Swap or Build up AMC 20 - JeepForum.com
 9Likes
Reply
 
LinkBack Thread Tools
post #1 of 26 Old 08-05-2020, 11:54 AM Thread Starter
gdselzer
Registered User
1984 CJ7 
 
Join Date: Oct 2015
Location: Littleton
Posts: 14
Swap or Build up AMC 20

I'm in need of your experience/insight/opinions. I recently put new springs on my 84 CJ-7 which gave me a enough room to go from 31" to 33" tires. But my 2.73 gears ain't gonna cut it with 33s. So I'm ready to move up to 4.10s.

In talking to the local shop I have two options that will cost about the same (+/- $200).

Option 1 - Upgrade my current AMC 20 (and Dana 30) with 4.10 gears, LSD, and new one piece axles.
Option 2 - Swap out the rear for a low mileage Ford Explorer 8.8 that already has 4.10, LSD and disc brakes. Because the 8.8 is ~5 inches wider and has a different lug pattern, I'll need to add 2" wheel spacers/adapters to the front. My old rims are pretty rusted out, so I'm not too concerned about the added cost of new rims.

Option 2 is alluring in that I get a stronger axle and disc brakes. Downside is that it introduces a lot of new variables. Does the extra width on the axles help or hurt me on the road/trails? Should I get rims with 2" of backspacing so that my tires are back where they started? Do I need to worry about the off-center pinion of 8.8?

Option 1 eliminates the extra variables, but I also don't get the stronger axle and disc brakes.

Like I said, cost wise it's about a wash. Which would you do and why?

BTW, the Jeep is garaged most of the winter and only comes out to play in the Summer and Fall. I mostly drive it around town but do go out and do some intermediate level wheeling 5-10 times a year.

gdselzer is offline  
Sponsored Links
Advertisement
 
post #2 of 26 Old 08-05-2020, 12:23 PM
Fourtrail
Registered User
1974 CJ6 
 
Join Date: Dec 2007
Location: Illinois
Posts: 4,742
Option 1. The 8.8 is better than a dana 35, but not than an AMC 20 with 1 piece shafts. Oh and you can't just throw spacer/adapters on the front to get 5 on 4.5" pattern to match the rear 8.8, they won't fit around the lockout hubs. You have to also add in the extra cost of replacing the master cylinder and proportioning valve to go to 4 wheel disc brakes correctly. For your use, the 20 with 4.10's, LSD and 1 piece shafts will be more then adequate.
80cj and 4Low2G0 like this.

80 CJ-5, 74 CJ-6, 56 CJ-5
Fourtrail is online now  
post #3 of 26 Old 08-05-2020, 01:54 PM Thread Starter
gdselzer
Registered User
1984 CJ7 
 
Join Date: Oct 2015
Location: Littleton
Posts: 14
I had a similar concern about the adapters on the front. I have it on my list to ask him about. Does it change your opinion if instead of an 8.8, the swap is for a Dana 44 from a 90's Isuzu Rodeo? We've located one with the same setup for about the same price as the 8.8. The lug pattern is 6x5.5. Would that adapter fit over the lockouts?

As for the brakes, he is confident (and my research seems to confirm) that the existing master is fine and that all that needs changing is the proportioning valve.
gdselzer is offline  
 
post #4 of 26 Old 08-05-2020, 03:05 PM
Fourtrail
Registered User
1974 CJ6 
 
Join Date: Dec 2007
Location: Illinois
Posts: 4,742
What is the isuzu ratio? already 4.10? a bunch of those were 4.30 and that isn't a ratio that is available for the 30, you can use 4.27 and be close enough though. the Isuzu will work and you can swap over the outers from a waggy 44 or chevy 44/10 bolt front so the pattern matches and you get better hubs. need to upgrade the dana 30 inner shafts to the chromo ones that take a 297 joint to match the outer. the existing master is 'fine', but if you want optimum braking, you need to swap the master. need the one with equal size reservoirs so you don't run the small one of a drum/disc dry as you wear down the pads. any gm disc/disc from the late 70's/early80's will work (corvette/firebird/camaro).



just not sure why you want to spend all the extra money over 1 piece axle shafts, lsd and a re-gear for only 33's.

80 CJ-5, 74 CJ-6, 56 CJ-5
Fourtrail is online now  
post #5 of 26 Old 08-05-2020, 03:19 PM Thread Starter
gdselzer
Registered User
1984 CJ7 
 
Join Date: Oct 2015
Location: Littleton
Posts: 14
The Isuzu 44 has 4.10 and lsd already. I'll look into the master cylinder a little more.

The reason I'm wrestling with the swap is that it will cost me exact same as upgrading the 20.

