The Stovebolt Site Forums The Shop Area Driveline Diff ratio change on a 49 half ton 4 speed ???

Just want to know before I go this way...it is an expensive mod.

Yes, my 4 speed has the granny first...basically too low to use. If I go to a 3.38 or so in the diff, will the tranny gears be at proper ratios for good driving at both low and higher speeds ?... What gear ratio diff would be best ?

It will improve in all the gears as long as your engine is running good. The specialty gears for that model are 3.55.

Yeah, I guess I knew it would improve all gears but just wondered if the resultant trans gear ratios will be good/correct for the rpm's ....likely a silly question...again...;)

Dogface,

If you want to know about change to ring & pinion gears in a 47-54 3100 torque-tube rear-end, the only conversion that is available is a 3.55 R&P set.

I have that conversion in my Suburban, with an SM420 4-speed. First gear is still too low, except when I need it with a full load (a full set of 7 passengers).

The big advantage of this setup is the the ~15% decrease in RPM in high gear. Also, if you install the bearing/bushing installation kit, you will most likely experience a much quieter cab.

Tim mentions many great points. I too have the 3:55 gears and with the overhaul kit makes for a completely different truck. Much quieter.

Depending on where you live, if you have hilly roads or larger and an original 216 it can make it under powered on longer grades.

Dogface,

Will you be running an original 216?

No...my 235 from a 56 ....but you knew that since I just bought that intake set up from you

The standard ratio for a 1954 was 3.9 and will fit right in.
It is not a huge improvement over the 4.11 but can be a little help.

Dogface,

Yep, I knew what engine you have - a 216 was commented-on, so I thought you should let folks know. I am looking forward to seeing your driving report.

Sorry, I did not mention that 4.11 to 3.9 option (of course, Dave is correct - thanks for the correction).

That ~9% gain from going from 4.11 to 3.9 is about what I got going from 3.9 to 4.11 (my only option). I gained about the same % by switching to 16" high profile radial tires.

You'd need the 1954 3.90's ring-gear carrier. I'll give you a 3.90 R&P and carrier for the cost of shipping, but I'd recommend going all the way to 3.55.

Thanks Tim, but I'd go to the better option. It won't be all that soon. I have spent a lot in a short time so far. My truck is ok for now ...even on the Hiway but won't do much on the interstate where I'd get blown away....it's a real free for all on I-80.