Truck 4-speed Transmissions As I Understand Them

Been working on this for a few days -

The forum gets a lot of questions about what transmission to use when upgrading from the original 3-speeds that came with these Jeeps. We will limit ourselves here (mostly) to the "early" Cj-5s and CJ-6s, which were built by Willys or Kaiser from 1955 through 1971. Also, this info generally applies to the M38A1 and M170 military models, which are essentially the military models that became the CJ-5 and CJ-6 respectively. We will touch briefly on the intermediate ('72-75) and late ('76-86) CJs after completing the discussion of the earlys and the transmissions.

The most common transmission upgrades for these Jeeps are the heavy-duty truck 4-speeds, including the Muncie SM420 and SM465, the New Process NP435, and the Borg-Warner (BW) T-98, T-18 and T-19. For a lot more background on these transmissions, read the pages dedicated to each type on the Novak conversions site Novak Conversions :: Manual

I will refer to the Novak site many times in this discussion. We like the Novak company here, but realize that their site aims to sell their products. Unlikely they will tell you of competing solutions to a need that they service. There will be other sources of info out there, including the Advanced Adapters product site. Unfortunately, their site won't work without allowing unfettered tracker placement, so I don't go there. Feel free to search in your favorite search engine (Google, Bing, whatever) for more info.

One of your best sources should be the archive of earlyCJ5.com. There is a search button at the top of the forum, but I strongly suggest you search with your favorite search engine (Google, Bing, whatever), restricting the scope of your search to the ECJ5 site. Use the "site" keyword as described online. There are plenty of web pages that describe advanced search with these search engines, and they will explain "site" among other useful modifiers.

If you have questions, search. If you don't find the answer, post. IMO you should limit PMs (personal messages, "conversations") to just that - messages about buying and selling, get-togethers, etc. Technical questions are both appropriate for the forum, and in keeping with its spirit. The archive is supposed to help everybody, and you deprive your fellow Jeepers of that info when you take the conversation off-line.

I am not the world's expert on these conversions. Several members of the ECJ5 community have more experience or knowledge or both of these conversions. I intend to provide an overview for those of you that are interested but overwhelmed by the breadth of the topic and the scattered nature of the information. I plan to write this article off the top of my head, and trust that you will go to the web and other sources and learn enough to complete your project.

Back to transmissions.

 

Why Convert to a 4-speed?

Reasons you might upgrade to a truck 4-speed:

1. The original 3-speed transmissions are not as strong as we would like, and most are not up to modern power levels. The truck 4-speeds are very strong. Most of the 4-cylinder CJs came with the BW T-90, a simple 3-speed that is syncromesh in 2nd and 3rd gears. The T-90 has been matched with a V8 in many Jeeps starting in the '50s when lightweight and compact V8s like the Chevrolet 265 and 283 and Ford 260 and 289 became available. With the small tires available at the time, reliability and durability of the T-90 was acceptable if not optimal in these lightweight Jeeps. Larger modern tires puts more stress on the drivetrain, and further stresses these original transmissions. Realize that these truck transmissions were designed to work in larger vehicles like dump trucks and buses, making them significantly overbuilt for use in a CJ-5.
2. Truck 4-speeds typically have a special first gear with high reduction, a "granny gear." Most of these transmissions have a reduction ratio in first gear of more than 6:1, which immediately doubles the gear reduction available in low range. To get similar reduction with the factory transmission requires exotic and expensive transfer case changes, or very deep axle gearing, or both, and even then only approaches the reduction provided by these transmissions.
3. These truck transmissions, while longer than the 3-speeds they would replace, are short enough that they will work with the required short rear driveshaft in the CJ-5. Other transmissions like 5-speed manuals and automatics are longer, and are tough to install without drastic relocation of the drivetrain. And the resulting short rear driveshafts constrain the amount of suspension lift and articulation that can be achieved.
4. The truck transmissions are widely available. Ford built (and still builds) something like one million light trucks annually, and Chevy/GMC produces similar numbers. These vehicles become parts when they are taken off the road, and potential donors for our Jeeps.

Reasons you might not upgrade:

1. It can be expensive. There are junkyard solutions available, but the most plentiful transmissions come from full-size 2WD light trucks. In addition to the transmission, you must buy a conversion kit and tear down the transmission and rebuild it with the conversion parts. Conversion parts for just the transmission are in the range of $600. Ballpark, say $1500 for the whole project if you do everything and fab/scrounge/shop for what else you need. There are turnkey transmissions available (see the Novak site), and these will increase the cost significantly.
2. If you want to make a junkyard solution to keep the cost down, the most likely starting point is a 4WD T-18 from a Jeep. Realize that Jeep production numbers have been way way lower than the million-plus annually light trucks that can donate a 2WD transmission. And only a minor fraction of the total Jeep production used a manual 4-speed truck transmission of the type you'll need. Most of these will require additional modification. There are very few Jeep 4-speed truck transmissions that can be taken from the junkyard and used without modification. All the possible Jeep donors will be covered below. It is possible to combine a Jeep or IHC T-18 transmission and say a Ford 2WD T-18, but you must source two complete transmissions, and the parts don't go together without some simple machining.

1. You must fabricate some parts. These transmissions are too large to go under the existing Jeep floors without changes. Driveshaft length must be adjusted to accommodate the longer transmission. A modified or new transmission cross member must be fabricated to support the new larger transmission. None of this is included in the kit and represents extra effort and expense.
2. These transmissions are big and heavy. I suggest investing in a hydraulic transmission jack. Don't let the dang thing fall on you!
3. Truck 4-speeds are a chore to shift. You never use 1st on the street, instead starting off in 2nd. Around town, you effectively have a 3-speed with long throws requiring muscle to shift. You also must be more careful about the action of shifting, shifting more slowly and deliberately. Clipping reverse on a 2-3 up-shift is very common with the earlier T-18s (though you can replace a spring in the shift top to make that better). The 3-speeds are quite a lot easier to drive around town, and won't wear you out in stop-and-go traffic.
4. The top gear of a truck 4-speed is the same as the top gear of a 3-speed. You do not increase top speed or get an overdrive by adding another gear. Unfortunately, there are comparatively few 5-speed overdrive options, and they are just too long for a CJ-5. If you want a better highway gear, suggest you combine a truck 4-speed with a Warn/Saturn overdrive if you are running a Dana 18 transfer case (more expense!)

(Some formatting goofiness that I can't fix in the middle of this - please just read over it).

 

Muncie SM420 and SM465

We will get the non-Jeep transmissions out of the way first.

Both of these transmissions are popular conversions for owners of the CJ with the 225 cid V6 engine. Their main appeal - they are GM transmissions that were used in Chevy and GM light and medium duty trucks. Check the Novak pages for a more thorough description. As GM transmissions, they bolt up to the formerly-Buick V6 without a lot of changes. There is no junkyard-way to adapt these transmissions to the Jeep transfer cases. You must buy the conversion parts (a "kit") from Novak Conversions or Advance Adapters.

The SM420 is pretty old, and parts support may be lacking. It does have the advantage of the most reduction (lowest) 1st gear of all these transmissions. The SM465 is newer, and has the reputation for being massive compared to the other 4-speeds.

Pretty sure than Novak only sells direct. This means that the price you see on the web site is the price you must pay. Advance Adapters will sell through retailers. I would expect that they will not discount a direct sale, preferring to protect the market of their retailers. I recall that Herm the Overdrive Guy is an Advance Adapters retailer, and should be able to sell their products at a discount to the list price on the Advance web site. In my experience, this kind of stuff will be cheapest from Summit Racing - worth investigating if you are in the market.

 

New Process NP435

The NP435 was used in Fords, Dodges and some Chevys. Novak sells a kit for the Ford and Dodge version. Notably this transmission was used in 4WD trucks, but I believe the true 4WD version (not the 2WD version with a divorced transfer case) has an adapter that's way too long for a CJ-5. So again, as with the Muncies, you must use a conversion "kit" to mate the NP435 to a Dana 18. Novak discusses the NP435 on its own page, which you can reach from the link above.

Many Ford NP435s have undrilled ears on the face of the transmission that allow it to be easily adapted to GM bellhousings, specifically to the Jeep 225 V6. Novak has a page - The Novak Guide to the Adapting Ford Style Transmissions to GM Engines The stickout (distance the input shaft protrudes from the transmission front face) turns out to be about the same for most GM and Ford manual transmission vehicles. You are not stuck with a GM transmission if you are using a GM engine, like the 225 V6. As described on the Novak page linked above, some minor machining may be required.

 

Borg-Warner T-98

The T-98 is essentially the predecessor to the BW T-18. IMO it's too obsolete to consider for conversion, and despite what Novak claims, parts support may be lacking. I expect the most common version is the 2WD type used in Ford trucks '48-64. I would avoid these for anything except their original Ford applications.

