original diff ratio 1972 4wd blazer? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

jrglobal · 03-23-2012, 09:52 PM

Does anybody know the stock ratio of the Dana 44 diffs of a 1972 4wd blazer?
it seems to be really high, something about 4.10 or something?

**landy** · 03-24-2012, 01:03 AM

I think the factory options were 3.07 or 3.73. My '72 has 3.73s.

jrglobal · 03-24-2012, 05:07 AM

Yeah thanks, I might have a 3.73 aswell, would like to go to a 3.07 cause for long distance driving with a TH350 tranny it would be much more gas efficient to have cruising speeds around 60mph instead of around 45mph with a 3.73.
The rpms are much too high at 60mph, should be at around 2500rpm isnstead of
3000-3500rpm, what I have at with my present ratio.

Does somebody know if this works out?

rsavage · 03-24-2012, 07:34 AM

Mine came with a 350/350 and 3.07 differentials. There is no axle ratio option listed on the SPID, so I assume that this was the "stock" gearing for the 350/350 combination. Do a little search as there was another recent discussion on this.

**landy** · 03-24-2012, 10:50 AM

There are lots of tire size/gear ratio/rpm/mph calculators on the internet. You can enter different parameters to see how it'll affect your speed and rpm.

Give that a try to see if you can get the combo you want.

Firebirdjones · 03-24-2012, 11:07 AM

My 72 originally is a 350/350 combo and had 3.07's. It also has air conditioning which I believe is a deciding factor in available gears.

With the 33" tires I run, the 3.07's were very friendly with that combo, cruising at 70 mph was only 2400 rpms and I got 16 mpg like that, and 13 mpg around town.

I have since installed an LS 6.0/4L60E combo and ran the 3.07's for a while. I removed both complete differential housings and installed a pair of them with 3.73's to try out. So far I'm liking it.

Firebirdjones · 03-24-2012, 05:00 PM

I forgot to mention, if you currently have 3.73's and the highway rpm is excessive (you say 3,000 3,500 rpm at 60??) That sounds a bit steep unless you have a very short tire on it??

A 3.73 gear with 33" tires (seems to be the common go to size on these blazers) will give you roughly 70 mph at 2800 rpms with no overdrive. That's a reasonable cruise speed and a very reasonable rpm to live with. I have a couple cars here running 3.73's and no overdrive, and it's very streetable even with a 28" tire.

It would seem that a simple tire swap to 33's would be the easiest cure for you.

03-23-2012, 09:52 PM	#1
jrglobal Registered User Join Date: Feb 2012 Location: Los Angeles Posts: 13	original diff ratio 1972 4wd blazer? Does anybody know the stock ratio of the Dana 44 diffs of a 1972 4wd blazer? it seems to be really high, something about 4.10 or something?

03-24-2012, 01:03 AM	#2
landy Senior Member Join Date: Jun 2000 Location: alb, nm Posts: 413	Re: original diff ratio 1972 4wd blazer? I think the factory options were 3.07 or 3.73. My '72 has 3.73s.

03-24-2012, 05:07 AM	#3
jrglobal Registered User Join Date: Feb 2012 Location: Los Angeles Posts: 13	Re: original diff ratio 1972 4wd blazer? Yeah thanks, I might have a 3.73 aswell, would like to go to a 3.07 cause for long distance driving with a TH350 tranny it would be much more gas efficient to have cruising speeds around 60mph instead of around 45mph with a 3.73. The rpms are much too high at 60mph, should be at around 2500rpm isnstead of 3000-3500rpm, what I have at with my present ratio. Does somebody know if this works out?

03-24-2012, 07:34 AM	#4
rsavage Registered User Join Date: Aug 2009 Location: Alden NY Posts: 2,705	Re: original diff ratio 1972 4wd blazer? Mine came with a 350/350 and 3.07 differentials. There is no axle ratio option listed on the SPID, so I assume that this was the "stock" gearing for the 350/350 combination. Do a little search as there was another recent discussion on this. __________________ 1961 C1 Corvette 1959 El Camino 350 TPI, 9" 4 w disc 69 Blazer K5 - sold July '20 2021 Durango RT 5.7

03-24-2012, 10:50 AM	#5
landy Senior Member Join Date: Jun 2000 Location: alb, nm Posts: 413	Re: original diff ratio 1972 4wd blazer? There are lots of tire size/gear ratio/rpm/mph calculators on the internet. You can enter different parameters to see how it'll affect your speed and rpm. Give that a try to see if you can get the combo you want.

03-24-2012, 11:07 AM	#6
Firebirdjones Registered User Join Date: Oct 2009 Location: Prescott, Arizona Posts: 2,396	Re: original diff ratio 1972 4wd blazer? My 72 originally is a 350/350 combo and had 3.07's. It also has air conditioning which I believe is a deciding factor in available gears. With the 33" tires I run, the 3.07's were very friendly with that combo, cruising at 70 mph was only 2400 rpms and I got 16 mpg like that, and 13 mpg around town. I have since installed an LS 6.0/4L60E combo and ran the 3.07's for a while. I removed both complete differential housings and installed a pair of them with 3.73's to try out. So far I'm liking it.

03-24-2012, 05:00 PM	#7
Firebirdjones Registered User Join Date: Oct 2009 Location: Prescott, Arizona Posts: 2,396	Re: original diff ratio 1972 4wd blazer? I forgot to mention, if you currently have 3.73's and the highway rpm is excessive (you say 3,000 3,500 rpm at 60??) That sounds a bit steep unless you have a very short tire on it?? A 3.73 gear with 33" tires (seems to be the common go to size on these blazers) will give you roughly 70 mph at 2800 rpms with no overdrive. That's a reasonable cruise speed and a very reasonable rpm to live with. I have a couple cars here running 3.73's and no overdrive, and it's very streetable even with a 28" tire. It would seem that a simple tire swap to 33's would be the easiest cure for you.



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