I never really understood why people changed their gearing and what all the gearing ratio numbers meant until switching from an '88 YJ to an '85 CJ7. My YJ could go a long way in first gear compared to the CJ7 ...I'm almost afraid to do anything serious with the CJ7 because shifting in the middle of mud is a no-no and revving too high is a no-no. I'm guessing that the gearing is to help solve this problem by extending the first gear? Maybe I'm wrong ...I really don't know much about this stuff. What I'm asking more than anything is if there is a tutorial somewhere that explains this in depth for a numbnut like me :)
CJ7.>My>YJ could go a long way in first gear compared to the CJ7 ...I'm almost
mud is a no-no and revving too high is a no-no.
You are sort of backwards, EXCEPT maybe for mudbogging. Lower gearing (first gear does not "last as long") is generally better, and is pretty much mandatory when the tire size gets bigger.
You could always start in 2nd gear, if you don't want to shift in the middle of a 'bog.
I have an 86 CJ7 258 with 3.31 gears and when running trails I stay in
3rd low. I find it is the best power gear for my setup. When running mud, I stay in 2nd low. I seldom need 1st low because I do not rock crawl like the desert rats on here. I bush trail run. 1st is handy for climbing over trees though.
I can walk up sand pit walls at 400 rpm in 3rd low and it has 'never' stalled out. Just get too steep and it digs holes.
Last week I was crossing a big wash out and I was in 4 high by mistake. I slipped off the hidden underwater 'trail' that was already up to the top of my 33's and had to floor it. My wife was saying, 'more gas, more gas, more gas' and I was 'well... I 'am' in 1st....' It barely chugged through at 300 rpm, but it didn't stall!
When it comes to running at the mud or hill, the 258 engine won't rev too high. If stock, the emissions computer governs the rpm to top out at about 3200 to 3500 max under load. If you have dumped the computer, the engine then will rev to it's mechanical redline of 4500 rpm under load. For me, this means 50 mph in 2nd high.
Some folks do 'not' like my ratios. 5th high is useless unless I am cruising over 80 mph. It still works at 65, but lugs the engine so gas mileage sucks. If I don't use 5th, I get an extra 5 mpg or so.
When they re-gear, they go 'lower' not higher, so you can need 1st, 2nd and 3rd before you are across an intersection, vs mine that will take
1st up over 20 mph.
Basically the lower the gear numbers, the higher or 'taller' the gears. So a 3.07 will 'say' allow 1st gear to top out at 25 mph and a 4.56 gear will only allow 1st to top out at 'say' 5 mph. Those numbers are not accurate, but an example.
Hope this helps,
Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's
Ah, that makes things alot clearer. Thank you for the quick lesson. I'm assuming my gearing is stock and it sure seems alot lower than my YJ because not even halfway thru an intersection I have to shift. I will definitely use the 2nd gear start from now on for mudding because the only times I've ever gotten hopelessly stuck is shifting in the middle and losing my torque. Unfortunately I only have the dumb 150CI 4cyl in my CJ. In a few years when I've got some time and money to burn I'll probably change the engine. I've been told that the Chevy 396 or 358 (I think?) fits nicely ...but I'll figure all that out later. My '85 only has 136k on it and runs great (knock on wood), so no rush.
It's important to remember to never shift while your tranny is submerged, even partially. When the clutch is disengaged, whatever you're driving through can flow right in to the space between the clutch plate and pressure plate... and if you're in mud or muddy water, your clutch could be TOAST afterwards.
I ran shotgun in a TJ a few years ago on a run and he used the clutch in the first mud hole. We barely made it out and it was a painful drive back. If he gave it any gas, it would slip like mad.
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