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Old 08-01-2018, 01:40 AM   #1
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What gear set should I go to- 4.56 or 4.88

Hey all, I need your help! Except for posting the question here, Iíve gone over this with almost everyone I know, and Iím still on the fence.

Just the facts maíam/As some of you already know-
2003 7.3L diesel SMB RB50
Quigley 4X4
FF rear end w/Detroit Truetrac
4.10 gears
Deaver rear springs w/Agile R.I.P. kit
Adjustable torque arms/larger sway bar/relocated track bar mount
315/70/16 (35Ē)Goodyear Duratrac
CCV pop top w/roof rack and solar
160K
~10,000lbs

Towing-

Custom built utility/cargo trailer
Unloaded~1,000lbs
Loaded~1,500-3,000lbs

***NEW TO US***
Lance Travel Trailer 2185
Dry ~4500lbs
GVWR~ 6000lbs

So the situation is-
We live in CO and drive mountain passes, my rig lugs on the hwy loaded up and when towing our utility trailer. I not only take it out of OD, but often need to drop it into 2 just to get the rpmís up to keep moving, Iím increasingly frustrated with my DP tuner, any tune spikes the EGTís and runs the tranny temp up, so I just put it back to running stock in the slow lane with the big rigs and my flashers on.
Iíll post up better data logs as soon as I can document them, but Iím close to around 2000 RPMís at 60 mph towing in OD.
The new Lance trailer will be used quite a bit after next school year, we will be traveling for 3 years for middle school after Lake finishes up 5th grade. Our idea is to be able to stage the Lance and use it as Home base in several locals throughout North America, Canada, down to Baja, Mexico and possibly beyond and still have the rig for exploring further. Iíll start a separate thread on that when the time comes.
I do use the SMB for running around town unloaded and often will haul stuff with the trailer. The potential of running the RPMís up too high on the hwy is slightly lower cause most of the time weíve at least got the rig fully loaded up going somewhere or will have the rig loaded up towing our loaded utility trailer and now the Lance, otherwise might have to watch my top speed with higher RPMís, but that might be the trade off.
So now weíve got this Lance trailer to haul around and I know itís not gonna work with the current gears. I havenít tried towing it yet, but will report back next week when I do.

4.56 or 4.88.....??
My friend whoís built up a Cherokee w/37ís is running 4.88 and says to go that route, but heís got a gasser and even winds it out a bit on the hwy.
Derek at CCV is running 37ís with his 7.3, tows a 10K boat over passes doing 80 with high 5.something gears, RPMís run a bit higher but no issues. Says for me to go 4.88
Don at BOR who built the FF rear says to go 4.56 as 4.88 might over rev the diesel. Iíve PMíd Caringb as he seems to be one of the tow kings around here, no word back yet.
Anyone else.....thoughts? Sorry for the long post, but figured the more info the better.
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Old 08-01-2018, 10:04 AM   #2
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I had a Quadvan 7.3 RB and towed a ton over passes and had 4.56. I also had the DP tuner you have and 4Ē exhaust. The freeway driving drove me crazy with RPMs right at 2250 at 65. That last 300 rpms was just enough that I was ready to lower ratio to 4.30. As far as tranny temps and EGTs over the pass I could not keep EGT down unless out of tow haul mode. My tranny was never an issue after I had it build right similar to what John Wood does. Because the hard pull with a fully loaded boat and van was only about 20 miles at 6% grade I considered the rest of my driving the more important part. If I had to do it again I would have 4.30 gears and a 10.5 sterling from a truck. I can give more details if you want to PM me.

Brad
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Old 08-01-2018, 11:19 PM   #3
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I have a 2001 with 7.3, 4” UJoint and 35’s also with the DP tuner and 4” exhaust sterling 10.5. I just regeared to 4.30’s recently for some of the same reasons. RPMs still get higher then I would like frwy cruising not pulling. I have pulled my 6k boat around town but not really on the frwy or over the pass yet. So not much help at this point, do have a trip plan in 2 weeks pulling the boat loaded over some steep hills. I will report back.

Good luck
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Old 08-02-2018, 12:05 AM   #4
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What gear set should I go to- 4.56 or 4.88

Well, as expected thereís quite a range of responses, including some PMís, depending on how heavy a load youíre hauling, buildout weight of your rig, tire size and certainly what engine youíre running. Maybe in responses, it would help to know what those specs are on your rig to get a better idea of what Iím looking at. Thanks for the replies so far.
Also, it looks like thereís several gear ratio calculators out there that some have relied on that I donít think would give accurate results.
The Spicer calculator doesnít seem to take into consideration the stock tire size or stock gear ratio to give you the new ratio needed, so thatís essentially useless.
A better one Iíve found is Tiresize.com that at least takes stock tire size and the stock gear ratio into consideration when calculating.
Keep in mind however that none of them take stock vs. current vehicle weight, towing weight or engine specs into consideration. Much of this really depends on all of these factors combined and perhaps Iím more apt to get the results I need following the lead from someone whoís running very similar specs as me in regards to engine, tire size, vehicle weight and towing weight.
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Old 08-02-2018, 08:02 AM   #5
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Do you suspect your 7.3 is down on power? You could be loosing boost, or have a bad injector or injector harness. It's worth investigating.


