Panther Differential Equation

"Rusty Vandura - www.tinyurl.com/keepoppo" (rustyvandura) 01/13/2020 at 12:39 • Filed to: None

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The 3.55 LSD was an option for the P71. (Mine is 3.27 open...) Would this part interchange with the gear set in my existing differential? Wouldn’t be rocket science to swap them out, would it?

HammerheadFistpunch > Rusty Vandura - www.tinyurl.com/keepoppo 01/13/2020 at 12:42

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So you want to keep the LSD  carrier but use the 3.27 gears?

Rusty Vandura - www.tinyurl.com/keepoppo > HammerheadFistpunch 01/13/2020 at 12:48

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No. I want the 3.55 gears and LSD. Current gears are too tall.

Rusty Vandura - www.tinyurl.com/keepoppo > HammerheadFistpunch 01/13/2020 at 12:48

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I don’t have any experience with this beyond one-legged burnouts, which are pathetic.

RamblinRover Luxury-Yacht > Rusty Vandura - www.tinyurl.com/keepoppo 01/13/2020 at 12:51

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I believe that would come down to whether the spline count was correct. I would assume both the Mustang and the P71 have the heavier duty axle shafts, but I don’t know that for a fact.

Dana/etc. actually has a weird thing where nominally the same rear axle case would actually be a different casting on the pumpkin sometimes for different ranges of gearing, but I don’t think it’d be operative here. Not knowing 8.8s very well, swapping the new set in might include the use of shims or other specialty parts as well as tooling, but that’s a question to be resolved by research. Where it gets tricky in general is that a lower ring and pinion set are dimensionally different any time that, say, the ring isn’t made thicker to compensate for a smaller pinion or the pinion isn’t further back on the shaft - so there has to be some adjustment and alteration of the “known good” configuration to make it all work right.

I should note that even moderate “normal use” can end up with a set of clutches being worn out - I rebuilt a Jag rear diff that had maybe 100k on it, and the clutches were nearly completely shot despite still holding. Since the rebuild parts could easily run you some money, the most attractive part of this as a set is if you want the 3.55 gears - not as a cheap way just to get LSD.

Rusty Vandura - www.tinyurl.com/keepoppo > RamblinRover Luxury-Yacht 01/13/2020 at 12:55

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This is helpful. The 3.55 is definitely part of the objective. I’ve got a gear shop nearby I will also consult. I think my 2010 has 31 splines. I think everything after a certain year is 31 splines, from what I’ve read. I was hoping someone would say, “Oh yeah, I did that and it was easy .”

HammerheadFistpunch > Rusty Vandura - www.tinyurl.com/keepoppo 01/13/2020 at 12:56

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W ell, I think you would need to replace your pinion as well, which means a full diff setup.  I don’t mess with those.

HammerheadFistpunch > RamblinRover Luxury-Yacht 01/13/2020 at 12:57

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I hear clutch based are rebuild every 60k.  Clutches are dumb, torsens are the biz.

diplodicus forgot his password > RamblinRover Luxury-Yacht 01/13/2020 at 12:57

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Sounds like you’re dead on with the shims and tools

https://performanceparts.ford.com/download/instructionsheets/FORDINSTSHTM-4209-8.PDF

jimz > Rusty Vandura - www.tinyurl.com/keepoppo 01/13/2020 at 13:02

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you need to know what you’re doing when changing those things; not only verifying compatibility but knowing how to get the gear spacing right.  get it wrong and the thing will be trashed in short order.

Rusty Vandura - www.tinyurl.com/keepoppo > HammerheadFistpunch 01/13/2020 at 13:03

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There’s a reputable gear shop in town. 

Rusty Vandura - www.tinyurl.com/keepoppo > jimz 01/13/2020 at 13:04

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I figured something like that would be the case, but I thought I’d ask. As I told HHFP, I was hoping someone would say, “Oh yeah, I did that and it was cakey.” Wishful thinking on a Monday morning...

HammerheadFistpunch > Rusty Vandura - www.tinyurl.com/keepoppo 01/13/2020 at 13:05

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That would be my first stop.  

RamblinRover Luxury-Yacht > HammerheadFistpunch 01/13/2020 at 13:08

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I kind of agree, but in a lot of cases clutch style are the only thing going, and they’re easy to build into an existing open setup*, and they work, so...

Also, I don’t know for a fact, but I suspect most Torsens in addition to being spendier (all those helical gears ain’t cheap!) have higher moment of inertia than a simple clutch setup, if not much more than a more complicated PowrLok style with external spider shaft cams.

*Early Ford 9" limited slip is particularly lazy: I think it uses the majority of the same gear carrier, and has just one set of clutches, with the original style of spiders.

jimz > Rusty Vandura - www.tinyurl.com/keepoppo 01/13/2020 at 13:09

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by the way, *snerk* at the title.  We (not so) affectionately called that class “diff-e-screw.” 