Jeep used the T-98 as the truck transmission for their early J-trucks and Wagoneers. I can't tell exactly when this ended, but I know the earlier vehicles like the Utility trucks and FCs also used the T-98 when equipped with a truck 4-speed. The OHC 230s definitely got the T-98, and it may have survived into the AMC 327 era ('65-67ish). These transmissions are adapted to the Dana 20, and possibly could be adapted to other engines. There's not much info about this topic.

Jeep also used the T-98 with a divorced transfer case in the M715 military trucks. Since these used an oddball engine (the OHC 230) and were not directly connected with a transfer case, they would seem of little interest to us. This is the only T-98 application that Novak covers with an engine adapter kit. Advanced Adapters may have more.

Of more interest is the T-98 sold as an optional transmission for the CJ-5 when equipped with the F134 4-cylinder engine. There is some discussion of this combo in old forum posts. However, these Jeeps are not plentiful, and have some additional value because of their unusual and desirable drivetrain. Even if the original Jeep were otherwise a total loss, the drivetrain has value to owners of L134 and F134 Jeeps that lack the desirable T-98 option.

 

Ford T-18 and T-19

These transmissions are very popular for conversion of a CJ-5. The main difference between them is the T-18 1st gear is not synchromesh, and the T-19 is. Both use an adapter "kit" requiring complete tear-down of the transmission and replacement of the main shaft. Like the NP435, they can be rather easily adapted to GM bell housings, as used with the Jeep 225 cid V6. The reverse shift pattern in these transmissions changes in about 1978 from all the way right then forward to all the way right and back. This requires a more complicated shift top internally, but eliminates the common "missed shift" for these transmissions, where the driver clips reverse gear when shifting into third. These earlier transmissions typically have a broken spring in the shift top that makes this problem worse.

Combining a Ford and Jeep T-18

According to reliable sources, you can do it. You use the main shaft and output adapter of the Jeep transmission and all the rest of the Ford transmission. This requires tapping and drilling and plugging so the adapter will mate to the Ford case. The resulting transmission will have a 6-spline output and "Texas" pattern that will match to the Jeep Dana 18 or Dana 20 transfer cases, and a Ford case that can be adapted to the GM bell housing. Supposedly the IHC T-18s that came with a Dana 18 or Dana 20 transfer case can also be used as donors, but the resulting clocking is less optimal? Something. Search the archive for more info.

 

Jeep T-18

Jeep used a different case design from Ford, most recognizable in the shorter top-to-bottom spacing of the driver's side case bolts, compared to the passenger side. The Jeep case does not bolt to the GM bellhousing without making a new hole for the bottom left (driver's side) bolt in the bellhousing. If you decide to adapt a Jeep T-18 case to a GM bell housing, search in the archive for discussion. Jeep has the same shift pattern change in 1978 that Ford does.

Jeep T-18s came in two flavors, "wide ratio" and "close ratio." The wide ratio (WR) transmission has the same ratios as the Ford T-18 with a deep 1st gear (6:32:1). All trucks and Wagoneers got the WR transmission, AFAIK. The close ratio (CR) transmission only appeared in the CJs and Jeepster Commando, and has a 4.02:1 1st gear, with 2nd and 3rd proportionally closer in ratio.

Oldest to newest -

Jeep I6 J-trucks and Wagoneers (FSJs), WR, '67ish-71: This is the early 232, with the starter on the driver's side. These trucks got the T-18 with a shorter input gear than the V8s. The stickout is probably about 7", about the same as the later inline 6s in the CJs and FSJs. You could use this transmission as a donor for the combined Ford and Jeep T-18, or possibly you could make a plate adapter to connect the GM bell to the Jeep case. The combo will be short enough for a CJ, but not as short as a combined Ford-Jeep T-18.

These trucks are not plentiful, but if you find one, make sure the transmission is a T-18 and not a T-98. The 232 was offered as early as 1965, and could overlap into the T-98 era. Look at the driver's side of the transmission case - it will have "T-18" or "13-01" cast-in to the case side. The earlier T-18s used the same shift top casting as the T-98, and it likely will say "T-98" in the casting - that's not enough to ID a T-98.

Jeep V8 J-trucks and Wagoneers (FSJs), WR, '67ish-79: I'm not sure if the AMC 327 Jeeps got the T-18, but the '68-70 Jeeps with the Buick 350 certainly did. These transmissions were backed by the Dana 20, and will bolt up to a big hole Dana 18 with the right output gear (Maybe the small hole case too? Don't know).

