What rear end gear do I have??? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

HotRod929 · 01-22-2003, 09:31 PM

I recently put a tach in my truck and went out on the high way and got some RPM data. then I went to smokemup.com and tried to figure my rear end with my tires and what not. It said I had something like a 4.56...is this possible and how can I verify this? Sould I drop down to a 4.10 or something? I thought I had 4.10s but maybe I dont. Thanks

HotRod

Fred T · 01-22-2003, 11:22 PM

I can't recall the exact ratio number, but 4.56 was an option on the 3/4 ton trucks. Unless you're pulling loads all the time, I'd go for a 3.73, possibly even the 3.42. Both are available in the 14 bolt full floater, 3.73s are easier to find. $300 in the yards around here.

Longhorn Man · 01-23-2003, 12:11 AM

Bummer is though, he probably does have a 4.56 gear, and it is probably in the Eaton/Corp rear axle which is very expensive to find gears for.

HotRod929 · 01-23-2003, 02:15 AM

Is there any way for me to deffinatly tell if I have the old Eaton/Corp rear axle and if I have 4.56 grears? If I post a pick of the rear end can you tell if its and Eaton or not? My friend thats into Caprices said I had a 10 bolt but i dunno. Let me know please. Thanks

HotRod

HotRod929 · 01-23-2003, 02:23 AM

Also if I do have and Eaton/Corp axle is it worth anything? Will I be able to make some money by selling it and getting another rear axle? If I do get a new rear axle what would you guys recomend and what would be the easyest to swap in? Thanks

HotRod

HotRod929 · 01-23-2003, 11:50 AM

anyone???

lukecp · 01-23-2003, 01:53 PM

To find out your gear ratio, pop off the rearend cover, and divide the number of teeth on the ring gear by the number of teeth on the pinion gear. The fluid proably needs to be changed anyway.

BTW, i'm pretty sure that on the 350 powered 3/4 ton trucks, 4.10 gears came standard. The 307 and 6-cyl trucks came with 4.56 gears. 4.56 were optional though, and your rear axle might have been swapped out sometime in the past.
The 402 big block 3/4 ton trucks usually had a 3.54 gear ratio, which would be much, much better for highway driving.

MAC67 · 01-23-2003, 09:33 PM

to tell the differance between the eatons and the 14 bolt corp,,is pretty easy if im not mistaken,,the eaton will look like a ford nine inch on steroids,,it has a removable rear diff cover and a drop out third member from the front,,,youre 14 bolt will have 14 bolts holdin the rear diff cover on,,,the eatons have a smooth flowing lines where youre center meets the axle tubes,,,and a 14 bolts tubes are pressed into the centers

Fred T · 01-24-2003, 02:17 AM

Here's a shot of a 14 bolt corporate.

TERRYP · 01-24-2003, 03:15 AM

Eatons have a perfectly round rear cover, and the unit does drop out from the front, and only 4.10 and 4.56 were installed in chevy trucks.

casey · 01-25-2003, 06:23 PM

Put some 20" rims on her will that work, Might change you ratio enough to live with and would look real cool

*rustedchevy* · 01-26-2003, 09:36 PM

actual tire dimaeter hieght changes affect rpm at a given speed

4.56 was std ratio for dana 60 equipped trucks

4.10 was optional for dana 60 and eaton

and 3.54 weas optional in dana 60

4.57 is std in eaton, if its eato then its 4.57 or 4.10

mikep · 01-26-2003, 09:47 PM

3.54 was standard ratio for big block equipped dana 60's like mine...

mine has coil springs. Yours doesnt ?

01-22-2003, 09:31 PM	#1
HotRod929 Registered User Join Date: Mar 2002 Location: Bondurant, IA but in Worcester, MA for school Posts: 767	What rear end gear do I have??? I recently put a tach in my truck and went out on the high way and got some RPM data. then I went to smokemup.com and tried to figure my rear end with my tires and what not. It said I had something like a 4.56...is this possible and how can I verify this? Sould I drop down to a 4.10 or something? I thought I had 4.10s but maybe I dont. Thanks HotRod __________________ 1970 Chevy C-20 350 V-8 Turbo 350 w/ shift kit Dana 60 w/ 4.10 gears AND Powr-Loc POSI New Additions: Summit Headers 135amp alternator Proform HEI Edelbrock 1406 600cfm carb Sunpro Tach Powr-Loc POSI Edelbrock Performer RPM Intake MSD 6A Ignition Box AIM: HotRod929 Visit My Site: http://1970chevy.netfirms.com/

01-22-2003, 11:22 PM	#2
Fred T Cantankerous Geezer Join Date: Aug 2002 Location: Bel Aire, KS Posts: 6,264	I can't recall the exact ratio number, but 4.56 was an option on the 3/4 ton trucks. Unless you're pulling loads all the time, I'd go for a 3.73, possibly even the 3.42. Both are available in the 14 bolt full floater, 3.73s are easier to find. $300 in the yards around here. __________________ Fred There is no such thing as too much cam...just not enough engine.