Does the wider stance (2+" on each side) help or hurt me?
gdselzer is offline  
post #6 of 26 Old 08-05-2020, 04:02 PM
Fourtrail
Registered User
1974 CJ6 
 
Join Date: Dec 2007
Location: Illinois
Posts: 4,742
the extra 4" does help offroad, but you will need wider flares if you have to have tire coverage. What LSD did your rebuilder quote? a factory clutch type limited slip is really an open diff after a few thousand miles and if you are expecting a good limited slip, you need to be investing in something like a trutrac which hopefully is what was in the amc 20 build plan. you will be disappointed with a factory trac-loc limited slip if you expecting to spin both tires offroad.
80cj and jeepster4245 like this.

80 CJ-5, 74 CJ-6, 56 CJ-5
Fourtrail is online now  
post #7 of 26 Old 08-05-2020, 06:20 PM
only in a jeep cj
Registered User
1986 CJ7 
 
Join Date: Jun 2001
Location: Mobile
Posts: 6,140
Based on the factors of you only going to 33s and only doing light to medium trails a few times a year, I would regear to 3.73 if you have a 4 speed and 4.10 if you have a 5 speed. A lunch box locker in the front runs about 260 bucks or so. The locker in the front will surprise you off road with climbing and getting up and over obstacles. Help out the lock outs with either a stud kit or swap out to the earlier 6 bolt hub.

For the rear, one piece axles are almost a must. Save money with just an open diff in the rear. A limited slip is a waste of money long term. The clutches wear out and even when new, the other tire still slips and spins as power is transferred. The open diff will allow a lunch box locker later if needed. I agree with the gear driven true trac vs clutch disc if a limited slip type of diff is wanted.





https://www.eaton.com/Eaton/Products...trac/index.htm


IF IF IF you really see your self going to bigger tires an harder off roading in the future , then yes, the axle swap is a good idea. Spend the money once now.

The housing and disc brakes make the 8.8 the winner over any 20 with one piece axles. It has larger tubes and is overall a lager axle. In stock form the 8.8 is good up the 35s. The weak link is the shafts. This kit solves this and gives you the 5.5 bolt pattern so no new rims needed.


https://www.amazon.com/Yukon-Gear-YA.../dp/B0078U9CT0


Match it with an older thick walled front 44 such as out of a wagoneer/ chereokee chief or an older F150 depending on what side you need the diff on.
You can use the Ford hubs up front to give you the 5.5 bolt pattern and strong lockout hubs. Yes, it will be wider and will help on the trails with stability. the width is best with larger tires (35 up) and more lift. Id regear to 4.56 for 35s or 4.88 for 37s but that is not the route you want to go so the cost is not justified.



Again, for your situation Im back the stock axles with upgrades.

Ed
1975 CJ-6 1983 CJ-8
1986 CJ-7 Laredo 1986 2003 Inca Gold TJ Rubicon
2012 JKUR RHD
only in a jeep cj is offline  
post #8 of 26 Old 08-05-2020, 06:43 PM
jeepdaddy2000
Registered User
 
jeepdaddy2000's Avatar
1971 CJ5 
 
Join Date: Jan 2002
Location: Eagle Point
Posts: 8,777
I think the real question that needs to be answered is just how much abuse are you planning on doling out on the axles. While the 20 has a reputation for tube weakness, there have been literally millions of them installed in Jeeps and went their whole lives with no issues. If you are a mild wheeler and aren't planning on doing anything crazy,I think your axle in stock form will be just fine. If you are planning on carrying weight, towing, or heavy wheeling, you can truss the axle and have the strength you are looking for without a bunch of "fix it" modifications.


Rear disks are nice, but, since the rear is good for about 30% of total braking, I don't consider them critical.



I am assuming the 8.8 is going in used compared to a fully rebuilt 20 for the same cost? I would be angling toward the rebuilt unit.

Paperwork will ruin any military force.
Chesty Puller
jeepdaddy2000 is offline  
post #9 of 26 Old 08-14-2020, 11:02 PM
jwarner
Registered User
 
jwarner's Avatar
1986 CJ7 
 
Join Date: Oct 2018
Posts: 6
I did lots of research on this over the past year or so. Popular opinion is AMC 20 with 33s and stock drivetrain should handle most wheeling as others have stated. Searchers makes a nice weld on truss and you can weld the tubes to the housing (lots of possible problems here with dissimilar metals, warping of tubes, pitting of pinion bearing if you ground to the case -search the threads theres tons of info) as an alternative you can rosette weld the spreader holes in the housing where the tubes insert. Im going with this method and the Searchers. Probably more than I need for the setup I have (stock everything with 4:56 and 33s)but banking on overbuilding for longevity. Another common plus noted for the AMC 20 is the availability of replacements. I picked up my replacement 20 with one piece axles and an Eaton E-locker with 4:56 already installed for $800 out the door so that helped make my decision.
jwarner is offline  
post #10 of 26 Old 08-18-2020, 10:49 PM
Nucking1Futs
Registered User
 
Nucking1Futs's Avatar
1984 CJ7 
 
Join Date: Oct 2015
Location: Sacramento area
Posts: 198
Quote:
Originally Posted by gdselzer View Post
I'm in need of your experience/insight/opinions. I recently put new springs on my 84 CJ-7 which gave me a enough room to go from 31" to 33" tires. But my 2.73 gears ain't gonna cut it with 33s. So I'm ready to move up to 4.10s.

