Differential advice

Differential advice

stoney bones

Active Jeeper
Posts
273
Thanks
0
Location
michigan
Vehicle(s)
81 CJ7

258ci, mc2100 ,SR4 trans, dana 300 Tcase, dana 30 front, amc 20 2 piece rear
current set up:

AMC 258 i6 / 4.2l
T-18 (on its way)
Dana 300

Dana 30 front
AMC20 2 piece rear

33 x 12.5 x 15 (want to upgrade to 35's)

questions:

what diffs should i upgrade to? i want to run 35's. also this will be no crawler. i want it for mild to moderate trails and to be able to drive to and from the trails. so, please, some suggestions on what diff's and ratios would be best suited for my needs.
 
with that T-18 , i probably wouldn't go much lower than a 4:10, maybe 4:56. the T-18 should have a granny gear so 1st really won't be usable on the street, but will give you a nice low gear for off road, which basically leaves you with a 3 speed transmission.
 
With 35" and the T-18 I think 4.10 would be a good choice you'll be running about 2600 rpm on the highway at 65mph and with the low 1srt gear off the T-18 you'll have more then enough gearing for off roading. I have 33" with T-176 and 4.10 and run about 2800 rpms on the highway. Which is at the limit of the range of the AMC 258 i6 / 4.2l I think. I'd upgrade to the one piece axle, for sure on the AMC20 . and as for the Dana 30 upgrade to the 4340 chromoly axles look at the 30 spline upgrade to for the Dana 30 I didn't even think about it when I upgraded. Then you have to think about lockers or what, selectable lockers is the way to go but expencive. But would be the way to go, if you have the cash. For the upgrades expect about 2500-3000 for parts. That if you want to up grade the axles in front to and get lockers. But I would at the least up grade the AMC20 with a one piece axle at the least, when you upgrade the gearing. It really comes done to how much you want to spend when upgrading, and if you have the cash I'd do it all at once. I would check out what you want to spend. I would upgrade the lockers and ring&pinion at the same time one time to have to set up the gear mess. Also I would pay to have the ring&pinion set-up cause close isn't good enough for ring&pinion set-up. IT CAN BE DONE AT HOME IN YOUR OWN SHOP BUT SOME SPEICAL TOOLS ARE NEEDED AND IT HAS TO BE DONE RIGHT OR YOUR NEW GEARS WON'T LAST LONG. Should run about $800 for both axles. Have fun planning your upgrades:D:cool:
 
As others have said with the T-18 4:10's or 4:56's should work.
With no hard core wheeling in your future you might want to run Limited slips front and back to help keep your road maners. eaton truetraks would be my first choice.
 
thats kinda good to know.

i was under the impression that the Dana 30 and especially the AMC20 wouldnt stand up to much. good to know for my application i could keep them.

yea, as long as i can hold at least 65 on the highway with out revin the :dung: outa it. i dont drive this on the highway...never have but, cant take back roads everywhere (well in a timely manner at least). i still dont think ive had this thing over 55 mph lol

ill definitely scope out the axle options. 1 piece rear seems a must, pretty sure ive heard that before too so thats on the list for sure. the lockers will be where i need to choose wisely it seems. i have a decent budget but i want this thing painted, frame and all as well. flat army green with black accents!

thanks for the advice. you have given me a good direction to go in.



1 more question. would it be worth it to try and find something like some Dana 44 's for the front and rear? or am i getting into overkill country there?
 
IMO the 20 with 1 piece axles and the 30 will do fine with 33's or 35's as long as you don't get to stupid with it. If you go 35's you will have to do some body trimming so the tires don't rub.
 
I used to have an '82 CJ7 with a T-18 and 33 inch tires. I had it geared high and started out in 1st. With the granny low the T-18 was intended to be started in 2nd. It worked fine for me. It was a daily driver. This tall gearing with a T-18 is what everyone else in this thread is recommending.

Now I have a '79 CJ5 with 36 inch tires and a T-18 . The main use of my Jeep is for trail rides but I need to drive on the highway too. I have 4.88 gears and I can easily drive 65 mph. The tach is at about 3000 rpm at that speed. With all the off-roading I do I wish I could have gotten 5.13 or 5.38 gears. Yes I wouldn't be able to drive much over 55 but that would be fine with me. When I bought my CJ5 it had 4.11 gears and 35 inch tires. On the highway the tach was down nice and low but it was gutless. I got better gas mileage. If I wanted to pass someone on the highway I couldn't. No power. Sure I could down shift but with the wide ratio T-18 the tach will shoot way up when you are in 3rd gear on the highway. Too high. I didn't do that. I just sat behind the slowpoke. That's another reason I like 4.88 gears - no need to shift on the highway. Downside is I use more gas. I get 13 mpg with my AMC 304 . The higher RPM wears your engine if you do much highway driving.

After all that what do I recommend? I would say anything between 4.11 & 4.88 depending on your intended use. If you are more concerned about off-road get 4.88. If you are going to put on lots of highway miles get 4.11 and don't expect to be passing many people.
 
1 more question. would it be worth it to try and find something like some Dana 44 's for the front and rear? or am i getting into overkill country there?
Overkill? No
No and no, it wouldn't be overkill. Dana 44 's would be perfect for 35 inch tires.
 
