Regear quick help please
 

Alrighty, so I tow allot probably just as much as I am empty. I like to go a little faster than I probably should (60-65 mph in 55mph zones and 70-80 on the freeway) I tow my normal 16' tandom with my 4k crawler on it and my 40' gooseneck with two crawlers about 22k total. Now my question I blew my 3.73 rear end up (broke 3 ring gear teeth). I got a 4.30 front and rear end for free (was told they were 3.73) I'm on 35's going to 37's at some point after I buy a lift. My tow tune is 400hp so I have no problems with power, but I don't want my rpm's to go threw the roof at 70-80mph. Anyone running 4.30's with a zf6 that had 3.73's have any imput? I was really looking forward to the rpm drop going to the 37's with 3.73's but towing would kinda suck with that tall of gear.

What vehicle is the 4.30 coming out of stock?

F450........

Thank you for the replies, the axles came from a 450 I have the matching set i got gave to me. Has a rear sway bar too, so now I have sway bars front and rear.

Handy 1 thank you for that, I was wondering how bad the rpm's would jump seems like they don't do to bad being as you can carry those speeds too. There are allot of times I have wished I had a gear a little higher than my third but lower than my 4th when I am at 30k total gross going up some 7%grades 4th won't quite pull but third is wound out at 55-60. I just didn't want to loose my drive ability empty but I think I will love them towing. Also going to 37's in the near future will put me back at stock according to Dr. Google, so that sounds like it would be a good deal all the way around.

My '99 F-350 4X4 CC SB V-10 had factory 4.30s. They might be as rare as finding a 350 SB, but they exist. It's possible it was a special order truck since I've not heard of another with that combo. I went to 5.13 with 37" tires which put it to about where a 4.10 and stock tires would be. Towing with the 4.30s and 37s sucked, but woulda probably been fine with a warmed up 7.3.

For OP, 4.10 with 37s would be about equivalent to the 3.73 with 35s you have now so your RPM will be a little higher with the 4.30 and 37s, guessing around 100-150 RPM. The little extra gear reduction will compensate for the new tires' extra rotational mass when accelerating.

My last powerstroke (00) and current (01) both had 3.73's the (00) was a auto on 37's and towed allot with it but not the loads I do with the (01) and never really had issues with the towing but with some of the loads iv towed with the current truck I could use some extra gearing, I just love the low rpm cruise that my last 7.3 had. Just thought I would see what everyone else had experienced with the 4.30's, my brother's obs (5speed) on 35's is wound tight at 70mph and I just don't want that, dont stockish rpm but another 3-400 on top of stock would be annoying as hell to drive everyday would up that much. For instance 2500rpm at 60-65 I don't think I would do, 2000rpm wouldn't be bad. Currently 1700rpm at 65 ish.

My stock tire size and 3.73 gear ZF6 truck towed a 12K camper in 5th gear at 2000 RPM and got 12.5 MPG's measured over 1000 miles through mountains and plains.

Just trying to say that 2000 RPM is the happy place for me truck and is a good compromise between available power (versus lugging) and MPG's (versus wound too tight as you say). I would not feel comfortable towing heavy at 1700 RPM, but that is just me.

Sous..what are you considering 5th gear? L,12345 or..1234(5)6...when i had 3.73 towing 11k, i couldnt keep in 6th on flatland without egt rising let alone there was nothingvin the tank when stomping on pedal..

Brother Timmy, that is why I should not reply to forums shortly after waking up...

I refer to 5th as L, 12345, which is actually 5th if you do not count "low" as a normal forward gear.

5th gear is what I use 95% of the time when on the interstate or anything above say 55 MPH, even when towing heavy. My truck is happiest there and anything near 55 MPH should be 4th gear. Grades or long rolling inclines are usually 5th for a bit, then down to 4th or 3rd in some cases like in TN or CO mountains. All of that is/was loaded heavy, not unloaded.

It's not just you, the engine makes it clear to me that it starts to feel good @2000 RPM's and diesels will run all day at higher RPM's with no issue. Under normal driving conditions mine will drop into OD at around 42 MPH and drop my RPM's down into lugging territory (I don't know exactly what RPM's that comes to) and I will frequently lock out OD in my local trips around home. Mine is live tuned and if I ever send it out to get tweaked I'll try to get OD backed off to more like 50 MPH. And when I hear of someone towing heavy @60 MPH in high gear I know that they are going too slow for that gear unless they have something other than 3.73 gearing.

Without reading any other comments and having done the homework while I was running 3:73s and 38s. 4:30 gears are as close to the same ratio you can get that equate to 3:73s after its all said and done. So 4:30s and run it!

I have 35s and 3.73s with my ZF6 and I wouldn't want it any lower, I am at 2000-2200 rpm on the highway which is perfect.