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Old 09-11-2013, 04:14 PM   #1
Jdbfish
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Best rear gears for 700r4

What is the best rear end to run behind a stock 350 with a 700r4 auto? Most of my driving will be at hwy speeds. Will a 3.08 be ok?
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Old 09-11-2013, 04:26 PM   #2
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Re: Best rear gears for 700r4

Should be fine. The 700r4 has a real low first gear so take off shouldn't be too bad. Depending upon your tire size you may actually end up with a lower rpm at highway speeds than you would like. I say try it then adjust if you aren't happy.
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Old 09-11-2013, 04:28 PM   #3
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Re: Best rear gears for 700r4

From what i've seen people on the site using, a lot of them do not like the 3.08 because of to sluggish on the highway. Most seem to use 3.73's
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Old 09-11-2013, 04:30 PM   #4
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Re: Best rear gears for 700r4

most guys over the years have had very bad results and an actual decrease in fuel milage when useing a 700r4 and 308 rear gears// where the guys with the 700r4 and the 373 get best results and fuel milage increases
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Old 09-11-2013, 04:43 PM   #5
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Re: Best rear gears for 700r4

3.42 is the best ratio with tall tires for a mixed use. If you are pulling more, then maybe 3.73.
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Old 09-11-2013, 05:14 PM   #6
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Re: Best rear gears for 700r4

I have 3.08 gears, 700r4 trans, 255/70/15 tires, perfect from 60 mph up.

Around 55mph it feels like it is lugging a bit but my "RV" cam doesn't care.

I like it, I can't say they are the "best" gears as I haven't run it with any others to compare.

My mileage went from 11 mpg with the saginaw 3 speed to around 18 mpg overall (that was with 235/70/15 tires, haven't checked it since I upgraded).

Can't speak for others though.
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Old 09-11-2013, 05:30 PM   #7
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Re: Best rear gears for 700r4

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3.42 is the best ratio with tall tires for a mixed use. If you are pulling more, then maybe 3.73.
X 2 especially with a 28/29 inch tire.
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Old 09-11-2013, 06:03 PM   #8
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Re: Best rear gears for 700r4

3.73
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Old 09-11-2013, 06:41 PM   #9
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Thumbs up Re: Best rear gears for 700r4

I run the 700 r4 with 4:10's and get 16-18 MPG depending on how fast I'm running. At Highway speed (70MPH) I'm turning around 2300RPM's.
I like the way it runs and it performs well for a 305!
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Old 09-11-2013, 07:11 PM   #10
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Re: Best rear gears for 700r4

Literally over 75 percent of the 2wd 88-98 trucks that were V8 and 700r4/4L60/e overdrive equipped came stock with 3.42 gears. Perfect ratio. GM got it right on that one.
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Old 09-11-2013, 07:44 PM   #11
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Re: Best rear gears for 700r4

I am currently running 3.08's and my truck don't like it at anything below 60 mph, I am in the process of switching to 3.73 .
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Old 09-11-2013, 07:53 PM   #12
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Re: Best rear gears for 700r4

Is there a stock 3:42 6 lug rearend option for a 70 model? Thought only 3.08, 3.73 or 4.10 were available
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Old 09-11-2013, 08:21 PM   #13
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Re: Best rear gears for 700r4

350 FI / 4L60E / 3.08's / 30x9.5 tires great setup; take off is not a problem and at speed it works perfectly even with 6000 to 7000 lbs in tow in OD in the hills.

cruising speed of 70 MPH, rpm's are only 1650-1700 and fuel mileage is well above 17 MPG (unloaded)
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Old 09-11-2013, 08:27 PM   #14
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Re: Best rear gears for 700r4

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Originally Posted by Jdbfish View Post
What is the best rear end to run behind a stock 350 with a 700r4 auto? Most of my driving will be at hwy speeds. Will a 3.08 be ok?
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A 3.08 will lug around town with that trans. TX had it right when he said 3.48 is optimal but failing that try a 3.73. Below are the RPM vs MPH for a 700 R4 for the 3.08, 3.48 and 3.73 in that order
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Old 09-11-2013, 10:08 PM   #15
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Re: Best rear gears for 700r4

