3.15 rear diff swap woes

[euro23]

I read a couple of articles and was under assumption that this swap would be direct bolt on. I have a 1997 540/6, and installed the 3.15 rear diff from a 2001 automatic 540 however the rear axles are different. Bigger than what I have, now I have a question if I get automatic 540 axles will they fit my 1997 hubs? any help is appreciated

[StRaNgEdAyS]

I read a couple of articles and was under assumption that this swap would be direct bolt on. I have a 1997 540/6, and installed the 3.15 rear diff from a 2001 automatic 540 however the rear axles are different. Bigger than what I have, now I have a question if I get automatic 540 axles will they fit my 1997 hubs? any help is appreciated

They will fit.
The nut on the wheel hub is a killer though.

Absinthe makes the tart grow fonder

[geargrinder]

Yep.

The 540 autos, which got the short diff, also got fatter axles somewhere inbetween the standard axles and the M5 axles (or "halfshalfs" as they are often called in USA)

While the fatter axles might be appealing, your easy route is to just swap the flanges off your old diff. Would put you back in business in almost no time. As Stranger says, swapping axles is a whole extra project to take on, a bit more work than one would hope/expect.

[euro23]

ahh ok thanks for the info, yes those don't look fun luckily my car is pretty rust free

[geargrinder]

Yeah. It's not like the stock 540's are known whatsoever for blowing axles - they seem to be more than adequate... of course 'upgrades' are always evilly tempting to car dudes but chances of destroying an axle because it's not stout enough are extremely low on a standard car.

[JimLev]

Yep.

The 540 autos, which got the short diff, also got fatter axles somewhere inbetween the standard axles and the M5 axles (or "halfshalfs" as they are often called in USA)

While the fatter axles might be appealing, your easy route is to just swap the flanges off your old diff. Would put you back in business in almost no time. As Stranger says, swapping axles is a whole extra project to take on, a bit more work than one would hope/expect.

His old 97 flanges (I'm 99% sure) won't lock into the M5 LSD. The locking rings on the spline stubs are in a different location.
I can post some pics of them if needed.
Pretty sure I have a set of M5 flanges kicking around here if you want some measurements off them.

Getting the castle nut off the end of the half shaft is a piece of cake compared to getting the splined end of the half shaft out of the bearing assy.

[speed7]

Yeah that is true for the M5 diff.. but he's using an auto 540 diff. Which should work.

[geargrinder]

Yep, he's not an M5 swap Jim.

[StRaNgEdAyS]

The flanges will just pop out pretty easily with the help of a pry bar, and a short sharp tap with a dead blow hammer pops them back into place

Absinthe makes the tart grow fonder

[JimLev]

Yeah that is true for the M5 diff.. but he's using an auto 540 diff. Which should work.

Oops, missed that important part...