What kind of fuel mileage do you get?

[Stepperado]

My 84 short bed, 305, 700r4 got 15 on the way home after buying it. That was almost all highway miles. Last time I checked around town it's getting 12. I am currently on a quest to see how much better I can get it because honestly I expected it to be better. With the small v8, a 2.73 rear and overdrive, it should do better.

My next move is to remove the catalytic converter from the stock single exhaust and take the belt off the smog pump. Then I want to take a look at this transmission because I think it spends a lot of time in 3rd gear when it should be in overdrive.

 

[boneheaddoctor]

I get about 14 mpg on my V2500 GMC Sierra 4x4. 6.2 "J" code with TH400 and 4.10 gears with 33" tires. Considering changing the gears to something more highway friendly. I have a set of 3.72 gear and a set of 3.73 gears for the semifloater 14 bolt rear...would just have to buy a matching set for the front axel depending on what I go with.

 

[Stewzer55]

My 84 short bed, 305, 700r4 got 15 on the way home after buying it. That was almost all highway miles. Last time I checked around town it's getting 12. I am currently on a quest to see how much better I can get it because honestly I expected it to be better. With the small v8, a 2.73 rear and overdrive, it should do better.

My next move is to remove the catalytic converter from the stock single exhaust and take the belt off the smog pump. Then I want to take a look at this transmission because I think it spends a lot of time in 3rd gear when it should be in overdrive.

You have too high of a rear gear and its killing your mileage.

 

[MadOgre]

I get more than double before after changing the rods and jets on my Edelbrock carb 12% leaner !!! Still not nearly as great as my ol qaudjet

 

[Stepperado]

You have too high of a rear gear and its killing your mileage.

Not sure if you misread my post, but it's a 2.73 rear. I believe that's the most highway friendly gear offered in our trucks and should give you the best mileage.

 

[350runner]

My 84 short bed, 305, 700r4 got 15 on the way home after buying it. That was almost all highway miles. Last time I checked around town it's getting 12. I am currently on a quest to see how much better I can get it because honestly I expected it to be better. With the small v8, a 2.73 rear and overdrive, it should do better.

My next move is to remove the catalytic converter from the stock single exhaust and take the belt off the smog pump. Then I want to take a look at this transmission because I think it spends a lot of time in 3rd gear when it should be in overdrive.

What speeds is the trans in third gear that you feel it should be in od?

Sent from the dust in front of you!

 

[Stepperado]

What speeds is the trans in third gear that you feel it should be in od?

Sent from the dust in front of you!

Glad you asked 350runner..........

I spend a lot of time on the country back roads going 45-50mph, sometimes reaching 55mph. I will intentionally keep a very light throttle so my vacuum is at a minimum trying to get an OD shift, but it doesn't happen very often.

 

[350runner]

Ok it sounds like your tv cable is set perfectly. I wouldn't change where it is set for anything. If you wanted to adjust the shift points the governor adjustment kits are the way to go. More so a project for better weather. Mines reacts the same way and the acceleration response is light and swift like a new truck. Do you have a vacuum giraffe installed?

Sent from the dust in front of you!

 

[Boone83K10]

Do you have a vacuum giraffe installed?

Sent from the dust in front of you!

Yes everyone needs a vacuum giraffe...Best mod ever

 

[350runner]

Lol.... Ment to type vacuum gauge....

Sent from the dust in front of you!

 

[Stepperado]

I think you're right about the cable being set correctly. The shifts are smooth and very pleasant at light throttle, then they firm up and are a bit snappier when you start to get in it.

I'd love to get one of those giraffe's. If you could supply me with a vendor and part number I'd be really grateful!

I'm actually not even sure what inputs the transmission uses to initiate an OD shift. Do you know what all it's looking at?

I did a little research on the governor and it looks like a single governor is responsible for dictating all the upshifts, including 1st to 2nd, and 2nd to 3rd. At this point the first two shifts might be coming in a little early, but I wouldn't want to change them. It's only the last shift I'm not happy with. Any way to target just the 3rd to OD shift?

 

[350runner]

Not sure on how to easily change that last with out changing the tv setting... that will do it, BUT also drop the fluid pressure to the clutches and everything else :-( might be time to get a pressure gauge and see where your pressures are...

Sent from the dust in front of you!

 

[Boone83K10]

First let's establish something. On my truck, it feels like I have 5 gears because I feel it "shift" 4 times. This is all at light throttle. From 1st to 2nd at 10-15 mph depending on if cold or hot. Then 2nd to 3rd at 25 mph. Then 3rd to OD (4th) at 35 mph and finally it feels like a shifts when the converter locks at 45 mph. Essentially I am in OD at 35 mph but the torque converter isn't locked. You're vacuum reading should be high, not at a minimum when cruising. A 2.73 can hurt mileage because you are lugging the engine when trying to maintain speed, especially at a lower speed like 45-50. A 2.73 only yields better mileage in comparison when it is at interstate speeds of 70.

 

[350runner]

Honestly I feel it depends more so on the engines capability to make tq down low where you cruise. A reason why cam manufactures advise the use of low gears is the cam won't produce the proper amount of torque with factory gearing. Lots of guys that don't change gears when switching to big cams end up with the engine and trans "bucking" due to little tq being made. To simulate this all a person has to do is create a misfire in two cylinders or more. Any hoo that's just me

Sent from the dust in front of you!

 

[Stepperado]

First let's establish something. On my truck, it feels like I have 5 gears because I feel it "shift" 4 times. This is all at light throttle. From 1st to 2nd at 10-15 mph depending on if cold or hot. Then 2nd to 3rd at 25 mph. Then 3rd to OD (4th) at 35 mph and finally it feels like a shifts when the converter locks at 45 mph. Essentially I am in OD at 35 mph but the torque converter isn't locked. You're vacuum reading should be high, not at a minimum when cruising. A 2.73 can hurt mileage because you are lugging the engine when trying to maintain speed, especially at a lower speed like 45-50. A 2.73 only yields better mileage in comparison when it is at interstate speeds of 70.

You are right, I meant to say a high vacuum with light throttle.

However, I have to politely disagree with a 2.73 getting worse mileage due to lugging. If your engine is lugging, then the transmission needs some help because it should shift into a lower gear and keep the engine in its' happy place. Not to say that you are wrong, that's just been my experience.