These Jeep V8 FSJs with manual transmissions use a rather wild setup to allow both inline 6s and V8s in the same chassis. Recall that the original Wagoneer and J-truck was designed for the OHC 230 inline 6. When Jeep decided to offer V8s in these vehicles, positioning the back of the V8 where the back of the 6 would be interferes with the firewall. They put the fronts of the engines at the same place, and stretched the back of the V8 to put the transmission in the same place. They did this by using a very long input shaft and ca 5" thick adapter. Thus this transmission, being very long, won't fit in a CJ-5.

The earliest of the transmissions with the Buick 350 and maybe the AMC 327 got a special bell housing that included the long adapter. From then to '79, a separate long adapter was used that mates with the Jeep T-18 case and the T-14/T-15 bell. Jeep used this T-14/T-15 bell for this application through 1979.

If you have one of these transmissions, it will bolt up to your transfer case. To adapt the front end, you can substitute the Ford input shaft and bearing retainer. This will make the stickout the right length for either a Ford or GM bell housing. You will still have to modify the bell housing to work with the oddball Jeep case pattern. Parts Mike sells a kit with the input shaft, retainer and bearing (see reply below for link). Alternatively, you can use this transmission as parts to make the combined Ford and Jeep T-18 using the Ford case, as described above.

Jeep V6 CJ-5 '71 and maybe Jeepster '71, CR: This is the factory offering of a 4-speed with the 225. I'm not sure what bell housing and adapter was used with this. Possibly the Buick bell and a plate? Since it's the factory offering with the V6, it would be kinda neat to have, even without the WR gears. With 4.88 axles and an overdrive ...

Jeep I6 CJ-5 '72-75 and Commando '72-73, CR: This is the "unified" 232/258, with the starter on the passenger's side, with a CR transmission. This uses a thin (5/8") plate adapter and T-14/T-15 bell housing. Apparently Parts Mike sells the 4.02:1 input gear and retainer from a Ford T-19 that will work with these close-ratio transmissions. I presume you could use this to make a short stickout CR T-18. Or, you could use this transmission as a donor for the combined Ford and Jeep T-18. Novak sells an adapter to mate this transmission to a GM bell. Adapting the Chevrolet & GM Standard Shift Bellhousings to the Jeep CJ & FSJ Borg-Warner T14, T15 & T18 Transmissions The combo will be short enough for a CJ, but not as short as a combined Ford-Jeep T-18.

Jeep I6 J-trucks and Wagoneers (FSJs), WR, '72-79: This is the 258, with the starter on the passenger's side. These trucks got the T-18 with a shorter input gear than the V8s. This is the same combo as used in the intermediate Jeeps, but WR. The stickout is about 7", exactly the same as the T-18 with a 232/258 in the CJs '72-75 and Commandos '72-73. You could use this transmission as a donor for the combined Ford and Jeep T-18. Novak sells a GM engine adapter that's marketed for the CJ-5, but would work with this transmission if you have the plate adapter. This is a desirable setup for someone with a T-18 in an intermediate Jeep, and if you have one likely you should sell it or trade it plus some cash to an intermediate Jeep owner that wants wide ratio gears. Then use the Intermediate close-ratio T-18 to make a combined Ford-Jeep T-18.

Jeep I6 CJ-5 and CJ-7, CR, '76: This is the 232/258, with the starter on the passenger's side. This is a 1-year offering, which got rid of the earlier 7" stickout combo, replacing the plate adapter and T-14/T-15 bell with a 1-piece bell housing. This is the last year for the CR transmission in a CJ Jeep. This transmission should already have a short stickout, since it uses the same bell housing as the WR transmission that followed it '77-79. These may be adaptable to GM bell housings as described for the Ford T-18. The CR transmission works well in these Jeeps, and owners liked them, but a '76 gets 3.54 axle ratios standard, which seems less wonderful with the CR transmission.

Jeep CJ-5 and CJ-7, WR, '77-79: In 1977, Jeep got with the program and offered a wide ratio T-18 in the CJ. These are cool Jeeps on their own, but supposedly they are desirable as swap material. Possible they have a Ford-type stickout; they came with a Dana 20. These may be adaptable to GM bell housings as described for the Ford T-18.

Jeep J20 Truck, WR, '80-88: These transmissions are the last offering of the T-18 in Jeep vehicles. They have a very long input shaft and a very long output shaft, making them unsuitable for use in a CJ-5. They could be adapted at both ends, but you may as well start out with a Ford T-18 and get an easier-to-adapt case and no need to replace the input shaft.

 

Intermediate and Late Models

 

Alternative Transmissions

 

Very interesting notations concerning the factory T18 applications ! Well done.

