AdventureTaco - turbodb's build and adventures

You dont have as much rear lift.

Well id just keep an eye and ear on it. CB drop would help the life of the the bearing.

 

Awesome! Just finished reading the whole thread.

Build and adventure reports are really nicely done.
Truck looks great.

Subbed.

 

Replacing the Speedo Gear
February 21, 2018.

How many miles do you have on your truck? If you're anything like me, you'll answer this by looking at your odometer, reading a number, and concluding that you have that many miles - 83,078 miles in my case.

Like me, you're wrong.

Your odometer is lying to you. And so is your speedometer. I covered why that is here - go read it. I'll wait. Speedometers, Odometers, and Gas Mileage – All Lies!

OK, welcome back. Or not if you're like me and just skipped over that last link. Let me try to recap:

All that means that I don't actually have 83,078 miles on my truck. I've actually got about 75,000 miles on it. Not that I'm planning to sell it any time soon ever. But as much as I want to hit the 500,000 mile club, I would rather that my odometer be correct - or at least as close as possible.

To that end, I ordered the largest speedometer gear they make for a 2000 Toyota Tacoma - the 33-tooth model - to replace the 30-tooth model that was installed in the factory.

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It arrived, along with a new gasket and clip and I promptly set it aside while @mrs.turbodb and I drove several thousand miles down, through, and back from Death Valley.

It was an epic trip. Don't miss reading about it here: Death Valley (Jan 2018).

Now, several weeks later, it's time to install that gear, and hope that my speedometer reads slower than I'm actually going, and my odometer logs fewer miles than I've actually gone. You know, so the resale value of the truck is higher.

The first step was to remove the skid plates, since the speedometer gear housing is attached to the transfer case, which is well-protected by the @RelentlessFab mid-skid. Six bolts and a floor jack, and I lowered the skid to find about 5 lbs of Montana, Wyoming, and a bit of Utah dirt that had hitched a ride back from The De-Tour (another epic adventure you shouldn't miss).

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The speedometer gear housing is secured to the transfer case with a single 10mm hex bolt, which was easily removed after I disconnected the plug for the sensor.

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With the bolt removed, the housing can be pulled out of the transfer case easily (if the o-ring hasn't degraded) and mine came out with a rewarding sucking sound, along with a few teaspoons of oil.

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Fingers crossed that losing a bit of oil isn't the end of the world here. At this point, pop out the spring clamp, and pull the old gear out of the housing. Again, you'll get a nice sucking sound as it comes out. It was rewarding enough that I did it a couple times .

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In order to fit more teeth (thus rotating more slowly to bring the mph and odometer readings down), the new 33-tooth gear has to have a larger diameter than the old 30-tooth gear - which it clearly does.

As a bonus, it's also painted bright pink. And we all know, most ladies like pink. So if you install one of these, it's more reason for them to like your truck.

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The new gear slides right into the housing and is secured with the newly supplied clip. I also replaced the o-ring, though my original still seemed just fine, and was ready to re-install the housing assembly.

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Installation is simply the reverse of removal, and I found that the machining tolerances of the hole in the transfer case, and the speedometer gear housing were so close that it helped to wipe a bit of oil on the housing in order to get it to slide in (with a few gentle taps).

I then re-attached the bolt ("tight") and plugged in the sensor.

And then it was the moment of truth. Would my speedometer (and odometer) be accurate? There was only one way to find out - I started up the truck and headed out to I-5 to compare my GPS speed with my speedometer.

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Alas, it wasn't correct - but it was a lot closer. It now reads about 6% high (instead of 14%), which matches what the truck originally shipped with from the factory.

So - at least on my truck, the following configurations result in nearly identical speedometer/odometer margins of error (~6%):

• 31x10.5 R15 Goodyear Wrangler tires + 4.10 gear ratio + 30-tooth speedometer gear
• 255/85 R16 Cooper ST Maxx tires + 4.88 gear ratio + 33-tooth speedometer gear

And, other configs I've run:

• ~0% error
  • 255/85 R16 BFG KM2 tires + 4.10 gear ratio + 30-tooth speedometer gear
• ~14% error
  • 255/85 R16 BFG KM2 tires + 4.88 gear ratio + 30-tooth speedometer gear
  • 255/85 R16 Cooper ST Maxx tires + 4.88 gear ratio + 30-tooth speedometer gear

So yeah, my odometer still lies, but I don't really care. Because it just makes the adventure "longer."

 

Great Speedo-gear writeup, I’m going to do this when I get off work tonight!

