Ring and pinion gear ratio

[rpcraft]

To be honest I would keep the 3.73's for right now if it is not causing any overheating or other issues and just live with it for a while and then just look into an OD trans. If you do have some overheating check the normal stuff. Radiator, leaks, flush the motor, install a recovery bottle, and probably replace the clutch fan with either a new clutch or an electric pull fan that is T-stat controlled. Swapping out gears isn't just a matter of a crush sleeve and pop in the new R&P depending on most axles. Not sure what you are running. One ton full floaters are actually way easier to swap but if its a 10 or 12 bolt then its not, and if they are not putting in new gears and doing a proper setup then you will have other complains down the road to look forward to. The gears may be affordable but a new setup will require at least new bearings, spacers, accurate measurements, and then there is labor (assuming someone is installing it, unless it's a brother or good buddy).


Maybe you can find a late 90's OBD 4L80E that is used but still in good service. Usually as long as they are not tar whipped they can still be found to be affordable and serviceable and not "need" a rebuild. You do that and add a shift kit and a transmission controller for it to your older truck and it will be a really good strong combo for pulling and driving enjoyment. Way better than having a 700r4 in it waiting to start slipping or th400 with no OD (if you are wanting to stick with an automatic). Having a big block and 3.73's with a good OD and a 275/60-15 tire size (28 inch OD I think??) would set you up for great pulling when you need it plus the ability to cruise all day at 65 to 70 MPH or around that target and still have your engine speeds around 2200 RPM. Alternatively you could maybe check into a slightly taller tire and gain yourself some more RPM's and the big block will still pull. Maybe something like a 31 x 10.50. I think the 4th in the 4l80E is either .75 or .73 (sorry it's late lol) for your conversion ratios and this is the site I use for determining engine speeds with various combos of gear, transmission, and tire size. I have to use it a lot of time to figure out the pulses for adjusting PCM's on LS swaps.

https://www.hgmelectronics.com/gear-ratio-calculator/

This site can also show you differences between tires sizes in general and what it will do to your relative speeds..

https://tiresize.com/comparison/

Hope this helps you on your path to discovery

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[rpcraft]

One other factor is you could just find a 3.08 axle and swap it over to your truck for the time being. Essentially just take off the leafe spring bolts, shocks, brake lines, and roll the old away and the new one in for the time being. It's work but elbow grease and sweat equity can save money.

 

[SirRobyn0]

Plenty of torque from the 454. Hell, it would break them lose no problem with the 2.73 in it before. I'm afraid it will burn up the motor and transmission driving it long distance at 2700rpm. If not that bbc will empty the tank really fast. Lol

And here I have a 3.41 and am looking to go to 4.10 or 4.56 (with factory 31" tires), of course I have a smaller engine than you, I need to get the RPMs up to stay in the power band better when loaded. Consider that if you do much driving loaded or towing. You should be able to run that engine at 3K with the truck loaded all day long and it should be fine, it shouldn't overheat or blow up, if it's getting hot somethings wrong.

 

[crpntr78]

I have an 86 K10 with a 700R4 and 3.42 rear end with 29.5" tall tires. Coupled with a 305. It's a dog. struggles to get to 65 on a good day. Bucking the wind, forget about speed. Pulling hills sucks as well. So I would definitely stick with the 3.73.

 

[WebMonkey]

yup, big difference between a big block under the hood.

my k20 super double xtra heavy duty has a very nice 1969 4 bolt 350.
it likes the 3.73 with 35x12.50R15 OR stocks on 16" because it is NOT a big block.
it has the sm465

with the 'pep' i have, i'm confident i could go to 3.42 and be fine but i'm used to where i'm at now.
(60mph roads are the fastest i drive on anyway)



you've got 'room' to work with having the big block.
plenty of torque to turn over a 3.08.

good luck

 

[Camar068]

One other factor is you could just find a 3.08 axle and swap it over to your truck for the time being. Essentially just take off the leafe spring bolts, shocks, brake lines, and roll the old away and the new one in for the time being. It's work but elbow grease and sweat equity can save money.

right.....thats exactly what I said earlier. You can find the whole rear end for around $100. he don't like it, swap it back or change the ratio in his original while it's out.

 

[Grit dog]

3.73s and short tires and no OD does not make a highway driver as you found out.
55mph is doable but horribly inefficient. And your in Texas, so would seem you’d want to be able to cruise comfortably at 70mph +.

This is a have your cake or eat it too scenario.
Pick which you want.

 

[cstew47]

I'm having trouble following you. You said initially that you have a 3.73 then later you say 2.73? You don't say what engine you are running so I don't know what kind of torque you are generating. I assume you have a TH350 or possibly 400, so, if you are concerned over 2700rpms at 55mph, a reasonably torquey engine should be good with a 3.23 gear set. I have always run 700r4's so I can run a lower gear.

 

[Bextreme04]

I'm having trouble following you. You said initially that you have a 3.73 then later you say 2.73? You don't say what engine you are running so I don't know what kind of torque you are generating. I assume you have a TH350 or possibly 400, so, if you are concerned over 2700rpms at 55mph, a reasonably torquey engine should be good with a 3.23 gear set. I have always run 700r4's so I can run a lower gear.

He has been posting for a while(like almost a year) about having his rear end fully rebuilt. The old ratio was an open 2.73. The newly rebuilt rear end is now a posi-equipped 3.73. He is now thinking he doesn't really like how tall they are with the 454 running high RPM's at highway speeds.

 

[75gmck25]

What does the truck look like with your current tires (which seem like they might look small)?

- If you went to a 245/75-16 (very standard size) you would drop 200 rpm
- If you used 33's (which usually fit fine on most trucks) you would drop another 150 rpm (total of 350 rpm lower than current)

 

[cstew47]

He has been posting for a while(like almost a year) about having his rear end fully rebuilt. The old ratio was an open 2.73. The newly rebuilt rear end is now a posi-equipped 3.73. He is now thinking he doesn't really like how tall they are with the 454 running high RPM's at highway speeds.

Ah, thanks. That makes it a little clearer.

 

[DoubleDingo]

He has been posting for a while(like almost a year) about having his rear end fully rebuilt. The old ratio was an open 2.73. The newly rebuilt rear end is now a posi-equipped 3.73. He is now thinking he doesn't really like how tall they are with the 454 running high RPM's at highway speeds.

LOL...this thread was the first I saw of the gear swap, which is why I thought he got a new truck and was asking about the gears. 3.73 was definitely not a good choice for highway cruiser without some sort of overdrive unit going in at the same time. 3.73 or 4.10 and 4L80E would be a good route to go. Without overdrive, 3.42 or 3.08. It's a 2wd shortbed 1/2 ton, not like it's going to be used to haul heavy loads where you need the low end grunt of a 3/4 or 1 ton.

 

[DoubleDingo]

Ah, thanks. That makes it a little clearer.

You and I were both not in on the old info, just the new. And it does make more sense now

 

[Zoomalot]

295/60/15's
Super T-10, went from 4:11 to 3:23 made a huge difference for cruising and still enough power! (400 ft/lbs) rated.
The Gear Company people I used said 3:08 were a bit "High", I agree.

 

[Bextreme04]

You and I were both not in on the old info, just the new. And it does make more sense now

Well, I also thought he went and got a new truck... even though I had seen previous posts about him getting the axle rebuilt. It wasn't until I got a few posts in that I put 2 and 2 together.

Mine is 4.10's, 35's, and a 350... it will do 65mph without too much issue, but is definitely not "cruising". It will eventually get a 4L80 to calm it down when the 454 goes in.