3.73 Rear End Swap

[tgatch]

I tow a 12,500lbs 5th wheel and currently have a 3.73 rear end. What I'm looking for a little more ease starting out and to raise the RPMs vs mph when towing. I feel that my truck likes to run at about 2,000RPMs and with a 3.73 rearend that is 70 MPH, a little too fast at a GCW of 20,000 for my blood.

A 4.30 rear end would have me at about 1900 RPMs at 60 and just under 2100 at 65.

Short of a little less MPG when unloaded on the highway, what other cons are there? I know top speed will be hurt, but I don't really worry about that as my truck has only seen 90+ maybe twice.

I guess the other question is do they make a 4.30 gear for the SRW axle? I would guess they would since it is the same axle as the V-10 and I can be ordered with a 4.30.

Lastly, if anyone has done this, what has your experience been? Would you do it again? Those that now have the TowBoss trucks are welcome to share here too. I'm guessing some of you might have gone from a SRW/3.73 to this TowBoss Beast.

Thanks in advance.

 

[Hoss 350]

I tow a 12,500lbs 5th wheel and currently have a 3.73 rear end. What I'm looking for a little more ease starting out and to raise the RPMs vs mph when towing. I feel that my truck likes to run at about 2,000RPMs and with a 3.73 rearend that is 70 MPH, a little too fast at a GCW of 20,000 for my blood.

A 4.30 rear end would have me at about 1900 RPMs at 60 and just under 2100 at 65.

Short of a little less MPG when unloaded on the highway, what other cons are there? I know top speed will be hurt, but I don't really worry about that as my truck has only seen 90+ maybe twice.

I guess the other question is do they make a 4.30 gear for the SRW axle? I would guess they would since it is the same axle as the V-10 and I can be ordered with a 4.30.

Lastly, if anyone has done this, what has your experience been? Would you do it again? Those that now have the TowBoss trucks are welcome to share here too. I'm guessing some of you might have gone from a SRW/3.73 to this TowBoss Beast.

Thanks in advance.

You are on the right track. 2,000 RPMs is a good spot to shoot for when you are grossing 21K for cruising RPM. They make pretty much ANY gear ratio you want for pretty much ANY axle on the market, so don't let that worry you. The only caveat that I can give you is that unloaded, at those RPMs, you aren't going to be cruising 65 or 70 MPH anymore without taking it in the wallet. My old '95 PSD ran about 2400 at 70, which is what you'll be near. At anything 70 and above, my MPG went down by 5 MPG (from 18 to 13). Just get okay with going a little slower when unloaded, and then go for your re-gearing. Of course, with an endless pocketbook, you COULD re-gear, then get an overdrive unit for your truck, that would solve your unloaded cruising issue. Or, you might be able to find an UNDERDRIVE unit that would serve your needs without re-gearing.

 

[95_stroker]

Tom,

What you probably have to weigh out here is how many miles to do put on a year loaded vs. unloaded. Is it worth the loss of MPG to regear if your percentage of loaded miles is way disproportionate to unloaded miles. Are you a manual or automatic transmission?

 

[tgatch]

I have an auto trans.

I have thought about miles towing vs non-towing miles. The truck has 35,000 miles on it as we speak. About 35 to 40% of that is towing my 5th wheel. It has slowed down some this year with the towing, but that is because I just moved up to Idaho at the end of last year. This July I did take it out every weekend except one, and every place we go is pretty much a climb.

I figured this was a safer way to add towing power than adding a chip. I do have a Quadzilla Xzillaraider, but it is on the lowest setting when towing; if it is on at all.

I guess I'm trying to justify if it is worth the $500 to $700 to do the swap. I'm only a 4x2 so I only have to do one axle.

As far as the MPG when unloaded goes: I expect to lose some on the highway unloaded, but some of that could be made up in the town driving I would think since less pedal input would be needed. The numbers the 4.30 TowBoss Dually guys have been quoting are within 1 to 2 MPG of what I'm getting with my SRW 3.73.



BTW: Who watched 6'3"TO get shut down from any big plays by a 5'10" D-back??? Only 112 Yards and no TD's God I love to see a big mouth get shut down.

 

[Car_nut57]

Have you tried just towing with the OD turned off? This should put the rpm about where you want it. Also you might consider adding a little umph to it by making some simple mods. One I have done recently and have been very pleased with is changing the Cam Position Sensor to a unit made by International which advances the injector timing 4 degree. I have been running the CPS for several months and towing 10K with it. It works very well for me. The Banks chip is removed and other than the air flow enhancements in my signature the truck is stock.