Rear gears - The 1947 - Present Chevrolet & GMC Truck Message Board Network

pontiacvince · 01-22-2023, 10:57 PM

Taking my Suburban in tomorrow to get the rear gear changed from a 3.07 to a 3.42. The lil 307 engine needs a few more RPM's when the 700r4 is in full lockup.

**LockDoc** · 01-23-2023, 01:27 AM

Quote:

Originally Posted by pontiacvince

Taking my Suburban in tomorrow to get the rear gear changed from a 3.07 to a 3.42. The lil 307 engine needs a few more RPM's when the 700r4 is in full lockup.

I hope that takes care of it for you. I had a 350 crate engine and 2004r in my '69 Suburban with a 3.08 rear. Transmission overheated and blew the fluid out of the front seal when it had been locked up for quite a while, on a long trip. (250 miles) The bottom side of the truck and back window were coated with trans fluid.... I put a 3.73 gear in it and never had any more problems with it after that. Let us know if the 3.54 works OK for you.

LockDoc

**kwmech** · 01-23-2023, 02:02 AM

The swap to a 3.42 may not give you that much of a noticeable difference. You're only talking an 11 percent difference. 3.73 (18%) would have been a better choice unless you drive 80-85 mph all the time. 3.73 in overdrive will give you about a 2.72 final whereas the 3.42 takes you to a 2.49 final. 4.10s get you closer to the original 3.07s at a final of 2.99

Something to think about---talk to your gear guy and see what he says

**Richard** · 01-23-2023, 04:09 AM

Going from a 3.42 to a 3.73 in my 94 with 32" tires gained a little over 100 rpm. Right where I wanted to be. Around town results are very noticeable and the trans does not go in and out of OD like it used to on the highway. Did not look at any calculators for your situation and no idea about tire size, but would guess about +200 rpms over what you have now. A good gain without the annoying higher rpm on the highway.

**HO455** · 01-23-2023, 04:09 PM

Not exactly apples to apples but first gen 2wd S10's with the 4.3 and a700r4 used a 3.42 rear and the 4x4's used 3.73's. The 4.3 and your 307 are close in horsepower and and my S10 Blazer weighs in at 3850. So not a big difference there either.
I can say the the 3.42's in my Blazer are a pretty ratio with 700R4. The 30 to 60 mph hard acceration is better than you expect.

DBear · 01-27-2023, 05:18 PM

I would probably go to 3.73 gears....might get more of what you're after. Either way, hope it works out for you sir.

01-22-2023, 10:57 PM	#1
pontiacvince Registered User Join Date: Sep 2020 Location: Kennewick, Wash. Posts: 241	Rear gears Taking my Suburban in tomorrow to get the rear gear changed from a 3.07 to a 3.42. The lil 307 engine needs a few more RPM's when the 700r4 is in full lockup.

01-23-2023, 02:02 AM	#3
kwmech Senior Member Join Date: Mar 2003 Location: Colfax-California Posts: 8,628	Re: Rear gears The swap to a 3.42 may not give you that much of a noticeable difference. You're only talking an 11 percent difference. 3.73 (18%) would have been a better choice unless you drive 80-85 mph all the time. 3.73 in overdrive will give you about a 2.72 final whereas the 3.42 takes you to a 2.49 final. 4.10s get you closer to the original 3.07s at a final of 2.99 Something to think about---talk to your gear guy and see what he says

01-23-2023, 04:09 AM	#4
Richard Senior Member Join Date: Dec 1999 Location: Southern California Posts: 2,881	Re: Rear gears Going from a 3.42 to a 3.73 in my 94 with 32" tires gained a little over 100 rpm. Right where I wanted to be. Around town results are very noticeable and the trans does not go in and out of OD like it used to on the highway. Did not look at any calculators for your situation and no idea about tire size, but would guess about +200 rpms over what you have now. A good gain without the annoying higher rpm on the highway. __________________ Richard 1972 K10 Custom Deluxe SWB Fleetside My build https://67-72chevytrucks.com/vboard/...d.php?t=800746 Last edited by Richard; 01-23-2023 at 04:14 AM.

01-23-2023, 04:09 PM	#5
HO455 Post Whore Join Date: Feb 2016 Location: Portland Oregon Posts: 11,350	Re: Rear gears Not exactly apples to apples but first gen 2wd S10's with the 4.3 and a700r4 used a 3.42 rear and the 4x4's used 3.73's. The 4.3 and your 307 are close in horsepower and and my S10 Blazer weighs in at 3850. So not a big difference there either. I can say the the 3.42's in my Blazer are a pretty ratio with 700R4. The 30 to 60 mph hard acceration is better than you expect. __________________ Thanks to Bob and Jeanie and everyone else at Superior Performance for all their great help. RIP Bob Parks. 1967 Burban (the WMB),1988 S10 Blazer (the Stink10 II),1969 GTO (the Goat), 1970 Javelin, 1952 F2 Ford OHC six 4X4, 29 Model A, 72 Firebird (the DBP Bird). 85 Alfa Romeo If it breaks I didn't want it in the first place The WMB repair thread http://67-72chevytrucks.com/vboard/s...d.php?t=698377

01-27-2023, 05:18 PM	#6
DBear Registered User Join Date: Nov 2008 Location: Rowlett, TX Posts: 867	Re: Rear gears I would probably go to 3.73 gears....might get more of what you're after. Either way, hope it works out for you sir.

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