Axle Swap For Gear Ratio

[86 Silver]

Ok fellas, here's my plan. I have an '86 K10 with new 350 (290hp) and 700R4 tranny. Currently I run 33" tires on 15" rims with a 2.5" suspension lift. My gear ratio is 3.42. WHen i run down the highway its constantly shifting to accomodate for the slightest of inclines...i hate that. really sucks down the gas when its always shifting down. Take it out of OD and it doesnt shift, but sucks down the gas....i know...ignore the gas guzzling 350 comments. :-)

I want to steal axles out of a Sierra Classic 2500 (Camper Special) with 4.10 gears and lockouts. It'd be a dierct swap I'm sure, but are the 4.10's too much or should I be looking for 3.73's? I am thinking this will actually help with fuel economy and not having to shift so much...or am i dreaming the impossible dream?

I will be putting in a 4" lift with 35" tires so that is the reason for my swap thought, or if i kept it where it sits, I know a 3.73 would most likely be perfect.

Thougths?

[hyatt]

4.10s will be fine with 35 inch tires

[Rubble]

I have 4:10s in my 86 with 35s The 350 is turning about 2500 in direct,(465) so your 700R should be a couple hundred below that. 2500 is about 100km/h or 62 mph.I don't drive that fast so it works pretty well....
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[INSIDIOUS '86]

There's a better fix for that http://www.jegs.com/p/B-M/B-M-TH-700...48091/10002/-1
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[Rubble]

I would still look at swapping in those 4:10s,My 82 with 6.2 has 3:73s & A833 on 35s. It takes a lot of power to turn those big tires...I need to be running 100-110 km/h to use overdrive,poor 6.2 won't pull it under that in any hilly terrain.Your 350 will have more power,but will still probably seem sickly...
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[N2TRUX]

Originally Posted by 86 Silver

Ok fellas, here's my plan. I have an '86 K10 with new 350 (290hp) and 700R4 tranny. Currently I run 33" tires on 15" rims with a 2.5" suspension lift. My gear ratio is 3.42. WHen i run down the highway its constantly shifting to accomodate for the slightest of inclines...i hate that. really sucks down the gas when its always shifting down. Take it out of OD and it doesnt shift, but sucks down the gas....i know...ignore the gas guzzling 350 comments. :-)

I want to steal axles out of a Sierra Classic 2500 (Camper Special) with 4.10 gears and lockouts. It'd be a dierct swap I'm sure, but are the 4.10's too much or should I be looking for 3.73's? I am thinking this will actually help with fuel economy and not having to shift so much...or am i dreaming the impossible dream?

I will be putting in a 4" lift with 35" tires so that is the reason for my swap thought, or if i kept it where it sits, I know a 3.73 would most likely be perfect.

Thougths?

The 2500 is going to be 8 lug, not 6 lug.

[andrewmp6]

Depends which axles the 2500 has in it and how much power you want to make later on if you want more.

[74 stepside]

Not quite the same thing, but he's a comparison. I had a lifted 99 silverado 5.3 with 4 speed 4L60. Same as 700r4 but newer. It had 285/75r16 tires which come out to 33". Stock my truck had 3.73. With the taller tires I could feel the loss of power and the speedo was incorrect. I swapped 4.10s in and had my power back to original, speedo was correct and drove it daily for 5 years like that. Swapping those gears after the bigger tires was the best thing I did on that truck. So my opinion is 4.10 gears for you, especially since you have that OD trans.

[piecesparts]

The 3.42 gears are giving you around 1700 RPMs on the highway at 70 MPH, the 3.73 will give you 1860 RPMs at 70 MPH, and the 4.10 gears will give you 2045 RPMs at 70 MPH. I would believe for your tire size, your choice of the 4.10 would be good for you driving.

[86 Silver]

Originally Posted by INSIDIOUS '86

There's a better fix for that http://www.jegs.com/p/B-M/B-M-TH-700...48091/10002/-1
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So will that really work? Will that fix my tranny from slamming from 1st to 2nd too? How do I replace it? Drop pan & filter....then???
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[INSIDIOUS '86]

Yah it will help. The second to first slam can be the fact that your cable for the t.b isn't adjusted right. http://www.transmissioncenter.net/ these guys know thier stuff. Give em a call and the can ensure your trans will live long.

You may also still have to swap gear ratios
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