stock speedo gear tooth count?

[toddz69]

What is the stock tooth count on the speedo gear? I'm guessing that varied whether you had 3.50s or 4.11s in the axles. Info on either one would be appreciated.

TIA,
Todd Z.

 

[DirtDonk]

Depended on the year (maybe), the tire size option, the transmission and final gear ratio.
I would think anyway. Maybe there was one size, but I doubt it.
Oh, and there were two sizes of drive gear inside the transfer case too, just to muddy up the waters a bit more.

Someone will know for sure. I just thought I'd say howdy and rain on your parade temporarily. ;D

Paul

 

[DirtDonk]

You asking specifically for the '69 with manual trans? I wonder if Bajas got a different gear, depending on expected options, or if they all came with the same one and were changed at Stroppe's shop?

Paul

 

[NicksTrix]

i find a lot of them had the white gear (17T), and the bulk of what i see have 3:50's originally.

might want to try a 20T or 21 with your racer gear ratio.
hth

 

[broncnaz]

Ditto on the 17 tooth gear thats what I've found on most with 3.50 gearing. I need to check my 71 as it has 4.11's. The only thing I dont know is how many teeth the t case gear has in each.

 

[Viperwolf1]

I think the factory 4.56 and some/all 4.11 geared Broncos came with the 6 tooth steel drive gear and the 3.50 geared ones had the 7 tooth plastic drive gear. The difference in ratio between 3.50 and 4.11 is 17% and the difference between 6 and 7 teeth is 17%. That way the same driven gear could be used in both and it would leave some adjustability for different tire size options.

I can't remember what the stock driven gear was in my Bronco but it had 3.50 gears and the 7 tooth speedo drive gear.

 

[toddz69]

Depended on the year (maybe), the tire size option, the transmission and final gear ratio.
I would think anyway. Maybe there was one size, but I doubt it.
Oh, and there were two sizes of drive gear inside the transfer case too, just to muddy up the waters a bit more.

Someone will know for sure. I just thought I'd say howdy and rain on your parade temporarily. ;D

Paul

Yeah, thanks Paul! ;D The problem is that I don't think the t-case is original in our truck so I don't have any idea on which gear it has inside the case. In messing around with the gear calculator this morning on the EBR site, it appears that 28/29" tires with 4.11 gears is in the ballpark compared to our 32/4.56 combo (certainly closer than 3.50 gears anyway). We'll probably use a GPS and do some comparison readings at some point and go from there.

Nick - I'll take your advice and try a 20/21 tooth to start with. Gears are cheap enough that I can afford to buy another one later if need be.

Thanks everyone for your input.

Todd Z.

 

[Viperwolf1]

BTW, You can look inside the speedo gear hole and count the teeth on the drive gear. Or if you can't count them the steel gear has 6 teeth and the blue plastic one has 7.

 

[toddz69]

I think the factory 4.56 and some/all 4.11 geared Broncos came with the 6 tooth steel drive gear and the 3.50 geared ones had the 7 tooth plastic drive gear. The difference in ratio between 3.50 and 4.11 is 17% and the difference between 6 and 7 teeth is 17%. That way the same driven gear could be used in both and it would leave some adjustability for different tire size options.

I can't remember what the stock driven gear was in my Bronco but it had 3.50 gears and the 7 tooth speedo drive gear.

OK, that's helpful too, Phil. Running a few numbers assuming a stock tire size of 27-28", I come up with about a 13-15% delta in speeds at 3K rpm between stock and 32" tires. So assuming stock driven was a 17T gear regardless of drive gear tooth count, and every tooth is a 5% difference, it sounds like Nick's guess of a 20T gear is a good starting point.

Thanks,
Todd Z.

 

[toddz69]

BTW, You can look inside the speedo gear hole and count the teeth on the drive gear. Or if you can't count them the steel gear has 6 teeth and the blue plastic one has 7.

Unfortunately, that's option's not available to me since the truck is in the race shop in San Diego and I'm sitting here in downtown Phoenix .

Todd Z.

 

[Stroppe-Envy-77]

Just a thought...would there be a chart in a factory shop manual listing which speedo gears were used with with which axle ratio and tire combos?

 

[toddz69]

Just a thought...would there be a chart in a factory shop manual listing which speedo gears were used with with which axle ratio and tire combos?

Good idea, Dave! So I looked. In my '73 edition, it says:

The Ford Truck Master Parts Catalog shows the proper speedometer gears to use for various rear axle and tire size combinations.

Todd Z.

 

[needabronco]

My stock gear was the white 17 tooth with 3.50 gears. I stepped up to a red 21 tooth for 4.88's and 34" tires and it seems to be pretty close, although I haven't borrowed your GPS yet to verify...

 

[toddz69]

My stock gear was the white 17 tooth with 3.50 gears. I stepped up to a red 21 tooth for 4.88's and 34" tires and it seems to be pretty close, although I haven't borrowed your GPS yet to verify...

Cool - thanks Casey. Sounds like I'm close!

Todd Z.

 

[Stroppe-Envy-77]

Good idea, Dave! So I looked. In my '73 edition, it says:

The Ford Truck Master Parts Catalog shows the proper speedometer gears to use for various rear axle and tire size combinations.

Todd Z.

Alrighty then, I'll just leaf through my Ford Truck Master Parts Catalog...
:-[

Oh well, sounds like you're slowly getting the answer from the Group Mind anyway.

 

[ol gray mare]

My 70 came with a 19 tooth for the 3:50s. I'm the 3rd owner and knew the first two, so I'm pretty confident it's original.

 

[toddz69]

Oh well, sounds like you're slowly getting the answer from the Group Mind anyway.

Yes, the collective wisdom of this group never ceases to amaze me. Thanks for everyone's input.

Todd Z.

 

[77BroncoWag]

so for a stock 77 with 3.50 rear to 4.10 and 35" tires what should I get for a speedo gear? Are they easy to swap out?

 

[av bronco]

so for a stock 77 with 3.50 rear to 4.10 and 35" tires what should I get for a speedo gear? Are they easy to swap out?

Ive got 4.10s and 35s with a c4, im running a 19. they rae a cakewalk, just take the speedo gear out of the transfer case(1 bolt) then pull the tab off at the bottom of the gear, then slide off old-slide on new.