gearing questions for a rear end newb

[txchainsawgogi]

so i'd like to get a few more mpg out of my engine, but i know nothing about determining or changing the gearing.

what would be optimal for a 1978 2wd long bed with a stock 350, auto th350...

how difficult is it to do, and what am i roughly looking to spend on the job?


*i've been looking on here and trying to figure it out... i've decided im no good with ratios. http://www.drivetrain.com/parts_catalog/ring_and_pinions/gm_8.5_ring_and_pinions.html

[chevymanrob]

for ultimate economy something like a 2.73 or 3.08. and if you have never done a gear swap or have access to someone that has, just buy a complete rear and swap it. it actually ends up about the same $$$ anyway.

[txchainsawgogi]

Man it seems like it would be easy to do! I don't think I'll be searching the junkyards around here...they're pretty crappy.

[zieg85]

So many things to consider... What is the main use for the truck?  What kind of driving do you do?  What is your tire size currently?  What is the current gear ratio?  You should be able to get around 15 on the highway with a properly tuned good running truck with your combo.  Do you tow anything?

[txchainsawgogi]

I never tow...my tire size is pretty small. 15 inch cragars with smaller profile tires...not lowpro or anything. I do around town driving...no highway and no long distance.

[Lt.Del]

no highway....well that changes things.  3.42 or 3.73, so you won't have to keep your right foot down all the time to get it up to speed, because a stoplight is just feet away.
What do you have now in it?

[topp]

Man it seems like it would be easy to do! I don't think I'll be searching the junkyards around here...they're pretty crappy.

It is not easy at all.
Requires a bunch of "1 use" tools, measurements that need to be perfect, and if you've never done it, someone to teach you...

[Psycho71]

Doing a gear swap yourself depends greatly on your mechanical ability and understanding. As well as your will to learn for the sake of learning. if any of those items are not qualities you possess, it's my advice you have someone else do it, or just buy a different rear end and swap it out. But honestly, you can buy a lot of fuel for the price of a gear swap. So do some math on that before you jump in.

In all, the gear change is not all that hard. i did my first one a few years back, really enjoyed the learning experience, and knowing I now have the ability, as well as the tools, to do it again if/when i need to. I had no-one around to show me how to do it. but I did research it extensively, and felt confident it was something I could do right, or I would not have attempted it.

As to whether you need to re-gear.......First you need to know what you have in there now. Honestly, no gear ratio is going to have a huge effect on MPG's when you drive around town all the time. Speeding up and slowing down all the time is a gas consuming way to drive, no matter how it's geared. It might be better to just install a vacuum gauge so you can assess your driving habits and adjust them to make the most of what you have now. Keeping the engine pulling the most vacuum you can means you are consuming less fuel.

That's my 2 cents.

[Irish_Alley]

Keeping the engine pulling the most vacuum you can means you are consuming less fuel.

shouldn’t that be less vacuum means less fuel? i know on my 04 impala at idle it was -10 when i got on her she went to +5

[1979C20]

Sounds like your impala had some issues! Haha

[Irish_Alley]

lol nope she was supercharged