 

Thanks! It's fun writing since I get to relive the doing!

Well yes, in fact, irrelevant. But I still like my speedo to be right. Call me crazy. Oh, wait...you probably already do.

Nice! What are you switching from and to? I thought I was going from 31->33, ended up being 30->33. Not sure if that's because I had a MT vs. AT or what.

 

Great write up! Do you happen to know the 30 tooth speedo gear part number? I have the 255/85 R16 BFG KM2 tires + 4.10 gear ratio and would like to have the speedo match the actual speed I am going. Thanks!

 

Why not just use a Dakota Digital and have your speed match exactly to your GPS?

 

30 is the stock speedo gear. I used a 28 tooth to correct my speedometer for 33s and 4.10s.


FWIW, I have 295/75/16s and a 33 tooth gear and my speedo is dead on per GPS. Surprised your still that far off with the 255s.

Edit - and 4.88s

 

Ah okay, I'm not super far off with the mph readings. Just about 4 mph off at higher speeds. Just enough to be annoying.

 

Seems like a reasonable plan! I (sort of) wondered if I should stick with my stock gears when I saw the speedo was right on with the 255/85R16's. But then...gears are so nice.

Here are the part numbers for all the combos. Also, keep in mind that MT/AT will have an affect as well so 30 may or may not be what you have/need. It'd be relatively easy to take the gear out, check out the number on it (or count the teeth), and then order the right gear to replace it. You want to move ~2 teeth for 4-5mph @ ~70mph.

Automatic Transmission

• 30-tooth: 33403-39365
• 32-tooth: 33403-39425
• 33-tooth: 33403-39415

Manual Transmission

• 28-tooth: 33403-39585
• 30-tooth: 33403-39365
• 31-tooth: 33403-39345
• 32-tooth: 33403-39425
• 33-tooth: 33403-39415

As much as possible, I like to keep my electrical stock (at least, the stock part of my electrical, hahahahaha). Plus, the gear seemed really cheap and easy.

Definitely interesting. I was right on - like dead on accurate with my 30-tooth and 255/85R16 KM2's and 4.10's. Of course the KM2's had ~25K on them...so not brand new.

 

What is your speed (indicated by the GPS) when your speedo reads 70 mph? Also, what are the RPMs for the same, in 5th gear?

 

The speed limit around here is 65, how am I supposed to get you these numbers? Tomorrow, likely.

99% sure I'm going to tell you the GPS speed is 66 mph when the speedo is at 70 mph; not sure about RPMs.

 

Why do I hear your post in my head in rain-man voice?

 

OK, here are the numbers.

Speedo @ 70 mph - GPS reads 66 mph, tachometer at ~2800 rpm
Speedo @ 80 mph - GPS reads 76 mph, tachometer at ~3300 rpm

Perhaps obviously, but I'll mention it anyway... obviously one/both of the numbers above are wrong, or more correctly - not completely accurate. That is to say, at 80 mph, there must be a larger difference between the speedo and GPS than at 70 mph. (since the ratio remains constant). So, it's likely that the GPS is rounding to the nearest MPH, and/or I am reading the speedo slightly incorrectly at a given speed.

Net though - I'm somewhere about 6% higher on the speedo than reality.

 

That is a little surprising. I would have thought ours would be more similar. We have a lot in common, 4.88s, 33 tooth with new 33's. I am not surprised your RPMs are higher (jealous) because of the overdrive ratios between the two transmissions is different. I wonder if your tires are just shorter/smaller circumference.

FWIW, my speedo @ 70 mph - GPS reads 68 mph, tachometer @ 2500 rpm.

 

the manual tranny is geared way lower.

From my experience, the manual in 5th is about 400-500rpm higher at highway speed vs the manual.

 

Been subbed for a while, but wanted to thank you for this. Saw it in the detour thread and I think it' going to be an ideal location for me to relocate my winch solenoid.

 

kinda makes for long cable runs for that..

 

Yeah that's also a concern. I won't know till I have the winch tonight but running out of ideas where I can stick it. Something tells me it won't fit on the winch, already needing to cut my grill a smidge for the winch housing.

 

Sure thing. For me, one of the few open spots up there under the hood. Really wish I had another spot too, for a future second battery.

This is a great point. I know my winch came with 2ga wires between the solenoid and motor, and I was already worried about the load over the few feet of those cables. You'd want to run something like 1/0 or 2/0 welding cable if you were going to go as far as the firewall, I'd suppose. Not cheap.