HammerheadFistpunch > RamblinRover Luxury-Yacht 01/13/2020 at 13:10

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if you are using a drop out diff where you dont have to re-shim each time I wouldn’t mind.  For me and my 3rd member diffs...hell nay.  

CalzoneGolem > Rusty Vandura - www.tinyurl.com/keepoppo 01/13/2020 at 13:15

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You could go cheap and dirty with a mini spool.

https://www.rockauto.com/en/catalog/ford,2009,crown+victoria,4.6l+v8,1443415,drivetrain,differential+mini+spool,574

RamblinRover Luxury-Yacht > HammerheadFistpunch 01/13/2020 at 13:18

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The XJS unit I’m sticking in the Ranchero has no casing to drop out of, requires unbolting at the top, and disassembly of the rear axles *from* it, because the rear axles are suspension members. (borrowed pic):

I may pick up a spare and rebuild it to do swaps with, but it’s... more involved to pull than most, if not to rebuild.

With the Rovers, the rear pumpkin is easy to swap (six bolts to each axle shaft, ~12 bolts on the pumpkin, out of the case), but less so on the front since you have to unbuckle the whole swivel housing each side. Same number of bolts, just way sketchier and requiring blocking and/or jack stands, wheels off...

Tristan > Rusty Vandura - www.tinyurl.com/keepoppo 01/13/2020 at 14:03

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Wait, you have a P71? I’ve got some catching up to do...

The best bet would be to find a junkyard 3.55L rear diff. You can’t just swap the R&P without setting up the gears for the different housing. At that point, you should just pay a little more and ge t some 4.10s... It’s a heavy car and the 4.6 isn’t known for low-end grunt. Then J-mod the 4 R70W. It would increase the fun factor tremendously.

Gone > Rusty Vandura - www.tinyurl.com/keepoppo 01/13/2020 at 14:04

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Mustang 8.8s from 2005+ (S197) are all 31 spline. The older Mustang 8.8s (Fox, SN95) are 28 spline. T he Fox and SN95 have different length axle shafts because of the drum to disc change. Not sure where the Panther lies for splines, but would assume if they were 28 as the Mustang (2004 down) then they also changed to 31 in 2005. As long as the carrier spline count is right, any diff should drop in (Trac -Lok , Torsen, etc).

Torsens ( specifically the T2) are great for auto-x/open track, but are a bit more expensive . The clutch diff/Trac-Loc  should be fine for most situations. Whenever you have to get it rebuilt (after a bunch of miles), be sure they swap do the ol’ clutch swap and make it CSCSCSC instead of CSSCSSC. Seemed to make an improvement on my Mustang back in the day.

Doing the gear change/diff swap isn’t hard, but you’ll need tools and a lot of time. Also, a lift makes it a lot easier. Sometimes it’s worth the money to take it somewhere...

Rusty Vandura - www.tinyurl.com/keepoppo > CalzoneGolem 01/13/2020 at 15:49

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Does that just keep both sides locked together full time?

CalzoneGolem > Rusty Vandura - www.tinyurl.com/keepoppo 01/13/2020 at 15:50

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Yes.

Rusty Vandura - www.tinyurl.com/keepoppo > jimz 01/13/2020 at 15:51

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I could not recognize a differential equation now if I saw one, but I didn’t mind the class too much.

Rusty Vandura - www.tinyurl.com/keepoppo > Tristan 01/13/2020 at 15:53

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I’d have to learn whether the ECU has a setting for 4.10. I fear that would be pretty short final gearing.

Talk to me more about this J-mod thing... are you talking about shift kit kind of thing?

Personally, I’m not a fan of the P71, but yes, now I have one because reasons. 

Rusty Vandura - www.tinyurl.com/keepoppo > Gone 01/13/2020 at 15:57

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I have more research to do. There’s a first-rate gear shop in town. I have an ECU-related challenge right now that I have to resolve in order to get smogged. I’m not at all opposed to tackling it myself, but like you said, might make more sense just to let the pro do it. He’d leave the axle in situ and work on it under the car.

Rusty Vandura - www.tinyurl.com/keepoppo > CalzoneGolem 01/13/2020 at 15:58

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Be a lot of stress on the axle shafts, wouldn’t it? But I like cheap and dirty...

Have you ever used one?

CalzoneGolem > Rusty Vandura - www.tinyurl.com/keepoppo 01/13/2020 at 16:00

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I’ve nev er used one but I’ve heard that they’re pretty rowdy and don’t like turning.

Rusty Vandura - www.tinyurl.com/keepoppo > CalzoneGolem 01/13/2020 at 17:18

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I’d expect something to break. Like an axle.