Differential Equation

"Rusty Vandura - www.tinyurl.com/keepoppo" (rustyvandura) 01/30/2020 at 13:16 • Filed to: None

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Would a 1998 F-150 have a 31-spline, 8.8-inch rear end?

RamblinRover Luxury-Yacht > Rusty Vandura - www.tinyurl.com/keepoppo 01/30/2020 at 13:27

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Assuming that the tag that is supposed to be on one of the cover bolts is missing, can you see the end of one of the spider gears easily enough to count? As even Rangers with 8.8s ended up with 31 spline in some applications, I’d assume an F-150 that new would have 31, but I have yet to find a chart with certainty.

Discerning > Rusty Vandura - www.tinyurl.com/keepoppo 01/30/2020 at 13:29

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I think all of the f150's with anything but the 5.4 had the 8.8 for that gen and I’m fairly certain they were all 31 spline.

E asiest way to check is to just get under the truck though.

RamblinRover Luxury-Yacht > Rusty Vandura - www.tinyurl.com/keepoppo 01/30/2020 at 13:37

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Update: hardly authoritative, but I found a mention on the f150online forum stating that all F150s with 8.8 are 31 spline. Although, granted, in the same thread someone stated the falsehood that only Mustangs got the 28 spline (and was corrected).

Rusty Vandura - www.tinyurl.com/keepoppo > RamblinRover Luxury-Yacht 01/30/2020 at 13:45

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Thanks. I’m waiting for the VIN... The VIN on the Vic told me what rear end I have and I’m waiting on the VIN from the F-150 I discovered on FB Marketplace...

Rusty Vandura - www.tinyurl.com/keepoppo > Discerning 01/30/2020 at 13:46

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Yes. The truck is listed on FB Marketplace and I’m waiting for the VIN from the seller. Hopefully I can learn from the VIN and the rear end is 3.55 Posi...

Gone > Rusty Vandura - www.tinyurl.com/keepoppo 01/30/2020 at 13:58

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AFAIK all F-150s w/8.8s are 31 spline, so anything 83(?) up. They made the 9in until 85-86 IIRC, but the 8.8 started showing up a few years earlier. Then the 97+ style brought the 9.75 mini-Sterling with the 5.4   or high GVWR . Also the 97-99 F-150 looking F-250LD had 7 lugs and a semi-float Sterling 10.5.

Aremmes > Rusty Vandura - www.tinyurl.com/keepoppo 01/30/2020 at 14:29

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I t was my understanding that there would be no calculus.

Rusty Vandura - www.tinyurl.com/keepoppo > Gone 01/30/2020 at 14:41

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So, I’ll read this as a yes , though I have some trouble following it. I’m lazy: throw my questions out to Oppo and enthusiasts  are usually eager to fill me in.

Rusty Vandura - www.tinyurl.com/keepoppo > Aremmes 01/30/2020 at 15:04

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I did not realize that Differential Equations was  Calculus...

Sammyno55 > Aremmes 01/30/2020 at 15:05

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I thought I was going to get to maths. I haven’t used my dif- eq training since college. And the only time I've balanced a chemistry equation was watching Breaking Bad. 

nerd_racing > Rusty Vandura - www.tinyurl.com/keepoppo 01/30/2020 at 15:50

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It’s applied calculus.  

Rusty Vandura - www.tinyurl.com/keepoppo > RamblinRover Luxury-Yacht 01/31/2020 at 12:17

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So I’ve got a wrecking yard telling me they have a 3.55 locker, 8.8 inch, code H9 . Would this be the correct part?

RamblinRover Luxury-Yacht > Rusty Vandura - www.tinyurl.com/keepoppo 01/31/2020 at 12:34

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From what I’m seeing, that is an 8.8 limited slip 3.55 truck diff (aka 31 spline), yes. So, suitable for use whole on an appropriate year truck or for migrating parts over to the Vic, or should be. It is possible the existing Vic axle shafts would be 31 spline already, but if not and if the shafts out of the truck axle are different length, you should be able to get them pretty readily.

The casing is, I think, a different track width than on the Vic, so swapping over those axle shafts probably wouldn’t work - *probably*.