Gear ratio surprise

[Speedrdr]

Well, I'm just gonna say that after digging through the Ford service manual, I discovered that my ‘77 came with 2.50 gears in the axles. I never even knew that broncos HAD that ratio OFFERED. Having said that, There's no tag on either chunk and I haven't got the guts to do the “string on the driveshaft and rotate the rear tire to count rotations. Is there another method that can be used?? Really don't want to do the string thing. Anybody got suggestions for me?

Randy

 

[MarsChariot]

Why not just jack up the rear at the pumpkin, spin the wheel by hand, and see how many turns the drive shaft does per one wheel revolution. I too have never heard of 2.50s on a Bronco. Sounds like a cruiser.

 

[Yeller]

Seen that in lots of cars from that era but never a 4x4. There is a 2.59 gear available for a d44, I've only seen that in corvettes.

 

[okie4570]

Pop the cover on the front pumpkin and count teeth on the R&P. 2.50 would be something like 39/15 or something close to that I'd think. Ring teeth divided by pinion teeth.

 

[Broncobowsher]

The reference book is probably a typo.
What is the code on the glove box plate? We can tell what it was born with anyway. Doesn't mean anything about what may have been changed.

 

[Madgyver]

hang a string to your driveshafts, engage front hubs, push rig so tire make 1 full rotation, count wrap of string around driveshaft. Simple.
https://classicbroncos.com/tech/whats-my-gear-ratio


you can also open up the diffs to count gear tooth but then you will get oil on your hands.

 

[Speedrdr]

The reference book is probably a typo.
What is the code on the glove box plate? We can tell what it was born with anyway. Doesn't mean anything about what may have been changed.

Glove box door is marked 18 J. What I'm looking in is the Ford Service Manual. The J is for power steering and the 18 is corresponding to the 2.50. It could very well be a typo, but who knows. I'm HOPING that the PO changed out the gears in th chunks as it's sitting on 37” tall tires…don't think it would turn those tires over with gearing that tall.
Thanks for all the suggestions and tips. Looks like the old string and tape is coming out of the toolbox.


Randy

 

[Broncobowsher]

My quick look shows the axle to be a factory 3.50 small bearing.

 

[okie4570]

Glove box door is marked 18 J. What I'm looking in is the Ford Service Manual. The J is for power steering and the 18 is corresponding to the 2.50. It could very well be a typo, but who knows. I'm HOPING that the PO changed out the gears in th chunks as it's sitting on 37” tall tires…don't think it would turn those tires over with gearing that tall.
Thanks for all the suggestions and tips. Looks like the old string and tape is coming out of the toolbox.


Randy

Like said above, that is a 100% typo. 18j is small bearing 3.50 open gears, with power steering.

 

[Rustytruck]

1977 should only have a big bearing rear end. with 37 inch tires your going to have to change gears and carriers anyway unless your running a diesel and a super low first gear.

 

[Speedrdr]

1977 should only have a big bearing rear end. with 37 inch tires your going to have to change gears and carriers anyway unless your running a diesel and a super low first gear.

From memory, as said ‘77 is not with me, is that the rear axle DOES have the “swelled” end at the tire as does the large bearing has. Unfortunately for my restoration, had hand surgery today and will be off for 2 months. Guess I'll get caught up on my designs and specs. Thanks everyone for the suggestions and at least confirmation that factory gears were NOT 2.50 and FoMoCo service manual has errors!

Randy