Don't tow in OD, unless, you're on flat ground. Having the trans hunt, slamming in and out of OD is really hard on the trans, running in too tall a gear makes the torque converter slip too much, and heat up the fluid, reducing the fluid's ability to lubricate. I have 7.3 and E4od, 33" tires, 4.10 axle ratio, and tow a 32ft 3axle trailer, 8k lbs loaded. I routinely downshift into 2nd, hold it at 50mph going over passes. For towing my gearing is a little tall, I've thrown on and towed 1200miles with 29" tires and proved that. But I'm ok with that, myself.



Gearing is a funny thing, I've changed gearing in everything from swapping out 5th gear in my MR2 (to a taller 5th from a Corrolla to give the sportscar a true overdrive 5th), My old 4cyl Nissan dually w/7-1/2ft cabover camper and 8ft trailer, my Suzuki Samurai's 3rd member and transfer gearcase ratios (rock crawl stuff), my old Geo Metro's final drive for the best freeway fuel economy, and many VW transaxle gear stack changes for top performance in both the 1/4mile drag, and 2 mile land speed racing.



A few things come to mind... 1) it's all a compromise 2)knowing your goals is very important 3)math is your friend


Since you already know your current set up has, tire size, etc. Find an on-line gear ratio calculator that's centered around automatic transmissions. I've done this the old fashioned way with a pad of paper and 5 function calculator for fun, but at the end of the day the online tools (or set up an xlx spreadsheet to do the same thing if math is your thing) an on-line tool will get you to an answer the quickest.



Goals; I once thought these guys with the 5th wheel toyhauler at 12k lbs behind their lifted Diesel 4x4 lifted 'Bro-Truck' pouring soot out the pipe, cruising up the grape vine or Barker Grade at 75mph, AC cranked up, headed to Pismo, Dumont, or Sand Mountain, really had it goin' on. What I've learned since is those guys pay dearly for that performance in upgrades and maintenance. Unbelievable money that a younger buddy of mine has spent.



If it were me, I'd start with making sure it's running right, then play with the gearing calculator. If you had up to 37"s, my guess is 4.56 would be good.
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Old 08-02-2018, 08:29 AM   #6
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Iíve edited my post above too.....
Yes, Iíve considered that Iím down on power, but Iíve got a scangauge and havenít thrown a code? Maybe Iíll have a shop hook it up. Also, I live in CO and drive in the mountains, the air ainít what it is down at sea level, and thatís something Iíll have to take into consideration when re-gearing knowing weíll be traveling at different elevations.
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Old 08-02-2018, 09:04 AM   #7
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I know the pinion gear gets smaller and smaller as you "go up", and the contact between the pinion and the ring gear typically gets smaller, but I don't know at what point that becomes an issue on these gear sets.


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Old 08-02-2018, 11:49 AM   #8
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What percentage of the time do you or will you tow up steep hills? My guess is way less than half, so is it worth it to gain 5 or 10 mph while towing up hills, but raising your RPM's 100% of the time? If you choose a slightly higher ratio, and end up having to down shift a bit more often, you still have the higher ratio for freeway use. If you choose the lower ratio, you are stuck with higher revs forever. Down shifting one or two gears once in a while isn't the end of the world, hell the mighty 5.4 gasser wants to be down shifted alot on any real hill, but that doesn't seem to hurt anything, and spending quality time in the slow lane with the semi's is fine with me. Once over the hill, and back in O/D, the engine loaf's along the remainder of the day at a comfortable RPM. If you choose a lower ratio, you might arrive at your destination a few minutes earlier, but at what cost? I'd say go a bit higher, down shift, slow down enough to keep temps in check, and enjoy the ride.
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Old 08-02-2018, 12:38 PM   #9
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My wife and I live and travel full-time in our rv. Our setup is a 2000 DP tuner tuned 7.3 E-350 U-joint equipped van on 35ís pulling a 30í Airstream weighing between 8-9000 lbs fully loaded. We have been on the road for 8 months and started out in Florida with 4:10ís and had it re-geared with 4:56ís in Denver in May of this year. While it is no rocket ship by any means there was a very noticeable difference in towing since re-gearing. We pulled Wolf Creek Pass with the 4:10ís, finishing the the climb @ 15mph in first gear. Since re-gearing we have traveled through northern Colorado, Wyoming, Montana and Washington with much more ease, even being able to use the cruise control at times which wasnít possible before regardless of the terrain. Again, we are still not winning any races, but it feels like we are lugging less and fuel economy has actually improved. RPMís arenít noticable enough for me to complain about, but we typically are towing at slower speeds for safety reasons. Hope this info helps.

Hereís a link to our YouTube channel where we have a van details video:
https://www.youtube.com/channel/UCa3AOeTpagC3D532A-39iOA
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Old 08-02-2018, 08:37 PM   #10
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What gear set should I go to- 4.56 or 4.88

Tlave, thatís exactly what I needed to hear, thanks.
Think Iím going with 4.56, Iíll report back, gotta be better than whatís going on now. You guys are right, itís all about comprise, Iím not looking to rocket up these passes, but the thing has to be able to climb them without this much difficulty with my small trailer, let alone the new TT that weighs much more, and yes, I still want my top speed without winding out the 7.3
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