In talking to the local shop I have two options that will cost about the same (+/- $200).

Option 1 - Upgrade my current AMC 20 (and Dana 30) with 4.10 gears, LSD, and new one piece axles.
Option 2 - Swap out the rear for a low mileage Ford Explorer 8.8 that already has 4.10, LSD and disc brakes. Because the 8.8 is ~5 inches wider and has a different lug pattern, I'll need to add 2" wheel spacers/adapters to the front. My old rims are pretty rusted out, so I'm not too concerned about the added cost of new rims.

Option 2 is alluring in that I get a stronger axle and disc brakes. Downside is that it introduces a lot of new variables. Does the extra width on the axles help or hurt me on the road/trails? Should I get rims with 2" of backspacing so that my tires are back where they started? Do I need to worry about the off-center pinion of 8.8?

Option 1 eliminates the extra variables, but I also don't get the stronger axle and disc brakes.

Like I said, cost wise it's about a wash. Which would you do and why?

BTW, the Jeep is garaged most of the winter and only comes out to play in the Summer and Fall. I mostly drive it around town but do go out and do some intermediate level wheeling 5-10 times a year.
You have lots of advice from members based on your description of driving as around town and intermediate wheeling.

My $0.02, I would stay with the AMC 20.
You have a 1984 CJ7, so a T-5 tranny with the I6 4.2L? If so, I would recommend 4.10 gears. The 33's are heavier which will require increasing the rotational forces needed to turn over the heavier wheels. The engine will thank you, and save some unnecessary strain on drive train. If you have the T177, you can think about 3.73 but depends on how much time you spend in the hills. How you drive, and where you drive, engine and drivetrain will dictate your gearing.

Highway time vs town driving vs back country are all considerations you need to make. Go to http://www.grimmjeeper.com/gears.html to see what changing your gearing and tire sizes does slow (crawling) and cruising at various speeds. I suggest to keep the highway rpm under 2500 for the 4.2L.

The Dana 30 up front is pretty strong for its size. Adding spacing to the axle will increase stresses. I ran 33's through the hills on my 3.31 gearing 30/20 axles and T-5 tranny twisting her up on rocks where I go hunting. So far all I broke was a front shackle hanger. Very capable axles, if you keep them within their limits and don't bounce her and rough her up.

If you drive mild to moderately, with an occasional intermediate wheeling trip, I suggest keep the stock drivetrain. Swap out the gears, swapping in one-piece axles are must as you've experienced (the biggest weakness in the 20), and understand the limitations of the drivetrain. And as jeepdaddy2000 expressed, consider beefing up the tubes. I have not and have not had an issue (yet). There are so many jeepers doing what you are doing with minimal swaps.

Good luck and happy jeeping.

O\IIII/O
[]-o-[]

4.2L w/Howell TBI, T5, D300, Dana 30 w/locker/AMC 20 posit, 3.31 gears
Nucking1Futs is offline  
post #11 of 26 Old 08-18-2020, 11:46 PM Thread Starter
gdselzer
Registered User
1984 CJ7 
 
Join Date: Oct 2015
Location: Littleton
Posts: 14
I've decided to stick with the 20. Fortrail really helped me with that. Looking into the TrueTrac vs factory LSD was the clincher for me. Seem to be a significantly superior option. Thanks for the good advice.

Nucking1Futs, you nailed my newest question. I was just looking at the Grimmjeeper site today. I have the T 176, so no overdrive. With 4.10s I'll be doing 60 at 2550 RPMs. My powerband is tapped out at 3k. And at 2500 it's screaming. 3.73s equate to 2300 @ 60. (60 is about as fast as the Jeep will go before it feels like it's going to start disintegrating). Crawl speeds between the two seem insignificant (3.8 vs 4.2 mph @ 1500).

I got the 33 tires installed last week and they look and fit great. They're plenty big for what i do. I don't ever see wanting to go bigger on this Jeep.

So, what say you? Stay the course and go with 4.10s. Or are 3.73s the better option?
gdselzer is offline  
post #12 of 26 Old 08-19-2020, 07:44 AM
BagusJeep
Web Wheeler
 
BagusJeep's Avatar
1981 CJ7 
 
Join Date: Jul 2009
Location: Bali
Posts: 7,789
T176 is a fine transmission, 3rd gear is 1.46:1, 4th is 1:1

2.73 to 4.10 is an addition of 50% to the gearing.

