Lower first gear for AX-15 / HD input shaft

BugoutJeep

BugoutJeep

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Does anyone have experience with swapping to a 4.3 first gear for the AX-15?
Does anyone know if the HD Input shaft (14 Splines) is an upgrade from, what I assume is a 10 spline shaft OEM (I don't know, just saw this on a blow up of the AX-15)?

I have to pull my transmission and I'll probably just replace the broken adapter, but I really want to go slower in 4lo 1st gear and I can't afford an Atlas or NP241 at the moment (well I can kinda, but if I'm going to spend money, I lean toward doing something with my old transmission, like maybe getting a new one, though I have no signs of problems). In any case I'm still trying to figure out if it's time to do some upgrades to my transmission, get another one, etc and I'm really not sure what all is available for the AX-15.

Since I've got a bit more torque than OEM, if there's a way to beef up the trans, then I'd be interested, just for insurance, but like I said I'd really like to slow my Jeep down and it looks like 5.15 is possible, but then I've got to rev to over 3k RPMs before shifting to 2nd or else lug the engine. 4.3 is pretty close to what I've got and then when I change my rear end, I'll be a bit slower still. Even if those ratios are possible, I have no idea where to source them. I thought I saw they were stock with some Toyota transmissions so I could order them based on that transmission I assume. I haven't had much sleep, so I apologize on the lack of clarity and redundancy at times.
 
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I know this is an old thread but I'm curious if you got anywhere with it. I've come across references to this possibility but I have yet to find someone that actually has a running example. The R151F is the Yota transmission that had the countershaft and 1st gear that is supposedly needed, and they're not easy to find, but they're out there new if you're feeling spendy, and maybe you could get a salvage R151F and take the parts you need out of it. I don't know what all it came in, but I know at least the pickups with the 22R turbo had them.

I recently swapped my NSG370 with the 4.46 first, for an AX15, and that's the one thing the NSG had going for it.
 
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freedom_in_4low said:
I know this is an old thread but I'm curious if you got anywhere with it. I've come across references to this possibility but I have yet to find someone that actually has a running example. The R151F is the Yota transmission that had the countershaft and 1st gear that is supposedly needed, and they're not easy to find, but they're out there new if you're feeling spendy, and maybe you could get a salvage R151F and take the parts you need out of it. I don't know what all it came in, but I know at least the pickups with the 22R turbo had them.

I recently swapped my NSG370 with the 4.46 first, for an AX15, and that's the one thing the NSG had going for it.
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No I never got anywhere with this. Basically I've decided to go away from the AX-15 at some point, partly because I want a modest tune on my engine and the AX-15 probably will have trouble with 400 ft lbs and considering I don't care for the first few gear ratios, it's not a hard decision. I'm not in any hurry though, but I plan to more than likely go with a TR-4050, though possibly some 6 speed Auto. For a manual the TR-4050 just looks amazing for what I want from an off-road and towing perspective and really even just on road. I like having the granny gear option, but also a second gear I can take off in when I want to move a bit quicker in traffic.

The only big problem to me for going that route is that it really makes me want a longer wheelbase.
 
Yasha said:
Sorry to revive an old thread, but I am attempting to undertake this project with guidance from https://www.pirate4x4.com/threads/4-3-1st-gear-to-ax-15.746537 while I'm replacing my synchros... will update if it works.
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I'm about to pull my AX-15 and install a new one so I'm going to have a spare AX-15 soon to play with so I'm going to follow closely.

Which transmission are you pulling parts from? Where did you get the transmission parts?
 
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It was hard to find the correct parts... well, it might be easier than I found, here's the thing. AX-15 cluster shaft has 43-32-21-13-12 tooth count and 1st gear has 31 teeth. The correct R151F cluster shaft for 4.31 1st gear has 43-32-21-13-11 tooth count and 1st gear has 32 teeth. The part numbers in that thread I linked to should be the correct R151F cluster shaft with 43-32-21-13-11 tooth count but there seems to be a lot of conflicting information on some other forums and some parts websites which describe the same part numbers as 43-32-21-13-12... very confusing and frustrating. Anyway I got my 43-32-21-13-11 shaft from megazip.net, Toyota part 33421-60161 and the 1st gear is Toyota part 33032-60081.

There are possibly cheaper places to get these parts, but when the descriptions said 43-32-21-13-12 or 43-32-23-13-12, I skipped out even if those were incorrect descriptions as I did not want to risk getting the wrong part. I want to get my Jeep back in service in the next month or two. My megazip order is still in processing, I will update here when I receive the parts and as I fit them in my transmission, and confirm tooth count compared to the stock AX-15 shaft.

