Baldbaron;
Read this, from a thread entitled," "51 3800 216 gear ratios" in "Big Bolts". I had the same problem.
And... here it is. Picked her up a couple hours ago, and I've driven 20 or 30 miles in a bunch of different conditions. To review, what I've done is change the differential gear ratio from a far-too-short 5.14 to 4.10. Nothing else substantial except for whatever bearings were exposed in the process (all of 'em), and the front wheel bearings to boot.
Here are my early impressions: First gear is now useable for something other than rock climbing. I stopped on a 15% grade. 1st gear was (of course) an easy start almost without any throttle. At about 10mph I shifted to 2nd smoothly and easily without having raced the engine, and 2nd pulled away nicely. Ditto 3rd, and I levelled off at around 30 mph in the middle of third at a moderate throttle setting. Keep in mind that at 15%, the grade I ran was almost 3 times as steep as the steepest interstate. I could easily have gone fast enough to pick up 4th, but I'd have been exceeding the speed limit. Probably couldn't have held fourth anyway. So at the top I shifted up and idled very nicely at around 35mph at the very bottom of 4th.
Then I took to a freeway. Evelyn followed me with her certified speedometer. It's German, you know. Therefore, of course, superior. Right. First I tried for my fastest comfortably sustainable cruise: 58 or 59 mph, she said. I could do that all day. But I also tried a "fuel miser" cruise, which turned out to be exactly 50mph. At that speed I could actually downshift, dump the throttle and scream up to 55 just like that! I didn't do that - no reason to - but I could have. I have the distinct feeling that the next time Epic is asked to haul a load that would void a new truck's warranty, she'll do it without a hitch, exactly like this, but at a slightly higher rate of fuel consumption.
There is no problem here, I'm telling you.
This is exactly what I was looking for. A truck that will still lift your house, but can now eat great distances without straining. I think I'll stay with this for a while. 2nd is still a flat ground starting gear. I don't need an overdrive, and probably wouldn't unless I really started to sock on the featherweight highway miles. Even then, this would do nicely, I think.
-Mark
p.s., My transmission is a SM420, synchro in 2-3-4.
