New speedo gear suuuuuuuucks

The_Josh_Bear · Feb 27, 2019

So I recently switched from 4.10 to 3.55 in the rear and finally got around to the speedo gear swap yesterday.

But it doesn't read really at all. Under 25mph it doesnt read and at 80mph it reads 40-45 at best but vacillates pretty wildly the while time.

I took it out to reinstall it and nothing changed, tried it a 3rd time and nothing better.

I can say the gear itself is already worn and has a little dish to it after just two days driving to work, 17 miles each way. But the dish is like a nickel only 1/16" deep, far less than the gears should be meshing, right?

My old OEM gear was perfect all day every day. It was 19 tooth. I did math and figured my gear to be right between 16 tooth and 17, so I did the 16.
The new gear was off of Ebay but has the same stamp as the gear that came on my rig. "LEM" or something.
What am I missing guys?

Thanks,
Joshua

YJMike92 · Feb 27, 2019

I wonder, maybe the wrong gear? Is the diameter the same as the old one?

The_Josh_Bear · Feb 27, 2019

YJMike92 said:
I wonder, maybe the wrong gear? Is the diameter the same as the old one?

I guess it must be? Looked pretty close the other day but of course I was getting over the flu and wasn't all there. I'll put my calipers on the new and old to compare.

YJMike92 · Feb 27, 2019

I never paid attention to the mounting on my Fords but some rigs have a speedo gear housing that allows the driven gear to be turned closer or further away from the drive gear. Do our Fords have that kind of set up?

The_Josh_Bear · Feb 27, 2019

Well I mic'd the old gear and new gear of the same tooth count(19):

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And here's a 17-tooth:

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I'm no machinist but I doubt these variances would cause my issue. I'm sure the 16 tooth is just that much smaller but still... maybe the gear inside the tcase is worn also? Is it plastic? How stupid would it be if it were plastic :frustrate

Shadetreemechanic · Feb 28, 2019

How is the condition of your cable?

The_Josh_Bear · Feb 28, 2019

Shadetreemechanic said:
How is the condition of your cable?

I imagine its fine, since the original gear worked perfectly 3 days ago.
It spins quite freely by hand but I otherwise dont know how to test it.

FordGuy100 · Feb 28, 2019

The gear in my transfer case is stripped as best as I can tell. Perhaps thats your problem too.

Rdnck84_03 · Feb 28, 2019

The drive gear is also plastic.

FordGuy100 · Feb 28, 2019

Rdnck84_03 said:
The drive gear is also plastic.

Exactly.

YJMike92 · Feb 28, 2019

Most drive gears are plastic.

BrianX128 · Feb 28, 2019

They seat strange sometimes. Mine worked great and then I unhooked it to get some slack to pull it from the dash to change bulbs in the dash and it shook. I pulled out the trans side and re seated it and now its fine. :dunno

laserjock · Feb 28, 2019

FordGuy100 said:
The gear in my transfer case is stripped as best as I can tell. Perhaps thats your problem too.

This^

I changed my gear and the new one worked half way for a short time. The drive gear inside the tcase housing was worn.

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You can see it down through the hole even. Took picture in truck with phone.

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Not that hard to change. I changed the rear seal at the same time.

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If you do change the rear seal make sure it’s driven solid. Mine popped out and emptied the tcase going down the interstate coating the front of the camper.

[emoji849]

chillman88 · Feb 28, 2019

laserjock said:
Mine popped out and emptied the tcase going down the interstate coating the front of the camper.

At least the front of your camper won't rust out :dunno

The_Josh_Bear · Mar 2, 2019

laserjock said:
This^

I changed my gear and the new one worked half way for a short time. The drive gear inside the tcase housing was worn.

You must be registered for see images attach

You can see it down through the hole even. Took picture in truck with phone.

You must be registered for see images attach

Not that hard to change. I changed the rear seal at the same time.

You must be registered for see images attach

If you do change the rear seal make sure it’s driven solid. Mine popped out and emptied the tcase going down the interstate coating the front of the camper.

[emoji849]

Thanks for the photos! Looks like a lot more work than the speedo gear was... grrr. Good call on the tail shaft seal as mine leaks a little anyway.
Did you have to drop the tcase or is it doable in the pickup?

New speedo gear suuuuuuuucks

The_Josh_Bear

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YJMike92

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The_Josh_Bear

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YJMike92

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The_Josh_Bear

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Shadetreemechanic

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Rdnck84_03

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YJMike92

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BrianX128

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laserjock

Almost there...

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