As others have said with the T-18 4:10's or 4:56's should work.
With no hard core wheeling in your future you might want to run Limited slips front and back to help keep your road maners. eaton truetraks would be my first choice.
Old dog is right about the Limited slip which is what I have in both front and back diff. There also alot cheaper then selectiable lockers, and no extra cables, wires or air lines and compressors to buy also. For the AMC20 truetrac had to have 4wd order it from the factory they dont carry it in stock. :)
 
Im not sure if its been said but when your regearing your 20 look into 1 peice axles.. theres alot of debate between the strength of the AMC20 verses the 44.. for the rear the 20 has a bigger ring gear wich should make it stronger but the axle tubes are smaller and tend to bend.. they also have the 2 peice axles to deal with.

as far as getting 44's for the front and rear goes its hard to find a bolt in 44 for a CJ. scouts have some that are the same width but have a caster angle issue and need to have the C's cut and turned. You can get a waggy front then have the long side shaft cut down to the right width but now you have a 6 lug axle so you need to change your rims.

If you decided to run waggy 44's front and rear and not cut em down the rear is just a new set of perches but the front in stock width needs to outboarded and new 2.5" springs, spring hangers and shackle bought.

SOOO... If its just gonna be a mild trail truck and road driver I would polish the turds you have.. good one peice shaft for the rear and Locker.. (id stay away from the LSD).. and the same for the front.. oh and get a winch. yeah you will dump some cash into the front and rear and every one will tell you if your gonna do that to go to 44's or bigger but there is a lot of head aches that come about when you do that.
 
as always good info for me to consider.

for poops and giggles i e-mailed currie to ask for a quote for Dana 44 's front and rear...waiting to see what they say.

i definitely may end up just beefing up what i have per your guys suggestions about the chromoly front axles and 1 piece rear. seems to be a split audience on the lockers tho.
 
this will be no crawler. i want it for mild to moderate trails and to be able to drive to and from the trails.

seems to be a split audience on the lockers tho.

stoney, since you live in mich. and have to drive in snow and ice I don't think full auto lockers would be a good idea as they can handle really bad on slick roads. If you have the money selectable lockers would be the best for on road driving,open for good handling and locked when needed. If money is tight than I believe Limited slips would be the best even though they too can be a handfull on slick roads.
 
Forget any Limited slip with 35's

You Can always unlock the hubs on the street with a Detroit locker in the front.

Selectable are the best but the most expensive.
 
looks like i better go selectable.

is ARB's air system better than say an OX locker? only about a $200 difference from what im seeing and i always thought ARB was one of the best but im not really sure. the only detroit locker on this site im looking at is a Limited slip.

ive already checked morris 4x4 and quadratech...any other sites i could look at for a better price maybe?
 
Another question:


i want a wider stance on my CJ. pretty sure i have the narrow trac axles. If i get the wide tracs....how much wider are they? i wanted the wider stance without having to add the wheel spacers cause i hear there is a debate about those. and it was mentioned already that the AMC20 has thinner tubes that may be prone to bending...soo suggestions?

EDIT: might as well add another question....is it possible to convert to disk brakes? any kits made? or if its possible, would i have to look for a 'donor' vehicle?
 
Last edited:
Ox lockers are cable activated.. ARB are air.. So if you want an ARB you need to intall a compressor and the run air lines. if your on the trail and you compressor craps out or you break a line your out of luck for a locking diff. Ox's cables are pretty good but as with any cables get crud in them and become hard go operate.

If you want noticeable wider stance either get rims with less (I think) back spacing or spacers for your current axles. Your next option for a wider axle would be waggy axles and those would need to be outboarded. If your not a mechanically inclined person then you will need to buy a out board kit that will set you back a few hundred. If you can set up your own suspension and handle some welding you can make your own for about $40. Then you need to buy 2.5"wide springs for the front and new perches for the back. With the waggy axles you will need new rims since they are 6x5.5 bolt pattern. You would need a front axle from a 80 or earlier waggy and a rear from a 90 and up (again I think) so that you will have the right diff side for the front and centered rear.
 
Another question:


i want a wider stance on my CJ. pretty sure i have the narrow trac axles. If i get the wide tracs....how much wider are they?

App. 4" and will bolt right in.
 
Scout Dana 44 axles and 4:10. Scout axles are still pretty easy to find and 4:10 gears are a great choice being there so many out there. 35's you want a decent set up specially if your heavy on the gas at times! Good luck!!!!
 
I want a wider stance on my CJ. pretty sure i have the narrow trac axles. If i get the wide tracs....how much wider are they? i wanted the wider stance without having to add the wheel spacers cause i hear there is a debate about those. and it was mentioned already that the AMC20 has thinner tubes that may be prone to bending...soo suggestions?

Like Old Dog stated above its around 4 inches. Its not a bad idea to look for a donor Cj to grab your parts from. The hard part will be finding one with the the ring and pinion you want. I grabbed a rusted out 85 Cj for $400.

partscj1.jpg

If you have the room and are willing to do the work I think this is the way to go. You can sell some of whats left for scrap and a Dana 300 t-case will get you $AMC 150 to $200 on the internet all day long. I gave the scrap to a buddy who helped me cut it up and he got $90 for it. Anything else is bonus. Im using the whole drivetrain to rebuild while I still drive the Cj in its current form. :) I settled for 2.72 gears in my case and will just get them re geared. Look around though , never know what youll find. ;)
 
Ive stayed away fron the scout axles because ofthe caster issues.. I hear they are set at 0 degrees which makes for bad road handling.
 

Jeep-CJ Donation Drive

Help support Jeep-CJ.com by making a donation.

Help support Jeep-CJ.com by making a donation.
Goal
$200.00
Earned
$25.00
This donation drive ends in
Back
Top Bottom
AdBlock Detected

I get it, I'm a Jeep owner and ad-block detectors kinda stink but ads are needed on this site. This is a CJ site, all the ads are set for autos (some times others get through.) I cannot make them just for Jeeps but I try.

Please allow ads as they help keep this site running by offsetting the costs of software and server fees.
Clicking on No Thanks will temporarily disable this message.
I've Disabled AdBlock    No Thanks