rear end conversion or ratio change? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Tim240Z · 03-19-2005, 01:20 AM

Great to have the search feature back!!
Anyways.....I have a 99 5.7L and 4L60E on a pallette in the garage waiting to go into the truck, but it appears that I have a 'corporate'/eaton/spicer diff out back in the truck. From the searches I've done, it also appears that the ratio is 4.1 or higher (numerically), and I am doing the conversion to get the best fuel consumption possible (removing my 360hp 350/TH350).

So, I would like to get some better ratio gears to that end (maybe 3.7, 3.05 etc). It also seems that gearsets for these rears are impossible to find (?), so my questions are:
Are gearsets available?
or
Is there another rear that I can use (maybe from a newer truck with 8 lug)?
My truck is 3/4 ton with coils....

Thanks,
Tim

1972 · 03-19-2005, 08:58 AM

If you have a 4.10 ratio with a tire 31" tall in overdrive at 65 mph you will be at 2022 rpm, which isn't that bad. Of course those numbers may be different than what you have, but it gives you an idea. You can use THESE and put in any rear end that will fit if you are able to fab a panhard bar bracket.

OhioDan · 03-19-2005, 09:28 AM

You might try and go here>

http://www.drivetrainspecialists.com/about.html

And check with them. That's what they do. Hope this helps?

Tim240Z · 03-19-2005, 04:36 PM

I have 245/75-16 tires and at ~65 I am pulling ~3200 rpm. I know my speedo is not accurate, so take those numbers with a pinch of salt. According to This Calculator the tires are 30.5" diameter.

1972 · 03-20-2005, 01:34 PM

With the setup you have now, an OD tranny will put you at abut 2250 RPM at the same speed ~65 Calculators, enter "1"for transfer case ratio, "1" for 3rd gear on either tranny, and ".7" for OD.

Tim240Z · 03-20-2005, 01:46 PM

Thank man!!
I guess I will just open the diff, clean it nicely, change the oil and hope for another 100K miles out of it. The truck only has 100405 now.

03-19-2005, 01:20 AM	#1
Tim240Z Senior Member Join Date: Jan 2005 Location: LAX area, So Cal Posts: 499	rear end conversion or ratio change? Great to have the search feature back!! Anyways.....I have a 99 5.7L and 4L60E on a pallette in the garage waiting to go into the truck, but it appears that I have a 'corporate'/eaton/spicer diff out back in the truck. From the searches I've done, it also appears that the ratio is 4.1 or higher (numerically), and I am doing the conversion to get the best fuel consumption possible (removing my 360hp 350/TH350). So, I would like to get some better ratio gears to that end (maybe 3.7, 3.05 etc). It also seems that gearsets for these rears are impossible to find (?), so my questions are: Are gearsets available? or Is there another rear that I can use (maybe from a newer truck with 8 lug)? My truck is 3/4 ton with coils.... Thanks, Tim __________________ 1972 Suburban C20 454/TH700R4, eaton-corporate 4.10 (looking for 3.7) Sold: 71 Cheyenne 20 Installed a 99 5.7L L31/4L60E from Suburban 1500 (2005)

03-19-2005, 09:28 AM	#3
OhioDan Registered User Join Date: Apr 2002 Location: New Carlisle, Ohio,USA Posts: 1,404	You might try and go here> http://www.drivetrainspecialists.com/about.html And check with them. That's what they do. Hope this helps? __________________ LIFE AIN'T EASY WHEN YER FAT AND GREASY! GMC= Got More Class! 1970 GMC LWB, Fleetside, 350/4spd, Flowmaster "40's", 2002 GMC 16" Rallies, cowl hood,and added a bunch of options that weren't there when I started.

03-19-2005, 04:36 PM	#4
Tim240Z Senior Member Join Date: Jan 2005 Location: LAX area, So Cal Posts: 499	I have 245/75-16 tires and at ~65 I am pulling ~3200 rpm. I know my speedo is not accurate, so take those numbers with a pinch of salt. According to This Calculator the tires are 30.5" diameter. __________________ 1972 Suburban C20 454/TH700R4, eaton-corporate 4.10 (looking for 3.7) Sold: 71 Cheyenne 20 Installed a 99 5.7L L31/4L60E from Suburban 1500 (2005)

03-20-2005, 01:46 PM	#6
Tim240Z Senior Member Join Date: Jan 2005 Location: LAX area, So Cal Posts: 499	Thank man!! I guess I will just open the diff, clean it nicely, change the oil and hope for another 100K miles out of it. The truck only has 100405 now. __________________ 1972 Suburban C20 454/TH700R4, eaton-corporate 4.10 (looking for 3.7) Sold: 71 Cheyenne 20 Installed a 99 5.7L L31/4L60E from Suburban 1500 (2005)

03-19-2005, 08:58 AM	#2
1972 Majician Join Date: Nov 2004 Location: In the Middle Posts: 329	If you have a 4.10 ratio with a tire 31" tall in overdrive at 65 mph you will be at 2022 rpm, which isn't that bad. Of course those numbers may be different than what you have, but it gives you an idea. You can use THESE and put in any rear end that will fit if you are able to fab a panhard bar bracket.

03-20-2005, 01:34 PM	#5
1972 Majician Join Date: Nov 2004 Location: In the Middle Posts: 329	With the setup you have now, an OD tranny will put you at abut 2250 RPM at the same speed ~65 Calculators, enter "1"for transfer case ratio, "1" for 3rd gear on either tranny, and ".7" for OD.



Register or Log In To remove these advertisements.

Register or Log In To remove these advertisements.