1988 Sierra: Manual transmission won't go on reverse

[RayInAlaska]

A couple of days ago I noticed that the 5-speed manual transmission was getting difficult to shift into reverse, and today it won't shift into reverse at all. There is no problem shifting into all the forward gears, just reverse.

Does anybody know if there is a reverse linkage or something like that outside of the transmission, or do I have to drop it to work on it? I do have the repair manuals for this truck, but I can't tell by just looking at the pictures of the transmission.

Thanks in advance for your help.

P.S.
Could it be a "roll pin, and reverse shifter" that have caused the problem? I imagine that I would have to drop the transmission to replace both (?)

[ChevyTech]

Hi Ray,
All the linkage is internal.

See if it shifts ok with the engine off. If so the clutch may not be fully releasing.

That is one of the most difficult, if not the worst transmission, to work on.

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.

If your truck has the original transmission then it would have the first design input bearing. I would not recommend trying to repair it.

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.

There are several design levels of this unit. The different transmissions appear the same from the outside. Due to all the design variations it is critical to positively identify which model transmission you are working on in order to get the right parts.

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.

In 1987 it was referred to as MG-290 My guess is the G is for Getrag
In 1988 it was referred to as HM-290 HM= Hydramatic / Muncie
In 1989 it was referred to as 5LM60
In 1991 it was referred to as NVG 5LM60 NVG= New Venture Gear
1993 New Venture Gear releases the NV3500. Externally the earlier GM units "look like" the NV3500 however internal components were extensively re-designed.

I have wrote about that transmiision extensivly on several of the truck message boards.

[RayInAlaska]

Thanks, ChevyTech.

I will print all the information above for reference, since I will be taking the truck to a local transmission shop for the following reasons:

This morning on my way to work, as I upshifted from 4th to 5th, I could not get the transmission on 5ft, so I carefully put it back on 4th and drove to work at 50 MPH with the motor at little past 1,700 RPM. It seems that the problem is not just with reverse, but all the gears, like the whole shift lid is loose. I had to guess which gear was the next one when upshifting, and several times it was not the right one.

There was a problem with another forum member's truck that seems to be exactly like the problem I am having with this truck (he used a nail in place of a pin that broke inside). I found it last night on a Google search, and it led me to this forum, but I didn't keep the link. Anyway, it will be expensive, but since my truck is in pretty nice shape I don't want to get rid of it. If it is too expensive to repair, then I will probably buy another transmission.

Thank you again.

[ChevyTech]

You're welcome!

Here is a link to the thread you mentioned:
http://67-72chevytrucks.com/vboard/s...d.php?t=353603

When the pin breaks it feels like the shift lever is all sloppy to me. People explain things differently so it is hard to know exactly what people are experiencing.

When the front bearing fails, which is common on the first design like you have, the shafts get excessive play. Some times it can be very hard to get it in fourth when this happens. A friend of mine had this happen and he could not get it in 4th but his wife could with relative ease. He drives them hard, she babies them. After they removed the transmission, I wiggled the input shaft, and after some discussion we decided not not even open the tranny. It had 80w-90 in it – to thick for this transmission.

If you buy another transmission, get a newer design, at least 1991, but 1993 is better.

[RayInAlaska]

Originally Posted by ChevyTech

You're welcome!

Here is a link to the thread you mentioned:
http://67-72chevytrucks.com/vboard/s...d.php?t=353603

When the pin breaks it feels like the shift lever is all sloppy to me. People explain things differently so it is hard to know exactly what people are experiencing.

When the front bearing fails, which is common on the first design like you have, the shafts get excessive play. Some times it can be very hard to get it in fourth when this happens. A friend of mine had this happen and he could not get it in 4th but his wife could with relative ease. He drives them hard, she babies them. After they removed the transmission, I wiggled the input shaft, and after some discussion we decided not not even open the tranny. It had 80w-90 in it – to thick for this transmission.

If you buy another transmission, get a newer design, at least 1991, but 1993 is better.

This is an update, and a note of appreciation to ChevyTech for his help.

Good news about my truck's transmission. It took around three weeks before the mechanic could bring the truck into his shop to check the transmission, but I didn't mind waiting since this shop is perhaps the best in town. Anyway, the service manager called me today to tell me that the mechanic pulled the top portion of the transmission with the shifter, and found that a pin had broken. It sounds exactly like the thread you posted above, ChevyTech. He replaced the pin and drove the truck, and it's shifting as it should now. The mechanic didn't even have to drop the transmission from the truck, so the work didn't cost very much.

I will pick the truck next week because I asked the mechanic to go ahead and replace the transmission oil.

[ChevyTech]

You're welcome!

And thank you for letting us know what was wrong.