Gearing a CJ

I currently run a 1974 CJ5, 304, T-18 (4:1), D20, and have 3:73 gears in it. I am wanting your opinions on what gear, ratio and brand, that have been used in this application. I run 33x12.5 tires. Looking to do this soon, so your input is appreciated. Have you had any failures, whining, ect. My jeep is also locked front and rear, so the thick ring gear is needed for the rear end.
Thanks for your help.

 

whtat do you use the Cj for mostly? street, trail, hardcore trails, ect...

I have a '74 with a warmed up 360, 3 speed/dana 20 (stock) and 3:73s. I run 35x12.50x15 TSL Super Swamper tires on 8" wheels.
My real handicap is on tight trails as I can't slow the Jeep enough for the technical stuff. But when I race it in the mud, those same gears keep the wheel speed high so I can clean the tires out effectively. Not to mention I can run on the street about 70 MPH with no problem and still get 'decent' mileage (from a 7 ft tall brick LOL)

 

I use it for trails and street to get there. Tow a small trailer (Sears David Bradley). It doesn't matter, sand, hills, mud, snow, it's all good stuff. No hard core rock stuff, body damage is expensive!

 

Sounds to me like you have the right gears.

 

I guess my main gripe about the current gearing is take off. 2nd gear is 2.41 now, and was 3.0 with the T-15. Have to ride the clutch a little more.

 

OT - What color is your Jeep?

 

It is PPG #2176, gold. Unusal color, but it works! Just painted it about a month ago.

 

Instead of starting off in second, use first. I agree that you have good gears for what you use the jeep for. You could change to 4.10's or something but that's a big expense for not a lot of change.

 

I ran the gear/tire applett and it recommended a 4.29 gear to return it to original specs, performance and milage with the current trans/tire combo. So right in between a 4.56 and 4.10 gear.

 

4.27s were available from the factory in 1974. If cost were no object, I'd probably go with 4.27s or 4.56s.

Also, if you don't like the 2.41 2nd ratio of the T-18, there's no problem using 1st if you aren't rolling. If you're stopped, go to 2nd then into 1st to prevent clash.

 

I have the same set up, well, I have the 258. I have no problem off the line. On steep hills I do on occation drop it into first. I know it's not syncro'd but slow shifting or double clutching helps. If anything I would like to do the teralow conversion of the t case.

High5

 

Like High5 suggested. Keep the gearing you have and put terra lows in the Tcase. that way you do not loose any of your highway performance but you get much lower gearing for the tough stuff. The terra low will probalby be as cheap if not cheaper then regearing the axles.

 

I have a 75 with a Chevy 350, turbo 350 auto trans, 33x12.50's and 3:31 gears, powertrax in the front, tracloc in the back. I put the terra low in the D20 and LOVE it. I still think it'd be better with at least 3.73's but i'm pretty happy the way it is, and highway driving is piece of cake.

 

Or learn to double clutch. My brother had the close ratio T-18 in his 68 V-6 CJ-5 and always drove it on the street like a conventional 4 speed.

 

Your overall 1st gear ratio is about 29.8:1. I have had almost your exact set-up. It will work on the trails, but could be better. You probably use 1st and 2nd a lot on the trails, and 3rd is just for traveling on a dirt or gravel section. On the street, you probably find that it can't quite take off great in 2nd, and 1st just seems a little low. (I would just use 1st, it is tolerable at 4:1).

Anyway; You would be happier with lower gears, but you might want to make a change that is more significant. If you switch to 4:88's, that will only take you to 39:1 overall. A nice difference, and about as low as you could tolerate on the street (especially with 33's). If you were to keep your 3.73 gears and convert your t-18 to a 6.32 1st gear, you would have a 47:1 overall low ratio and keep your same highway gears, that would be better. Even if you do not do hard core rock-crawling, low gears are nice for things like creek crawling or other obstacles.

A change to your transfer case gears is always good, since it effects your off-road only.

A few things to consider. Are you planning on larger tires? What kind of gears do the people you go 4-wheeling with have? Do you plan on gradual upgrades to your Jeep as time and money allow?

 

if you are going to regear, i'd think 3:73's to 4:10's would not be worth the trouble.... 4:56's may be a little much for 33"s but would be great off road and would leave you plenty of geaing if you ever go to 35"s

4:88's takes some getting used to with our T-18 tranny and would for sure be way too much for 33's

i run 4:88's with my T-18A and 36" Iroks and at 60MPH i am right under 3k RPMs

i know that my T18 is the granny geared 1st gear but our 4th gear should be the same 1:1 ratio.

if you do gear to lets say 4:56 and plan to go up to a 35" tire you gotta really think about axle strength.. esp being locked f/r.

 

Just a comment - changing from the close ratio to the wide ratio T-18 is not a bolt-in swap in most cases. The easiest change would be to a T-18 from a 70.5-79 6-cylinder Jeep truck or wagon - that should have the same stickout, also use the T-15 bell, and should be a bolt-in replacement. These transmissions are not widely available though. Any other option would need the Ford input shaft and would require a different bellhousing, moving the crossmember, and changing the driveshaft lengths.

 

There is your best option. May be hard to find, but hold out for one. You also get a lower 2nd gear for the street, so you won't have to take off in the low 1st.
Keeps your MPG's good on the street.

 

Tim - I thought the only straight T-18 bolt in with a 6.31 first was from a late 70's cj. I thought the ones form the truck or wagon would need the input shaft repalced so the tranny would not be to long. Or is this something other than what I'm thinking of?

 

The largest number of J-trucks, Wagoneers and Cherokees (FSJs) from that era were delivered with V8s, and most of those were automatics. The V8 version of the FSJ T-18 from that era uses a very long input shaft, and these are the FSJ manual transmissions you find most often. The long input shaft and a spacer between the bellhousing and the transmission moves the shifter back into the cabin on the V8 T-18 FSJs. Use a Ford T-18 (or NP435) behind a V8 in a FSJ and the shifter will come up under the dash.

There are a lot more differences between the V8 FSJs and the 258 FSJs than you'd expect. This topic comes up a lot in reference to converting a 258 FSJ to a V8, and more recently, vice versa. Conversions are not so straightforward.

Now, the 258 is a different overall length from the V8, and it does not need a spacer behind the bell for proper shifter placement. My truck with a T-15, for example, has no spacer at all between the transmission and bell, and the shifter is not under the dash. The FSJs with a 258 and T-18 used the T-15 bell and a plate adapter between the bell and transmission, same as the close ratio T-18 in a 258 CJ-5. The plate adapter converts from the bellhousing T-14/T-15 pattern to the Jeep T-18 transmission pattern. Now, I can't prove that these are the same part, but I think they are, and I recall that this has been confirmed by Nick or somebody (John Nutter?) in another thread.

If someone had the parts book from this era, a confirmation of this would be to compare the part number for the 258 T-18 FSJ plate adapter with the plate adapter for the 258 T-18 CJ-5.

:AMC: :tea: