Speedo inaccuracy (3 Viewers)

[Gippster]

Yes, I searched the forum, but didn't specifically see the answer to this question. I realize the speedo will never be as accurate as it should, but it should be close, right? I have:

• H55F 5-speed transmission
• Stock axle gearing
• 33” tires

I assume that larger tires cover more distance per revolution, which causes the speedo to read slower than I'm actually going. If that assumption is correct, then wouldn't swapping the gear from 6x16 to 6x18 (33403-69065) slow down the rotations to improve speedo accuracy?

 

[jclark]

You’re correct on the tire size, but you’re missing swapping the gear. Your idea will actually make the situation worse. You want to go in the opposite direction. Tire size goes up, gear teeth go down.

Good luck.

 

[Gippster]

Thanks! Eesh, I don't know if there's a part with a lower teeth count :/

 

[CruiserTrash]

You would need the set of gears, not just the one that plugs into the hole on the transfer case. That requires removing the back nose cone off the t-case, which requires making sure the preload is set correctly when you reinstall it. when I rebuilt my transfer case I looked into this but could only find the plastic gear and not the correlating metal one that sits on the rear output shaft.

Or just adjust your speed and odometer UP by 14-16% depending on the *actual* diameter of your "33" inch tire. Use a GPS speedo or a roadside radar speedo and then check against the speedo in your gauge cluster. EDIT: I'm talking about mental math. Before I put in 4.11 gears I just kind of got a feel for where the speedo gauge was and what number that actually meant. After about a week I didn't even have to think about it anymore. Speedo says 60? That means I'm going ~68, for one example.

Or get a set of 4.11 diffs and you'll only be 4% over. Although with that first gear on the H55 and the 4.11s leaving a stoplight might be kind of annoying.

 

[OSS]

31" tires on a stock FJ60 with stock 4:10 gears slows down the speedometer and odometer by approximately 10%. Thats the combo I had. I just mentally accounted for it. I suggest you do the same (with a different offset) for your 33" tires. It becomes 2nd nature.
There isn't a Toyota speedo gear set you can buy that will mechanically do it for you.

There was a long conversation about this years ago on mud and the verdict was: not worth adding on a 2nd gear reduction box just to offset the speedo

 

[cps432]

I’m running that setup with 40 series diffs using 4:10 as @CruiserTrash mentioned. My speedometer is dead on. My tires are actually more like 32.5”
It also responds way better than the stock 60 series differentials.

 

[MWM1]

I just do the mental conversion
40 speedo 36 actual
35 speedo 31 actual
and so on...

 

[Eurasiaoverland]

You would need the set of gears, not just the one that plugs into the hole on the transfer case. That requires removing the back nose cone off the t-case, which requires making sure the preload is set correctly when you reinstall it. when I rebuilt my transfer case I looked into this but could only find the plastic gear and not the correlating metal one that sits on the rear output shaft.

This is only correct in certain cirumstances - and not this one.

The speedometer drive gears accomodate a range of speedometer driven gears. Here is the standard speedometer drive gear (the one that sits in the transfer case) for a non-US 60 Series running 4.11 diffs:

The stamped mark on the gear 6:15-17 is telling you:
(i) the drive gear has six teeth, and
(ii) it will mate correctly with driven gears (the plastic-toothed gear shaft) with 15, 16 or 17 teeth.

So if the OP is running a 6x16 gear set, this could be swapped to a 15 tooth gear using the same drive gear. That is the lowest ratio gear set you can get from Toyota.

 

[jclark]

Thanks! Eesh, I don't know if there's a part with a lower teeth count :/

Call the guys at @cruiseroutfit Jason and Chase are A-1 and should be able to help point you in the right direction.

 

[cps432]

This is only correct in certain cirumstances - and not this one.

The speedometer drive gears accomodate a range of speedometer driven gears. Here is the standard speedometer drive gear (the one that sits in the transfer case) for a non-US 60 Series running 4.11 diffs:
View attachment 3949442
The stamped mark on the gear 6:15-17 is telling you:
(i) the drive gear has six teeth, and
(ii) it will mate correctly with driven gears (the plastic-toothed gear shaft) with 15, 16 or 17 teeth.

So if the OP is running a 6x16 gear set, this could be swapped to a 15 tooth gear using the same drive gear. That is the lowest ratio gear set you can get from Toyota.
View attachment 3949449

That’s great tech info. Thanks!

 

[CruiserTrash]

This is only correct in certain cirumstances - and not this one.

The speedometer drive gears accomodate a range of speedometer driven gears. Here is the standard speedometer drive gear (the one that sits in the transfer case) for a non-US 60 Series running 4.11 diffs:
View attachment 3949442
The stamped mark on the gear 6:15-17 is telling you:
(i) the drive gear has six teeth, and
(ii) it will mate correctly with driven gears (the plastic-toothed gear shaft) with 15, 16 or 17 teeth.

So if the OP is running a 6x16 gear set, this could be swapped to a 15 tooth gear using the same drive gear. That is the lowest ratio gear set you can get from Toyota.
View attachment 3949449

Very interesting. Thanks.

 

[franklin40]

this is also a simple way to fix it….

Home - Deluxe Speedometer

DELUXE SPEEDOMETER AND CABLE SERVICE, INC. - Premium Automotive SPEEDOMETER REPAIR And CABLE Service And Repair In Denver, Colorado.

deluxespeedometer.com

they were super great to work with

 

[cps432]

this is also a simple way to fix it….
View attachment 3950090

Home - Deluxe Speedometer

DELUXE SPEEDOMETER AND CABLE SERVICE, INC. - Premium Automotive SPEEDOMETER REPAIR And CABLE Service And Repair In Denver, Colorado.

deluxespeedometer.com

they were super great to work with

I wonder if you could also install a cruise control sensor or find one that changes the ratio and has a sensor. That would be neat.