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#1 |
Love That '69
Join Date: Oct 2007
Location: Sherwood Park, Alberta, Canada
Posts: 360
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Swapping from 4.56's to 3.73's
Im not very knowledgeable in this area so I thought id ask some people who might be able to give me some information. This fall/winter id like to swap the rear end gears in my '69 C10 from 4.56's to 3.73's, but im not sure what all is needed or how hard it would be for myself to do?
I like my 4.56 gears around town, but they aren't the least bit highway friendly with my TH350 (about 3900 RPM at 70 MPH), so id like to buy a new 3.73 gear set and install em in my 12 bolt rear end. What all needs to be done when swapping? Can anybody shed some light for me? Thanks!
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I AM CANADIAN!!!!! ![]() 1969 Chevy C/10 Truck - SBC V8, TH-350, 3.73 Posi, 1000W Rockford Fosgate Stereo System, B&M Megashifter, GT Grant Steering Wheel, Dual Magnaflow Exhaust System, Dynomax Headers, Lowered 1" Front & 3" Rear, Front/Rear Sway Bars, Racing Seats, 6000K HID Headlights 2008 Chevy Colorado LT - 3.7L I5, 4 Speed Automatic, Crew Cab, 4X4, Z71 Off-Road Package, "Ground Effects" Package, K&N Cold Air Intake, Supermod PTB, Magnaflow Exhaust w/ Resonator, 500W Kenwood / Rockford Fosgate Stereo System, Custom LED Lighting, 6000K HID Low's / High's, Blackcat Customs Gauges / Needles, Carbon Fiber Interior Accents, KrFabs 2" Lift Shackles / Torsion Bar Crank with Rancho RS5000 Shocks, Superskids Skid Plates |
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#2 |
Registered User
Join Date: Aug 2010
Location: Nederland, TX
Posts: 429
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Re: Swapping from 4.56's to 3.73's
I think other people will chime in shortly and they'll all tell you this is not something you want to do yourself unless you know what you are doing. I asked the same question a couple months back and that's the reply I got. Take it to a reputable shop and let them do it for you.
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#3 |
Senior Member
Join Date: Jul 2010
Location: South Dakota
Posts: 4,093
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Re: Swapping from 4.56's to 3.73's
It's very difficult to get it right if you don't know exactly what your doing. Find a rear end with the gear you want, it might be cheaper....
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1969 Chevy c20(Miss Hackjob) |
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#4 | |
Love That '69
Join Date: Oct 2007
Location: Sherwood Park, Alberta, Canada
Posts: 360
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Re: Swapping from 4.56's to 3.73's
Quote:
![]() True...but I dunno what kinda shape a used rear end would be in and does it matter if its a 5-bolt or 6-bolt axle with 3.73 gears...even though my '69 is a 6-bolt?
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I AM CANADIAN!!!!! ![]() 1969 Chevy C/10 Truck - SBC V8, TH-350, 3.73 Posi, 1000W Rockford Fosgate Stereo System, B&M Megashifter, GT Grant Steering Wheel, Dual Magnaflow Exhaust System, Dynomax Headers, Lowered 1" Front & 3" Rear, Front/Rear Sway Bars, Racing Seats, 6000K HID Headlights 2008 Chevy Colorado LT - 3.7L I5, 4 Speed Automatic, Crew Cab, 4X4, Z71 Off-Road Package, "Ground Effects" Package, K&N Cold Air Intake, Supermod PTB, Magnaflow Exhaust w/ Resonator, 500W Kenwood / Rockford Fosgate Stereo System, Custom LED Lighting, 6000K HID Low's / High's, Blackcat Customs Gauges / Needles, Carbon Fiber Interior Accents, KrFabs 2" Lift Shackles / Torsion Bar Crank with Rancho RS5000 Shocks, Superskids Skid Plates |
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#5 |
Senior Member
Join Date: Jan 2003
Location: daytonabeach
Posts: 22,956
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Re: Swapping from 4.56's to 3.73's
changing gears really depends on what rearend you have// 12bolt can b changed but best done by a pro larger rears 8lug pattern i dont think 373 is available easily or cheaply
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71c-10 350/2004r/4:11 lowered3/4 longbed/dead by hurricane MEANING OF DEATH::::: SOMEBODY ELSE GETS YOUR STUFF DONT BELIEVE EVERYTHING YOU THINK TAKE MY ADVISE;I DON'T USE IT ANYWAY |
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#6 | |
Account Suspended
Join Date: Jan 2007
Location: Tucson
Posts: 2,183
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Re: Swapping from 4.56's to 3.73's
Quote:
The Chassis Overhaul manual devotes 4 or 5 pages on how to do what you want to do. if you don't have one go here: http://www.themotorbookstore.com/fac...e-manuals.html Just be sure you get the OVERHAUL manual, not the service manual. the 12 bolt diff for 67-72 trucks are the same internally with different length axle tubes so don't panic if you have to pick another year. The new gearset (if you go to a place like DTS) will be about $200.00 and you will need the complete install kit for somewhere around $125.00. There are two diff shops here in Tucson that will charge over $800.00 to do this so you decide if your skills are up to it or not. There are TWO critical adjustments you must make....engagement depth and backlash. The engagement depth is set with the pinion shims, backlash is adjusted with carrier shims. The first two pictures show engagement depth which was too deep in the first then just right in the second. The second picture also shows the contact pattern with the backlash set to 0.008 in. which was in the middle of the allowable range. It took about 4 hours to set this diff up correctly so if you decide to do this take your time. One trick I use to set engagement depth is an old pinion bearing that a machine shop has turned on a lathe to enlarge the inner hole until it is a slip fit on the pinion shaft. This will let you test fit and change shims without ruining the new bearing and crush sleeve in the assembly kit by attempting to remove it to change shim sizes. if you can't get a machine shop to turn it dod for you you can always do this by hand using crocus cloth but that's going to take some tiome as those bearings are hard. |
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#7 |
Moderator
![]() Join Date: May 2007
Location: Southern Cal
Posts: 20,005
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Re: Swapping from 4.56's to 3.73's
take it to a shop....that way you get a warranty and guarantee that it won't howl at the moon.
