CJ-7 Projects


Lightforce Lights - H.I.D. High-intensity discharge Upgrade

HEI Ignition System (GM Style) Installed in the AMC 360 V8
Getting rid of gremlins and improving performance

Installing 23,000 Volt Offroad Lights

Autogage Tachometer Installation

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 Centralia PA
Project CJ-7
Offroaders Guide
to Gearing up
for Offroad

From Basic Equipment to Well Equipped.  An extensive list guide to help you prepare your vehicle for the offroad.


Onboard Air
Converting a York
AC Compressor
to Pump Air

Trailering Safety and Trailer Hitch Information


Off-Road Truck Driving Techniques and Safety

Off-Road Lights
by LightForce Product Review / Installation.
from Off-Road Lights


Jeep Dana 300 TeraLow - 4:1 Gearset for the Dana 300 Transfer Case

AMC V8 Engines
GEN-1 Nash/Hudson/Rambler V-8s (1956-1966) through to the GEN-3 AMC Tall-deck (1970-1991)

Chevy Small-Block V8 Engines
Chevy Small-Block V8 Engines Manufactured by General Motors - Production: 1955?2002

Hemi Engine - All about the Hemi Engine

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Ford V8 Engines
8 Cylinder Engines manufactured by Ford

Ford 351 Cleveland V8 Engines
351 cubic inch V8 Engines manufactured by Ford

Chrysler Hemi Engine

AMC V8 hp/Torque, Compression & Bore/Stroke by year

Engine Size Conversion Table
Converting engine displacement from CID, Liters, C.C.

Engine Overheating Basics - 16 Common Causes of an Overheated Engine

Fan Clutch Diagnosis
How to tell if the Fan Clutch in your Cooling System is failing or has failed.

Automotive Gauges & Instrument Functions
Information they display & their importance.


From the
Department of Cheap   Tricks and Useful Tips

Ultra-Cool Hand Throttle for Free!

Jeep V8 Swap Tips

The Exploding Clutch

Radiator Protection using 6 bucks worth of material

Cracked Under Pressure - Fixing a smashed fingernail

A Cheap, effective alternative to undercoating

Home-built Saginaw Gearbox Brace for the cost of lunch!

Ammo Box Storage - Mounting Them for Quick Disconnect

Home-built Serious Skid-Plate protection for the Oil Pan for under 20 bucks!

Ramp Travel Index
RTI / Ramp Travel Index  What it is and how to calculate it, with and without the ramp.





Project Jeep CJ-7
TeraLow Gears
in the Dana 20 Transfer Case

Back to Project Index

Disassembly of the Dana 20
Breakdown of the Dana 20 case

Grinding the Case of the Dana 20 Transfercase
Grinding the metal to clear the Teralow gears

Reassembling the Teralow Dana 20
How it all goes back together.

Teralow Dana 20 Reviews
What people think of the Teralow Dana 20 Kit

4x4 Related Calculators

Crawl Ratio Calculator


The Need for less Speed - With 3.07 gears in my Dana 44 axles and 2.03 gears in the Dana 20 transfer case, one or both had to be swapped to improve the offroad gearing.  The T-18 with a 6.32 to 1 1st gear made 4 wheeling bearable, especially with a hand throttle controlling a strong AMC 360 V8, but rock crawling was sometimes a little harsh and I knew lower gears would mean better control. 

So there was going to be a gear ratio swap in either the Transfer case or the differentials, or eventually both.   But money is always an issue.  An axle gear swap would definitely be the more costly upgrade.  So I brought up the handy little crawl ratio calculator and did a few gear Ratio comparisons. 

Changing the transfer case gears from 2.03 to 3.15 has a better net gain towards a better crawl ratio than lowering my axle gears to 3.73.  3.73 because that is the lowest I can go and keep my Detroit Locker.   Additionally, I could keep a decent high range for good highway driving and without losing strength in the ring and pinion set.  For my type of offroading, which is Mountain trails, mud and occasional rock crawling, I actually didn't want to go too low.  So the math came out like this:

1st gear
Transfer case
Low Range Gearing
Crawl Ratio
T18 (6.32) 2.03 (Stock) 3.73 47:1
T18 (6.32) 3.15 (Teralow) 3.07 61:1
T18 (6.32) 3.15 (Teralow) 3.73 74:1

As the math figures, the Teralow yielded a better crawl ratio than an axle gear swap.  When I eventually reduce the gears in the axles to 3.73, I'll have a very nice 74:1 ratio.  But for now, the Teralow seems to be the most cost effective way to get a better crawl ratio.  On top of that, I can do install the new gearset myself.