3rd gear will add 46% to the gearing if you use it instead of top gear.

If you drive in 3rd gear you are as close on ratios from the swap to 4.10 as you are going to get. Why not try driving round in 3rd and see if you have reserve power and if it is screaming too badly?

BagusJeep lives in Bali.

1981 CJ7 258ci - Bagusjeep
1984 CJ7 258ci - Puthijeep
1981 J20 258ci - Gladys
1951 Willys CJ3A/MB/M38 - Little Willy
1995 Cherokee 4.0 - CHEROKEE
BagusJeep is offline  
post #13 of 26 Old 08-19-2020, 05:11 PM Thread Starter
gdselzer
Registered User
1984 CJ7 
 
Join Date: Oct 2015
Location: Littleton
Posts: 14
Bagus, that's so brilliant and simple. Why didn't I think of it myself? Guess that's why they pay you the big bucks.

I took it out on the highway this afternoon and played around with driving @ 2200 and 2500 RPMs in 3rd gear (~50-60mph). Didn't get to hit any serious inclines like I will going up I-70, but a few hills. At 2500, the Jeep seemed to handle the extra throttle needed on the hills better. Little bit of a lag at 22. Interestingly, I found it way easier to maintain steady speed at 2500. At 2200 I kept slowing down or speeding up.

So I'm going to stick to the original plan and go with 4.10s and the rebuilt 20. Thanks to all for their time and help.
gdselzer is offline  
post #14 of 26 Old 08-20-2020, 11:17 PM
Nucking1Futs
Registered User
 
Nucking1Futs's Avatar
1984 CJ7 
 
Join Date: Oct 2015
Location: Sacramento area
Posts: 198
Quote:
Originally Posted by gdselzer View Post
I've decided to stick with the 20. Fortrail really helped me with that. Looking into the TrueTrac vs factory LSD was the clincher for me. Seem to be a significantly superior option. Thanks for the good advice.

Nucking1Futs, you nailed my newest question. I was just looking at the Grimmjeeper site today. I have the T 176, so no overdrive. With 4.10s I'll be doing 60 at 2550 RPMs. My powerband is tapped out at 3k. And at 2500 it's screaming. 3.73s equate to 2300 @ 60. (60 is about as fast as the Jeep will go before it feels like it's going to start disintegrating). Crawl speeds between the two seem insignificant (3.8 vs 4.2 mph @ 1500).

I got the 33 tires installed last week and they look and fit great. They're plenty big for what i do. I don't ever see wanting to go bigger on this Jeep.

So, what say you? Stay the course and go with 4.10s. Or are 3.73s the better option?
I think you have made a wise decision keeping the M20.
If you are okay with limiting your top speed, I agree with you that 4:10 is the best option considering it looks like you live in CO according to your profile location. 3.73 would be okay, but first gear will struggle a bit. You will be in Low-range in the transfer-case more often-than-not.

O\IIII/O
[]-o-[]

4.2L w/Howell TBI, T5, D300, Dana 30 w/locker/AMC 20 posit, 3.31 gears
Nucking1Futs is offline  
post #15 of 26 Old 08-21-2020, 11:14 AM Thread Starter
gdselzer
Registered User
1984 CJ7 
 
Join Date: Oct 2015
Location: Littleton
Posts: 14
Got a chance to drive up I-70 yesterday into the mountains. Still with my 2.73s, third gear, 60mph, and 2500 the whole way. The power was fantastic while going up hill, no complaints at all. So as I understand it, that will be very close to what 4th gear will be like once the 4.10s are in. But on flatter stretches I was REALLY tempted to drop into 4th to give the engine a break. I think I'm going to miss having an "overdrive" (I know that 4th with a 1:1 is not technically an overdrive) once the 4.10s go in. So it got me thinking (never a good thing).

If I stick with 2.73s, I am actually fine on the highway. I'll just use 3rd gear if there's any upslope and use 4th gear on flat/downhill. The problem I'll still have is the low end, 1st in particular. Right now it's a dog to get started from a stop sign. Wheeling over any obstacle will suck. That's why going to 4.10s will help.

But what if I had a granny gear like in a T-18 and kept the 2.73s? Compared to my T-176 with 4.10s, the final drive ratio in 1st gear would actually a little better with the T-18 (17:1 vs 14:1). And 3rd gear with the 18 and 2.73s would be almost exactly what I have now and like on the highway (~4:1). And the gravy is that I will still have my "overdrive" 4th.

Anyone have any insights on the cost/difficulty of swapping the T-176 for a T-18 with 6.32:1 1st gear? Is there a downside to this that I'm not considering? Anyone have experience they can share?
gdselzer is offline  
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the JeepForum.com forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid e-mail address for yourself.



Email Address:
OR

Log-in











Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page



Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome