Stick with T15 or find T18?

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volkswaben
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Stick with T15 or find T18?

Post by volkswaben »

Well, I'm finally putting my 360 back together for my 74' Cherokee. Finished with the bottom end and timing set yesterday, and am now waiting for the dipstick tube so I can install the oil pan. I should be done assembling in a few weeks, which leads to the next piece of the puzzle, the transmission. The Jeep currently has the factory T15 and Dana 20. I have only ever driven it about 300 feet, that's when I tried to put coolant in and it went straight to the crankcase. :D I was wondering if the T15 is a suitable trans for moderate wheeling and camping, or if I should try to get my hands on a FSJ T18. I'm planning on lifting the Jeep with 33s, and I've heard that the T15 is plenty strong, but am wondering if I will regret not having the low first gear a T18 would get me. Anybody driven a T15 or similar fsj and have any advice? Thanks!
1974 Cherokee 360/T15
1979 Cherokee - parts rig/ future project?

will e
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Re: Stick with T15 or find T18?

Post by will e »

If you are going to wheel it and put on bigger tires then the lower first gear ratio will pay big dividends. Maybe even avoid re-gearing the axles.
81 Waggy 'WILL E' Retired
82 Cherokee WT - SOA/SF/high steer/Alcan springs/agr box/Borgeson steering shaft/AMC 401/performer/holley TA/HEI/BeCool/727/ALTAS (2.0/2.72/5.44)/D60 Snofighter(Yukon Zip,hubs,stubs,4.56)/14 Bolt (FF,BF shave, Discs, ARB,Artec Truss)/MTR 37X12.5/Corbeau XRS Baja & 5 point retractable harness/Hella Aux lights/tuffy console/killer32 sliders/Evil Twin bumpers, rack and roll cage/WARN 8000/TT Fabworks steering brace/dual batts/custom TC skid plate/ARB fridge
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tgreese
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Re: Stick with T15 or find T18?

Post by tgreese »

I own a J10 with a T-15, and a J20 with the T-18. I drove shop J-trucks with T-18s when I worked at a Jeep dealership. This is my second CJ with a T-15, and I've also owned a CJ with a T-14.

The main issue I see with tall tires is the axle ratio. Likely you have 3.07s in a Cherokee which is a tall gear with 33s. You'll be under 2200 RPM at 70, without the low speed torque multiplying advantage of an automatic transmission. The T-18 in these Jeeps is basically a 3-speed with a super-low auxiliary 1st gear. However, I expect you won't want to use that gear to get rolling. It's really low, and the shift is long, slow and unsynchronized. The T-15 is an easy shifter compared to a T-18, and shifting a T-18 in traffic gets tedious quickly, especially if you need to double clutch or stop completely to get into that low-low 1st gear. My J20 has 3.83s and 31s and it's fine off the line - though I never use 1st on the street, except maybe in my driveway. The J10 has a 258 and a T-15 with 3.54s and short tires, and it takes a bit more finesse with the clutch to start off.

If you are thinking of a transmission swap, I'd skip the T-18 and go with an AX-15 or NV3550 5-speed, and much deeper axle gears, like 4.10s or 4.54s. I'd also upgrade the Dana 20 with Tera gears to provide a better low range. That will give you a crawl ratio of about 50 and about the same engine speed on the highway. Or switch to a Dana 300 or a Dana 300 with Tera gears which will put you closer to 65:1.

To me, the problem in your immediate plan is your wanting such tall tires with the T-15 and 3.07s. Plus you'll need a lot of lift with a narrow track body and those big tires, or a bunch of trimming, or both. If you haven't driven this Jeep a lot (not at all!), I'd suggest you get something like the factory tires (maybe 29s or 30s?), put it together and wheel the snot out of it. These are real Jeeps - nothing like the all-weather mall crawlers that are so abundant today. Your Jeep will go a lot of places in factory form, and you'll learn about what you'd like from it.
Tim Reese
Maine beekeeper's truck: '77 J10 LWB, 258/T15/D20/3.54 bone stock, low options (delete radio), PS/PDB, hubcaps.
Browless and proud: '82 J20 360/T18/NP208/3.73, Destination A/Ts, 7600 GVWR
Copper Polly: '75 CJ-6, 304/T15, PS, BFG KM2s, soft top
GTI without the badges: '95 VW Golf Sport 2000cc 2D
Dual Everything: '15 Chryco Jeep Cherokee KL Trailhawk, ECO Green
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Phils67
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Re: Stick with T15 or find T18?

