View Full Version : T-18 close ratio question
02-15-2008, 02:42 PM
I retrofitted my street driven J10 with a granny T18/J20 combo from a late model J20. I like the strength of the T18 for towing, but have no need for the granny gear and would prefer a close ratio gearset. I also want to keep the 208 transfer case. Is it possible to swap most of the internals from an early close ratio gearbox into the later transmission (while retaining the 31 spline output (main) shaft for the 208 transfer case)? Would there be problems with the different reverse gear shift pattern/location, or is there a way around that? Thanks
02-15-2008, 03:46 PM
Is it possible to swap most of the internals from an early close ratio gearbox into the later transmission (while retaining the 31 spline output (main) shaft for the 208 transfer case)?
I presume you are thinking of the close ratio T-18 that was used in 6-cylinder CJs and Commandos from 1971-77.
The short answer is no - the gears aren't compatible.
The main problem is the input shaft. The CR T-18 uses the T-14/T-15 bellhousing, a plate adapter and its own input shaft. The input shaft has a different number of teeth from the WR input shafts, and can only mate with the CR cluster gear. The rest of the gears are also different from the WR, and mate with the CR cluster gear.
If your truck has a V8, it uses a very long input shaft that is only available in the WR tooth count. If you switched to the CR gears and used the much shorter CR input shaft, your shift lever would come out under the dash. This can be dealt with by bending the shifter stalk to come back more so it will clear the dash and can be reached, and you'd have to cut a new hole in the floor. Plus, the crossmember position would change and you'd need to change the lengths of the driveshafts.
A six cylinder truck would probably be ok if you use the CR bell and plate. Not exact, but close to the same length.
I think you can use your T-18 main shaft and adapter and convert the CR T-18 to the NP208's pattern. This would require disassembly of the transmission and reassembly with the new main shaft though. You may have to drill some new holes in the case and tap and plug some others - not sure. The CR transmissions only came with the Texas TC pattern, which only fits the older geared Jeep transfer cases like the Dana 18 and Dana 20.
Not sure about the shift top. My guess is that you'd have to use the shift top from the CR T-18.
02-15-2008, 04:29 PM
The truck has a 360 and I don't want to start moving location of major components again. I guess I'm confused, as in a related thread from a couple weeks ago I asked whether close ratio T18 ever came with the long input shaft and "Rustywagoneers" commented that he has one in a '74 V8 Cherokee. That's what got me to wondering about swapping the internals around. Seems the more fundamental question is did the C/R come with a long shaft. If that's a yes then from your description it might be possible to swap gear sets between boxes to reach the objective? If I understood you correctly, it sounds like the input shaft/gear and the countershaft/cluster gears are the key and they could be interchanged? Anyway, thanks for the very informative response.
02-15-2008, 05:01 PM
Email Herm, he'll know whether you can swap.
I asked him about adding an overdrive gear to the T18 and he said it could be done but expensive.
02-15-2008, 05:16 PM
....sent Herm a note. Thanks.
02-15-2008, 06:12 PM
There may have been a close ratio long input shaft T-18, but I've never seen one. If you can find one, then the swap will work. You'd have to change all the gears including the input shaft. Good luck finding one ...
AFAIK the 6-cylinder CJ transmission is the only application for the close ratio T-18.
02-16-2008, 05:16 AM
if you consider the 4.x to 1 first gear to be the close ratio transmission then yes they built them. I found one in a 1978 widetrack cherokee. I have it sitting in storage right now, I can't advise what pattern it uses for the transfer case. It came with the dana 20.
I pulled the transmission and transfer case seperate since the junkyard i found them in wouldn't allow jacks. while they were apart I put it into first gear and spun the input and counted the rotations to spin the output once. I have not disassembled and counted teeth.
close ratio for a passenger car 4 speed would mean a 2.21 first gear. its hard to consider 4.x to be close ratio.
02-16-2008, 08:25 AM
It's the 3-4 spacing that I'm wanting to improve. Thanks for the info.
02-16-2008, 09:22 AM
What about a T19 from an IH? Those are close ratio aren't they? Maybe you could get lucky and find one IH had mated to an AMC V8? You would still have to make it fit your 208 though.
02-16-2008, 09:27 AM
close ratio for a passenger car 4 speed would mean a 2.21 first gear. its hard to consider 4.x to be close ratio.
Compared to 6.32:1, 4.x:1 is WAY close ratio. LOL
Not nearly as close as your average car, but they never put a T-18 in a car either.
02-16-2008, 09:40 AM
I didn't know that IH used the AMC V8 with the T19. Yes, swapping the all synchro gearset into my case while retaining the output shaft for the 208 would be as good as it could get. I do wonder if the input shaft length/bellhousing spacer setup for the D20 transfer case arrangement would be the same as for the 208 case setup. I've seen at least two different "long shaft" lengths. Won't know until I start looking I guess. Thanks for the info. Any recommendations as to where to find a T19...is there a Scout website?
02-16-2008, 10:28 AM
The adapter for the D20 is about 1" for all the setups I've ever seen. The adapter for the NP208 is considerably longer. You will definitely have to use your output and adapter.
02-16-2008, 11:28 AM
I was thinking about the front end of the transmission...the present setup uses the T150/T176 style bellhousing, which I believe is shorter than the one used with early T18/D20 arrangement. I thought there was a spacer between the bell and transmission on my truck, but I just went out and checked, and it's a direct bolt up. So the input shafts must be different lengths. That would screw up the whole installation...new drive shafts, etc.
By the way, I just did some poking around on Novak's site. Looks like the IH T19 used an oddball input shaft/front bearing retainer, which Novak says makes the IH difficult to work with in terms of swapping parts.
Think I'd have to go with a D20 and front axle swap to get there. If I have to get back into that level of mods, I'd rather just install a drop axle in the front, lower the truck a couple more inches, and go with a 2WD arrangement...shed a bunch of weight in the process. Anyway, thanks everyone for the help, I have a much better sense of what's (not?) possible given my set of limitations.
02-16-2008, 11:36 AM
Yes, the T-19 came with three different sets of ratios, adding another that split the difference between the T-18's 4.02:1 and 6.32:1... something like a 5:1 1st gear.
IIRC IH used the 258 and a few 401s ... if the T-19 you found bolts up to a 258, it will bolt up to your 360.
AFAIK only Jeep used the long input shaft though, and any T-19 you find will have a short input shaft. You'll be back to the problem of the shifter being under the dash. Also think you can use the T-18 main shaft and adapter with a T-19 with some minor case mods ... pretty sure the T-18 and T-19 main shafts are the same.
02-16-2008, 11:50 AM
I was thinking about the front end of the transmission...the present setup uses the T150/T176 style bellhousing, ...
You sure? All the FSJ T-18s that I've seen have either had a special looooong bellhousing or else used the T-14/T-15 bell with a 5" long adapter. There are pictures of the late-70s setup here: http://www.jeeptech.com/trans/t18.html
The spacer shown here goes with the T-15 bell.
I have not seen a late J-20 T-18, but I'd think the easy way for Jeep to do this would be to continue to use the T-15 bell and spacer. If they used the Ford T-18 case pattern (the butterfly pattern) rather than the Jeep T-18 case pattern, they would have needed to come up with either a new bellhousing or a new spacer to go between the bell and transmission. Or else they would have needed to change the shifter to come out of the transmission about 5" further back.
02-16-2008, 12:26 PM
Duh...you're absolutely right....geez, I even took it off and painted it before installing it in the truck...what a dork. It uses the big spacer...like in the photo. Well, that makes things more positive. Thanks.
02-16-2008, 06:08 PM
02-17-2008, 07:39 AM
Hey Eric, I know you really don't want to swap around your drivetrain any... but the NV4500 5sp with a short throw shifter would sure be sweet in that truck. Only certain year range trannys can adapt to the short throw kit though. :hide:
02-17-2008, 01:36 PM
As you know I was looking around for a 4500 a while back. Then I decided it's not very cost effective for the limited amount that I use the truck. Plus I'm thinking about a VW or Mercedes V6 diesel swap, or maybe a V10 VW in conjunction with some serious street rod mods somewhere down the road...would probably use that entire drivetrain if I ever get around to it.
Then about a month ago my spouse's VW turbo broke a timing belt down near Waco (trashed 12 of 20 valves by the way) and I had to retrieve it on the trailer. While the truck/trailer rolls along just fine (65-70 mph) in 4th once it's up to speed, it's not so hot in that 40-55 mph range...either have to lug the engine in 4rd gear or rev the snot out of it in 3rd. I felt a little nervous with that howling hoard of 80 mph semis stalking my little rig out on death ally (I-35). Anyway, on the flip side, the 2nd gear ratio in the granny tranny is just about perfect for launching the truck without the trailer (using the transmission as a 3 speed around town). As pointed out by a couple guys in this thread, the close ratio still has a very low (4:1) 1st gear for stop light lauches in "truck only" operation, and I suspect 2nd might be too high for truck only starts...so it would be a lousy truck-only setup for a minor improvement in towing capability. So, after looking at this closer (thanks to the commenters), I have concluded that either T-18 gearset is a compromise (for my two applications of short errands and towing). Maybe I should take another look at the 4500 ratios!
By the way, I sold my V8 Bitter a few weeks ago...two to go, then on to the Jaguar...then some serious street rod mods to the J10..maybe those new common rail diesels will start showing up in wrecks by then. Hope you're well...did you ever find an NV4500? Regards, Eric
02-17-2008, 04:15 PM
Mmmm, Jaguar. :cool: Yes, I found a rebuilt NV4500 for $600... but as typical I didn't have the $$$ when I stumbled onto it (he had two actually).
02-18-2008, 04:18 AM
I may be wrong, but I'm pretty sure that the only difference in gear ratios between the wide ratio and close ratio T18, is the first gear. The rest of the ratios should be the same. The T15 in my CJ5 has the same ratios as the T18, just missing the low first gear (first gear in a t15 is the same ratio as second gear in a t18)
You are supposed to use second gear to start off in in a t18.
The difference between the t18 and t19, is the ratio of first gear, and the t19 has a syncroed first.
02-18-2008, 07:13 AM
I may be wrong, but I'm pretty sure that the only difference in gear ratios between the wide ratio and close ratio T18, is the first gear. The rest of the ratios should be the same.
No, all the ratios are different.
wide ratio T-18: 6.32, 3.09, 1.69, 1, R7.44
close ratio T-18: 4.02, 2.41, 1.41, 1, R4.73
Same deal with the T-19, though the exact ratios are slightly different. This is done by changing the number of teeth on the input gear and matching cluster gear. All of the other gear ratios are changed proportionally, though some or all of the main shaft gears change too.
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