80Baby

TKO 5-speed with a 3.08 rear in my '80. The car has been resto-modded as a highway cruiser. I'm way past the age of smoking tires so this is the best arrangement for truly enjoying my baby.

ddawson

I have 3.36 with a wide ratio.

70MPH is just at 3K. Not bad but at 85MPH thing sound a little more hurried.

I looked at doing a TKO and with the .82 overdrive it just didn't seem to be enough.

1:1 @ 70MPH is 2927
.82 @ 70MPH is 2400

.64 would have been too low at 1873 but with better rear gearing like 3.73 it would be perfect.

69427

My factory setup was an M21 and 3.70s in the rear. I was young and stupid at the time, and the higher cruising RPM didn't bother me much. I eventually put a 5 spd and 3.08 in it. Nice cruising RPM and lots of torque off the line. However, I recently put the M21 back in the car (to take 30# off the car, as I like to do track days with it), but kept the 3.08 rear gears. Even with a lightweight 10.5" flywheel & clutch setup the car is easy to drive off from a stop (it's a big block though).

68/70Vette

My 69 BB and my 70 BB each came stock with 3.08:1 differentials. This worked out well with the extra torque of the BB's. When I replaced the BB in my 69 with a clone L88, the 3.08:1 and the L88 cam shaft were not a happy couple. A lot of fuss getting the 69 rolling. I replaced the Muncie in the 69 with a Richmond 5 speed. The Richmond had a 1:1 fifth gear, but a lower (numerically higher) first gear...happiness. The 70 currently has a 3.73:1 diff and a TKO600 five speed.

The Richmond 5 speeds have 1:1 fifth gears, the TKO600's have overdrive 5th gears.

labhound

My '74 454 with a close ratio 4 speed runs 3k rpm at 77 mph, I don't do much highway driving, it'll do burnouts when I dump the clutch though!, it's fun to drive though.
I'm building a low rpm big power motor for it now, but, if you want to trade rears then let me know........

Priya

Whaaaat??? I have a close ratio and 3.70 rear gears and I never find second gear useless or think it would be anything but a bad idea to go from 1st to 3rd.

bj1k

You have 3:70's not 3:73's There is a difference. And just so you know it doesn't hurt anything to go from 1st to third , it just feels like a normal wide ratio transmission .

Priya

LOL, yes, that's a huge difference.

Sunstroked

I go 1st to 3rd, even 1st - 4th. M20-3:55-383. Lots of low end grunt. If I feel like rowing the gears, I'll do that too. Our freeway speeds are 65 mph in town and 75 mph at the city limits. I see an overdrive in my future.

Mod75

I have a mild 350 with mods, TB 400 and a 3:08 gear

If my tack was working it would read about 2,300 rpm at 60 i think.

cagotzmann

A 5 speed has a single over drive gear in the range of .82 - .64

A 6 speed has 2 over drive gears 5th ~ .8 and 6th .64 - .5

4th is still a 1:1 like what you have.

bj1k

Now I'm getting somewhere. When I bought my car I was told that they thought the rear end gears were 3:73's but over the weekend I was talking to a guy that knew the car and the guy a couple owners back that changed the gears and he said that they were definitely 3:90's instead of 3:73's so it's even worse than I thought and explains why it seems so low. The numbers on the rear housing say it was originally a 3:36 gear rear so I decided that is what I want to go back to. The same guy was telling me that if going from a 3:90 to 3:36 that there might be a difference in the size of the carrier maybe needing shims between the carrier and the gear. Can someone enlighten me on this and recommend what I will need to order.

BKbroiler

This thread is driving me crazy. I'm not looking to offend anyone and I've been criticized for doing this in the past but I have to point out that the correct terminology for gear ratios is 3.08, 3.36, 3.55, etc., NOT 3:08, 3:36, 3:55. This is a number, not a time of day. It is derived from dividing the number of teeth on the ring gear by the number of teeth on the pinion gear. Like 37/12 = 3.08 or 41/10 = 4.10. Some confusion probably results from the full mathematical terms for a gear ratio as in 4.10:1. There the ":" is short for the word "to". But we normally talk about gear ratios in shortened terms so 4.10:1 becomes just 4.10, hopefully.

bj1k

Sorry to confuse you but I didn't think it is that important to worry about. A result from "Qwikke " typing.

bashcraft

There are 3 carriers and 4 carriers. All 3.XX gears fit in a 3 carrier and all 4.XX gears require a 4 carrier.

As far as 3.90 gears, there may have been some aftermarket sets but no factory 3.90 gears that i know of.

Are you sure you have an M-21 trans and not an M-20?

lowbuck72

I run a T5 with a .63 overdrive in my C3 which is great and you should consider something like that. On the other hand, many years ago, I had a '63 Biscayne with a 409, an M21 and 4:11's. It was fun, but ridiculous as an everyday driver. So I put in a set of 3:08's and it solved the problem. Kept the 4:11's for racedays. Those old third members could be swapped out in a hour.

BKbroiler

I'm not the one who is confused. Also, it is quicker to type a . than a :

loup68

For years I would skip second gear, first to third and then fourth. I had my M-20 rebuilt and third gear was really worn badly. I was told to use second gear, that it is a lot beefier gear than third gear. Been using second gear ever since. Lou.

bj1k

Thanks for the information . That will help. I did check all of the numbers when I had the transmission out and it appears to be a close ratio M-21.

bj1k

Sew I tipe funee butt youz boyz frum joyze tok funee !