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Sorry - another gear question...

3K views 32 replies 9 participants last post by  80cj 
#1 ·
Howdy - I'm having trouble deciding b/wn 3.73 and 4.10 gears. Fixin' to do a one piece axle swap since I have a leaky seal and may as well stick some more appropriate gears in there. Mine is an '84 CJ-7, 2.5" lift, 258, T4, 32" tires. 90% on-road, hilly country. The off-road portion would only be logging roads. I need to be able to run 65/70mph. Would the 3.73 be better with 32's and the 4-speed?
 
#4 ·
I agree with Techlight. 410’s will be a little low for 65-70 mph, if that is truly what you want.

What gears are you currently running?
 
#6 ·
I agree with Techlight. 410's will be a little low for 65-70 mph, if that is truly what you want.

What gears are you currently running?
I'm not sure but according to the VIN it originally had a 5-speed. I'm going to find out tomorrow what gears are in it. It's currently at my Brothers dealership (he's the ops manager) for the axle seal repair. I'm going to have them count the teeth to get the ratio unless it's marked on the ring and pinion somewhere. Who knows, they may have been replaced at some point in the past.

If it still had the 5-speed, I'd just go with the 4.10 and put 33's on it when these tires wear out.
 
#5 ·
Gearing generally effects three things:
First gear (crawl)
Closes/opens the shift points
High gear (highway running)



What you have and what your intended usage is determines the best ratios for you.
Given your running a mild sized tire (32"), have a four speed (no OD), and you are looking at mild offroad use that doesn't require a low first gear, IMHO, 3.73's would give a nice boost in performance across the board.
 
#7 ·
[QUOTE. If it still had the 5-speed, I'd just go with the 4.10 and put 33's on it when these tires wear out. [/QUOTE]

That would work good, but since you apparently have a 4 speed without overdrive, 373 might be best for you.
 
#10 ·
3.31 to 3.73 is a 9% difference, quite a lot.

Peak power is around 2400 rpm, you need to be cruising slightly below this to avoid lugging the old girl.

3.73 = 61mph , a bit slow if you have aspirations of highway work, you will feel the engine is coming out of the hood at 65 at 2550rpm.
3.31 = 69mph , a bit faster than I would cruise in a CJ, dangerous in fact. At 65 it would be turning 2130rpm.

So if your aspiration is the highway, I would be tempted to stick with 3.31:1. Of course it depends on getting enough power from your 258 and its weight as to whether you can cruise at any speed. There are performance improvements which on a 1985 could be significant. What is the current on road performance like?

When you move to larger tyres, you will need to consider regearing.
 
#11 ·
I need to be able to run 65/70mph. Would the 3.73 be better with 32's and the 4-speed?
The answer is yes.

I have 32" tires with 4.10 gears and "had" a T4 trans. With the T4 on the highway, it was a little high on rpm range so we opted for a T5 transmission instead. Now the Jeep's 258 engine is happier on the highway.

Around town in our very hilly area of PA I never use 5th gear and the 4.10 gears pull nicely. A lot of get up go but I can shift into 5th @ 50mph if I wanted to and it will still accelerate.

My CJ original came with 3.31 gears, only option available for the I6 engine due to the 80's fuel economy crisis, and it was a dog with 33" tires. It couldn't get out of its own way on the highway and forget about passing a semi on a hill. The wind resistance alone that comes off the front of a semi was enough to hold the CJ back from passing.
And you must also consider the weight of larger diameter tires too. Much more mass to turn so proper gearing is a must.
 
#15 ·
3.73's.
I made the switch from 3.73 to 4.10 running 31's (looking for a lower first gear). Too low for open road driving (55MPH). I'm forcing myself to step up to 33's in an attempt to counter the added RPM's, since I don't want to regear. I wouldn't hesitate to run 33's with the 3.73's given your projected usage.
I've driven a number of rigs with 33"'s and 3.54 gearing and felt that setup was right on the edge of being too high.
 
#18 ·
If your planning any kind of locker and can afford now would be the time.

On a side note: I just regeared all my stuff and put lockers in as well as new axle shafts. So I have all the stock stuff sitting in a box in my garage. Let me know if you can't find a reasonable priced carrier...we can work something out. I'd have to snap some pics cause I know squat about carriers lol. I'll have to check the gearing though. Can't remember what was in there and what the carrier break is on the 20 (but i think it's 3.08 and up).
 
#19 ·
Mine is an '84 CJ-7, 2.5" lift, 258, T4, 32" tires. 90% on-road, hilly country. The off-road portion would only be logging roads.
Given you don't need a deep first gear, I would look more toward your street drivability and use the low side of the t case when necessary.
jeepdaddy, a Warn OD is not an option? Yes, I ran 33's with 3.54's and it felt too high. My First gear is 3.52.
Warn/Saturn OD's are compatible with the D18 transfer case.

Other OD options are an OD chain and sprocket for the BW1339 (auto transmission), the Ford 4 speed RUG adapted in, or an AX15 also adapted in.
There are probably a couple of other options as well. All will require drivetrain changes.
 
#20 ·
Given you don't need a deep first gear, I would look more toward your street drivability and use the low side of the t case when necessary.

Warn/Saturn OD's are compatible with the D18 transfer case.

Other OD options are an OD chain and sprocket for the BW1339 (auto transmission), the Ford 4 speed RUG adapted in, or an AX15 also adapted in.
There are probably a couple of other options as well. All will require drivetrain changes.
Jeepdaddy, referring to your Jeep and reluctance to go to 4.10's. Your 71 CJ-5 came with D18. The Warn OD suggestion I made was in reference to your situation.:)
 
#26 ·
I apologize that I've been slow on responses on this thread. I'm a facilities manager and got hit with a surprise OHSA audit. No fun.

This is the carrier. I was told it was a true trac or whatever. I'm pretty sure its stock. I'll pull the ring gear before I ship it. They were 3.31. I know squat about carriers and spider gears so let me know if you need better pics. We can work out a cheap price and I'm also ok with you getting the carrier and then deciding you dont want it as long as you pay the shipping there and back.

Itll also come with the bearings on so you'll need to pull those.

PM me or post back with more specifics if youd like different pics.



Sent from my SM-G950U using Tapatalk
 
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