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Old 03-22-2018, 01:30 PM   #26
leddzepp
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Re: 3:07 Rear End

I believe truck is 3.07, car 3.08. Longhorn Man used to correct everyone on here when the subject came up as it was a pet peeve of his I think he has close to every book GM ever published and was a wealth of knowledge. Search some of his old posts and you’ll find it.
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Old 03-22-2018, 01:43 PM   #27
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Re: 3:07 Rear End

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Originally Posted by leddzepp View Post
I believe truck is 3.07, car 3.08. Longhorn Man used to correct everyone on here when the subject came up as it was a pet peeve of his I think he has close to every book GM ever published and was a wealth of knowledge. Search some of his old posts and you’ll find it.
Using the numerical ratios is a recipe for errors anyway, so you're better off with the actual tooth count, which is how I keep them straight. Plus, when you look in the parts book, that's how they identify them.

For example:

A 3.08 gearset is 12/37 which is 3.0833333…
A 3.07 gearset is 13/40 which is 3.07692307…

You could have other setups as well, like in a larger rear end you could have a 14-43 setup which would give you 3.0714
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Old 03-22-2018, 04:15 PM   #28
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Re: 3:07 Rear End

I have a vortec 350 with a lot of low end torque with a th350 and a 307 rear. It works out great for me. Torque to get it going and gears for highway driving.
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Old 03-22-2018, 05:54 PM   #29
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Re: 3:07 Rear End

3.07 can work. Needs to be a V-8, preferably a 350 or larger. I drove my 67 Bel Air with a 283, TH350 lockup and 2.73 gear for 175,000 miles. I experimented for try for some fantastic MPG number. 20 MPG was all I got. If I were to do it over it would be a small block 400, TH350, maybe a 3.08 gear. screw the absolute MPG numbers. A heavy vehicle LIKE a pickup needs gearing to make things easier for the engine.

I'm not a proponent of O.D. transmissions. My 67 and 68 pickups will both have 3.73 gears when they get back on the road. I will compromise on the side of power the rest of my life. Needs to be at least a little fun to drive. My Bel Air ran great, just wasn't any kind of a powerhouse...
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Old 03-22-2018, 05:58 PM   #30
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Re: 3:07 Rear End

My 383 runs great with a 700R4 very powerful truck
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Old 03-22-2018, 06:22 PM   #31
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Re: 3:07 Rear End

Im in need of a set of 307 gears
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Old 03-24-2018, 06:57 AM   #32
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Re: 3:07 Rear End

I guess I somehow got it reversed at some point. I could swear we went over this time and again and the correction was trucks were 3:08. I mean the threads from when Andy was here. He was the book smart knowledge and I was the knowledge from personal experience and conversing with the other 67-72 truck owners since new. And 3.08 was always the common knowledge reference, as I recall. I better stop recalling . Honestly, I never paid heed to any ratio taller than 3.73. In fact, 90% of my trucks have had 4.10/4.11 and lower gearing for the grunt. I ordered my '92 K3500 with 4.10/5spd and loved it. I got a '95 with same powertrain except 3.73s and hated it off the line. Was looking to go to 4.10s before it lost it's life. Not until the dollar has gotten so hard to spread that I've given a hoot about better hiway gearing to save on fuel. I routinely drove my 4.10 equipped trucks down the interstate at 70-80 mph and never gave it a thought. In fact, I love that sound! The engine in my '72 GMC I rebuilt in '91. It was in my Cheyenne Super K/20 and in '04 I swapped it into the Sierra K2500. That same motor, still healthy and strong, has countless hours of the RPMs that 4.10s and that speed produces. I also had 4.10s in the '71 Custom Camper I had for 18 years and traveled as far as Grand Canyon in it at hiway speeds. I have that uncracked (except no-lead head job and timing chain) original still healthy motor on a stand waiting for it's next assignment. O/D definitely adds life to a vehicle...if you don't make up the drop in RPM with higher speed driving. But in my experience, driving at 3 grand plus never hurt a thing. And if I want to save on gas I just drive slower.
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Last edited by special-K; 03-24-2018 at 07:03 AM.
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Old 03-24-2018, 12:48 PM   #33
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Re: 3:07 Rear End