A couple of notations:

Jeep used two different transfer case adapter plates.
If your Jeep Adapter plate is embossed “T18” then it has a 4” index bore.
If your adapter plays is embossed “T98” then it could be either 3-5/32” index bore or 4”.
It should be obvious that 3-5/32” index bore was for use with the earlier small hole transfer cases.

Also I will briefly bring up the topic of T98 and T18 parts interchange.
Some parts do interchange between T98 and T18.

And Some parts do interchange between Jeep , Ford , IH and the very many other industrial applications.
But roughly half the parts are not directly interchangeable from one make to another.
A notable example is that you cannot simply install a short Ford maindrive gear in place of a Jeep main drive gear. Many other parts will need be swapped in too.

 

Why? Parts Mike sells a kit specifically for that purpose. 1T18-SBR T18 short shaft kit Jeep installation

It was my understanding that you could take these parts from a Ford transmission.

 

Not familiar with what he is selling in his kit.

Many Ford and Jeep parts are not a direct interchange between the WR T18’s.
The cases are much different.
Most notable to me is the location of the PTO port.
The countershaft gears bearings and countershaft are a direct interchange.
The shift towers are different in a few ways such as the reverse switch yet can always be interchanged as a whole.
Obviously the Jeep mainshaft must be used and it fits in place of the Ford output.
The reverse idler gears can be different .
Some have bearings and some have bushings yet can be interchanged as a set.
The large reverse gear itself is normally a direct interchange with Jeep.
The large rear (2nd speed) blocking ring and synchronizer assembly can directly interchange.
The 3rd/ 4th gear is different than Jeep due to a larger diameter cone clutches used on Fords.
Mating requires a blocking ring with a larger bore than what Jeep uses.
High or 4th gear directly implies that the Ford main drive has this larger cone clutch.
So no interchange without using proper blocking rings to fit the cone clutches.
That said the foreword synchronizer assembly less blocking rings can be directly interchanged.
So Yes they can be swapped in with correct blocking.
In theory one could even use Jeep 3rd gear with small cone and small blocking then use Ford large cone input and blocking up at front of the same synchronizer assembly.
Perhaps weird yet should be do able.

 

Excellent write up, Ron

 

No personal experience with this, and I don't want to go beyond the bounds of my understanding.

From what you write, it seems the only requirement is that the blocking ring match both the Ford main drive gear and the Jeep 3-4 synchronizer. You are noting that the combination would use one Jeep blocking ring and one Ford blocking ring. There is a blocking ring included with the Parts Mike kit.

I don't know how plentiful the V8 FSJ transmissions are today. A decade ago, they seemed easy to find. Apparently there are still enough of them that it's worthwhile for Parts Mike to continue selling this kit.

Interesting that there was a transfer case adapter that mates with the small bore Dana 18 case. Are you suggesting that you can exchange one for the other?

 

Yes I see a single blocking ring in his kit.
A Ford small synchro should fit right onto the Jeep 3 - 4 synchro assembly.
These days I see very few Jeep T 18’s available here in the Midwest anymore.
The original Jeep T98-A was mated to a small bore transfer case.
To the best of my knowledge the Jeep T18 began service on big hole cases only.
I think the last of the Jeep T98-A would be the standard engime (134) 1971 CJ having the 4 speed option.
No reason to keep the small bore transfer adapter plate after the 1972 changes occurred.
That said I am a little sad to imagine that the Jeep T98-A could initially have been designed to bolt direct to the “Texas” pattern as opposed to using an adapter plate.

 

Thanks for pulling this all together, Tim! This will be a great resource.

Mods this should be a sticky.

 

X2!

 

Very good read/information.

I feel lucky that I did my swap about 10 years ago and had acquired the right parts to do it on the cheap. I had found the WR J-truck T-18/Dana 20 and early Ford 2WD T-18. Then only having to purchase a new clutch and input bushing and get the input bearing retainer machined to mimic the T-14.

 

I have this exact factory transmission set-up to go in my 71' . Ill end up with 4.88s T-18 and maybe keep the overdrive. With the 33s I run I haven't really needed the over drive with my current Saginaw 4 speed(with noisy bearings)

This is the bell housing. Its the standard T-14 with the t-14 adapter built into the housing.

This is the adapter plate for the bell housing and the adapter for the transfer case.

And this is the adapter plate for the transfer case.

Not the greatest pictures. I will take a few more tonight and post them. Both Adapters are 1" think I believe and the stickout length on the input shaft is~10.25"( I'll verify this also)