Posted via Mobile Device
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1972 C/10 Cheyenne Super SWB. Restored, loaded, slammed. 1968 C/10 50th Anniversary LWB. Unrestored, stock, daily driver/work truck. RIP ElJay RIP 67ChevyRedneck RIP Grumpy Old Man |
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#8 |
Registered User
Join Date: Aug 2009
Location: Alden NY
Posts: 2,705
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Re: Swapping from 4.56's to 3.73's
Another option, rather than changing gear set, would be to change the 350 to a 200 4R overdrive transmission. Same length as your current transmission. I would only do this if you have a V8 with a 4 bbl carb (quadrajet or holley) where you can get the proper throttle valve cable bracket and carb linkage swing. If you have a 6, I'd go with the gear change as the throttle valve cable adjustment and the degree of arc and position at 1/4 throttle are critical to its proper operation. Not easy to do if you are fabbing bracket and linkage on a six, but easy to do with a quadrajet as that is what they mostly came with or with a Holley where aftermarketers make a setup (BowTie Overdrives for example) that will work.
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1961 C1 Corvette 1959 El Camino 350 TPI, 9" 4 w disc 69 Blazer K5 - sold July '20 2021 Durango RT 5.7 |
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#9 | |
Love That '69
Join Date: Oct 2007
Location: Sherwood Park, Alberta, Canada
Posts: 360
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Re: Swapping from 4.56's to 3.73's
Quote:
Soo...I called around to a few different shops in town and got some quotes: $750, $850, $1100, and as high as $1500!!! Every place offers a 1 year / 20,000 km warranty which is good...
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I AM CANADIAN!!!!! ![]() 1969 Chevy C/10 Truck - SBC V8, TH-350, 3.73 Posi, 1000W Rockford Fosgate Stereo System, B&M Megashifter, GT Grant Steering Wheel, Dual Magnaflow Exhaust System, Dynomax Headers, Lowered 1" Front & 3" Rear, Front/Rear Sway Bars, Racing Seats, 6000K HID Headlights 2008 Chevy Colorado LT - 3.7L I5, 4 Speed Automatic, Crew Cab, 4X4, Z71 Off-Road Package, "Ground Effects" Package, K&N Cold Air Intake, Supermod PTB, Magnaflow Exhaust w/ Resonator, 500W Kenwood / Rockford Fosgate Stereo System, Custom LED Lighting, 6000K HID Low's / High's, Blackcat Customs Gauges / Needles, Carbon Fiber Interior Accents, KrFabs 2" Lift Shackles / Torsion Bar Crank with Rancho RS5000 Shocks, Superskids Skid Plates Last edited by Classic69; 08-31-2011 at 06:52 PM. |
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#10 |
Love That '69
Join Date: Oct 2007
Location: Sherwood Park, Alberta, Canada
Posts: 360
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Re: Swapping from 4.56's to 3.73's
Huh...so I guess I had 3.73's in my '69 C/10, but I dunno why it screams so high on the highway, it should be about 600-700 RPM lower!! Because right now 65 MPH im at about 3600 and at 70 MPH im around 3900 RPM, when it should be closer to or just over 3000 RPM's....
