Hey everybody, im new to blazer forum and need some advice. My 89 k5 has a 3.07 geared front and 3.73 geared rear (bought it that way)

I was wondering if I should match the front or back? Im runnin 36's, and its my daily driver so I need decent mileage.

I definitely want 3/4 or 1 ton axles, and I may go to a 4.11 gear with an overdriven trans. HELP!

Thanks
-Jim

 

Running 36s you will want to runner a lower gear to help make up for the larger tire. I'm not a expert on gearing but I would say somewhere in he 4.? range should be ok. Possibly 4.56s even?

 

Not a gear expert either, but you definitely want to match front & rear gears in a 4x4. I think Rex is right that if you're running 36" tires you want a lower gear ratio. You want to pick the right gear ratio for your driving and use of the truck. If you do a lot of highway driving you don't want to go with a too low ratio or your highway mileage sucks. If you only do highway driving, and never go off road then a taller ratio (lower number) will help with a little better mileage.

Give some examples of your driving style and use of the truck. Is it a commuter? Do you offroad sometimes? Is it only a trail rig? Things like that.

 

Running 36's I think any hope of decent mileage is gone. The 4.3 is very thirsty and the huge tires are only going to make that worse.

With that big of tire I would have at least 4.11's. I would also be worried how long the previous owner had the front and back geared differently and if he use 4wd during that time. 3.07 and 3.73's with that large of a tire is going to put a lot on added stress on your transmission.

 

With 36" tires I would start looking in the 4:56
or lower range possibly 4:88. If you gear it right most of the lost mpg can be regained.just dont expect unreal gains

 

According to the table on 4lo.com, 4.27s or 4.11s would give me good mileage and good offroading ability...thinking about going that way with it...ill be driving it around daily and offroading kinda often as well. My cousin who I bought it off of had them different and it DOES put stress on everything in 4low or high....thanks everybody for your advice, I'm only lookin to get at least 10 mpg....what're you all gearing yours?

 

3.73 rear with 36" tires isn't that bad... My 70 I run 3.73's with 35" tires. But, since you have an overdrive you definitely need to up the ratio.

4.56 will be close to stock ratio. I had stock 86 with 3.73's and after putting 4.56's and 37" tires the speedometer was spot on.

Think about physics here though... Just because the speedometer is correct does not mean that the engine is able to move the heavier tires while doing the same amount of work.

I have 4.88's and 38's on my 89 and they are fine, 5.13's would be even better as with a lock up torque converter highway rpm is just fine.

When searching craigslist for a set of suitable replacement axles you will find that most are 4.10 and 4.56. If you're looking for an easy swap stick with the 4.56 and you won't be sorry.

 

Well im not on an overdrive yet, right now its the stock 3 speed t350. Like I said, id like to throw some 4.56's in or 4.88's but its my daily driver so I gotta think about mileage...im thinking 4.11's with a 4 speed overdriven trans may be ok. What do you think?

 

You said you had an 89 in the first thread, the stock transmission in 89 was the TH700R4.

The last year you could have gotten a TH350 was 1985.

If you have a non-overdrive transmission then highway revolutions will be your limiting factor. You're stuck at 4.11 IMHO.

 

Sorry I missed the 89 k5 part somehow when I made my first comment.

If you are going to put a 4 speed auto in it why not go with the 4.27's.