Ok, here we go again.
My 67 f-100 has a diffrent rear end installed by the truck's previous owner. It's a ford 9", but the strange part is, that as far as I can tell, it has somthing like a 1:85 gear ratio. I found this out by jacking up the truck and rotating the axle while counting rotations to one tire rotation. Did I do this right?
If that wasnt enough, the transmission is geared low enough, that even with this rear end, the truck tops out at about 60-70 mph in 4th gear. (manual 4 speed). My quesion is: Is it possible to rebuild the tranny, at least the 4th gear, to increase the top speed of the truck, or would it be easier and cheaper to simply get another tranny? If that's the case, can anyone suggest any? Cruising around in 4th gear at 30 mph just doesnt seem right.



The only thing that's impossible is that no other possiblties exist.

 

Yea ,you did it backwards.
Turn the Tire One revolution and count the turns of the driveshaft instead.


Dennis

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<Yea ,you did it backwards.
Turn the Tire One revolution and count the turns of the driveshaft instead.>

Allright...tried it that way, and got the same answer...

The only thing that's impossible is that no other possiblties exist

 

Corwin, A couple of things there are no 9" 1:85 ratios that I am aware of, and your tranny ratio is 1 to 1 in high gear, just like all none overdrive trannys, regardless what is in front of high gear. If your truck is hitting the wall at 70, I would guess you have something like a 4.11 in it. My truck has used all of the numbers on the speedo (100) at 3600 rpms. It has a 2.75 gear in it.

Try rolling the truck on a lever area with a friend pushing the truck and watching the tire while you count the drive shaft revolutions. You can tape a piece of string to the ds and count the winds with one roll of the tire also.
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John

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In the cool still quiet of night, you can hear chevies rusting away.

 

Thanks..I'll try that tomorrow.
I figured there wasnt any such gear ratio, that's actaully why I posted the question. It didnt seem right...

The only thing that's impossible is that no other possiblties exist

 

Letr us know what you come up with.
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In the cool still quiet of night, you can hear chevies rusting away.

 

If the rear-end is 'open' (non posi or non trac lok etc) I think you have to multiply your revs by 2 to get the real gear ratio when you do it on jack stands. So you probably really have a 3.70. Your count should reflect this if you do the rolling it on the level ground method as mentioned.

 

>If the rear-end is 'open' (non posi or non trac lok etc) I
>think you have to multiply your revs by 2 to get the real
>gear ratio when you do it on jack stands.

That is a fact.

Plus with an open, if you're on a hill, don't try to jack up one rear wheel unless you apply the e-brakes. Soon as it gets off the ground, the other one will roll.

Dan Blackwell

'68 Ranger, 360, Pop bought it for $2605 brand new
I put in the c6, ps & pdb; original took too many hands 'n feet to drive, shift, signal, brake and dim.