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glen_roepke@yahoomai 04-08-2006 02:08 AM

rear end
 
i am the new kid please help i have a 78 chev 4x4 full time 4x4 with 307 gears how can i get better gas milage i get about 6 miles a gallon thanks

Crosley 04-08-2006 09:42 AM

Quote:

Originally Posted by glen_roepke@yahoomai
i am the new kid please help i have a 78 chev 4x4 full time 4x4 with 307 gears how can i get better gas milage i get about 6 miles a gallon thanks


I moved this thread here from the tranny & rearend section.

It seems to be a general question about fuel mileage that could use many different answers to help with the MPG of the vehicle.


We need more information on the truck. Model 1/2 or 3/4 ton , engine , tranny type, tire size ??????

30desoto 04-08-2006 03:53 PM

glen
Are you sure you have 307 gears, I have never seen a 4x4 with those gears or you would get better milage than you say most gears are closer to 390's on 4x4. Do you have a 350 in the truck what size carb, do you have headers, have you thought about putting in hubs it would help a bunch in milage to get it out of 4 wheel drive, what size and type of tires are they big lug or all weather, how does she run, does the carb need rebuildt, when did you change the oil last, how is the air filter, what type of air filter, when was the last tuneup on your rig, I know these are all small problem questions but each one can make a difference in your milage. :thumbup:

By the way welcome aboard :welcome:

30dee

lakota 04-08-2006 09:56 PM

Get that front end out of full time. If you have a 3:07 rear then it's not in sync with the front. Most Chevy 4X4's are 3:73 or 3:90. You don't need to change the rears. The 3:07 will give you good highway speeds and fair MPG's. Just get your front end to freewheel. 6 Miles to the gallon??? My 80,000 LB, 880 cubic inch 6 cylinder, 18 wheeled Peterbuilt got 7 MPG.

M&M CUSTOM 04-09-2006 12:00 PM

I had a 1978 GMC ton 4X4 with the full time hubs and transfer case.
I never removed the solid hubs, or installed the part time kit in the transfer case, but I did rebuild the rear axle because it leaked from everywhere.
I ran a 305 with a new cam and lifters slightly over stock specifications, the TH-350 transmission got rebuilt as it lost first and reverse along with leaking from every place it could, I had a set of 31X10.5X15 tires and the gears in it were 3.55, I got 18 mpg when I did more highway driving.

I had a 77 Chevy that came form the factory with a 400, TH-350, NP-203, and after replacing the engine with a 350 (the 400 spun a rod bearing) and swapping a set of 33X12.5X15 tires on it, I got a rough average of 13 mpg, and this truck had the part time kit and hubs BUT had a set of 3.08 gears.

Over the years I ended up using the engine out of the first above mentioned truck, the transmission out of the second above mentioned truck and a NP-205 transfer case along with a 1983 8.5 inch GM front axle and 1974 10.5 inch rear axle containing 4.10 gears, along with the 33X12.5X15 tires from the second above mentioned truck and got an average of 14 mpg.

Your mileage will vary greatly with the amount of highway use, stop & go traffic, idle time, etc. but the tires need to match the gearing you have to keep the engine rpm's in the lower end of the power band to get better mileage, a general rule of thumb for mileage and power trade-off is keeping the engine revving around 2100 rpm's.

farna 04-10-2006 10:39 AM

To see how tire size affects engine rpm, go to www.4lo.com and check out the gearing calculators. You need to keep the engine up to 2500-3000 rpm at cruising speed (say 70-75 mph, if that's how you drive). A lot more (or less) and mileage will suck. If you have a lot bigger tires than stock, it's the same as reducing the gear ratio. That in turn over works the engine. If you have stock gears, you need to keep very close to stock tire size. If you put big tires on, you have to change the gears (in front AND rear -- they MUST be the same in a 4x4) to compensate for the tire size. Like I said, use the gear and speed calculators on www.4lo.com to see how tire size really changes things. You can't change one thing without affecting others.

xntrik 04-13-2006 03:36 PM

Quote:

Originally Posted by glen_roepke@yahoomai
i am the new kid please help i have a 78 chev 4x4 full time 4x4 with 307 gears how can i get better gas milage i get about 6 miles a gallon thanks



WELCOME :welcome:

Did you buy my son's worn out 454 4x4 ???? There was NO HOPE for it.

We increased gas mileage 200% (from 5 to 15) by buying something different and only was out of pocket $ 100. no joke :thumbup:

red65mustang 04-13-2006 04:05 PM

1 Attachment(s)
welcome....and just to help you feel better about bad mpg.....

a picture of my son's toy.....hell, the four tires weigh 2,000 lbs!


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