I'll tell you the ones I know, perhaps others can fill in the empty spaces:

GM 10-bolt car: 3.07 12/37 3.08333
GM 12-bolt car: 3.08 40/13 3.07692
GM 12-bolt trk: 3.08 40/13 3.07692

So that leads me to believe the cars and trucks are the same ratio, at least they have the same tooth count. I'm getting the truck numbers from this Yukon gearset for the GM12T-308:

https://www.summitracing.com/parts/yga-24459
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Old 03-24-2018, 05:01 PM   #34
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Re: 3:07 Rear End

I have a 1970 TDE coded rear in my shop and it comes back to a 1970 3.07 open rear. Here's a thread talking about the same TDE coded rear.
http://67-72chevytrucks.com/vboard/s...d.php?t=578793
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Old 03-24-2018, 05:24 PM   #35
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Re: 3:07 Rear End

Don't make a lot of dif [no pun] 308/307 , Only if counting to replace one or other,[ring or pin]......just get in the boat and row,no need to count the waves !
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Old 03-24-2018, 10:29 PM   #36
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Re: 3:07 Rear End

The 3:07 is a 3:08, just as the 3:08 in many cases is referred to as a 3:07. Car, truck, standard or automatic, it doesn't matter, they are the same. Davepl pretty well clears it up with the varying tooth counts, there is no such thing as an exact 3:07 or 3:08. I think the "three-o-eight" won notoriety because it's easier to say than "three-o-seven".
Tim is correct in that although the eight lug Dana 44's are referred to and matched with 4:11 Dana 60's or 4:11 14-bolts, it's actually a 4:09. No gear set is dead nuts, you can call it what you want, but the terminology will forever be a 3:08, it's just easier to say. Besides, a 307 is a motor not an axle.
Harpo your correct in that it dont make a difference, and incorrect because you never change out just a ring gear or pinion. They are married sets lapped together from the foundry, when one goes the other must go with it.
LockDoc is also correct in sharing his experience with OD transmissions, six cylinder motors and high geared axles. Cant compare a 5000 LB panel truck to a 3000 LB later model unibody. GM did not put 3:08 axles behind six cylinder trucks for obvious reasons.
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Old 03-24-2018, 10:35 PM   #37
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Re: 3:07 Rear End

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I run a 3.08 with a 200 4r in my 68 with no issues, I dont understand when you say they dont play well together , a lot of Chevys' Buicks' and Olds came in this configuration in the 80s and 90s even the 1990 Caprice Police pakage came with a MW9 (200 4r ) Trans and 3.08 rear diff.
What motor? Thats the decisive factor in this equation. Cant really compare a 69 straight six pulling a truck to later model V6's or V8's in lighter packages..."just sayin"
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Old 03-26-2018, 07:15 AM   #38
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Re: 3:07 Rear End

Corporate rears and Danas ran ratios right next door to each other. When I blew a ring & pinion in an HO52 I found there was a 4.56 and a 4.57 in the same year. The 4.57 GM listed as "non-Dana" and that was the ticket.

Like I said before, the ID tag on the front of my '72 K/20 Highlander read 4.09. The difference between that and the HO52's 4.10 doesn't make enough difference to matter and if it had a Dana 60 that would be 4.11. So the trucks care a lot less about this than we do
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Old 03-28-2018, 11:17 PM   #39
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Re: 3:07 Rear End

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Corporate rears and Danas ran ratios right next door to each other. When I blew a ring & pinion in an HO52 I found there was a 4.56 and a 4.57 in the same year. The 4.57 GM listed as "non-Dana" and that was the ticket.