The following are my notes on this Teralow Dana 20 gear swap.

IMPORTANT: I'm not an expert!  I'm an average backyard mechanic.  These pages are not meant to replace the manufacturer's instructions, rather are just my account of the installation for your amusement only just like the rest of the project and the website for that matter.  You might find a few tips in here and and maybe even a few blunders.  If you choose to engage in these activities or undertake any project, it is by your own free will and at your own volition. I assume no liability for how any particular individual chooses to use the information presented here or anywhere else in the pages of this project.

Whenever I get a new toy, I like to inspect the parts and take inventory.  The kit comes with a set of 5 new gears, needle bearings, a new center shaft, and new seals and gaskets. 

The gear set is impressive when compared to the stock gears and are a little more beefy than the stock gears. 

I also noticed that the gear teeth are a little more finer with more teeth than stock, and thus how the kit attains a lower ratio.

Before you get started, it's a good idea to look over the exploded view diagram and familiarize yourself with the parts and their names.  Post the sheet in plain view while you're working on it so you can glance up to see the diagram when you need to.
TIP: Use plastic Ziplock bags to store your bolts and small parts in and label each bag with what the part is and any other important note you may think of.  It might be weeks before you get it all re-assembled and people tend to forget the details.  I know I do.
ANOTHER TIP: Take Pictures!  I can't tell you how many times I've gone back to refer to pictures (digital pics are nice, no film) when I can't remember how something went back together or what part in the diagram was what part in reality.

Transfer Case Removal

Irony - Though I had planned to do the Teralow kit eventually, ironically, the whole reason that prompted me to get the Teralow kit was because I had a transmission problem, or so I thought.  On my last trip the sound of gears grinding on gears was coming out of the transmission.  After removing the top of the T-18, then removing the transfer case, I found that the adapter between the two was coming loose.  Bolts were backing out and the T-18 upper gear set was drifting backwards, causing the sound of grinding gears.  With the top of the transmission off, I could see this occurring.  I tightened the adapter and the sound went away.  So now that I have the Dana 20 out, I might as well do the gears as I've wanted to do for a while.  I called Mike at OK 4 Wheel Drive, who gave me a great deal on a Teralow Dana 20 kit.  If you are looking for anything 4 wheel drive related it's worth it to at least give these guys a call for a price. (OK4WD - 908.454.6973).  The following pages document the installation of the Teralow Dana 20 gear set. 


Removed the Dana 20
1.   All 4 of the Jeeps tires were chocked very well so there was not possibility of it drifting.  Also the Transfer case lub was drained.
2.    As I said, I had the transfer case out already but in the process of doing so I had removed the gear shift cover plate in the transmission hump, the shift lever assembly.
I found a nice way to support the transmission while the drive train skid plate was removed.  Using a piece of 1/4 inch angle iron across two floor jacks it supported the T-18 transmission directly so I could remove the Dana 20.  During the process when it wasn't in the way I kept a floor jack under the transmission mount just in case.  Redundant support is a good idea for safety reasons.
3.   I removed the drive shafts.
4.   I disconnected the speedometer cable at transfer case.
5.   I removed transfer-case-to-transmission attaching bolts and muscled the transfer case out and onto the floor.  It's a good idea to have eye protection on while under a vehicles, especially my Jeep with all the mud and crud that falls out when I'm working on it.
6.   While I was down there, I remove transmission-to-transfer case gasket.  I had also discovered that the transfer case to transmission adapter was loose, thus the cause of the noise.  When I tighten it up again, I'll clean the bolts and treat it to some Locktite so they don't back out again.


With the transfer case on the bench it was time to break it down.



NOTE: Refer to exploded view for part identification.
1.   Removed bottom cover and gaskets.
2.   Removed bolts attaching rear bearing cap assembly to transfer case and remove assembly.

3.   Remove the main shaft gear through front of case.
4.   Remove intermediate shaft lock plate.
5.   They recommend using brass drift and a plastic mallet to drive intermediate shaft out of rear of case.  I used a block of wood and a framing hammer.  When the wood started shredding, I finished the job with a long bolt making sure not to nick the case where the shaft goes through.  The kit has a new intermediate shaft so I wasn't worried about it.


