Gears?

[bamabaxter]

I am thinking about putting 3.08 gears in my 72. Does anyone else run these. I currently have 3.73 and I get about 10 mpg @ 65mph@ 3200 rpm. Just wondering if it will be completely gutless with that high of a gear? I still have the TH350 tranny. If anyone could give me their opinion it would be great. Thanks.

[oldspowered67C10]

I have 3.08s in mine, I like em. I also have a Oldsmobile big block so low rpm torque isnt a issue. I wouldnt recommend them for a drag car but for a daily driver they work great and are alot cheaper than a overdrive transmission.

[jayharrell]

Originally Posted by oldspowered67C10

I have 3.08s in mine, I like em. I also have a Oldsmobile big block so low rpm torque isnt a issue. I wouldnt recommend them for a drag car but for a daily driver they work great and are alot cheaper than a overdrive transmission.

What Olds BB and trany are you running ?? I've got a Buick BB and love it. Thing gets about 18mpg. Gotta love that torque.

[HavinSomeFun]

Originally Posted by bamabaxter

I am thinking about putting 3.08 gears in my 72. Does anyone else run these. I currently have 3.73 and I get about 10 mpg @ 65mph@ 3200 rpm. Just wondering if it will be completely gutless with that high of a gear? I still have the TH350 tranny. If anyone could give me their opinion it would be great. Thanks.

I wish we were closer, we could swap. I want to go to the 3:73 set up.

[larry may]

I do have 3:08 in one of my ole heaps, with 27 tall tires. I like them just fine. Steady speed 55-60 was around 15 mpg mabe a bit more. Also There was some turbo blue mixed with this pump gasoline

[71stub]

I am wondering the same thing. Ive got a small block and turbo 350 with a 4:11 posi and have a complete 3:08 setup to put in so i can hopefully boost my mpg's. I do not have a tach so am unsure of where i am even running at right now.

[LockDoc]

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I have a 454/TH400 combo in the white truck and it had a 3.73 open rear in it. It seemed to work the motor a little hard so I changed it to a 3.07 open and it made the truck a lot more drivable and it still has plenty of low end torque. You don't say what engine you have so I am going to presume 350. I think you would be in good shape with the 3.07.

Just my 2¢ worth.

LockDoc

[lilred67]

i changed my rear end from 3.73's to 3.08's and i like it. 350/sm465 w/31" tires. not as responsive as i would like at 55mph in high gear. but running 65mph or in 3rd gear it will pull pretty hard. no tack and haven't checked the milage, but it is not screaming going down the highway!!!

[28buick]

My 72 K5 came with the 3.07. It will generally get 13.5 mpg on the highway doing 65 to 70. The truck presently has a low hp goodwrench crate engine in it with the factory 4 speed. When towing with this combo there is no low end power. Once you get the truck up to speed its no problem but you better not be in a hurry to get there. When the truck was new and had a higher compression 350 it wasn't actually that bad for power. The dish piston 76 cc head crate motor is just a dog. If you have a true 9 to 1 motor and aren't in a rush the 3.08 will be fine and get you a little better gas milage.

[Psycho71]

I have the 350/350 combo in mine w/3:08's & 275/60/15's.

At 65mph it twists 2500rpm. My motor is nearly stock, with a mild cam, Headers, Performer intake, and Street Avenger 670 carb. I avg around 12-14mpg. But I've never gotten thru a tank w/o having my foot in it quite a few times. So it's hard to tell what mileage it really gets.

Mine is not completely gutless with the 3:08's. And runs well once the rpm's get above 1500.

For a driver, I think it's a good combo.

I do ave a set of 3:73's just waiting for me to get a locker/posi unit of some kind. Shortly after those go in, I'll be getting a GV overdrive, or 700r upgrade to get my mileage back (and hopefully then some).

Jay

[airdale94]

I had 2 2nd gen Trans Ams, one with 3.08 and the other 3.23 both basically the same 400 Pont. eng. and the one with 3.23's was alot quicker. Gas mileage was the same about 12mpg. and both ran 2500RPM at 65 mph.

[71stub]

Were there any other gear sets available? I have heard of a 3:42 gear ratio. Can anybody verify if trucks were available from the factory with this ratio?

[bamabaxter]

I did not mention it but I have the 350sb motor. intake manifold, headers, mild cam, decent carb. I don't know if anything came with 3.42's. I know that you can get them though. Anyone have any experience with these?

[Bus Ted Knuckle]

FYI guys, the truck ratio is 3.07, not 3.08. 3.08 is a car ratio. I'm anal like that

[bamabaxter]

Sorry man, just going by what they have in Jegs. I will definitely tell you that this is not my field of expertise.

[oldspowered67C10]

What Olds BB and trany are you running ?? I've got a Buick BB and love it. Thing gets about 18mpg. Gotta love that torque.

Its a 67 400 from a 67 442, the trans is a 68 pontiac th400(PX valve body). The engine is the last remaining piece from my oldsmobile past, I just couldnt bear to sell it. The torque is great, it can smoke the tires just by rolling on power at 40 mph and can still spin well past 6000 rpms. Do you have a 455?

[bamabaxter]

Well folks, after some research I don't think I will be changing the gears. The 3.07 and 3.42 use a smaller carrier, something I can't get rid of. I have ARB air locker and I don't want to have to buy a new chunk. Oh well....unless someone here knows where I can get a gear that will work on my carrier or if it even exists, I guess I am SOL. Looks like I may have to go with the tranny swap.

[OrangeCrush1970]

Originally Posted by bamabaxter

Well folks, after some research I don't think I will be changing the gears. The 3.07 and 3.42 use a smaller carrier, something I can't get rid of. I have ARB air locker and I don't want to have to buy a new chunk. Oh well....unless someone here knows where I can get a gear that will work on my carrier or if it even exists, I guess I am SOL. Looks like I may have to go with the tranny swap.

You just need to find a used axle that is already set up w/ the 3.07's. I am in your same boat except I have 4.11's. Just make sure that when you do find a direct bolt in axle (from one of our trucks) that it's the same length axle...I beleive that the 69 and older axles are 3/4 inch shorter than the 70's and up. This is what I have been told in my search (for a 12 bolt that is...).

[jayharrell]

Originally Posted by oldspowered67C10

Its a 67 400 from a 67 442, the trans is a 68 pontiac th400(PX valve body). The engine is the last remaining piece from my oldsmobile past, I just couldnt bear to sell it. The torque is great, it can smoke the tires just by rolling on power at 40 mph and can still spin well past 6000 rpms. Do you have a 455?

Yup, 76 buick 455 out of an electra. I'm looking for some 71 or 72 heads for it. That should boost about 75 more hp just from the head swap.
But like you said, the torque is great. Stock specs are 205 hp and 345 torque for this year. 71 or 72 had more like 360hp and 480 torque. i like it.