The difrence between a thre and four speed? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

chopper john · 03-25-2010, 05:46 PM

I have a three speed in my truck right now, what are the advantages if i go to a four speed? ON THE FWY

martindc1 · 03-25-2010, 06:09 PM

You'll have granny gear. Unless you go with a later transmission with overdrive there will be no difference in high gear, it will always be a 1.00:1 ratio. If you were to use a Muncie 4 speed car transmission, you would have a closer ratio through the gears than with your 3 speed, but high gear will be the same. So on the freeway, there is no advantage of a 4 speed over a 3 speed.

markeb01 · 03-25-2010, 06:12 PM

If the 4 speed does not have an overdrive 4th gear, there is little advantage on the freeway. Direct drive is direct drive with either one. Depending on what engine you have, the smaller drops between the gears could be an advantage, since the 4 speed can drop down into 3rd for passing gear. If the vehicle is at freeway speeds, going down to 2nd in a 3 speed usually isn't practical. The main advantages of the extra gear being to provide more flexibility around town and getting up to speed, the cool factor, and having 4 synchronized forward gears if the 3 speed is the older design with a non-synchro 1st gear.

Having a wide ratio 4 speed also provides more flexibility in selection of a rear axle ratio, since you can run a higher rear end gear for better freeway mileage, while having a very low gear for good acceleration from a dead stop.

Rogue · 03-25-2010, 09:13 PM

If your talking Saginaw 3 vs 4, then none.
Final drive is the same.
There's an OD unit for the 3sp that will fit a 4sp too.

On the freeway you need an OD, and/or better gear ratio.

daxloves · 03-25-2010, 11:09 PM

The biggest differenc is a 3spd 1st gear is around 3:1 and the 4spd 1st is around 7:1

chopper john · 03-26-2010, 12:36 AM

cool thanks for all tyhe good info i have a 235 engine with a 3 spd ,my rearend is a 96 caprice so it has 308s or 293s but my truck cruizes about 60 with the rpms kinda high. but im putting a 327 together for it . so i guess i wont change it to a four speed till i do the v8.

sailed2japan · 03-26-2010, 01:31 AM

I didn't know that the od unit from a 3 speed could be fitted to a 4 speed. How hard is that?

Rogue · 03-26-2010, 12:00 PM

Quote:

Originally Posted by sailed2japan

I didn't know that the od unit from a 3 speed could be fitted to a 4 speed. How hard is that?

I have not done it personally, but hear its nearly a bolt on.

chopper john · 03-26-2010, 02:11 AM

ive never seen the od unit

03-25-2010, 05:46 PM	#1
chopper john Registered User Join Date: Oct 2009 Location: anaheim ca Posts: 274	The difrence between a thre and four speed? I have a three speed in my truck right now, what are the advantages if i go to a four speed? ON THE FWY Last edited by chopper john; 03-25-2010 at 05:49 PM.

03-25-2010, 06:09 PM	#2
martindc1 Registered User Join Date: Jul 2009 Location: La Crosse, WI Posts: 218	Re: The difrence between a thre and four speed? You'll have granny gear. Unless you go with a later transmission with overdrive there will be no difference in high gear, it will always be a 1.00:1 ratio. If you were to use a Muncie 4 speed car transmission, you would have a closer ratio through the gears than with your 3 speed, but high gear will be the same. So on the freeway, there is no advantage of a 4 speed over a 3 speed. __________________ Currently truckless, previous trucks: 67 K20, 87 K10 aka V10 & 72 C10

03-25-2010, 06:12 PM	#3
markeb01 Senior Enthusiast Join Date: Feb 2007 Location: Spokane Valley, WA Posts: 8,356	Re: The difrence between a thre and four speed? If the 4 speed does not have an overdrive 4th gear, there is little advantage on the freeway. Direct drive is direct drive with either one. Depending on what engine you have, the smaller drops between the gears could be an advantage, since the 4 speed can drop down into 3rd for passing gear. If the vehicle is at freeway speeds, going down to 2nd in a 3 speed usually isn't practical. The main advantages of the extra gear being to provide more flexibility around town and getting up to speed, the cool factor, and having 4 synchronized forward gears if the 3 speed is the older design with a non-synchro 1st gear. Having a wide ratio 4 speed also provides more flexibility in selection of a rear axle ratio, since you can run a higher rear end gear for better freeway mileage, while having a very low gear for good acceleration from a dead stop. Last edited by markeb01; 03-25-2010 at 06:14 PM.

03-25-2010, 09:13 PM	#4
Rogue Airport Bum Join Date: Jan 2005 Location: Propwash (16Xray) D/FW, Texas Posts: 320	Re: The difrence between a thre and four speed? If your talking Saginaw 3 vs 4, then none. Final drive is the same. There's an OD unit for the 3sp that will fit a 4sp too. On the freeway you need an OD, and/or better gear ratio. __________________ 1964 Chevrolet C-10 1941 Chevrolet coupe 1962 Thunderbird 1959 Edsel Villager 1963 Skylark

03-25-2010, 11:09 PM	#5
daxloves Registered User Join Date: Mar 2010 Location: Kettle Falls WA Posts: 48	Re: The difrence between a thre and four speed? The biggest differenc is a 3spd 1st gear is around 3:1 and the 4spd 1st is around 7:1

03-26-2010, 12:36 AM	#6
chopper john Registered User Join Date: Oct 2009 Location: anaheim ca Posts: 274	Re: The difrence between a thre and four speed? cool thanks for all tyhe good info i have a 235 engine with a 3 spd ,my rearend is a 96 caprice so it has 308s or 293s but my truck cruizes about 60 with the rpms kinda high. but im putting a 327 together for it . so i guess i wont change it to a four speed till i do the v8.

03-26-2010, 01:31 AM	#7
sailed2japan Jonny Join Date: Apr 2008 Location: Outside the Box, Austin,TX Posts: 741	Re: The difrence between a thre and four speed? I didn't know that the od unit from a 3 speed could be fitted to a 4 speed. How hard is that? __________________ 1966 C30, Cummins, stacks, and a flat bed in progress... "Honor.....simply put, A veteran - whether active duty, retired, national guard or reserve is someone who, at one time in his life, wrote a blank check made payable to 'The United States of America', for an amount of 'up to and including his life.' That is Honor, and there are way too many people in this country who no longer understand it." -AEC Hundley USNR

03-26-2010, 02:11 AM	#9
chopper john Registered User Join Date: Oct 2009 Location: anaheim ca Posts: 274	Re: The difrence between a thre and four speed? ive never seen the od unit



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