6.   Then I removed the intermediate gear assembly through bottom of case collecting all the bearings and washers.  These will be replaced.
7.   I removed the front output shaft nut and washer.  I had to use a piece of wood to stop the gears from turning.
8.   I removed the front output shaft yoke.
9.   I think removes the cover plate attaching screws and removed the cover.
CAUTION: When removing cover plate, take care to avoid damage to the shims between the cover and case.
10.   I positioned both shift rods in neutral.
11.   I then removed the rear output shaft shift fork setscrew.
12.   Removed the plugs that cover access hole to the poppet ball and spring.
13.   Inserted a punch through pin hole in rear shift rod (the one closer to the center of the case) and rotate rear shift rod 1/4-turn counterclockwise and pull rod out of case.
NOTE: When shift fork is free of rod, use hand to catch poppet ball and spring under shift rod.
14.   Removed the front shift rod housing attaching screws and slide housing from remaining shift rail.
NOTE: When housing is free of the rod, use hand to catch poppet ball and spring under shift rail.
15.   Using hammer and brass drift, drive front output shaft towards rear of case.  Teralow's instructions say "rear output shaft" but if you look at the diagram, you'll see it the front output shaft.  I had to make sure I was doing what they suggested for disassembly. It helps if the terms are correct in the instructions.

I found that the I would be driving the gears against the case so I put a few pieces of wood between the gears and the case to I wouldn't be damaging anything by driving the output shaft back.  

16.   Remove gears, spacer, and thrust washer from inside case and rotate shift rod to expose the setscrew.
17.   The next step is to remove setscrew and pull out the remaining shift rod.  I had a hell of a time trying to remove the setscrew.  I decided to leave the shiftrod in the case and just work around it rather than risk breaking something trying to get the screw out.  Having the shiftrod there turned out to not be a problem.  I just had to clean around it and work with it there.  So you'll see shots with the rod still in the case when it shouldn't be.  If you can get yours out, do it. 


Disassembly of the Dana 20
Breakdown of the Dana 20 case

Grinding the Case of the Dana 20 Transfercase
Grinding the metal to clear the Teralow gears

Reassembling the Teralow Dana 20
How it all goes back together.

Teralow Dana 20 Reviews
What people think of the Teralow Dana 20 Kit

Crawl Ratio Calculator


Tera Manufacturing, Inc.
5251 South Commerce Dr.
Murray, Utah 84107


Torque Specifications:

Torque Specifications     Foot-Pounds
Front and Rear Output Shaft Yoke Nuts   225-250
Right and Left Shift Fork Setscrews   12-15
Shift Rod Housing to Case Bolts   28-30
Front Output Shaft Rear Bearing
Cover to Case Bolts
Intermediate Shaft Lock Plate
to Case Bolts
Rear Bearing Cap Assembly
to Case Bolts
Lower Cover to Case Bolts   12-15
Transfer Case to Transmission Bolts   28-32


Click to zoom in

Items underlined and bold below are included in the Tera Low20 low range gear kit

1. Shift Rod    33.  Intermediate Gear Shaft
2. Shift Rod   34. Thrust Washer (2)
3. Shift Rail Seal   35. Bearing Spacer (3)
4. Shift Rail Interlock   36. Needle Bearings
5. Shift Rail Interlock   37. Intermediate Gear (TL20-B)
6. Detent Springs         38. Cover Gasket
7. Detent Balls   39. Cover
8. Front Output & Shift Rail Housing Seal   40. Drain Plug
9. Washer   41. Main Drive Gear (TL20-A)
10. Front Output Bearing Race   42. Rear Sliding Gear (TL20-E)
11. Front Output Bearing   43. Set Screw
12. Shift Rail Caps   44. Rear Wheel Drive Shift Fork
13. Case Housing   45. Rear Output Shaft
14. Tranny to Transfer Case Gasket   46. Rear Output Bearing
15. Front Output & Shift Rail Housing   47. Rear Output Bearing Race
16. Front Yoke Seal   48. Speedometer Drive Gear
17. Front Output Yoke   49. Rear Output Shaft Shims
18. Yoke O-ring   50. Rear Output Housing Gasket
19. Flat Washer   51. Rear Output Housing
20. Companion Flange Nut   52. Breather
21. Washer   53. Rear Output Bearing Race
22. Front Output Gear (TL20-C)   54. Rear Output Bearing
23. Front Sliding Gear (TL20-D)   55. Rear Output Yoke Seal
24. Shift Fork Set Screw   56. Rear Output Yoke
25. Front Wheel Drive Shift Fork   57. Flat Washer
26. Front Output Shaft   58. Companion Flange Nut
27. Front Output Bearing   59. Speedo Driven Gear Busing
28. Front Output Bearing Race   60. Speedometer Driven Gear
29. Front Output Bearing Cap Set   61. Speedometer Driven Gear Sleeve
30. Front Bearing Cap      
31. Intermediate Gear Shaft Retainer      
32. Intermediate Gear Shaft O-ring      