Post by Phils67 »

Basically what everyone else said. The T18 is pretty much a 3 speed. 1st gear is useless for street driving but when you want to crawl through some gnarly terrain or rip a tree out by the roots its awesome to have. I drive my T18 on the road as a 3 speed. If I start in first I have to shift by like 5mph tops, but I also use my truck like a tractor, and for that purpose the 6.32 first gear is worth its weight in gold. Could always find a NV4500 with the low first and also gain an OD if you feel frisky. You'd gain the best of both worlds. If I ever had to build it again, that is route I would go. A stump puller with OD
Last edited by Phils67 on Fri Sep 07, 2018 3:54 pm, edited 2 times in total.
1967 Gladiator J2000, 1998 4.0L OBD2, T18, D20 twin sticks, D44HD/D60, Detroit lockers, 3.73s, 4wheel disc brake, FSSR, Dakota digital, etc.
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volkswaben
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Re: Stick with T15 or find T18?

Post by volkswaben »

Well I was planning on rebuilding the whole chassis anyway and to go through the axles, transfer case, disk brakes all round, hydroboost and whatever transmission I decide to go with. I've considered a transmission swap, but wasn't sure if an ax-15 or similar could handle the 300-350 hp. Can they?
1974 Cherokee 360/T15
1979 Cherokee - parts rig/ future project?
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Phils67
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Re: Stick with T15 or find T18?

Post by Phils67 »

I do not know for sure the specs the AX15 can handle but they are a good midsized gearbox. I have owned them in XJs with engines pumping near 300hp and they did very well. The gear ratios arent the best for crawling or real life work, but highway they do very well. They are pretty tough little transmissions. If you go the AX15 route you will need to move the shifter hole further back as the shifter is more towards the rear.
1967 Gladiator J2000, 1998 4.0L OBD2, T18, D20 twin sticks, D44HD/D60, Detroit lockers, 3.73s, 4wheel disc brake, FSSR, Dakota digital, etc.
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tgreese
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Re: Stick with T15 or find T18?

Post by tgreese »

It all depends on the driver. If you hammer it, you'll break it.

You have millions of acres to explore where you live. And you're young, you've got plenty of time to build up this Jeep... or another one. I looked at the pictures of your Jeep, and IMO it's going to require plenty of effort and expense before you are ready for a major drive train swap.

In this era, Jeep drive trains were - in general - strong and durable. A 360 has plenty of poop for a Jeep, IMO. I'm trying to diplomatically suggest that you may be getting way ahead of yourself, and that you don't yet appreciate what changes will be worthwhile for you. You are fortunate that a '74 is currently smog exempt in California, so you can proceed without worrying about passing an inspection. However, some systems (like vapor recovery) are useful and you should keep them.

The platform you have is basically sound. I suggest you focus on durability and reliability at this stage, using what you've got. There's nothing wrong with it the way it is - it will go lots of places. It's a Jeep V8 with terrible aerodynamics, and it's going to be thirsty even in stock form. You could use the money you'd spend on go-fast accessories to buy gas to go places. Go places.
Tim Reese
Maine beekeeper's truck: '77 J10 LWB, 258/T15/D20/3.54 bone stock, low options (delete radio), PS/PDB, hubcaps.
Browless and proud: '82 J20 360/T18/NP208/3.73, Destination A/Ts, 7600 GVWR
Copper Polly: '75 CJ-6, 304/T15, PS, BFG KM2s, soft top
GTI without the badges: '95 VW Golf Sport 2000cc 2D
Dual Everything: '15 Chryco Jeep Cherokee KL Trailhawk, ECO Green
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Phils67
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Re: Stick with T15 or find T18?

Post by Phils67 »

There are tons of transmissions you could install. No matter what you decide it all boils down to the axles. That is the final drive. In my brain the axle is the most important part of the build. Everything in between is just a matter of opinion. If you are building a vehicle for offroad/work purposes, build the axles first and the rest of the vehicle around it. Start from the ground up. The final drive will dictate whatever you decide for driveline. Thats just my 2 cents and I am sure some may disagree but the proof is in the pudding when it comes to the diffs. You want streetability? Go with something like a 3.73, it will give you the best of both worlds. If you want a low range monster with bigger tires keep it low 4s and up. Everything in between is a technicality. Worry about the axles. Build them to do what you want and install whatever driveline falls into your lap. The right way is to plan the build, but no matter what you build, the axle ratio will determine the performance of it. You sound like you want crawl and driveability to me. For that i say pick your poison for an engine, run a NV4500, pick a transfer like a D20 or 300, build the axles with something between 3.73 and 4.56, lockers, etc, and modify as necessary. I don't care who disagrees, I am in a very depressed mood and feeling a bit froggy tonight. Build your jeep and disregard the naysayers. If it isnt what you want, change it. These things are never ending money pits. Welcome to jeeping. Sorry if I come off wrong but screw miles per gallon. All that matters are smiles per gallon. These things have the aerodynamics of a brick. Just build it and enjoy it man. If you break 15mpg with anything you did, you beat the system. Sorry for venting
1967 Gladiator J2000, 1998 4.0L OBD2, T18, D20 twin sticks, D44HD/D60, Detroit lockers, 3.73s, 4wheel disc brake, FSSR, Dakota digital, etc.
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Phils67
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Re: Stick with T15 or find T18?

Post by Phils67 »

I feel better now. My bad if I let loose. I love all you people
1967 Gladiator J2000, 1998 4.0L OBD2, T18, D20 twin sticks, D44HD/D60, Detroit lockers, 3.73s, 4wheel disc brake, FSSR, Dakota digital, etc.
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volkswaben
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Re: Stick with T15 or find T18?

Post by volkswaben »

tgreese wrote:It all depends on the driver. If you hammer it, you'll break it.

You have millions of acres to explore where you live. And you're young, you've got plenty of time to build up this Jeep... or another one. I looked at the pictures of your Jeep, and IMO it's going to require plenty of effort and expense before you are ready for a major drive train swap.

In this era, Jeep drive trains were - in general - strong and durable. A 360 has plenty of poop for a Jeep, IMO. I'm trying to diplomatically suggest that you may be getting way ahead of yourself, and that you don't yet appreciate what changes will be worthwhile for you. You are fortunate that a '74 is currently smog exempt in California, so you can proceed without worrying about passing an inspection. However, some systems (like vapor recovery) are useful and you should keep them.

The platform you have is basically sound. I suggest you focus on durability and reliability at this stage, using what you've got. There's nothing wrong with it the way it is - it will go lots of places. It's a Jeep V8 with terrible aerodynamics, and it's going to be thirsty even in stock form. You could use the money you'd spend on go-fast accessories to buy gas to go places. Go places.
You are right, I am probably getting way ahead of myself in terms of modifications. My OCD is probably kicking in. I should probably get it up and driving first before I dig myself too deep. It'll probably be better to take it one step at a time rather than all at once. In the end, all I wanna do is have a good time with it!
1974 Cherokee 360/T15
1979 Cherokee - parts rig/ future project?
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tgreese
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Re: Stick with T15 or find T18?

Post by tgreese »

A couple of other observations, if I may.

Pretty sure used NV4500s are wildly expensive.

Big tires and big lift will increase fuel consumption a lot. Just so you know.

You are thinking about tires. Being an LA native and having driven many thousands of miles of trails in CA and surrounding states, in your location I would skip any kind of mud terrain tire and pick something in the all-terrain category. You're going to see lots of rocks and sand and plenty of highway miles. The drone of an aggressive tire gets tiresome after a while, ATs are a lot less expensive then MTs, and they last longer. This is a whole other topic in itself, that you might want to post about.
Tim Reese
Maine beekeeper's truck: '77 J10 LWB, 258/T15/D20/3.54 bone stock, low options (delete radio), PS/PDB, hubcaps.
Browless and proud: '82 J20 360/T18/NP208/3.73, Destination A/Ts, 7600 GVWR
Copper Polly: '75 CJ-6, 304/T15, PS, BFG KM2s, soft top
GTI without the badges: '95 VW Golf Sport 2000cc 2D
Dual Everything: '15 Chryco Jeep Cherokee KL Trailhawk, ECO Green
Blockchain the vote.
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Re: Stick with T15 or find T18?

Post by fulsizjeep »

Tim raises good points. When you say 33s, I usually think 33x12.5. Those are a tight fit in the rear fender wells unless you go more than 6" lift or start trimming sheet metal. 33x10.5 do fit pretty well with a 4" lift. My thoughts on the tranny. Drive it and see if you like it. I really like the granny first in the T18. It helps stay in Hi range until you are really stuck. Otherwise, yeah, it is a 3 speed (2-4) and you won't use 1st much.
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Tanker
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Re: Stick with T15 or find T18?

Post by Tanker »

Wifes J20 with factory 4:11 T-18A,She uses 1st gear not 2nd but 1st due to fact that a the beast has a utility bed,b-mountains c-traffic lights on inclines.Not counting snow driving. So trans goes with what your doing and terrain. Rear end gearing helps out alot if it had a 3?? I would have to re gear it do to weight and mountains. What I'm saying it all works hand to hand. If you run 33s with a 272 rear gear you have a dog. Change that to 4:11 and you have a trail/road Jeep. If she had a regular J20 then the first gear would not be used. My point is build it for your use,trail rig or street or both,how offend. The motor on hers is a built 360 torque monster flow bench heads intake,custom cam,headers,carb.
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will e
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Re: Stick with T15 or find T18?

