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Old 04-17-2015, 08:17 PM   #1
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Rear axel gearing

I have a 2wd 98 e150 with a 6 inch lift, 5.4 triton v8 and an Aod transmission. I am going to install a trutrack and new gearing. I am not super familiar with the ford 5.4 liter triton motor. I plan on running at 285-70-16 tire. Currently have 3.55 gears, but I am not sure what the optimum RPM for that motor would be for 70mph. I may occasionally pull a light raft trailor but nothing heavier then that.
Any help would be appreciated.
Thanks
Mike
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Old 04-17-2015, 11:13 PM   #2
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Re: Rear axel gearing

A helpful calculator: http://www.offroaders.com/info/tech-cor ... #GearRatio

Some light reading on the trutrac: viewtopic.php?f=39&t=6949
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Old 04-18-2015, 05:10 AM   #3
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Re: Rear axel gearing

joeH the calculator and info in the trutrack was helpful. I am more concerned with gear ratio selection. Currently with the 3.55 gears @ 70 MPH the engine runs about 1800 RPM. I don't think the converter is even locking up and I cant use overdrive unless I am driving on a perfectly flat road with nonexistent headwind. From the aforementioned calculator @70MPH 4.10=2046 RPM, 4.30=2145 RPM, 4.56=2275.
Which one would be the best choice?
Mike
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Old 04-18-2015, 05:28 AM   #4
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Re: Rear axel gearing

I would go with 4.56
4.1 is still too long and 4.3 is a bad choice as it is a not very durable combo.
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Old 04-18-2015, 09:38 AM   #5
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Re: Rear axel gearing

I don't know what the optimum RPM is on the triton but 4.56 seems a bit much unless you're really off-roading or pulling a 10,000lb load. I suspect your raft trailer is much lighter than that. 2000lb?

4.10 gears with 35" tires is about right for me. Enough gearing to tow but not too high of an rpm on the hwy.
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Old 04-18-2015, 09:55 AM   #6
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Re: Rear axel gearing

I don't know if he sold it but you could by Oldbonesclimbers semi-float rear axle with 4.10 gearing for cheap. Might be bolt and play and you could upgrade to discs on the rear.
viewtopic.php?f=7&t=15383

Have a look at Carringb's post regarding putting gears bigger than 4.10 in a semi-float rear axle.
viewtopic.php?f=39&t=13531
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Old 04-18-2015, 10:38 AM   #7
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Re: Rear axel gearing

I think that for your intended use 4.10 would be ideal. I have a 2wd e350 EB with 5.4L and 285/75/17 (34.1" tall) tires and 4.56 gears and it has the pulling power I needed but is much lower than necessary for non-towing freeway driving. If the van is empty, it can hold overdrive up most grades with 4.56's. I'll probably go to 35"s next time I need tires to bring the RPM down a hair (ya, ya, that's why!)

With your proposed 285/70/16 tires (31.7" tall) 4.10's would have you at 2129rpm at 70mph or 1977 at 65mph. That's pretty much the same RPM you would see with 4.56 and 35"s...sounds about right to me.
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Old 04-18-2015, 04:12 PM   #8
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Re: Rear axel gearing

Thank you everyone, that's exactly the info I was looking for.

Mike
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Old 04-19-2015, 01:48 AM   #9
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Re: Rear axel gearing

Please keep us update what your experience is after the change
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Old 04-19-2015, 06:51 AM   #10
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Re: Rear axel gearing

4.10 is just barely enough gear for a 33" tire and 5.4L on a heavy rig, not enough for 35" tires. I would say that it also depends on what year your 5.4L is.
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