Other Teralow Resources:
Great deal on the Tera Low20 from OK4WD
Dana 20 Tera Low20 for Manual Transmissions

Related: Dana 300 Tera Low Install
There are several models of the TeraLow, there are TeraLow's for Dana 300 (4:1), Dana 20 (3.15:1), Dana 18 (3.15:1), and NP 231 (4:1).

Transfer Case Upgrades, Modifications, and Options
Jeepfan.com - There are several modifications that can be performed on a Jeep transfer case.  Most involve replacing the gears in the case to lower the gear ratio to improve slow trail performance.


Teraflex Dana 20 Low Range Kit install / Review
Pirate4x4.Com reviews the Teraflex Low20 Kit including Case Grinding, Installing and testing

Installing TeraLow Gearset - Dana 20 Transfer Case
For hard-core 'wheeling, slower speeds mean greater control and less strain on your drivetrain...Swapping in lower (numerically higher) gears into the axles will certainly help..

Tera Low Dana 20 Gears Review / Install
JeepWire.Com product Review of Tera Low Dana 20 gears.


Project Jeep CJ-7 ~ The Dana 20

Back to Project Index




Offroad Tire Info
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Tires for your Truck
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Super Swamper Bogger
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Super Swamper TSL Radial
Super Swamper Narrow
Interco SS-M16 Swamper
Thornbird TSl Radial
Thornbird TSl Bias
Thornbird TSL
Parnelli Jone Dirt Grip
BFGoodrich Krawler
BFGoodrich MT T/A KM
BFGoodrich MT T/A KM2
BFGoodrich AT TA KO
BFGoodrich Mud King XT
Bridgestone Dueler MT
Cooper Discoverer ST
Cooper Discoverer STT
Cooper Discoverer ST/C
Firestone Destination MT
General Grabber MT
General Grabber AT2
Green Diamond Icelander
Ground Hawg Mud Tire
Hankook Dynapro MT
Hankook Dynamic MT RT01
Hercules Terra Trac MT
Hercules Trail Digger MT
Kelly-Springfield Safari DTR
Kelly-Springfield Safari MSR
Kumho Road Venture MT
Kumho Road Venture KL71
Kumho Road Venture AT
Dick Cepek Mud Country
Dick Cepek F-C II
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Dick Cepek Fun Country Nylon
Dick Cepek Fun Country Kevlar
Mastercraft Courser MT
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Mastercraft Courser HTR Plus
Maxxis BigHorn Radial
Maxxis Creepy Crawler
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Maxxis MT-754 Buckshot
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Nitto Mud Grappler
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Goodyear Wrangler MT/R
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Toyo Open Country MT
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Mickey Thompson MTZ
Mickey Thompson MTX
Mickey Thompson Baja Claw
Mickey Thompson Baja Crusher
Competition Claw
Dunlop Mud Rover
Yokohama Geolandar

Latest trips Offroad
... trail reports with the Project CJ-7
click here.

Sounds System, Raised the Rear Seat
Storage below and a great place to mount 6x9 Speakers for Great Bass ... In a Jeep!

York AC Compressor Conversion.  What used to pump Freon, now pumps compressed air to the front and rear bumpers.  125 psi,  2 gallons of storage, air fittings at the bumpers, enough CFM to power air tools!.  Click Here for more  Details


Dick Cepek's 2008 F-250 Super Duty Project Vehicle ? Project CRUSHER

Warn X8000i
Winch Installation

ARB Air Locker Install
Jeep Wide Track Axles Swap

Mud Tire Reviews

Building a Garage?
Need a Garage Plan?

Reader's Rigs and Seriously Stucks!


Jeep Trans Swap Info
T-18A Transmission Rebuild & Short Shaft Conversion