October 18, 2024
Sometimes, in an effort to make a Tacoma work really well off-road, modifications to the drivetrain result in the on-road performance being a little less than ideal. That's what happened to me - inadvertently - when I installed 4.88 gears in my front and rear diffs.
I've loved those gears - they are one of my best mods on the trail and at slower speeds - but the side effect has been that my RPMs are significantly higher than stock when I'm cruising on the freeway. In fact, I've ended up finding that 62 mph - at about 2700 rpm - is about where the 5VZFE of the Tacoma likes to cruise, and that is... slow. It takes a long time to get just about anywhere.
Moving at 70 mph, the engine revs at a little more than 2750 rpm.
(Except this isn't really 70 mph on my truck, here's why.)
I am not the first one to run into this problem, and in 2015, a thread by ToyotaLux over on Pirate4x4 was the first to gather most of the necessary information into one place, outlining the steps to swap the existing 5th gear in the R150F transmission of a 1st gen Tacoma for the 5th gear out of a Toyota Dyna R452 transmission.
The point of the Dyna 5th gear is to get a 30% overdrive as opposed to the standard [16% provided by the stock 5th gear], but more on that later.
There is plenty of info on this scattered over the web but I couldn't find a single source that had all the info for someone that was coming from a basic understanding of gearboxes and wanted to try this themselves.
ToyotaLux
The problem was that - even with most of the information in one place - there were still gaps. The full list of necessary parts was difficult to piece together, many of the photos were hidden behind watermarks of the platforms on which they were hosted.
And of course, there was the fear factor. To do this modification, I'd be semi-blindly buying a bunch of parts and cracking open a part of the Tacoma I'd never worked on previously. It was a situation that would end gloriously or as a complete disaster.
It was also a situation that had a deadline - I was scheduled to drive the Tacoma south for the winter at the end of October. So, when I discovered that Dan @drr - who'd tried to make the swap but ended up running into trouble - had most of the parts in his possession, I jumped on the opportunity to pick them up. My hope was that - by supplementing his collection with a few more parts, and enlisting the help of Zane @Speedytech7 when doing the work - I'd come out the other side with a different result.
Still, I estimated only a 50% chance of success. Dan is a smart dude after all, regardless of sharing a first name with yours truly.
If you're here looking to do this modification yourself, I've written a Step-by-Step Taller 5th Gear Swap (Dyna R452 into Tacoma R150F) guide that links to all the parts and tools necessary, then provides photos of the entire process.
What follows here is the story of the work Zane and I did, one Friday afternoon in his shop.
I headed over to Zane's on a Friday morning. My plan was to show up just before lunch, grab a burrito at Tacos El Guero in Spokane Valley - one of the best taco trucks I've ever tasted - and then get most of the disassembly of the Tacoma taken care of before Zane even got home from work.
Naturally then, I rolled up around 2:30pm having not eaten lunch at all, only a few minutes before Zane also pulled into the driveway. It was a solid start!
Hungrily watching Zane polish off a burrito he'd picked up on his way home - while also unbolting bits of the driveline at lightning speed - I set about some of the interior work. Ultimately, in the time it took me to remove bits of the center console and the shift levers, I think Zane got both drive shafts pulled and the transfer case ready to come out!
Things were moving so quickly that the only photo I got before the truck was completely immobile was just after we got it up on ramps!
As we supported the transfer case on the transmission jack, I warned Zane that we'd see a good amount of oil on the floor when we separated the two components. This was something I'd learned the last time I'd removed the transfer case, since the seal between the two had failed, filling the usually-dry-cavity between the two gear sets with nearly a quart of oil!
I could tell by Zane's reaction, that we had drastically different concepts of "a good amount of oil." As we wrestled the transfer case off the transmission, a few drops, then a steady stream, and then a torrent of oil flooded onto the floor. Unable to position the oil catch can under the transfer case due to the transmission jack supporting it, Zane scrambled for some shop rags as I wondered whether I'd ever be welcome back.
Eventually - and with a liberal dousing in not-saleable-in-California full-strength brake cleaner - we got the mess cleaned up and the transmission jack positioned under the transmission itself. We wouldn't be removing the transmission for this job, but we would be removing the crossmember that supported it, and we certainly didn't want the whole thing to come crashing down on us as we pondered our next steps.
Hold my transmission, would you?
To this point, I'd felt comfortable that everything we'd done was easily reversable, since I'd done it all myself a few times in the past. Now, however, it was time to remove the transfer adapter from the transmission. This - which would expose the gears we'd be swapping out - entailed splitting components that were bound by form-in-place-gasket (FIPG - aka RTV - aka glue), and that - to me - was scary.
Ready to break the transfer adapter (left) away from the cast bearing plate (center), which at this point was only attached to the transmission (right) with red FIPG.
To Zane - who is much more experienced with FIPG - I think we were still in the easily reversable territory of the job. Still, he warned that we really didn't want to break the FIPG seal on the transmission side of the bearing plate, because that would force us to pull the entire transmission and make the job "a lot bigger."
