Swap a 3:08 rear diff of a crown vic for my 3:27?

[NickStorey]

Hey guys,

I have an 05 X with the 4.6 v8, not sure if this has been done before, but my rear diff needs to be replaced, as per the usual on the X, I have found one for a sick deal, its less than a hundred for parts, but its off a crown vic. Its still an 8.8, complete assembly, but its a3:08 gear ration over the 3.27.

My Question is, since both run an 8.8 with the 4.6 v8(thats what Im running) could it be used? are they not the same part just with different gearing? if so any benefits or downfalls?


Sorry to ask so much in one post, ANY help would be useful,


Thanks in advance

 

[boominXplorer]

Are you sure you have 3.27s? I didn't think they had less than 3.55s in any 02+. I would replace with the same unit especially if your 4x4

 

[NickStorey]

from what I found online, a replacement for my truck shows 27 splines, would that not make it a 3.27?

 

[2Trux]

The splines on the axle shaft have nothing to do with the gear ratio.

 

[imp]

Don't the Crown Vics/Mercs have a solid rear axle, as opposed to independent suspension in Explorer?

If so, absolutely impossible to put Vic rear center section in Explorer. imp

 

[NickStorey]

Thanks for the quick answers, but you guys are right about the Vic's solid rear axle. The 3.08 was a nice thought but not possible.... Fack

 

[colintrax]

You wouldn't want 3:08 anyways. Look for something closer to 3:55 ~3:73

 

[zpn_by]

hmmmmm....

0 - if it's a 4x4 truck, I wouldn't bother looking into changing the gears. you would need two sets anyway, and there may be other issues with the robot nanny sitting in the transfer case - it might get angry with you. If you're RWD, read on....

1 - 4.6L trucks came with 3.55 gears UNLESS they had the class III/IV hitch (2" receiver) and the trailer package, in which case they had 3.73 gears. This was to get better torque when taking off with a load. It will also hurt highway mileage, but you'll get into 5th gear in-town.

2 - based on my experience with mustangs and the 8.8" rear in that car, the pumpkin could be changed from the factory 2.73 pinion and ring gear all the way up to 4.10 (or higher too IIRC) while still maintaining the factory axle housing and pumpkin. Shims would sometimes be necessary. There is every reason to assume that the pinion and ring gear are similarly interchangeable on ANY Ford with the 8.8" ring gear/axle. This means that if you want to take your truck from having a 3.55 gearset to a 3.08 gearset, you could theoretically do it. I don't see a reason why not, however you would want to measure the diameter of the shaft of the pinion, as well as the bolt holes for the ring gears, to make sure they are identical. Really, any performance shop should be able to give you a definite answer on this. The critical part is the size of the ring gear and the similarity of the connecting parts. This should not be affected by having a solid axle or an IRS.

Hope this helps! FYI, taking an 8.8" Fox 5.0 mustang and swapping the 3.08 gears to 3.55 is still a very popular and common upgrade, so it should be sufficient for our trucks too.

***** BIG NOTE *****
make sure you can adjust the spedometer drive - when changing the axle ratio, your spedometer would be WAY off, meaning you would either be driving too slow, or getting too many tickets. I think with the downsize, you would be travelling much faster than your speedo would indicate. This may need to be done electronically with a tune, or through the dealer's IDS interface.