Most reliable way to ensure you get the correct parts would be to find an R151F transmission and confirm it has the correct gear ratio then pull parts. To my knowledge all R151F transmissions came with 4.31 1st gear, except so many websites seem to imply it got a 3.83 in later years.
 
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Well I can't wait until your parts show up.

I'm in a very transmission mindset today too. I'm supposed to get my new AX-15 delivered today at work and I've been waiting for 6 months and it took me much longer to even make a decision on what to purchase. I always wanted something over 5:1 for my first gear, but will certainly admit that for my current engine that the 4.3 might be a really nice compromise. Of course I've just spent the last couple of years splitting mostly theoretical hairs.
 
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Yasha said:
It was hard to find the correct parts... well, it might be easier than I found, here's the thing. AX-15 cluster shaft has 43-32-21-13-12 tooth count and 1st gear has 31 teeth. The correct R151F cluster shaft for 4.31 1st gear has 43-32-21-13-11 tooth count and 1st gear has 32 teeth. The part numbers in that thread I linked to should be the correct R151F cluster shaft with 43-32-21-13-11 tooth count but there seems to be a lot of conflicting information on some other forums and some parts websites which describe the same part numbers as 43-32-21-13-12... very confusing and frustrating. Anyway I got my 43-32-21-13-11 shaft from megazip.net, Toyota part 33421-60161 and the 1st gear is Toyota part 33032-60081.

There are possibly cheaper places to get these parts, but when the descriptions said 43-32-21-13-12 or 43-32-23-13-12, I skipped out even if those were incorrect descriptions as I did not want to risk getting the wrong part. I want to get my Jeep back in service in the next month or two. My megazip order is still in processing, I will update here when I receive the parts and as I fit them in my transmission, and confirm tooth count compared to the stock AX-15 shaft.

Most reliable way to ensure you get the correct parts would be to find an R151F transmission and confirm it has the correct gear ratio then pull parts. To my knowledge all R151F transmissions came with 4.31 1st gear, except so many websites seem to imply it got a 3.83 in later years.
Click to expand...

Ive never had an issue with trying out parts to see what works but I've never been able to get past the hump of having to completely take my transmission apart without knowing for sure the parts would even fit. Thanks for being the trailblazer! If you come back with a successful report that just might be enough for me to go ahead and order the parts and just let them wait until I have an opportunity to drop the transmission out.
 
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BugoutJeep said:
Well I can't wait until your parts show up.

I'm in a very transmission mindset today too. I'm supposed to get my new AX-15 delivered today at work and I've been waiting for 6 months and it took me much longer to even make a decision on what to purchase. I always wanted something over 5:1 for my first gear, but will certainly admit that for my current engine that the 4.3 might be a really nice compromise. Of course I've just spent the last couple of years splitting mostly theoretical hairs.
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Where did you order your ax-15? I just ordered one last Friday from Novak and didn't check if it was in stock. Did you wait 6 months on shipping?
 
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DougyintheBushies said:
Where did you order your ax-15? I just ordered one last Friday from Novak and didn't check if it was in stock. Did you wait 6 months on shipping?
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I ordered this one from Advanced Adapters and the original shipping was 2 or 3 months, but it kept being delayed though I think Advanced noted that delays were likely. The delay hasn't been a problem for me, especially since it took me a year or so just to decide which transmission I wanted to purchase/install.
 
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BugoutJeep said:
I ordered this one from Advanced Adapters and the original shipping was 2 or 3 months, but it kept being delayed though I think Advanced noted that delays were likely. The delay hasn't been a problem for me, especially since it took me a year or so just to decide which transmission I wanted to purchase/install.
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I just called Novak, the ax-15 is in stock and should ship today.(y)
I'm interested in this mod also.
 
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Are you doing a core return or anything or are you about to have a spare transmission as well?

I'm probably not going to buy all the parts immediately, but I'm going to try and keep an eye out for everything. Honestly the AX-15 probably isn't the best for my application, so I am wanting to keep a spare transmission around in case I find out that the AX-15 is only going to hold up very long, especially since I haven't even had this engine tuned yet for the worldwide 360 ft lbs tune.

I knew when I did my swap that my transmission was old and weak, so I babied it, but it just finally succumbed to age. I don't plan on babying this transmission, though I'm not an aggressive driver, so we'll just see.
 
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BugoutJeep said:
Are you doing a core return or anything or are you about to have a spare transmission as well?

I'm probably not going to buy all the parts immediately, but I'm going to try and keep an eye out for everything. Honestly the AX-15 probably isn't the best for my application, so I am wanting to keep a spare transmission around in case I find out that the AX-15 is only going to hold up very long, especially since I haven't even had this engine tuned yet for the worldwide 360 ft lbs tune.

I knew when I did my swap that my transmission was old and weak, so I babied it, but it just finally succumbed to age. I don't plan on babying this transmission, though I'm not an aggressive driver, so we'll just see.
Click to expand...

I didn't have a core to return or at least an ax-15 core. I have the turd called NSG370.
I thought the ax-15 was a common tranny that was used behind v8 power.
 
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DougyintheBushies said:
I didn't have a core to return or at least an ax-15 core. I have the turd called NSG370.
I thought the ax-15 was a common tranny that was used behind v8 power.
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Most V8s still don't have lots of torque, especially in the RPMs one normally drives a Jeep. I think a lot of LS engines are just a bit over 300 ft lbs @ over 2000 rpms, but once I do the basic tune I'll be at 360 ft/lbs at 1,500 RPMs.

I think the AX-15 isn't rated for beyond 300 ft lbs and though I'm detuned at 306 ft lbs, that's kind of on the threshold. For a V8, most of your driving wouldn't be high RPM so you're not seeing much torque, but with the low RPM torque, it's there anytime I get my foot close to the floor.

In any case I hope that it'll hold up for a reasonable amount of time, but I've seen diesels break these and the similar Toyota transmissions quickly once they are swapped into high mileage donors. Considering almost every other option I was considering was $6k or more, I was willing to give this transmission a shot again, especially since I didn't just break the transmission I think it just finally wore out and the front bearing was getting really loud and I was getting oil coming out of the input shaft area of the transmission.
 
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In any case mine just arrived and honestly the main reason I was hesitant to go with the AX-15 again was the gearing, not strength or anything. I'd be willing to baby the transmission if my gearing was more to my liking. So the 4.3 would be a nice option as would the 5.15 first gear if I could figure out how to get those parts, though I kinda think the 4.3, might be a much nicer compromise.
 
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freedom_in_4low said:
Ive never had an issue with trying out parts to see what works but I've never been able to get past the hump of having to completely take my transmission apart without knowing for sure the parts would even fit. Thanks for being the trailblazer! If you come back with a successful report that just might be enough for me to go ahead and order the parts and just let them wait until I have an opportunity to drop the transmission out.
Click to expand...

Megazip just got back to me last night and said the counter shaft is actually out of stock :eek::cry: I am searching for anywhere else I may be able to find a suitable part. I've got a good $500 I've already mentally committed to investing into this experiment, so if anyone sees a proper Toyota part 33421-60161 R151 countershaft/layshaft with tooth pattern 43-32-21-13-11 please respond here and let me know. I would love to do this experiment while my AX-15 transmission is in pieces on the bench and I'm still waiting for my synchro kit to arrive anyway, so...
BugoutJeep said:
Well I can't wait until your parts show up.

I'm in a very transmission mindset today too. I'm supposed to get my new AX-15 delivered today at work and I've been waiting for 6 months and it took me much longer to even make a decision on what to purchase. I always wanted something over 5:1 for my first gear, but will certainly admit that for my current engine that the 4.3 might be a really nice compromise. Of course I've just spent the last couple of years splitting mostly theoretical hairs.
Click to expand...

I think you can go with some internals from an R154 to get a ~5:1 1st gear, although at that point your shift down to 2nd would be rough. Plus, as I am seeing with R151F parts... good luck getting the parts.
 
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Yasha said:
My final chance to do a 4.31 first gear swap is to buy a complete R151F transmission for $1000 just to remove the cluster shaft and 1st gear. I'm still thinking about it, although I'm not sure it's worth that kind of investment.
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just do it.gif
 
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Yasha said:
My final chance to do a 4.31 first gear swap is to buy a complete R151F transmission for $1000 just to remove the cluster shaft and 1st gear. I'm still thinking about it, although I'm not sure it's worth that kind of investment.
Click to expand...

If it 100% guarantees that you'll never need to buy a $3k transfer case to get a lower ratio, then it's still the cheaper option.

For me, I'm not sure it would be enough to not still feel like I want a 4:1.
 
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