Post by will e »

You're not getting ahead of yourself. It's good to have a plan. I looked at a lot of options before deciding on what I wanted for my Jeep. Sure, drive it for a while and get a feel for it.

When you are looking at options nothing makes as big a difference as the first gear ratio of the transmission. Small changes to the ratio mean much more than changes to the transfer case or the axle gears. Use grimmjeepers calculator and play around a bit.
81 Waggy 'WILL E' Retired
82 Cherokee WT - SOA/SF/high steer/Alcan springs/agr box/Borgeson steering shaft/AMC 401/performer/holley TA/HEI/BeCool/727/ALTAS (2.0/2.72/5.44)/D60 Snofighter(Yukon Zip,hubs,stubs,4.56)/14 Bolt (FF,BF shave, Discs, ARB,Artec Truss)/MTR 37X12.5/Corbeau XRS Baja & 5 point retractable harness/Hella Aux lights/tuffy console/killer32 sliders/Evil Twin bumpers, rack and roll cage/WARN 8000/TT Fabworks steering brace/dual batts/custom TC skid plate/ARB fridge
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volkswaben
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Re: Stick with T15 or find T18?

Post by volkswaben »

Thanks for all the tips y'all! I think I'm gonna stick with the stock drivetrain for now, and see how I like it. I've opened the cover of the trans and it looks very nice inside. I can always go in later and change it if I need to. I was thinking about the 33x10.5 BFG ko2's, but I am leaning towards getting 31"s as they seem a bit more practical for my usage. Once I get the engine fully back together I'll refresh/paint the bay, and update my build thread.
1974 Cherokee 360/T15
1979 Cherokee - parts rig/ future project?

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Re: Stick with T15 or find T18?

Post by Nikkormat »

Go with the 31's, you'll have more fun on those anyway. Crawl under the Jeep and figure out what axle gears you have. I've seen 74 Cherokee's with 3.54's and 4.10's. It wouldn't surprise me if you had the 4.10's.
Gabe, "reformed" Jeep hoarder.
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volkswaben
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Re: Stick with T15 or find T18?

Post by volkswaben »

Nikkormat wrote:Go with the 31's, you'll have more fun on those anyway. Crawl under the Jeep and figure out what axle gears you have. I've seen 74 Cherokee's with 3.54's and 4.10's. It wouldn't surprise me if you had the 4.10's.
Unfortunately looks like I have 3.07's, so a regear may be in my future anyway.
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1979 Cherokee - parts rig/ future project?

Nikkormat
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Re: Stick with T15 or find T18?

Post by Nikkormat »

volkswaben wrote:
Nikkormat wrote:Go with the 31's, you'll have more fun on those anyway. Crawl under the Jeep and figure out what axle gears you have. I've seen 74 Cherokee's with 3.54's and 4.10's. It wouldn't surprise me if you had the 4.10's.
Unfortunately looks like I have 3.07's, so a regear may be in my future anyway.
Are you sure? Haven't even seen that in the TSM.
Gabe, "reformed" Jeep hoarder.
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volkswaben
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Re: Stick with T15 or find T18?

Post by volkswaben »

Nikkormat wrote:
volkswaben wrote:
Nikkormat wrote:Go with the 31's, you'll have more fun on those anyway. Crawl under the Jeep and figure out what axle gears you have. I've seen 74 Cherokee's with 3.54's and 4.10's. It wouldn't surprise me if you had the 4.10's.
Unfortunately looks like I have 3.07's, so a regear may be in my future anyway.
Are you sure? Haven't even seen that in the TSM.
Yup, I just double checked now. I do in fact have 3.54's in my parts Cherokee, so that is an option as well.
1974 Cherokee 360/T15
1979 Cherokee - parts rig/ future project?

Nikkormat
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Re: Stick with T15 or find T18?

Post by Nikkormat »

volkswaben wrote:
Nikkormat wrote:
volkswaben wrote: Unfortunately looks like I have 3.07's, so a regear may be in my future anyway.
Are you sure? Haven't even seen that in the TSM.
Yup, I just double checked now. I do in fact have 3.54's in my parts Cherokee, so that is an option as well.
Bizarre! California special emmisions stuff maybe. In that case, a T18 may be a great future upgrade.
Gabe, "reformed" Jeep hoarder.
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