What gear with M21 ? I got a dog now. - Team Camaro Tech
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post #1 of 24 (permalink) Old Aug 1st, 01, 06:52 AM Thread Starter
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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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post #2 of 24 (permalink) Old Aug 1st, 01, 07:02 AM
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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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post #3 of 24 (permalink) Old Aug 1st, 01, 07:10 AM
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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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post #4 of 24 (permalink) Old Aug 1st, 01, 08:56 AM
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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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post #5 of 24 (permalink) Old Aug 1st, 01, 08:57 AM
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Oh yeah the muncie has got to be better than the old slip and slide, right?
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post #6 of 24 (permalink) Old Aug 1st, 01, 09:19 AM
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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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post #7 of 24 (permalink) Old Aug 1st, 01, 10:20 AM
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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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post #8 of 24 (permalink) Old Aug 1st, 01, 12:04 PM Thread Starter
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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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post #9 of 24 (permalink) Old Aug 1st, 01, 12:22 PM
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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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post #10 of 24 (permalink) Old Aug 1st, 01, 02:07 PM Thread Starter
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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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post #11 of 24 (permalink) Old Aug 1st, 01, 02:29 PM
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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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post #12 of 24 (permalink) Old Aug 1st, 01, 04:16 PM
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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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[This message has been edited by YenkoYS100 (edited 08-01-2001).]
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post #13 of 24 (permalink) Old Aug 1st, 01, 04:30 PM
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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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post #14 of 24 (permalink) Old Aug 1st, 01, 06:32 PM
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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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post #15 of 24 (permalink) Old Aug 2nd, 01, 08:28 AM
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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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