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Old 08-28-2003, 02:48 PM   #1
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Question Manual 3-Speed Transmission Ratios


I recently replaced the 250 six engine in my 1969 Chevy C10 with a 350 V8. I left in the original 3-speed manual transmission from the six cylinder engine. My concern is that the gear ratios from 1st and 2nd are not conducive to the power curve of the faster turning 350V8. I am getting conflicting information regarding the gear ratios of the 3-speed manual transmissions. It seems that all the places that I have contacted about getting a 3-speed manual transmission from a 350V8, say that as far as they know, there is no difference in the gear ratios. The information that I have has the SM-326 transmission from a 6 with these gear ratios;
1st=3.50, 2nd=1.89, 3rd of course is 1.00. The gear ratios from a SM-326 transmission from a 350V8 are listed as;
1st=2.85, 2nd=1.68, 3rd of course is 1.00. I got this information out of the book titled 'Chevy & GMC Pickup Performance Handbook' written by Jim Allen.

The next question is, how does a person tell these transmissions apart? The places that I have talked to about this, say that they donít know how to tell these transmissions apart, if there is in fact a difference. So, I guess that is why they are saying that they are all the same???

Can anyone shed any light on this for me?

Thanks for your time.

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Old 08-28-2003, 03:13 PM   #2
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I thought all 3 speeds were all the same also.
I know the 4 speeds are different.
I will be watching this one also.
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Old 08-28-2003, 04:51 PM   #3
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Hmmm, i would like some info on this as well. I am swapping my inline 6 out for a 350 as we speak and I am stickin with the 3 speed from my inline. good topic!!
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Old 08-28-2003, 10:26 PM   #4
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As far as i know the trucks(I6 & v8 sb ) had a 2.85 gear. some of the BB stick trucks were listed with a 2.52 gear(not a saginaw, but a muncie trans). The cars had some different ratios, but in my travels the 3.11, & the 3.50 were found in a 4 spd saginaw (vega, Monza in that order). I beleive the vega also had a sag 3 spd that was a 3.11 1st gear. The spacing on these trannies is a little wide, as compaired to a camaro sag 4 spd , with a 2.52 1st(v8). You might also find the lower geared versions on the 4 spd in a 6 cyl camaro(2.85, or possibly 3.11). I ran a Monza 4 spd behind a warm 327 in a c10 , with 3.73 about a screamer with that 3.50 1 st gear. it also ran in my longhorn behind a 355......but only for part of a season(6500 rpm shift to 3rd gear took it out!). That trans was id'ed by 3 rings around the input shaft . I ran a 3.11 vega box , but many yrs ago, but dont remember how many grooves the input shaft had. either of these trannies will take a little "spirited street driving behind a sb V8 for quite a few miles, but have less teeth on the input shaft to get the ratios, so are not as strong as the camaro sag /with 2.52 1 st. Im sure ther are some details I have forgotten along the way(time is a tough thing) LOL! good luck, crazyL
69 longhorn,4" chop,3/5 drop, 1/2 ton suspension/disc brakes,1 1/2" body drop,steel tilt clip, 5.3/Edelbrock rpm intake/600 carb, Hooker streetrod shorties,2 1/2" exhaust/ H pipe/50's Flows , 6 spd Richmond trans,12 bolt/ 3.40 gears....

Last edited by crazy longhorn; 08-28-2003 at 10:28 PM.
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Old 08-30-2003, 07:52 AM   #5
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OK here's what I could find; RPO code ZW4 73-80= 2.85, 1.68, 1.00:1. ZW4 was changed to M-15 for 77-87. M-15 81-87= 2.85, 1.68, 1.00:1 w/350. 3.11, 1.84, 1.00:1 w/305. 3.50, 1.89, 1.00:1 w/250. Also the Saginaw 3-Spd 2.54, 1.88, 1.00:1. I do not know how you would tell the differences but this is what I could find out. Good Luck...Jon
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Old 08-31-2003, 01:21 AM   #6
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They also have info for Muncie & BW.
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Old 08-31-2003, 09:26 PM   #7
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std equipment 250 engine(CS models std equipment) synchromesh SM318: 2.94, 1.68, 1.00, rev 3.14

M17 fully synchronized SM326(292 and larger engines- 2.85, 1.68, 1.00, rev 2.95

warner T16D(used with 396/402 in the 10 and 20 series trucks and is the heaviest three speed tranny used in the trucks): 2.86, 1.72, 1.00, 2.86 rev

el caminos did get the same sm326 with the 230, 250 and 307 only,

the 325hp engine Saginaw three speeds were re-geared to: 2.54, 1.50, 1.00 and 2.63 rev

the same warner t16D was available in el caminos with 230, 250 and 307 also, but with floor shift when console was ordered,

and the T16D was regeared in el caminso with the 327 and 396 to: 2.41, 1.59, 1.00, and 2.41 rev

saginaw have seven-bolt side cover

the sm318 was four-bolt side cover

the 318 is not listed on the above listed page url
the above listed URL listings on four speeds dont match the elcamino four speeds, there were four el camino four speeds and the listings dont match any of them exactly right,
a couple are close to GM specs

Last edited by gmtrucksaddict; 08-31-2003 at 09:40 PM.
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Old 09-02-2003, 10:48 AM   #8
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I've got some different numbers as '69, (3) different 3-speeds were offered; (1) 3-speed fully synchronized, (2) HD 3-speed fully synchronized, (3) 3-speed overdrive. I don't know what each of these trannies are, saginaw or the like, but for tranny (1)...specs are

(1) Standard on all 10-20 series except with 307 or 350.

(2) HD tranny included with with either 350 or 396, and on PE20 models with a 307 or 350. Standard on all 4WD applications (KA10-20)

(3) Available ONLY on C10 models with the 4.11 rear axle.

Either way you slice it, there really isn't that much difference gearwise until you hit the OD tranny.
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