My son's 71 GMC with a 350, 700R4, and 3.08 gears is a bit sluggish for my liking. We will probably change to 3.73 sometime in the future.
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Old 09-11-2013, 10:30 PM   #16
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Re: Best rear gears for 700r4

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I changed the 3.08 to a 3.73 in the '69 Suburban. Made all the difference in the world.... it has a 2004r OD trans in it. Averaged 16 mpg on a 550 mi round trip to Kansas City, MO last weekend. I'm lovin' it...

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Old 09-11-2013, 10:34 PM   #17
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Re: Best rear gears for 700r4

My '89 C1500 has a 350 FI, 700R4 and 3.08s in the rear with 31in tires on it.

Thinking of going to a 3.73 since its got a bigger tire on it.
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Old 09-11-2013, 10:35 PM   #18
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Re: Best rear gears for 700r4

Great information here my 700r should be installed by the time i get back from vacation.
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Old 09-11-2013, 10:45 PM   #19
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Re: Best rear gears for 700r4

3;73 gears ,28" tall tires nasty 327 / 4L60 street or highway I freeking love it
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Old 09-11-2013, 11:55 PM   #20
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Re: Best rear gears for 700r4

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Originally Posted by lha1992 View Post
My '89 C1500 has a 350 FI, 700R4 and 3.08s in the rear with 31in tires on it.

Thinking of going to a 3.73 since its got a bigger tire on it.

My Burb has 31's on it too.

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Old 09-12-2013, 06:26 AM   #21
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Re: Best rear gears for 700r4

I have a 700r4 and 3.73s in my '63. It is a good combo with my 275/60/15s, but I think that 3.42 would be a good combo too. I went from 4.11 to 3.73, so the difference was significant. I like the gearing currently for quick take offs, and crusing rpm (~2300 @ 70).

I am considering a Monster 700r4/3.42s in my '68 w/ my 427 BBC. It should have plenty of torque to feel strong on take off.
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Old 09-12-2013, 07:00 AM   #22
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Re: Best rear gears for 700r4

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Originally Posted by Tx Firefighter View Post
Literally over 75 percent of the 2wd 88-98 trucks that were V8 and 700r4/4L60/e overdrive equipped came stock with 3.42 gears. Perfect ratio. GM got it right on that one.
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That's it ^

That's the sweet spot. 3.42s weren't offered in these trucks back when needs (for the most part) were different from now. 3.08-3.73 leaves a wide gap and 3.42s fill it perfectly. It's a great ratio for hiway with or without O/D,yet spill has grunt. I'm building my '67 with an M22 and 3.42s and it's a hiway machine who's bed will get used. When I can afford it,a Gear Vendors will go in. This ratio will work either way.
I know this is manual/no overdrive talk,but this give perspective on the the range of ratios we're talking. The truck I helped my neighbor with ('68 SWB) has a 4spd and he didn't want it to suck the gas too hard. He went with 3.08s...hated it. Changed to 3.42s and it's good. Now he's got a ZZ3 in there and realizes he just wants a hot rod and,no matter what,it's going to like gas and he's not going to commute or travel in it. So,he's wanting 3.73s now for bit more grunt. If it was me,now,I'd be swappin' 4.11s!!
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Old 09-12-2013, 10:31 AM   #23
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Re: Best rear gears for 700r4

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So basically the only way to get 3.42's is to use the later, wider rear end and weld on new mounting pads?

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Old 09-12-2013, 10:36 AM   #24
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Re: Best rear gears for 700r4

3.73's are perfect.

The overdrive in the trans brings it back as though they are 3.42's.

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Old 09-12-2013, 10:36 AM   #25
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Re: Best rear gears for 700r4

Does it hurt a 700r4 to drive it in third gear and only manually shift to OD when necessary?
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