Swapping Rear-End Gears - The 1947 - Present Chevrolet & GMC Truck Message Board Network

MandarinSixSeven · 08-21-2002, 01:46 PM

I am going to swap my 3.08 rear-end gears to some 3.73's to get some more of that good ol' "poor-man's-torque", i just would like to know if you all you have to do is swap just the ring and pinion, or is there more involved?

minibike · 08-21-2002, 01:51 PM

The carrier or differential is different between those two, I believe. One of them is a #3, and one is a #4. I may have them reversed, but I believe the #3 is good up to 3.42 or something like that. Then the other one si good for 3.73 to 4 something.

Michael A. K. G · 08-21-2002, 02:11 PM

When changing gearsets, you have to make sure the pinion depth and backlash are set correctly, and adjust them precisely. If you don't, your gearset may not last through the break-in period.

This is not an operation to be done lightly or quickly.

Longhorn Man · 08-21-2002, 07:38 PM

While there is certianly a gamble in doing this, the easiest way to do it would be to find one that already has the gearset you are looking for.
I'll agree, the 3.07's in your truck blow.

Tracy Focht · 08-22-2002, 11:07 AM

I agree. I had the stock 3.07's,a dn went to the 4.11's...wow!

busterwivell · 08-22-2002, 11:30 AM

Yah, but 4:56 ain't too good either!

Yellow Cheyenne · 08-22-2002, 11:34 AM

If you buy aftermarket gears and tell them which carrier you have, they can give you a set of 3.73 gears that will fit your carrier. Backlash would still have to be set up correctly.

Longhorn Man · 08-22-2002, 05:35 PM

I know what your talking about on the 4.56 gears...I am scared to doa tooth count on the one ton...caddy motors don't like 4.56 gears.

*Fast68Chevy* · 08-23-2002, 02:38 AM

originally posted by: Yellow Cheyenne
If you buy aftermarket gears and tell them which carrier you have, they can give you a set of 3.73 gears that will fit your carrier. Backlash would still have to be set up correctly.

even so, they will give him 3 series 3.73 set which is not good idea, reason being because the stock 4 series ratios use alot smaller diameter of pinion gear head than 3 series ratio sets do, they make 4 series sets for use on 3 series carriers, but its a cheap trick, the ring gear would have to be thicker than a stock 4 series ring gear to make up for the difference in distance from the ring gear mounting flange on the carrier to the pinion gear head(closer on 4 series carriers, and fartehr away on 3 series carriers, all by about 9/16" or 5/8" or so), would need longer ring gear attachment bolts..

i think i said that all right, i hope,,

finding a 4 series carrier form someone for cheap would be preferable, or complete 3.73 rear, they are not uncommon rears, 3.73 '67-72 axles are common place, especially '64-'70('70 will readily accept '71-up 5 lug shafts, and '64-69 will if you put a 3/4" spcer between brake backing plate and axle tube flange)

if you find an axle with HA tube stamping prefix code tell its a 64-69 3.73, thats the most common stamping before '71, ive come across many more 3.73 axles that ive parted or scrapped than i can remember('68-'69 mainly)

good luck

minibike · 08-23-2002, 08:16 AM

If you don't want the spacer, you can use a 74 drum, which closes the gap perfectly on a 69 backing plate.

Woody · 08-23-2002, 08:49 AM

minibike,

Nice pic! Could you tell us a little more details on the '74 drum/69 backing plate setup? I want to install 71-71 axels in my 69 without swapping out the whole rear.
1) Swapping the axels and drums, is that all you changed?
2) What shoes are you using? 11" x 2"?
3) Would '74 backing plates and the wider shoes fit?
4) How long have you been running this setup?

nate68 · 08-24-2002, 08:12 PM

get a 9", a lot easier to swap gears, so then u can have street gears and track gears. then u wont have to worry about backlash

minibike · 08-25-2002, 08:02 AM

1) Swapping the axels and drums, is that all you changed?

I replaced the bearings outer bearings and seals also, but the only parts that are not 69 are the axles and drums.

2) What shoes are you using? 11" x 2"?

Yes, It looked like I could use the bigger ones, but I was afraid of changing the overall pad area. The proportioning valve for the 71 brakes is designed for 2", I believe.

3) Would '74 backing plates and the wider shoes fit?

I don't know about the 74 backing plates...didn't have any handy.

4) How long have you been running this setup? I haven't driven with it on.

All I have done ans assembled it, rolled it and pulled on the parking brake cable to make sure it works. It will be a few months before it gets a road test. The inside dimension on the drum is within the tolerance of the original 69 drum, so I don't see any problems with it. There cold be some problems as the drums are turned out beyond the tolerance of the original 69 drums, but it will be a long time and a lot of miles before the drums were turned a couple of times or so.

08-21-2002, 01:46 PM	#1
MandarinSixSeven Seasonal Poster Join Date: Apr 2002 Location: Kelowna BC Canada Posts: 896	Swapping Rear-End Gears I am going to swap my 3.08 rear-end gears to some 3.73's to get some more of that good ol' "poor-man's-torque", i just would like to know if you all you have to do is swap just the ring and pinion, or is there more involved? __________________ 67 GMC Short Step 350/4-Speed/3.08 Posi Front/Rear Sway Bars Kelowna BC, Canada Member of DTPW

08-21-2002, 01:51 PM	#2
minibike Registered User Join Date: Jun 2002 Location: Lafayette, LA Posts: 500	The carrier or differential is different between those two, I believe. One of them is a #3, and one is a #4. I may have them reversed, but I believe the #3 is good up to 3.42 or something like that. Then the other one si good for 3.73 to 4 something. __________________ 69 SWB LT1/4L60E www.classicplace.com

