Possible to change gear ratio? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Zogbert · 08-09-2017, 09:06 PM

1972 C-10 with 250 and three on the tree.

At present it has 3.73 ratio. I'm getting the rear end rebuilt next week and am wondering if it's possible to have 3.42 or maybe 3.07 gears installed in the existing housing. I do mostly highway driving on a slightly hilly road. Truck is actually decent on fuel, but does rev fairly high at 60 mph.

Anyone out there with a 3.42 or 3.07 with a 250 and three speed? What's it like on the highway?

Is that particular gear swap even possible?

Thanks!

**kwmech** · 08-09-2017, 10:08 PM

With only a 250, you may need the gearing to get any type of feeling of power. I usually see them with 4.10 in them

Zogbert · 08-09-2017, 10:12 PM

I'm actually looking for highway cruising, not a feeling of power.

Zogbert · 08-09-2017, 10:17 PM

I've been reading it may not be possible to easily convert a 3.73 to a 3.42.

**kwmech** · 08-09-2017, 10:53 PM

Yeah, you'll need a different carrier and the gear set, new bearings and seals Not all that difficult, it's only money. However since cruising is your only concern you may want to look at a taller ratio. From the 3.73 to the 3.42 is less than a 10% change.. 9.4 to be exact

**jocko** · 08-09-2017, 11:02 PM

If you're just highway cruising and gonna keep the 6 cyl, a T5 is an easy swap and keeps the low end gearing and has o/d - will drop cruising rpm approx. 30%. If you can tell us your current tire diameter, we can tell you your cruising rpm at different speeds. Are you certain you have a 3.73? If you plan to swap in a V8 and/or lay the occasional rubber patch, then skip the T5 idea. It's a good trans, but not strong enough to be abused.

Zogbert · 08-10-2017, 07:31 AM

I'm thinking the T5 may be the best option. Thanks!

67 chevelle · 08-10-2017, 01:42 PM

t5 would be much better , you would keep your low end grunt and have another gear when you need it

Zogbert · 08-10-2017, 08:54 PM

I agree!
Posted via Mobile Device

**jocko** · 08-10-2017, 10:12 PM

Use this as a ref if you like, it's my old 66, but all the same principles apply.
http://67-72chevytrucks.com/vboard/s...d.php?t=482069

08-09-2017, 09:06 PM	#1
Zogbert Registered User Join Date: Feb 2008 Location: Falcon Beach, Manitoba Posts: 37	Possible to change gear ratio? 1972 C-10 with 250 and three on the tree. At present it has 3.73 ratio. I'm getting the rear end rebuilt next week and am wondering if it's possible to have 3.42 or maybe 3.07 gears installed in the existing housing. I do mostly highway driving on a slightly hilly road. Truck is actually decent on fuel, but does rev fairly high at 60 mph. Anyone out there with a 3.42 or 3.07 with a 250 and three speed? What's it like on the highway? Is that particular gear swap even possible? Thanks! __________________ 1972 Chevrolet C-10 "Ba-Lou"

08-09-2017, 10:08 PM	#2
kwmech Senior Member Join Date: Mar 2003 Location: Colfax-California Posts: 8,628	Re: Possible to change gear ratio? With only a 250, you may need the gearing to get any type of feeling of power. I usually see them with 4.10 in them

08-09-2017, 10:12 PM	#3
Zogbert Registered User Join Date: Feb 2008 Location: Falcon Beach, Manitoba Posts: 37	Re: Possible to change gear ratio? I'm actually looking for highway cruising, not a feeling of power. __________________ 1972 Chevrolet C-10 "Ba-Lou"

08-09-2017, 10:17 PM	#4
Zogbert Registered User Join Date: Feb 2008 Location: Falcon Beach, Manitoba Posts: 37	Re: Possible to change gear ratio? I've been reading it may not be possible to easily convert a 3.73 to a 3.42. __________________ 1972 Chevrolet C-10 "Ba-Lou"

08-09-2017, 10:53 PM	#5
kwmech Senior Member Join Date: Mar 2003 Location: Colfax-California Posts: 8,628	Re: Possible to change gear ratio? Yeah, you'll need a different carrier and the gear set, new bearings and seals Not all that difficult, it's only money. However since cruising is your only concern you may want to look at a taller ratio. From the 3.73 to the 3.42 is less than a 10% change.. 9.4 to be exact

08-09-2017, 11:02 PM	#6
jocko Senior Member Join Date: Oct 2009 Location: Godley, TX Posts: 17,975	Re: Possible to change gear ratio? If you're just highway cruising and gonna keep the 6 cyl, a T5 is an easy swap and keeps the low end gearing and has o/d - will drop cruising rpm approx. 30%. If you can tell us your current tire diameter, we can tell you your cruising rpm at different speeds. Are you certain you have a 3.73? If you plan to swap in a V8 and/or lay the occasional rubber patch, then skip the T5 idea. It's a good trans, but not strong enough to be abused.

08-10-2017, 07:31 AM	#7
Zogbert Registered User Join Date: Feb 2008 Location: Falcon Beach, Manitoba Posts: 37	Re: Possible to change gear ratio? I'm thinking the T5 may be the best option. Thanks! __________________ 1972 Chevrolet C-10 "Ba-Lou"

08-10-2017, 01:42 PM	#8
67 chevelle Registered User Join Date: May 2013 Location: WEST PALM FLORIDA Posts: 1,174	Re: Possible to change gear ratio? t5 would be much better , you would keep your low end grunt and have another gear when you need it __________________ 68 Long Fleet , ly6 , turbo 350 , 3-5 drop , original paint , front discs 67 Small window , 7 foot bed , tweaked 6.0 LSX 2004R Medium Olive 58 Apache fleet , 235 , offy intake , dual exhaust , 4 on the floor , red/white 69 Long Fleet , Custom , 6.0, 4l60 , AC , Medium Olive

08-10-2017, 08:54 PM	#9
Zogbert Registered User Join Date: Feb 2008 Location: Falcon Beach, Manitoba Posts: 37	Re: Possible to change gear ratio? I agree! Posted via Mobile Device

08-10-2017, 10:12 PM	#10
jocko Senior Member Join Date: Oct 2009 Location: Godley, TX Posts: 17,975	Re: Possible to change gear ratio? Use this as a ref if you like, it's my old 66, but all the same principles apply. http://67-72chevytrucks.com/vboard/s...d.php?t=482069



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