shift fork or something broke in the trany case? Thanks for the help an suggestions in advance.

[ChevyTech]

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.

[Free88]

Chevytech, thank you. I have the original build sheet for this truck. I just looked up the option code for the trans and it is MG5. Description calls it a Manual Transmission 5-speed (Getrag). It also says MM5 Transmission manual 5-speed Provisions (Merchandising Option) 5-speed M/Trans (MM5). Both numbers appear in the RPO Description Detail sheet. I do not know if this is helpful but I thought that i would post it as it differs from the ones that you listed. Any more help would be appreciated.

[ChevyTech]

You’re welcome!

MM5 - MERCHANDISED TRANS MAN 5 SPD PROVISIONS

MG5 - TRANSMISSION MAN 5 SPD, GETRAG, 84MM, 4.00 1ST, O/D

This fits the 5LM60 but I think that MG5 was also used in other years with the other designs of this same transmission group.

[Free88]

Thanks. So when I go to look for a transmission do I look for one that says Getrag or one that says 5LM60?

[ChevyTech]

1993 New Venture Gear released the NV3500. Externally the earlier GM units "look like" the NV3500 however internal components were extensively re-designed.

I would look for a NV3500 for a replacemnet out of a newer truck.

Note: All the illustrations in the 1993 service manuals are of a 5LM60, with multiple shift rails, so I don’t know when they switched to using only the NV3500 in production.

I would stay away from anything built before 1991

Remember from the outside these transmissions look alike.

Sorry – I have not saved any identification number information for identifying them.