08-22-2002, 11:30 AM	#6
busterwivell Registered User Join Date: Jan 2002 Location: Sahuarita, AZ USA Posts: 2,033	Yah, but 4:56 ain't too good either! __________________ Bill - Tucson, AZ 47 Chevrolet 2 dr sedan 56 Chevrolet 210 2 dr sedan 66 Chevrolet Malibu 2 dr 4 speed 71 Chevrolet C30 Longhorn 86 Chevrolet Monte Carlo SS (Sold) 01 Chevrolet Tahoe IM - BUSTERWIVE@aol.com

08-22-2002, 11:34 AM	#7
Yellow Cheyenne Registered User Join Date: Jun 2001 Location: Eastern Kansas Posts: 488	If you buy aftermarket gears and tell them which carrier you have, they can give you a set of 3.73 gears that will fit your carrier. Backlash would still have to be set up correctly. __________________ '72 Cheyenne. AC, PS, PB, Rear slider window, tilt. Light yellow (grapefruit yellow according to new sales literature from '72) '56 Chevy short step V-8 (My dad bought it new!!) '70 Olds 442 convertible '70 Olds Rallye 350

08-23-2002, 02:38 AM	#9
Fast68Chevy Account Suspended Join Date: May 2000 Location: IL Posts: 0	originally posted by: Yellow Cheyenne If you buy aftermarket gears and tell them which carrier you have, they can give you a set of 3.73 gears that will fit your carrier. Backlash would still have to be set up correctly. even so, they will give him 3 series 3.73 set which is not good idea, reason being because the stock 4 series ratios use alot smaller diameter of pinion gear head than 3 series ratio sets do, they make 4 series sets for use on 3 series carriers, but its a cheap trick, the ring gear would have to be thicker than a stock 4 series ring gear to make up for the difference in distance from the ring gear mounting flange on the carrier to the pinion gear head(closer on 4 series carriers, and fartehr away on 3 series carriers, all by about 9/16" or 5/8" or so), would need longer ring gear attachment bolts.. i think i said that all right, i hope,, finding a 4 series carrier form someone for cheap would be preferable, or complete 3.73 rear, they are not uncommon rears, 3.73 '67-72 axles are common place, especially '64-'70('70 will readily accept '71-up 5 lug shafts, and '64-69 will if you put a 3/4" spcer between brake backing plate and axle tube flange) if you find an axle with HA tube stamping prefix code tell its a 64-69 3.73, thats the most common stamping before '71, ive come across many more 3.73 axles that ive parted or scrapped than i can remember('68-'69 mainly) good luck Last edited by Fast68Chevy; 08-23-2002 at 02:42 AM.

08-21-2002, 02:11 PM	#3
Michael A. K. G Registered User Join Date: Jul 2002 Location: California central coast Posts: 126	When changing gearsets, you have to make sure the pinion depth and backlash are set correctly, and adjust them precisely. If you don't, your gearset may not last through the break-in period. This is not an operation to be done lightly or quickly.

08-21-2002, 07:38 PM	#4
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	While there is certianly a gamble in doing this, the easiest way to do it would be to find one that already has the gearset you are looking for. I'll agree, the 3.07's in your truck blow.

08-22-2002, 11:07 AM	#5
Tracy Focht Registered User Join Date: Dec 1999 Location: Stillwater, OK 74075 Posts: 2,936	I agree. I had the stock 3.07's,a dn went to the 4.11's...wow!

08-22-2002, 05:35 PM	#8
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	I know what your talking about on the 4.56 gears...I am scared to doa tooth count on the one ton...caddy motors don't like 4.56 gears.

08-23-2002, 08:16 AM	#10
minibike Registered User Join Date: Jun 2002 Location: Lafayette, LA Posts: 500	If you don't want the spacer, you can use a 74 drum, which closes the gap perfectly on a 69 backing plate. Attached Images __________________ 69 SWB LT1/4L60E www.classicplace.com

08-23-2002, 08:49 AM	#11
Woody Registered User Join Date: Feb 2000 Location: Georgetown, KY, USA Posts: 631	minibike, Nice pic! Could you tell us a little more details on the '74 drum/69 backing plate setup? I want to install 71-71 axels in my 69 without swapping out the whole rear. 1) Swapping the axels and drums, is that all you changed? 2) What shoes are you using? 11" x 2"? 3) Would '74 backing plates and the wider shoes fit? 4) How long have you been running this setup?

08-24-2002, 08:12 PM	#12
nate68 Registered User Join Date: Jan 2000 Location: ca Posts: 1,110	get a 9", a lot easier to swap gears, so then u can have street gears and track gears. then u wont have to worry about backlash __________________ 68 short step, 406/700r4, 9" w/discs.

08-25-2002, 08:02 AM	#13
minibike Registered User Join Date: Jun 2002 Location: Lafayette, LA Posts: 500	1) Swapping the axels and drums, is that all you changed? I replaced the bearings outer bearings and seals also, but the only parts that are not 69 are the axles and drums. 2) What shoes are you using? 11" x 2"? Yes, It looked like I could use the bigger ones, but I was afraid of changing the overall pad area. The proportioning valve for the 71 brakes is designed for 2", I believe. 3) Would '74 backing plates and the wider shoes fit? I don't know about the 74 backing plates...didn't have any handy. 4) How long have you been running this setup? I haven't driven with it on. All I have done ans assembled it, rolled it and pulled on the parking brake cable to make sure it works. It will be a few months before it gets a road test. The inside dimension on the drum is within the tolerance of the original 69 drum, so I don't see any problems with it. There cold be some problems as the drums are turned out beyond the tolerance of the original 69 drums, but it will be a long time and a lot of miles before the drums were turned a couple of times or so. Attached Images __________________ 69 SWB LT1/4L60E www.classicplace.com



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