01-23-2003, 02:15 AM	#4
HotRod929 Registered User Join Date: Mar 2002 Location: Bondurant, IA but in Worcester, MA for school Posts: 767	Is there any way for me to deffinatly tell if I have the old Eaton/Corp rear axle and if I have 4.56 grears? If I post a pick of the rear end can you tell if its and Eaton or not? My friend thats into Caprices said I had a 10 bolt but i dunno. Let me know please. Thanks HotRod __________________ 1970 Chevy C-20 350 V-8 Turbo 350 w/ shift kit Dana 60 w/ 4.10 gears AND Powr-Loc POSI New Additions: Summit Headers 135amp alternator Proform HEI Edelbrock 1406 600cfm carb Sunpro Tach Powr-Loc POSI Edelbrock Performer RPM Intake MSD 6A Ignition Box AIM: HotRod929 Visit My Site: http://1970chevy.netfirms.com/

01-23-2003, 02:23 AM	#5
HotRod929 Registered User Join Date: Mar 2002 Location: Bondurant, IA but in Worcester, MA for school Posts: 767	Also if I do have and Eaton/Corp axle is it worth anything? Will I be able to make some money by selling it and getting another rear axle? If I do get a new rear axle what would you guys recomend and what would be the easyest to swap in? Thanks HotRod __________________ 1970 Chevy C-20 350 V-8 Turbo 350 w/ shift kit Dana 60 w/ 4.10 gears AND Powr-Loc POSI New Additions: Summit Headers 135amp alternator Proform HEI Edelbrock 1406 600cfm carb Sunpro Tach Powr-Loc POSI Edelbrock Performer RPM Intake MSD 6A Ignition Box AIM: HotRod929 Visit My Site: http://1970chevy.netfirms.com/

01-23-2003, 11:50 AM	#6
HotRod929 Registered User Join Date: Mar 2002 Location: Bondurant, IA but in Worcester, MA for school Posts: 767	anyone??? __________________ 1970 Chevy C-20 350 V-8 Turbo 350 w/ shift kit Dana 60 w/ 4.10 gears AND Powr-Loc POSI New Additions: Summit Headers 135amp alternator Proform HEI Edelbrock 1406 600cfm carb Sunpro Tach Powr-Loc POSI Edelbrock Performer RPM Intake MSD 6A Ignition Box AIM: HotRod929 Visit My Site: http://1970chevy.netfirms.com/

01-23-2003, 12:11 AM	#3
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	Bummer is though, he probably does have a 4.56 gear, and it is probably in the Eaton/Corp rear axle which is very expensive to find gears for.

01-23-2003, 01:53 PM	#7
lukecp Formerly yellow72custom Join Date: May 2001 Location: Austin, TX Posts: 7,531	To find out your gear ratio, pop off the rearend cover, and divide the number of teeth on the ring gear by the number of teeth on the pinion gear. The fluid proably needs to be changed anyway. BTW, i'm pretty sure that on the 350 powered 3/4 ton trucks, 4.10 gears came standard. The 307 and 6-cyl trucks came with 4.56 gears. 4.56 were optional though, and your rear axle might have been swapped out sometime in the past. The 402 big block 3/4 ton trucks usually had a 3.54 gear ratio, which would be much, much better for highway driving. __________________ '72 Chevy C10 Mild 350/TH350/3.07. Ochre/White. Old high school ride. '70 GMC C2500 '62 327 4bbl/SM465/4.56-geared Dana 60. White/White. Project or parts truck. '97 Saturn SL DD. 1.9/5-speed. 40+ highway mpg

01-23-2003, 09:33 PM	#8
MAC67 " SHOW ME" Join Date: Jan 2003 Location: shelbyville illinois Posts: 2,624	to tell the differance between the eatons and the 14 bolt corp,,is pretty easy if im not mistaken,,the eaton will look like a ford nine inch on steroids,,it has a removable rear diff cover and a drop out third member from the front,,,youre 14 bolt will have 14 bolts holdin the rear diff cover on,,,the eatons have a smooth flowing lines where youre center meets the axle tubes,,,and a 14 bolts tubes are pressed into the centers

01-24-2003, 02:17 AM	#9
Fred T Cantankerous Geezer Join Date: Aug 2002 Location: Bel Aire, KS Posts: 6,264	Here's a shot of a 14 bolt corporate. Attached Images __________________ Fred There is no such thing as too much cam...just not enough engine.

01-24-2003, 03:15 AM	#10
TERRYP GYRO GEARLOOSE Join Date: Jun 2000 Location: Nevada City, CAEverett, WA Posts: 361	Eatons have a perfectly round rear cover, and the unit does drop out from the front, and only 4.10 and 4.56 were installed in chevy trucks. __________________ Nevada City, CA Everett, Washington 57 3/4 rat, 235, 3spd 66 C-10 Panel, SWB. 350 from '68, 200R4 tranny, 3.07 rear ratio, restoring 68 C10 LWB 350 4spd, 4.56 rear dump runner 82 Camaro, 305, THM-200-R4 84 Monte Carlo 305 TH350, land tuna 85 Tercel SW, snow runner DISGRACED OUTLAW MEMBER OF THE DRUM BRAKE CLUB

01-25-2003, 06:23 PM	#11
casey Registered User Join Date: Jan 2003 Location: Kelowna B.C. Canada Posts: 2,048	Put some 20" rims on her will that work, Might change you ratio enough to live with and would look real cool

01-26-2003, 09:36 PM	#12
rustedchevy Account Suspended Join Date: Jan 2003 Location: il Posts: 115	actual tire dimaeter hieght changes affect rpm at a given speed 4.56 was std ratio for dana 60 equipped trucks 4.10 was optional for dana 60 and eaton and 3.54 weas optional in dana 60 4.57 is std in eaton, if its eato then its 4.57 or 4.10

01-26-2003, 09:47 PM	#13
mikep Used to have a truck Join Date: May 2002 Location: port orchard WA Posts: 1,552	3.54 was standard ratio for big block equipped dana 60's like mine... mine has coil springs. Yours doesnt ? __________________ No truck :-(

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