I'm working at going from a 1994 6 speed to a 1990 6 speed, what changed in the trans? I see in add that so are labeled differently. I saw one add that said a 1990 had straight cut gears.

 

There were some changes between black and blue tags.

Neither of them were straight cut gears, but the black tags were straighter than than the blue tags. This change made the blue tags somewhat quieter (although I don't notice the difference). and the black tags have a higher torque rating (although I don't know of problems with either one behind strong motors).

Not specifically black tag to blue tag, but the trans input shaft guide tube was changed to a different diameter ('94-'96 guide tubes are smaller diameter), so make sure you get the right throw out bearing for your transmission.

Some early years had a different speed sensor (the wiring connections are different). The gears that drive the sensor are different depending on which axle ratio.

I swapped a '96 to a '90 and it was pretty straightforward swap. On mine the speed sensor and gears were different, but I was able to use the '96 sensor on the '90 trans. I was able to swap the driven gear to use the '96 gear and it all went smoothly. The '95-'96 also used a crash through trans and shifter instead of the reverse lift ring on the shifter. So keep the shifter with the transmission. The '94's still used the lift ring so it should not be a change for you.

Good luck.

 

Forget the black-tag blue tag ID... look at the actual part numbers. ZF doc is the best resource to figure out the changes. The straight/helical gear transition was 1991 and they were still black tag, until GM/US started manufacturing the ZF with blue tag. The big differences to watch out for are the size of the input shaft with different TB required, the shift lockout mechanism and shifter, early or late bellhousing, and most importantly whether it's a ZR1 trans. Hope that helps, but check with Bill ZF doc (google website and he has it listed there somewhere with a lot of calls on this I'm sure).

 

is there any reason to look for one over another? It doesn't sound like one is necessary any better than the other.

 

You never mentioned the 'WHY' you're wanting/needing to maybe make the change. In your original post I interpreted working at to mean looking at!

Where are you located?

 

I have a 1994 that I'm working on getting the opti spark replaced and then it going up for sale (been 4 weeks of trying to get one), At the same time, I'm working at getting a 1990. The 1994 shifts very nice, I wasn't able to test drive the 1990 that I'm trying to buy. If I end up with both car at the same time, and the 1994 as a better trans, I was thinking of swapping them. From what I'm reading, if the 90 shifts smooth, I'm not messing with it.

 

Both versions shift beautifully when they are in good working order and have a good trans oil in them. The change in gearbox if you decided to swap them wouldn't be worth the trouble; it would require swap of the throwout bearing, and if you're in there you probably would do the clutch too, fork, pressure plate, etc... and it snowballs quickly. I have a black tag and it's excellent. I remember when it was new I thought it was the best shifting trans I had ever used, and it's still about the same at 127K miles.

 

got the 1990 yesterday, shifts just as nice as the 1994. Now I need to sell the 1994