Is this normal M21 noise

[GRAND SPORT #12]

My 74 has a M21. Trans shifts normal, but in first gear when i accelerate i get a whine noise, only in first. Is this normal. Is first gear a straight cut gear which is making the whine or is this a sign of a problem. Thankyou.

 

[Hib Halverson]

My 74 has a M21. Trans shifts normal, but in first gear when i accelerate i get a whine noise, only in first. Is this normal. Is first gear a straight cut gear which is making the whine or is this a sign of a problem. Thankyou.

First gear is helically cut.

There should be a slight amount of gear whine under acceleration in first. If the trans is excessively noisy in first, there could be a problem.

 

[GRAND SPORT #12]

I think the whine may be a little excessive. I also am not crazy over the first gear ratio of 2.20. So realy dont know if i should rebuid it and replace first gear. Have considered swaping to a m 20 for the better first gear ratio, or doing the 5 speed swap. If anyone has done any of these things i sure would love to hear your comments. Thanks

 

[GRAND SPORT #12]

I priced out a rebuild kit for my m21 and including purchasing a first gear cog am looking close to 400. I will do the labor myself if i go that route.

 

[Hib Halverson]

I priced out a rebuild kit for my m21 and including purchasing a first gear cog am looking close to 400. I will do the labor myself if i go that route.

Keep in mind that you can't just change first gear to make it an M20 with 2.54 low gear. I think you need to change other gears along with the counter gear. Also, you might need more than just a rebuild kit if you have some worn gears or bearings. Some parts may require a press to assemble/disassemble.

I would be hesitant to try rebuilding yourself without a service manual, especially if you've never done a four-speed before.

Not trying to discourage you from DIY but I am trying to make sure you have the right information and tools.

If it were me, I'd just buy a rebuilt M20 on an exchange basis.

Maybe GTR1999 will get on this thread as he knows a lot about Corvette driveline issues.

 

[GRAND SPORT #12]

I am ok with doing the rebuild I am a mechanic at a toyota dealer. I have had no luck with finding different gear ratio's for the m21. If i rebuild my m21 I will replace the fist gear back to original 2.20, but was thinking i may be better off with a m20 for a more street friendly first gear ratio. Had one company quote me 3500 for a 5 speed conversion tko. Just am not sure for that kind of money i need a 5 speed that bad. Oh yea going to replace the radiator tomorrow the list is adding faster than the money going in my wallet..