speedo correction revisited...gearheads only:) (1 Viewer)

[F-junker]

I pulled the trigger the other week and ordered a new "gear, driven" plastic speedo gear. I saw the gear listed on an oem parts list post a few weeks ago. I dropped it in an no movement, I hope I've not stripped the teeth off in the 4mile test run. This is what you get when you don't do your homework!!! Tell your kids it never stops so get used to it!

I found a decent thread on the matter: https://forum.ih8mud.com/40-55-series-tech/131975-speedo-correction.html

After looking about here it seems (as I assumed) I need another gear to make up for the difference in tooth count and size. My truck is (mostly) a 78' 4speed, 4:11's with =33" tire. I ordered a 33403-60030 gear which I believe is a 16 tooth unit, I pulled out a "6x18" (stamped on the shaft) gear.

Reading the post made by IDave he used the same driven gear and matched it to a gear found in his case (I guess he ordered a new one too #33481-60030, 6x17). This gave him spot on speedo calibration with 33" tires. This is what I shooting for!!!

My questions and concerns. Is there any difference in these gears from the 3speed cases to the 4speed xfer cases? If so I'm going to have issues as I believe Dave's truck is a 70'.

If you've done this please post up so info or drop me a pm. I'd hate to have spent 24 bucks for a gear thats not gonna do it, not gonna do it!

 

[Mark W]

There are at least two different drive gears (the collar that fits over the output shaft).
They are slightly different ODs.

I assume it is a 3 speed/4 speed thing. It has been an eon or so since I looked into it closely.


Mark...

 

[DomSmith]

Junker-

Are you sure you need a correction? I spent countless online hours searching the subject and determining options only to find that with a true GPS speed test my 45 that is completely stock besides tires is nuts on with 33's in place of the stock rubber.

I have no idea why...

 

[65swb45]

Junker-

Are you sure you need a correction? I spent countless online hours searching the subject and determining options only to find that with a true GPS speed test my 45 that is completely stock besides tires is nuts on with 33's in place of the stock rubber.

I have no idea why...

That's funny! My speedo is spot on in the 45 with 32s, but 6% underread in the 40 with the 33s [both confirmed with GPS]. And both run 6x17 gears.

DEFINITELY need a matching steel drive gear on the output shaft, or you'll tear the driven plastic gear up.

Best

Mark A.

 

[F-junker]

No doubt about it the speedo in the 78 is off and does not register an accurate speed. Not a good truck to drive home from the bar... Not that I do that anymore, well not plastered....

On the serious side though I believe the tires are 285 65r16 and was told with the rims they would be exactly = 33". How far off this thing is I'm not too sure somewhere are 10+ maybe.

I've found a compnay online that sells the gear for 21bucks. I've never used them and might give them a shot. I;ve got to order some wheel cylnder rebuild kits for a buddy so we'll see how it works.

BTW- I pulled the gear and it can out with only a very small amount of plastic shaved off the teeth. Not enough to effect it with a proper sized unit. good thing I kept the test ride to a minimum.

 

[DomSmith]

Borrow a GPS from someone and find out how far off you are. It's the absolute best way to determine what you really need to bring the speedo into line.

 

[F-junker]

10mph to slow minimum. Ordered the drive gear today and will throw it in there next week. Ah s***, forgot to order the dag gone gasket. I replaced that seal last year or so. I might try and replace those little o rings inside the driven gear housing, any one done those with commonly found o rings??

 

[F-junker]

Well I'm being told the drive gear I needed is no longer available. I'm wondering if this gear is maybe used in an earlier 3speed case??? Anyone know? I'm pretty discouraged that toyota no longer has these available but hell it's only a 20+ year old part. What can I expect!!

 

[40's rock]

My stock 76 with 32"'s is 10% off on the low side verified by GPS. Caught myself hitting 78 on the spedo then remembered I was actually close to 85.

 

[Trollhole]

Your going about it the wrong way. Change the gauge face to show what your speed should be.

This took me about 15 min to do.
Move the MPH numbers where you need them and print it out on a lazerjet printer.

 

[cruiserbrett]

then what happens with the disparity between the MPH and the odo?

 

[Trollhole]

then what happens with the disparity between the MPH and the odo?

It's called SOL. I can put that down on the bottom in small letters if you would like.

 

[Sputnik40]

Changing the background seems like the best way to go about it - damn good idea that I'd have never thought of?

If you were able to identify the gear you need by model/year t-case I'm sure someone might have one lying around - especially given all the parts t-cases out there.

At one time - when I ran 33's with on a 76 FJ40 I was able to swap in an earlier 2.31 speedo gear set and nailed it almost spot on. Worked fine until a went to a bigger tire - have since swapped out tires so many times just gave up on having a speedo.

 

[BC40]

That's funny! My speedo is spot on in the 45 with 32s, but 6% underread in the 40 with the 33s [both confirmed with GPS]. And both run 6x17 gears.

Mark A.

x3. I used the speedo drive gears from a parts donor 78 fj45 which was factory equipped for the Cdn market with 16" split rims and 7.50x16 tires. It is nearly dead on accurate in my 40 with 33" BFG's. Been a while since I looked at it but IIRC it had a one tooth difference on one of the gears.

 

[F-junker]

Yeah I agree on just changing the numbers at this point, I'm just bummed I couldn't make that gear work. I bet one from a 3speed case would do the trick but I'm going to say F it and recalibrate the clock face instead. thanks for the nice pics

 

[Blue77FJ40]

Some old posts I've kept on this subject that may be useful:

Thanks to Scott Tate I was finally able to work out with local dealer that the correct gear was 16 teeth to match 4.11 rear to 33" tires. Toyota made three speedo gears with 15, 16 or 18 teeth for all of the later 40 t/cases [75-83].

The 18 tooth was original standard for 4.11 with smaller tires pre 01/79.

The 16 tooth was for 3.73 rear from 1/79-8/80 with smaller tires. It can be used to correct calibration errors per above or possibly 4.56's with 35" tires.

The 15 tooth was an option but I have no idea for what, cause presumably it was for higher gears than 3.73, bigger tires [35" w/4.11]. It would also be closer, but not dead on for 4.88 diff gears and 33"tires.

For those running or planning to run those larger 35s and up, 15 teeth is as close as you can get with stock speedo gear selection. Bullfrog