Transmission Questions

[spoonman]

Hello Everyone

A bearing in my transmission has failed, and it needs a rebuild. It has only been 70k miles since the last one. It is in a 90 GMC k1500 with a 350 (fairly mild rebuild by previous owner). The transmission is the stock aluminum bodied 5-speed (RPO MG5 produced by Muncie/Getrag). I believe the transfer case is a NP 241.

I was considering replacing instead of rebuilding. What transmissions will bolt in? What would you recommend? Are there any online sources you could point me to for information?

Thanks

[99-2door]

You could consider a NV4500, They were available in the heavier trucks. I believe they are a direct swap with the MG5 with the exception of some sensors.
Super stout trannies, but the gearing is set up a little different than the light trans.

[ChevyTech]

I received trining at the GM training center in Minneapolis in 1991 on the transmission I think you have. The training manual (which I still have) refers to it as a 5LM60 Formerly HM-290.

There are two designs for the inputshaft and input shaft bearings. The first design 1988-1990 had a ball bearing and a roller bearing behind it on the input shaft. The second design only has a ball bearing but it was a much larger bearing. The first design bearings often fail. They were failing when these truck were under warranty with very low miles on them.

There is no way I would suggest fixing your transmission. The bearing are very expensive. Last one I did an estamate on, it was over 2 hundred just for the input bearing. 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 a oven and melt sticks to heat the parts to the correct temp for reassembly.

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

[spoonman]

Thanks for the replies.

ChevyTech, do you recommend replacing it with a unit of the same type or with the NV4500.

Also, does anyone have any idea what issues would be faced installing a NV4500. What issues would there be with electronics/ controls of the pickup.

Could anyone recommend any references or online sources. I haven't had much luck with these and need to make a decision soon.

The help is appreciated.

[ChevyTech]

I would not use a 1988-1990 transmission, they were a bad design. I would not have a problem with a 1991-newer trans. The last time I looked for a 1991-newer trans the price started at $700 and there were not many to choose from.

I have never change one over to a NV4500 so I don’t know what all is involved in the changeover.

Here is a web site about the Getrag HM290, 5LM60
http://www.drivetrain.com/getragHM290.html

Here is a site that has a NV4500
http://www.motivegear.com/tech_info/...nny_guide.html

[spoonman]

ChevyTech- Thanks for all of the help. I'll see about getting a perlacment next week.

[ChevyTech]

Your welcome.
Let me know the price range you find, and how hard they are to find.

ChevyTech

[spoonman]

I haven't bought anything yet, but a friend of my dad has one with 10k since a rebuild. He is asking $800, though I think I could talk him down some. Does this seem like a decent price? I haven't seen much else.

[ChevyTech]

If it's been rebuilt, my guess would be that it is a 1988-1990 trans (first design). I would much rather have the 1991-newer design. $800 is is not out of line, and if it were a second design It would be a good deal.

[spoonman]

It is supposed to be out of a 91 or 92 (forget which). I believe I will go with that. Appreciate the help.

[454_72_4X4]

I've also got one of these trans with some sort of problem. Haven't torn it down yet. I've got a replacement so I've got nothin to lose by tearing it down!
Where could a person get a repair/assembly manual or something for these transmissions?

"The input shafts are different so you can put the better bearing in the earlier trans."

Confused me there ChevyTech. Can the new bearing be installed on an older trans?

[ChevyTech]

Originally Posted by 454_72_4X4

I've also got one of these trans with some sort of problem. Haven't torn it down yet. I've got a replacement so I've got nothin to lose by tearing it down!
Where could a person get a repair/assembly manual or something for these transmissions? ?

A GM unit repair manual for the model year you are working on. Of all the transmissions I have ever worked on including automatics, this is the worst(hardest to work on) if you have to disassemble the mainshaft.

Originally Posted by 454_72_4X4

"The input shafts are different so you can put the better bearing in the earlier trans."

Confused me there ChevyTech. Can the new bearing be installed on an older trans?

No, the snap ring for the 1988-1990 design sets against the flat front surface of the trans case. The 1991- newer design has a recessed area in the front of the trans case where that outer bearing race snap ring fits down into. The case, input shaft, bearing, front bearinr retainer, are all different. There was also a change to the reverse idler gear setup in 1990 before the front bearing was redesigned.

[454_72_4X4]

So I get the manual from a GM stealership then right?

I'm sure there's not much worth salvaging in my old trans but I would like to, (at the very least), replace the input shaft bearing on the other one before I put it in. Does the input shaft come out the front, (like the old saginaw 4-speeds)? Also is there a bushing or bearing between the input shaft and the main shaft?
Or should I just ask whats going to fall out when, (if), I pull the input shaft out?

I'll check into those unit repair manuals.
Thanks.

[ChevyTech]

Originally Posted by 454_72_4X4

So I get the manual from a GM stealership then right?.

I buy manuals on Ebay. The dealership may have ordering information, but they won't have a manual to sell you. These manuals are very expensive new.

I'm sure there's not much worth salvaging in my old trans but I would like to, (at the very least), replace the input shaft bearing on the other one before I put it in. Does the input shaft come out the front, (like the old saginaw 4-speeds)? ?

Look at a manual before you attempt this. I don't think the input shaft will fit out the front, but the bearing will. The bearing is held to the input shaft with a snap ring. To remove the input shaft, the procedure is to put the trans in a holding fixture with the front end up, and remove the front half of the trany case, leaving the input shaft with the inside parts. To do this you first remove the front bearing retainer and snaprings.

There is a selective fit shim/spacer on the front side of the bearing that controls end play for the transmission. If you change the bearing you must check/reset the end play.
Basically you assemble the trany without the selective shim and measure the end play with a dial indicator. Then you install the correct shim and do your final assembly. It depends on you abilities, wheather or not you should attempt this. This is not the average do-it yourself project.

Also is there a bushing or bearing between the input shaft and the main shaft? Or should I just ask whats going to fall out when, (if), I pull the input shaft out?

Roller bearings