My relief three minutes later - when the job didn't become "a lot bigger" - was palpable. And with that, it was time to recalculate our chances of success.
Where the rubber meets the road.
With the transmission - or at least the part of it we needed access to - opened up, we got our first look at the output and countershafts. This was a key moment, since it is by looking at how the gears and bearings are secured to these shafts that one can determine whether they have an R150F transmission that can be successfully modified.
I won't go into all the details - see the step-by-step guide for that - but if both shafts have circlips on the end, the chances of success increase dramatically.
Yay for us!
With our spirits high, we set about pulling off the various bits. Actually, it was mostly Zane who was doing all the work at this point - I was still too nervous - as I snapped photos along the way, in hopes that I could put together a more detailed guide for future mpg-obsessed maniacs to follow.
All the original bits removed!
With all the old bits out, it was time for dinner. Whenever I visit Zane, I like to treat him to whatever he wants to eat while I'm there, and this time I'd informed him that I expected something a little costlier than Dominoes and Subway for his time and expertise. Being Zane, he mostly ignored my expectations, on this particular evening we did head over to The Flying Goat - a slightly fancier pizza joint - where we enjoyed a fantastic "Lacrosse" pie.
Olive oil, fresh mozzarella, Italian sausage, red pepper preserves, fresh basil & shaved pecorino.
I was a bit after 9:00pm by the time we wrapped dinner, and I figured that after a week of work and a long evening of working on someone else's truck, Zane would probably be ready to call it an evening.
Nope. He wanted to get the new gears installed and the transfer adapter sealed back onto the transmission so that the new FIPG would have a chance to set up overnight before we pumped a few quarts of gear oil into the transmission.
So, that's what we set about doing, first bench assembling the new components and then baking them for installation.
Beginning assembly with the sleeve (top left) and then working the shift keys into position (top right), before adding the synchro ring and spline gear (bottom left), and finally the shift fork (bottom right).
All of this process was enjoyable, but the best part was when we worked out exactly how the three shift keys were installed - and secured - in the countergear assembly. This was the bit that Dan - or rather, the transmission shop he'd hired - ran into trouble, so when we figured it out, we finally eliminated our final failure point on the job, and it was smooth sailing from there.
Who says men don't cook?
With the bits that needed pressing on warming up in a 200°F oven - to expand them slightly and make the pressing process easier - we slid under the truck to start final assembly.
Everything fit!
Nearly there - and nearly midnight - the final step in the process was spreading a thin bead of Toyota Black FIPG on the transfer adapter and snugging it up to the transmission so it could set up overnight, allowing us to test drive the Tacoma the following morning before diving into the second project I'd hoped we could accomplish before I bombed back home at the end of the day.
A thin - but continuous - bead is all you need.
Ten bolts torqued to 27 ft-lbs, and almost ready for oil.
We retired to bed having accomplished significantly more than I'd thought we could in a single, 12-hour "afternoon." Surely, I thought naively, I'd be headed home much earlier the next morning than I'd planned.
In fact, after a sound night sleep, it took only 90 minutes to button up everything else we'd disassembled the night before, and a quick blast around the block revealed our work to have been a smashing success. The new 5th gear worked flawlessly, and - as a bonus - there didn't seem to be any leaks!
Same speed as before, with much lower RPMs. 500 lower to be exact.
Everything worked swimmingly on the 250-mile trip back home, though I found it difficult to maintain the 62 mph speed I'm used to traveling, since - apparently - I drive by engine sound rather than by reading any of the gauges on my cluster. Only after finding myself speeding along - at whatever speed 2750 rpm happened to be with the new gears - a handful of times did I finally resort to cruise control in order to maintain a more constant momentum.
I can't say yet whether these new gears will result in an MPG increase, but with an upcoming trip to the Mojave Desert I'll have a 1,000-mile trek to get a sense for any change. For once, I'll enjoy the 20-hour drive south, though I'm still looking forward to leaving the Tacoma in Las Vegas and throwing the dice on Spirit Airlines for the remainder of the winter!
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A big thanks to everyone who participated in this investigation/conversation/swap prior to me, and to Dan @drr and Alex @Bandido with help sourcing parts, and to Zane @Speedytech7 for help with the swap itself!
In this Series
Hopefully it is working out well. Seems like a good compromise to have trail and highway friendly gears.
DIY write ups are hard to do well. And again you have nailed it. I found it interesting and learned a few things even though I don't have a Tacoma. Also didn't know I needed a toaster oven in the shop until now. 🤔
Hahaha, I know what you mean! The dry one (where you don't learn anything, but that you're greatful for should you want to do the project yourself) is definitely not something I'd want to post up in the "normal" blog feed. 😉 It does have some interesting data about the gear ratios, but of course, only the nerdiest of nerds (he says, as he glaces behind himself sheepishly) would enjoy that.
Step-by-Step Taller 5th Gear Swap (Dyna R452 into Tacoma R150F)