AMC 20 Axle n Gearing Question...

[poppatello]

Hey folks, it's been a while. Life was crazy over the year but, I'm ready to get back into things. I am starting with the rear axle. Some already know I plan to keep the AMC20 . I already had it trussed n tubes wielded. I even had the one piece axles n gears picked out. However, I am second guessing my gear plan.

Here is the issue. I still have the stock 4 cylinder in the jeep. I purchased a AMC 304 for it but it's still incomplete. So I will be running the 4 banger for a bit longer. But, I am told if I plan to drop in the AMC 304 I would be better off keeping the stock 3:54 gears. I was planning on going to 4:56 gears.

What should I do???

 

[MadCJ95]

IIRC, shouldn't 4-bangers have 4.10s from the factory? If you haven't changed it before, you can confirm with the tag on the axle.
I have the AMC 258 i6 / 4.2l with 32s and 4.10s and its perfect. the gearing is still a bit too high to use the OD gear, but it have plenty of guts in direct drive. So I imagine that 35s with a V8 and deeper gearing would be immaculate!

 

[poppatello]

I've already checked n confirmed everything. I have 3:54's. I believe all 4 banger pre 86 came with them unless special ordered...

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[gert]

Well again it depends on what you are wanting to do with your jeep. 3.54 gears and a V8 on 33s is about right for the street, 35s and 3.54 gears is not so good unless you have a deep 1st gear. I had 3.54s and 34s with a T-5 for awhile which worked pretty well in the flat terrain I was in 4.10s-4.56s are better for off road and you would want an Overdrive tranny for street ability the lower gears will really wake up your V8 off the line. I think it pretty necessary for a 4 banger to have low gears to over come its lack of torque
Just remember the lower the gears to lower the top end the higher the gears the more of a pig it is off the line and the higher its top end. if you use a 5 speed with a deep first gear and Overdrive you can over come higher gears better and have an over all more useful and fun vehicle. Case in point I am trying to build my CJ7 with 3.91 gears 35 inch Goodyear Dura Tracs Dana 300 with 4 to 1 gears and using an NV3550 (currently installed) or NV4500 (my dream) so that I have a decent low range and off the line performance and still have good highway rpms/speed ….. and why you ask? I want to be able to commute to work and hit the trails when I feel like it

 

[Fastatv]

I've already checked n confirmed everything. I have 3:54's. I believe all 4 banger pre 86 came with them unless special ordered...

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I have a 76 CJ, 360, automatic, 3.54 gears and I'm running 32 inch tires. Its perfect in either road or off road and in actuality, I could have even went with a slightly taller tire and still been fine.

 

[BusaDave9]

What size tires do you plan on running? The tire size is more important than the engine.
Use this chart. It shows the RPM to expect at 65 mph with different tires and gears.

 

[Posi]

I have a 76 CJ, 360, automatic, 3.54 gears and I'm running 32 inch tires. Its perfect in either road or off road and in actuality, I could have even went with a slightly taller tire and still been fine.

It all depends on what roads and trails you run every circumstance is different. Your running 44.1 personally that would be too fast for the type trails in my area and most likely not enough gearing for the hills of PA, NH, or Co.

We need more info, what size tires will you be running? What kind of trails? What Transmission /tcase? Does the Transfer Case have a 3.15 kit (20) or 4.1 (300)?

If your running stock with no options your gearing at this time is 21.1

I feel 80.1 is a good number for 50% trail/road use in my area, my rig that will see 60% trail and 40% road is geared at 104.1

 

[Old Dog]

As Posi said it all depends on what you use the jeep for.
Personally I run a V8 with 4:10's, when I ran 33's it was about right
now with 35's I'm thinking 4:88's would be better.
That's for me though on the trails we have around here with
not a lot of road time.

 

[poppatello]

Sorry guys. It seemed like yesterday that I was talking about my plans.

I was planning on running an AMC 304 , T-18 with a low first gear n 4:56 gears. I am in fact currently running 35" Km2's with a T-4 tranny. The gear chart doesn't help when an engine swap is involved because different engines run in different rpm curves. That is my issue here. I wanted to really keep the old 4 as I hear if geared right it's awesome. I don't need a fast off the line race car. I'm looking to get over hills, climb, play in the sand or do some mudding with no serious issues.

70 on the Hwy at long periods of time is a plus...


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[poppatello]

I did the math and if I remember correctly I would be running around high 80's with the T-18 n 4:56 gears. The Dana 300 is stock. That is a different league for me so staying away from that for now...

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[Old Dog]

Your right every engine has it's own torque & hp. range.
here's a link to a good calculator. Gear Ratio Calculator

 

[poppatello]

Thats the one I used. It doesn't take into account what motor folks are running..m

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[poppatello]

Ok folks. I did some research again. I couldn't find my old notes so I just redid the numbers from the chart old dog gave me. Thank you again. I like this one better.

Ok, so what I've found like before was if I install my T-18 , running current 35" tires, stock Transfer Case and install 4:56 or 4:88 gears the outcome will be the same.

Here are the numbers;
crawl speed will be 100
RPM @ 70 mph in 4th gear will be 2800.

So what I'm thinking is whatever gear is cheaper I'll will go with them. If I remember correctly from a few months back the 4:88's were cheaper.

What do you folks think???

 

[poppatello]

Man, axle and gear prices have gone up since I last checked (about a year ago). Superior Axle and Gear has gone under. WoW.

What axles and gears do you folks recommend? I am leaning towards Moser one piece axles and US Standard gears. Just wondering if anyone has something that is a bit better priced but doesn't sacrificed quality...

 

[gert]

Man, axle and gear prices have gone up since I last checked (about a year ago). Superior Axle and Gear has gone under. WoW.

What axles and gears do you folks recommend? I am leaning towards Moser one piece axles and US Standard gears. Just wondering if anyone has something that is a bit better priced but doesn't sacrificed quality...

Those are great companies also look at Richmond gears

 

[poppatello]

Richmond doesn't make or sell a gear set for the AMC20 ...