Like I said before, the ID tag on the front of my '72 K/20 Highlander read 4.09. The difference between that and the HO52's 4.10 doesn't make enough difference to matter and if it had a Dana 60 that would be 4.11. So the trucks care a lot less about this than we do
I've got a Dana 44 out there in the shop I'm rebuilding for a kid that has that same tag. Has 4:09 and the tooth counts on it, he's going to run that with a 14-bolt rear with a 4:11 in it...I learned the hard way a long time ago, it's better to run a tic tighter in the front than in the rear...
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Old 03-29-2018, 12:11 AM   #40
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Re: 3:07 Rear End

IMO you would be better off with your 3.73 gears and OD. My truck with 3.08 and 700r lugs the motor at 55mph.But it will run the speedo back to zero.According to the gear charts with 29 inch tall tires,3.08 gears.at 5500 RPM in OD you will be going 212MPH. I read this in a old Street Rodder mag years ago.
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Old 03-29-2018, 01:51 AM   #41
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Re: 3:07 Rear End

this thread made me chuckle so I'll toss this in for my contribution

D60 4:10 LS FF GM truck 8 lug 41:10 = 4:10





I'm also considering a 200-4R upgrade, considering one of these from Art Carr here in town..

haven't had a chance to get over there yet, but I'll keep y'all posted if I find out anything of interest..

good luck!
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Old 03-29-2018, 07:16 AM   #42
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Re: 3:07 Rear End

^^^ That's just too simple. Please go away I'm sorry I ever made the correction in terminology, but I also did mention it really doesn't matter. On topic, it's power to weight ratio that determines the best ratio for any given vehicle. That and desired result. A farm truck, or even an urban taxi cab, will want a different ratio than a hiway hauler or commuter car. A farm pickup can run taller gears than the grain truck. Those USPS mail trucks built off of S10s are the 4cy/auto with no O/D and 4.10 posi. That was specific to the application for the perfect match. Them little puppies scoot on down the hiway to the far right but kick butt mailbox to mailbox through rain, sleet, and snow.
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Old 03-29-2018, 07:27 AM   #43
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Re: 3:07 Rear End

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Originally Posted by 71cheyennesuperlongb View Post
According to the gear charts with 29 inch tall tires,3.08 gears.at 5500 RPM in OD you will be going 212MPH.
212 Yikes! This was scary enough!
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Old 03-29-2018, 12:26 PM   #44
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Re: 3:07 Rear End

I understand that the actual gear ratio is not exactly 3.07. I was just saying it was listed as 3.07 on all the charts that I could find.
Doesn't make much difference either way though.
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Old 03-29-2018, 12:40 PM   #45
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Re: 3:07 Rear End

Just remember when you walk up the the parts counter to ask for a 3.07692 gear set for a GM truck 12-bolt and you should be fine (as long as they don't pull a car set)
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Old 03-29-2018, 01:18 PM   #46
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Re: 3:07 Rear End

just pulling your chain special-K

here's a couple of D44 tags with tooth count/ratio for reference..

note - the Dana advertised ratios are numerically accurate if rounding correctly

'71 3/4t D44 front 45-11 = 4.09 [4.090] [D60 above replacing the HO52 rear of this rig ]



'72 1/2t D44 front 43-14 = 3.07 [3.071]

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Old 03-29-2018, 01:55 PM   #47
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Re: 3:07 Rear End

Quote:
Originally Posted by Ironangel View Post
What motor? Thats the decisive factor in this equation. Cant really compare a 69 straight six pulling a truck to later model V6's or V8's in lighter packages..."just sayin"
What I am trying to Say ,the 200 4 r was used in many many configurations from the GM , my 200 4r came in the configuration that was mated to a 2.73 gear ratio so the trans I have was set up to shift to that gear ratio, this is why you will have conflicting results, you can to pull a 200 4r from the junk yard and just install it ,ibut needs to shift properly...A 3.73 ratio with a 2004r that was set up at Gm for a 3.23 ratio will not last long . its more about the the rear diff ratio then engine size.......
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