1966 F-100 Rear Diff

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Jun 12, 2015 | 05:35 AM

markeyd

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1966 F-100 Rear Diff

Through the forums I've been able to learn that the 1966 F-100 has what's known as a 9" Diff? Assuming that is correct I am pretty sure it has limited slip . . . which means I need to use a certain gear oil for it. I'll return what I have and get the right stuff . . .

Yesterday I noticed that the seal going to the drive shaft from the rear diff is leaking. In your experience is that a seal replacement, or a more extensive rebuild of some sort? I am not a mechanic . . .

I want to replace the oil (if there is anything left inside), but first I'll need to get the plug off, and it measures about 1.5 inches across. I'll have to pick up a big enough wrench because I don't currently own anything like that.

When I am driving and depress the accelerator starting from a stop, or moving relatively slowly there will be a thump upon initial acceleration. I've read that this could indicate a problem but is normal on some fords such as Broncos and F series trucks. Some people lubricate the drive shaft to minimize this. Any additional thoughts on that?

Thanks in advance.

Jun 12, 2015 | 05:47 AM

jowilker

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From: Creedmoor, North Carolina

Mark, May I ask how you determined that your rear is limited slip?

What gear oil do you have now?

We'll have some others chime in shortly.

John

Jun 12, 2015 | 06:22 AM

markeyd

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Quote:

Originally Posted by jowilker

Mark, May I ask how you determined that your rear is limited slip?

What gear oil do you have now?

We'll have some others chime in shortly.

John

Well, I kind of don't know what I am talking about . . .

I need to double check to make sure it is limited slip. The gear oil I have now is 80w/90 "limited slip top off only." I am thinking that if I get 80w/90 which is rated for LSD I can't hurt anything.

I have a lot to learn. The truck is 2WD, so maybe it is not LSD? I couldn't find a tag or plate on the axle or diff to identify.

Jun 12, 2015 | 07:16 AM

NumberDummy

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From: Simi Valley, CA

No F100 w/a 9" had Limited Slip until 1968. If optional Limited Slip is present, the rear axle is a Spicer/Dana, but for 1966, there are three different possibilities:

Spicer/Dana 44; Spicer/Dana 60.2; Spicer/Dana 60.3.

AXLE code stamped on the 2nd line-far right of the Warranty Plate, riveted to the left door face below the latch. Post what it is.

Jun 12, 2015 | 07:30 AM

markeyd

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1st line is VIN
2nd line far right says ". . . E81 G 17"
3rd line says " . . . 4000 22"

Thanks

Jun 12, 2015 | 07:35 AM

markeyd

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Jun 12, 2015 | 07:39 AM

NumberDummy

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From: Simi Valley, CA

Pic of Warranty Plate in post 6:

Quote:

Originally Posted by markeyd

VIN: F10YR789834

2nd line: WB: 115 / COLOR: J / MODEL: F100 / BODY: E81 / TRANS: G / AXLE: 17

3rd line: MAX GVW LBS: 05000 / CERT NET HP: 172 / RPM: 4000 / DSO: 22

Welcome to FTE

F10 = F100 2WD

Y = 352 2V

N = Norfolk VA Assembly Plant.

789834 = 1966 .. assembled December 1965.

115" Wheelbase.

J = Rangoon Red.

F100 2WD .. 5,000 lbs. GVWR.

E81: E = Red Crush Vinyl & Red Cody Pattern Woven Plastic / 81 = 81B Custom Cab.

G = MX Cruise-O-Matic.

17 = Ford 9" Rear Axle / 3.25-1 / No Limited Slip / 3,300 lbs. Rear Axle Capacity.

5,000 lbs. Gross Vehicle Weight Rating.

172 net HP @ 4,000 RPM

22 = Charlotte NC Ford District Sales Office, where the original selling dealer ordered the truck from.