3:1/4:1 gears in a split case (1 Viewer)

This site may earn a commission from merchant affiliate
links, including eBay, Amazon, Skimlinks, and others.

HemiAlex

Long live the 2F
Supporting Vendor
GOLD Star
Joined
Sep 28, 2015
Threads
250
Messages
4,005
Location
Texas
Website
yotaoilfilters.com
Has anyone here done this? I’d like to gain some gearing off road and be able to use 2nd and 3rd low for most of my off road time.

Ive got a set of 4.10 center sections locally that I can get but I’d like to leave the H55F and 3.70 diff gears alone. I only need more gearing in 4lo.

Has anyone done the gears and did it meet your expectations? I’ve the 38mm split case that came out of my truck as a core and I’m currently running a rebuilt stock geared split case by valley hybrids.
 
I’m partway thru with fitting my 38 split case with 3:1 Sumo gears.

I need to throw the case together and see if the clearances are good.

No experience with 3:1 with an h55 but that’s what will happen before summer. From my calculations it should be a really good combo.

I drove @lovetoski 4:1 and h55 (35’s and 4:10) a little and it was a game changer.

He can probably chime in on the gearing. From what I remember his 4:1 h55 4L 3rd was about 4L 1st gear on a 4sd.
 
Keep in mind that gunning it up a big steep sand dune (and making it) requires the almost perfect gearing ratio of 2Lo with the H55 (for this particular scenario). (31s, 3:70).
1Lo is too slow & you'll never make it, and 3Lo is much too high as the 2F doesn't have the umph to push it. Also you're going too too fast (while you can).

2Lo is the "race it up the hill" gear. If you gear the transfer down too far, you might lose your"fast" hill climbing ability. Make sure that 3 or 4 low with the new gears equals 2Lo with your old ones. 5Lo should never be used under any circumstances (except for an occasional giggle).

The cast iron transmission case was designed to handle the torque of the low gears in the transmission. The transfer case wasn't designed to handle increased torque of new bigger gears. Maybe it can handle it, maybe not. Id hate to find out not out on a hill in the boonies.
 
Last edited:
That’s a really interesting perspective, as always.

For me, I need a touch more gearing in second, lo. I don’t hit much stuff at speed, I’d like to see sand but it’s not on the radar.

After the calculations online, I’ll get more from 3:1 gears than I will from 4.10 in the axle.

Feels like the sweet spot might be the H55F/3:1 split case, 3.70 differentials with a rear locker. I could have don’t everything I had the guts to try.
 
The transfer case wasn't designed to handle increased torque of new bigger gears. Maybe it can handle it, maybe not. Id hate to find out not out on a hill in the boonies.

That is laughable. @boots4 has been running a compound turbo 4BT and a doubler in front of his split-case with 1-ton axles and 40” tires on the other end for almost a decade without issue. It has been very well established that the splitcase is very badass.
 
I would go for 4:1 gears. 3:1 isn't low enough in my opinion.

I second that. Personally I don’t feel you could be too low, at least with these scenarios mentioned. I suppose the 3:1 might be easier to fit into the housing though...other than that I don’t understand the reason for digging into a t case and not going 4:1.
 
I have 4:1 in my split case. Required clearance the case. I'm running a 4L60, not an H55, but low in first is now very, very low. We were running in the snow last weekend and it was too slow for everything. But I'm looking forward to it on the Rubicon this year.
 
Yeah, I don’t get why you’d go to the effort for only a 25% lower single gear. 4:1 is the way to go if you know you want lower gears.
The high range becomes a 1.1 underdrive so it turns your 3.70’s into 4.11’s essentially. Sounds perfect to me.

FWIW I have a 203 doubler in front of my stock transfer case so I have 4.5:1 in double low. And I am still looking at doing the 4:1 gears.
 
I would address the motor mounts too for anyone going with significantly lower geared Tcase. At least chain or improve the motor mount on the drivers side.

Been there and done that on my truck on a trail run.

3966DCFF-B42A-4A00-B8EA-16ABD96A7225.jpeg


93C902C9-19F9-46EB-9B7F-F907DCFEE1BD.jpeg
 
On the 4:1 gears do multiple companies make them? I thought there was an under and an overdrive available for hi gear.
 
Only company that makes 4:1 gears I know of is AA. If u find that 4:1 for a particular trail your on is too low for 1St through 4TH, just shift to 4hi. With 4:1 in 4 low in 4TH gear at top speed I'm about equal to first gear in 4hi. For crazy complex rock gardens I kinda wish I had a gear that gave 200:1.
 
Alex send Georg your spare 38mm “case” and ask him to get them machined to fit the new gears.

It will save you a bunch of time and guess work.

That’s the plan all along. He did my current case and he already has the business again.
 
That’s the plan all along. He did my current case and he already has the business again.

I wish I had him do the machining to take the guess work out of grinding the housing slowly to not mess it up.
 

Users who are viewing this thread

Back
Top Bottom