How would I know if I had a close ratio 4 speed?

 

If the car is running there is an easy way to tell by checking rpm changes vs speed, but I won't waste your time (or mine) with it if the car is not running. (I would have to look up the gear ratios and do the calculations, or find the last thread where the process was described)



ok.. http://forums.corvetteforum.com/1556491669-post2.html

 

Thank you both!

 

I think a close ratio trans is paired with gears like 278 or 308s and a wide ratio is paired with gears like 373 and 411s.

 

Check the numbers on the tranny case. They explain what you have.

 

I've done that, it tells me I have a super T10 and it's numbers matching. That's all I can glean from it.

 

Probably a wide ratio.. what year car?

 

it's a 76

 

Close ratio was available ONLY with L82 option.

 

I do have L82

 

Might be long gone but:
The first gear ratio was indicated by a 2-digit paint code on the main case below the side cover. "HS" is a 2.64:1 wide ratio, and "HW" is a 2.43:1 close-ratio.

 

yeah if it was painted on I didn't see anything. I just scraped off 36 years of baked on dirt and grime the tranny looks almost new now the part that pleased me the most is it's numbers matching to go with my motor (that I just pulled and will put away).

 

I had the same question of my car, so I performed a numerical analysis on the anticipated RPM drop through each gear for the M20 vs. the M21 (and M22, I guess, since their ratios are the same)

This is completely independent of speed, since that can vary based on your rear end ratio. This is STRICTLY the RPM drops by transmission types.

If you shift at 3,000 RPM, these are the respective RPM's for the gear you are shifting INTO.

M20 (shifting at 3,000 RPM):
2nd: 2238 RPM
3rd: 2345 RPM
4th: 2040 RPM

M21 (shifting at 3,000 RPM):
2nd: 2236 RPM
3rd: 2323 RPM
4th: 2362 RPM

Note that there really isn't much difference in first to second or second to third RELATIVE TO EACH OTHER. Of course, if you were driving an M21, you would be traveling faster in each gear versus an M20 since each of those three gears is numerically taller.

The big difference is shifting from third to fourth. This is where the taller gears in the M21 catches up with the identical 1:1 gear in 4th. There is only a ~650 RPM drop in the M21 while there is nearly a 1,000 RPM drop in the M20.

So. If you have a 1,000 RPM drop when shifting from third to fourth, making the shift at 3,000 RPM, then you have an M20.

 

1975 L82 with close ratio trans (still optioned as M21 on the order sheet) would default to the standard (GV7 option) 3.55 rear gears, unless specifically ordered otherwise.

 

I'm confused. So you have a "close ratio" transmission that actually has 1st, 2nd, and 3rd gears that DON'T have as much mechanical advantage over the car and you couple that with 2.78 or 3.08 rear gears?

Seems like that would make the thing a real dog off the line.

Unless the car with the M21 and 2.78 rears has a REAL HORSE of an engine, I'd politely offer that my M20 equipped car (with 15% shorter gear in 1st) with 3.73 rear gears would politely spring off the line compared to the other.

Granted, I'd be shifting more often, but I'd honestly rather have the "sprightlyness" of the shorter gears all around.

The benefit to having low rear gears is that my car will run out of steam about 120 MPH, while the 2.78 car would make it to nearer 160 MPH at the same RPM. But, again, at the cost of responsiveness all the way up to 160 MPH. And who among us have made it to 120 in a C3? I've made it to 100 and that's about all I have the stones for...

 

It's the other way around. M21 needs a numerically diff high ratio.

 

I agree with Mike. Looking at my 1970 brocure, the close ratio trans is always mated to higher gear ratio in the rear end.

I ficture that everyone wants the "better" transmission and there is a HALO around the M22 Rock-Crusher.

I was actually happy to have the 'lowly' M20, though. It just makes more sense for street use.

The M21 and M22 make more sense if you're on the track and start/stop, like, twice per race. You spend all your time "in the gears".

If I'm running from stop light to stop light, I'd prefer the first gear in the M20.