Keep old differential?

[Reasoned1]

Hi, folks.

I'm planning on replacing the OE rear differential on my 2004 ZHP with limited slip. I'm leaning toward MFactory, but very attracted to WaveTrac, and Quaife is still in the running. I'm willing to buy now, but my car is in storage, so I won't be able to get it to the shop to do the swap until Spring (I do some work myself--shocks, springs, accessory equipment, etc.--but want somebody with experience doing the diff). Unfortunately though, the vendors want the old diff back in 30 days, so here's my question: Is there any reason to keep my old differential and forego the $400-$500 core charge? I'm thinking I might want it in the event of a problem or, if hell freezes over, I might decide to sell to a buyer wanting the original equipment. Please advise...

[NoVAphotog]

Hi, folks.

I'm planning on replacing the OE rear differential on my 2004 ZHP with limited slip. I'm leaning toward MFactory, but very attracted to WaveTrac, and Quaife is still in the running. I'm willing to buy now, but my car is in storage, so I won't be able to get it to the shop to do the swap until Spring (I do some work myself--shocks, springs, accessory equipment, etc.--but want somebody with experience doing the diff). Unfortunately though, the vendors want the old diff back in 30 days, so here's my question: Is there any reason to keep my old differential and forego the $400-$500 core charge? I'm thinking I might want it in the event of a problem or, if hell freezes over, I might decide to sell to a buyer wanting the original equipment. Please advise...

I bought a 3.46 core off of E46fanatics and had the seller ship it to Mfactory. Avoided any core charge and down time for the car. Since your car is in storage you have time to shop around for a core that someone else is selling and use that and then just keep your old diff when the new one arrives like I did. I highly recommend upgrading the gearing to 3.38/46 unless you commute on the highway or go on a LOT of road trips. And even then it's not that big of a deal for the added punchiness around town.

[Reasoned1]

3.46 is what I was thinking since the car is for thrills not long hauls.

I would love to hear more about your upgrade. I'm in central Vermont, so not alot of BMW shops around, but I have a great garage I go to and they're all for attempting the swap. Shouldn't be a big deal, right? Pull the old one off the axles and drive shaft and slap the new one in, right? Please tell me it's that easy... My 2004 xi has 3.46 (among a few other things), and it feels punchier lower down but, of course, it peters out higher up whereas the ZHP just keeps building.

Just noticed you're in Arlington, VA--my son lives in Arlington, and he facilitated the purchase of my ZHP at Avazi Auto Group in Gaithersburg, MD.

[slater]

3.46 is great, and LSD is awesome in the winter - really, a safer option too. more grip, is, well, more grip!

where in central VT? i grew up in rochester (right on rt 100).

[wertyu78]

You might want to also consider Diffsonline. Yes, they aren't the most affordable option, but arguably, they are the best. Hands down the best mod I've done to the car, and Diffsonline made it painless. I had gone through two OS Gikens (both exploded) before going going with my Diffsonline unit.

[Sockethead]

3.46 is what I was thinking since the car is for thrills not long hauls.

I would love to hear more about your upgrade. I'm in central Vermont, so not alot of BMW shops around, but I have a great garage I go to and they're all for attempting the swap. Shouldn't be a big deal, right? Pull the old one off the axles and drive shaft and slap the new one in, right? Please tell me it's that easy... My 2004 xi has 3.46 (among a few other things), and it feels punchier lower down but, of course, it peters out higher up whereas the ZHP just keeps building.

Just noticed you're in Arlington, VA--my son lives in Arlington, and he facilitated the purchase of my ZHP at Avazi Auto Group in Gaithersburg, MD.

Yes it is that easy. I can do it in two hours start to finish laying on my garage floor. There are a few tricks to it but any good mechanic will be able to figure it out. I would have the mechanic check the rear differential bushing while they are in there. The rubber has a habit of splitting/cracking. Sometimes you can see it without removing the diff if it's bad enough but sometimes you can only see/test it with the diff out like we did with Daniel's car.
If your car is for thrills, then definitely go for the 3.46. There are only two performance upgrades that give you a real performance increase without going into the engine internals: Differential gearing change and forced induction.
Daniel gives good advise about getting a donor diff. I think that may be your best bet in your situation. You can always sell your original diff if you don't want it laying aound.

[Reasoned1]

I'm in Barre, and there are some very nice roads to tool around on up here--including Route 100 (to be avoided during peak traffic hours--especially during leaf-peeping season).

I fantasize about getting a supercharger, but it'd be REALLY hard for me to justify the expense, and it seems to me that going that route is opening a can of worms for minimal performance impact at low RPM--hardly worth it when I have as much fun as I do already with the car. Plus, I can do A LOT of maintenance and mods with the money it'd take to install a supercharger.

Diffsonline has an unbeatable reputation, but I am mighty attracted to that MFactory diff for $1,800 (including $500 core charge).

On further thought, why don't I just pull my existing diff, and send that to MFactory, since I'm not driving the car for a while? I might even get the cojones to put the rebuilt one back in...

Just watched the DIY for this by "TH"... It actually looks pretty straight forward--barring any broken or stripped screws.

[MFactory]

If your car is in storage for Winter, then best bet is to send us your core in advance and we can rebuild it for you.

It only takes us a couple of days to rebuild and ship it back out to you

[az3579]

Honestly, a factory diff isn't worth the core charge, so you might as well send in your old one.
If you really need to, I'm sure you can source a stock open diff from a junk car for peanuts.

[slater]

I'm in Barre, and there are some very nice roads to tool around on up here--including Route 100 (to be avoided during peak traffic hours--especially during leaf-peeping season).

I fantasize about getting a supercharger, but it'd be REALLY hard for me to justify the expense, and it seems to me that going that route is opening a can of worms for minimal performance impact at low RPM--hardly worth it when I have as much fun as I do already with the car. Plus, I can do A LOT of maintenance and mods with the money it'd take to install a supercharger.

Diffsonline has an unbeatable reputation, but I am mighty attracted to that MFactory diff for $1,800 (including $500 core charge).

On further thought, why don't I just pull my existing diff, and send that to MFactory, since I'm not driving the car for a while? I might even get the cojones to put the rebuilt one back in...

Just watched the DIY for this by "TH"... It actually looks pretty straight forward--barring any broken or stripped screws.

barre - awesome. yep, lots of good roads near there.

i agree about the supercharger. the power is tempting, but it is a LOT of money that could be spent elsewhere (like an LSD, which i personally feel is a better investment).

are you up for pulling the diff yourself? just because it would have to sit at your mechanics' place until you got the new diff back. like rob said, it's a pretty easy job.