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Discussion Starter #1
My dog's barkin' but it ain't got no bite...

Just took my conv. for it's maiden voyage last night and the 2.56 ain't cuttin it with this M21 (orig. 'glide).

What gear is best for good quick in town , but also highway speeds , with an M21 ?

Talk about slippin' the clutch and bogging off the line......whew , bad.

I'm thinkin' 3.73's.

What about 3.56?

Anyone been in this same boat ?

What RPM's on the highway with either one , or is there a final ratio calculator somewhere ?

Thanks,

Brian
 

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Brian,

I'd go with something in the 3.30-3.50 range. I had 2.73's with a 4-speed. I know what you mean about slippin' the clutch to get the thing rolling.


He's a calculator to figure rpm's depending on tire size, gears etc.
http://www.ring-pinion.com/RPMCalculator.html

Mark
 

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A close ratio Muncie is just about the worst street trans ever made. Personally I would sell the M21 and put in a 3.42 low ST10 you starting gear ratio would be almost as good as having 4.11s with your M21. I am assuming that you have a stock or near stock motor that has a wide power band. If you have much cam at all in the engine the 2.56s are going to have to go. I have had cars with 2.73s and 3.11 low Saginaws that worked just fine.
 

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I think origannally if you had 3.73 or lower you got a m-21 close ratio and if you had higher gears you got the wide ratio, look for a super T-10 mine has the 2.88 first gear compared to the m-21's 2.20 it comes of the line hard if it hooks up.
 

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I have gone real fast with race glides. Your problem is the combo. You have a trans that is made for a car with a narrow power band and alot of gear {3.70s} and lower and you are trying to make it work with a rear end that was made for gas milage and an engine with a broad power band. One or the other will have to changed. If you are rarely on the freeway put 3.73 or so in it. If you do a lot of freeway driving change the trans.
 

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Let me know if you decide to sell the M-21.

Yes, I agree with the rest 3.73 and above, 4.10-4.11's be better

Everett 68/350/PG/11.90/115mph
 

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Discussion Starter #8
Thanks everyone......

Here's the deal , as far as I can see right now , I'd rather stick to a Muncie , if I switched to anything I'd be an M20.

Here's what's up:

350 .40 over 9:1 - Balanced
Stock small valve heads-hardened seats
Comp Cams XE268H-10 12-242-2 , .470 .480 / .268 .280 110 separation.
Stock 1968 manifold
Holley Re-man'd. Q-Jet
Iron manifolds
10.4 flywheel & Centerforce 2-
M21
Goodyear Nascar Eagles 255-60-15 (not sure of height, car is at the top-shop and can't measure rollout or height right now)
Vintage Air -

Yes , we are going to drive it on the highway , I'm sick of having trailer queens , so I built/building this to be able to jump on the highway and drive to any show we want to go to with the air blastin' , reliably , no matter how far.

So , I'm not looking for an 11 second drag car that will go on the highway with low RPM's , just to be able to scoot around town with good acceleration AND highway drivable , hopefully right at 3000 rpm or below.

I agree the close ratio might suck for this , I deduced this within about 1 mile last night.

But not going back to a 'glide or any auto for that matter , and don't want to shelf this new Centerforce clutch , so I may have to switch to an M20 , but still need some gear....

Not to mention I need to get that open center section outta there and install this rebuilt posi unit I've got anyway (10 bolt) , so I knew it was coming to this gear swap when I started , I just wanted to see how bad it was gonna suck on the first drive.

And it did.

I used to have all this gear & tranny stuff mezmerized in 1984 , but I think I'm getting senile at 37.

Thanks everyone....

Brian

.
 

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Brian,

According to the calculator, your tires are 27 inches tall. With 3.55 gears you'd be turning about 2650 rpm's at 60 mph and around 3100 at 70 mph. Not too bad for the highway, but still has some pep for the street. Speaking from experience, stay away from the 4.10's if you plan on doing any highway cruising.

Mark
 

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Discussion Starter #10
Ok , tell me more about the Super-T10 with low first gear , I know they make several , what is the lowest and what is the 4th gear in that one? (really , I'd like to know what each gears' ratio is).

Is there anywhere I can study up on them ?

Anywhere they're available used , how much should they be ?

Will they work with a stock 10.4 bellhousing and fork , etc....

Will they work with stock 69 Camaro Hurst shifter/shifter plate & console.

Will it work with the correct hole (in the floor) I already cut to perfection ?

In other words what would I have to change to go from Muncie to T10 ?

Maybe I can just switch the disc for the Centerforce II , as I think I remember they're like 28 spline or something ? (input shaft)

Thanks for everyone's input , I think I'm going to change the rear no matter what , but it seems like I read the S-T10's have better synchro's and just a better more modern alternative to the Muncie ?

Brian
 

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My (unrestored/stock) '69 Z had the optional 4.10 and M-21; strong out of the hole, but finally got to me on the highway (3850 at 70). Swapped it out for a 3.55 (had to spring for a new Eaton series 3 Posi with it), makes a pretty decent combination - no problem around town, 3250 at 70 with 235/60-15's all around. I wouldn't go any higher (lower numerically) than a 3.55, though. Love that looooooong 1st gear!

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JohnZ
'69 Z28 Fathom Green
 

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$1400+ from Summit Racing. They have 2.43, 2.64 or 2.88 1st. gear ratios there. I think the shifter can be made to work. These are 26 splines on input and T-400 sized output shaft. I'm not sure on your bellhousing ? I have a real nice brand new 0 miles 1978 special ordered nodular iron cased 2.88 ST-10. Mine uses a ring insert around the front bearing retainer to fit my scattershield.
www.richmondgear.com
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Rick

[This message has been edited by YenkoYS100 (edited 08-01-2001).]
 

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Don't buy a new one most of the ones you find are 3.42 low. It will have 6 groves on the input shaft. you must change the clutch disk and rear yoke. The shifter will work but you need to make a shifter to trans mount the muncie uses a different mount.
 

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i have a m21....with 3:73 rear and i still have a real hard time getting off the line......i am going 4:10...........

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1969 z11/396 pace car
1969 z28/302 garnet red
1997 brickyard festival pace car #1
1965 chevelle malibu
 

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If you have the cash go with a Richmond 5 speed with the real deep 1st it would work perfect with your gears and fifth is 1:1.
 

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I am in the same boat as Z11/396. I have 3.73 posi with an M-21. My engine dynoed over 500 HP and over 400 ft-lbs of torque from 2,500 RPM to redline and my car can't smoke the tires to save its life.

Do you guys REALLY think that the minor difference in ratios between an M-21 and an M-20 will make that much difference on the take-off?

I'm solving this problem with a Tremec - can't wait for that 3.27 first gear


3.27 x 3.73 x 400 ft-lbs @ 2,500 RPM = 4,878 ft-lbs of torque at the tires!!
 

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I have a 68 396 400+ hp,m-21 and 3.55.Under 2300 it was a dog,played with carb 750dp,fixed it with primary at 71,10.5 powervalve,pink cam on 1 and 35 shooter,what a difference.We are at sea level
 

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I have a 350 with the m-21, and a 3.55 rear with posi, it comes off the line nice if I giv it enough rev. The gearing is more abou whether or not you want to drive on the freeway or not. I rev 3000 at 65 mph
 

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gheatly: I don't believe that your 396 can't roast the tires what size do you have are they 12 inch M/T's I had a 4 speed saginaw in my 73 camaro with 3.42's and I used to be able to roast them thru 1 to second.
 
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