I got new bearings and seals, along with an Eaton Posi (which wasnt cheap!), and I guess one of my axles needed to be replaced cuz it was worn pretty bad. Total cost will end up being about $1500. I pick it up in 2 days, so we'll see if it'll be worth it lol
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I AM CANADIAN!!!!! ![]() 1969 Chevy C/10 Truck - SBC V8, TH-350, 3.73 Posi, 1000W Rockford Fosgate Stereo System, B&M Megashifter, GT Grant Steering Wheel, Dual Magnaflow Exhaust System, Dynomax Headers, Lowered 1" Front & 3" Rear, Front/Rear Sway Bars, Racing Seats, 6000K HID Headlights 2008 Chevy Colorado LT - 3.7L I5, 4 Speed Automatic, Crew Cab, 4X4, Z71 Off-Road Package, "Ground Effects" Package, K&N Cold Air Intake, Supermod PTB, Magnaflow Exhaust w/ Resonator, 500W Kenwood / Rockford Fosgate Stereo System, Custom LED Lighting, 6000K HID Low's / High's, Blackcat Customs Gauges / Needles, Carbon Fiber Interior Accents, KrFabs 2" Lift Shackles / Torsion Bar Crank with Rancho RS5000 Shocks, Superskids Skid Plates Last edited by Classic69; 09-20-2011 at 05:35 PM. |
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#11 |
Senior Member
Join Date: Jul 2010
Location: South Dakota
Posts: 4,093
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Re: Swapping from 4.56's to 3.73's
They ant cheap
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1969 Chevy c20(Miss Hackjob) |
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#12 | ||
just can't cover up my redneck
Join Date: May 2004
Location: Columbus OH
Posts: 11,414
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Re: Swapping from 4.56's to 3.73's
Quote:
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You can review the site's rules here. Quote:
Bad planning on your part does not necessarily constitute an instant emergency on my part.... The great thing about being a pessimist is that you are either pleasantly surprised or right. ![]() |
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#13 |
Love That '69
Join Date: Oct 2007
Location: Sherwood Park, Alberta, Canada
Posts: 360
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Re: Swapping from 4.56's to 3.73's
Ya....I met a guy at a show n shine the other weekend who is doing it for me. He had a '70s Camaro and his old man had a '60s Chevy pickup. Him and his dad run "R & S Driveline", which does differential work, restoration, bodywork, etc.
ntm....they had the best prices & are close by lol ![]()
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I AM CANADIAN!!!!! ![]() 1969 Chevy C/10 Truck - SBC V8, TH-350, 3.73 Posi, 1000W Rockford Fosgate Stereo System, B&M Megashifter, GT Grant Steering Wheel, Dual Magnaflow Exhaust System, Dynomax Headers, Lowered 1" Front & 3" Rear, Front/Rear Sway Bars, Racing Seats, 6000K HID Headlights 2008 Chevy Colorado LT - 3.7L I5, 4 Speed Automatic, Crew Cab, 4X4, Z71 Off-Road Package, "Ground Effects" Package, K&N Cold Air Intake, Supermod PTB, Magnaflow Exhaust w/ Resonator, 500W Kenwood / Rockford Fosgate Stereo System, Custom LED Lighting, 6000K HID Low's / High's, Blackcat Customs Gauges / Needles, Carbon Fiber Interior Accents, KrFabs 2" Lift Shackles / Torsion Bar Crank with Rancho RS5000 Shocks, Superskids Skid Plates |
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#14 |
Senior Member
Join Date: Jul 2010
Location: South Dakota
Posts: 4,093
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Re: Swapping from 4.56's to 3.73's
^^^ can't beat that!
Posted via Mobile Device
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1969 Chevy c20(Miss Hackjob) |
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#15 |
Love That '69
Join Date: Oct 2007
Location: Sherwood Park, Alberta, Canada
Posts: 360
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Re: Swapping from 4.56's to 3.73's
Soo...I picked up the truck last night after work and I gotta say it was well worth the $1580 to get the rear end rebuilt...The guy even did a few "extras" for me...I got a new bearing/seal kit, along with an Eaton posi unit, 3.73 gears, replaced one axle and the steady bearing/rubber because they were worn out, as well, he adjusted my brakes because they were "grabbing" a bit
It stops alot better, takes off alot better, and drives alot better!! And I had to test out that new positraction by leaving 2 short black stripes lol ![]()
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I AM CANADIAN!!!!! ![]() 1969 Chevy C/10 Truck - SBC V8, TH-350, 3.73 Posi, 1000W Rockford Fosgate Stereo System, B&M Megashifter, GT Grant Steering Wheel, Dual Magnaflow Exhaust System, Dynomax Headers, Lowered 1" Front & 3" Rear, Front/Rear Sway Bars, Racing Seats, 6000K HID Headlights 2008 Chevy Colorado LT - 3.7L I5, 4 Speed Automatic, Crew Cab, 4X4, Z71 Off-Road Package, "Ground Effects" Package, K&N Cold Air Intake, Supermod PTB, Magnaflow Exhaust w/ Resonator, 500W Kenwood / Rockford Fosgate Stereo System, Custom LED Lighting, 6000K HID Low's / High's, Blackcat Customs Gauges / Needles, Carbon Fiber Interior Accents, KrFabs 2" Lift Shackles / Torsion Bar Crank with Rancho RS5000 Shocks, Superskids Skid Plates |
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