Differential Swap?
 

Hey Dudes. I've been reading this forum for quite some time now researching my future X5. You guys are great! I'm torn and go back and forth on which engine and transmission combo to go with. I've owed 3 BMW's (2 e30 318i's and an e36 325i with 320,000 miles and counting!) I have had bad luck with auto transmissions. After my 325i ate up two autos, I decided to rip the boat anchor out and put in a manual 5-speed. Waaay better. I am not abusive and am very meticulous with maintenance and I do all of my own. I know there are a few that will disagree with my statement but I really think these auto trannys are weak sauce and from what I've gathered, they haven't gotten much better. So I'm leaning toward a 3.0 with a manual 5 speed. The '04 and newer is a tad out of my price range. (Still in school, getting ready for med school.)I've read that they turn some high RPM's at cruising speed. I got to thinking, are the 4.4's (3.64:1 ratio) differential compatible with 3.0's (4.10) differential? If so you could swap both front and rear differentials, you gain lower cruising RPM and perhaps an increase in fuel economy. 71mph vs 63 mph @ 3000 RPM for one example. What do you think? Anyone know? Would this make it too lethargic? Thanks for any input in advance.

Seems like a lot of trouble to drop the engine rpm from 3000 to 2650.

If you liked your 318 and 325, you should be happy with the power of the 3.0 in the X5 (I had a 318i once as well, and an X5 3.0). Motordavid has an X5 with a manual, and can comment on his experiences on long highway trips. Yes, it revs a little high, but changing two differentials over just sounds like more trouble than it is worth.

Wouldn't it be easier to figure out if a six speed transmission would fit into it, and still work with the standard transfer case?

For background info, here is a similar thread with pricing for the swap: http://www.xoutpost.com/bmw-sav-foru...ive-ratio.html

Thanks Jeff.
I appreciate the heads up on the other thread. I'm will look into a six speed conversion and share what I find out. I heard its hard to find the six speed but I'm on it. I have sourced the diffs for under 800 shipped which is half of what was quoted, but I agree the six speed would be the cats meow. :p:

I'm pretty sure the 6sp 'box is longer, so at the least you'll need modified propshafts and you might run into problems with clearance between transfer box and chassis. I'm just guessing there though.

I'll admit the idea had previously crossed my mind to fit a 6sp manual and ditch the transfer box etc. to convert to RWD...

Me too. I was thinking that if the transfer case ever goes, just swap it over to RWD. Leave the front diff and half shafts unconnected.

The rear wheel drive only conversion would be awesome. But if you live in an area like northern Utah where you see snow 5 months out of the year, the awd system comes in handy.

Not sure what sensors are involved in disabling the the front drive train but can be done. The awd system most likely looks for a certain set of conditions so it would be hard to trick the ecu as I did on my e36 manual conversion. The automatic trans ecu is still intact and the vehicle operates perfectly like factory with cruise control and all. In the case of the X5, a reflash of the ecu would be needed (540i for example). I may make a phone call and talk with Mr. Conforti himself about that. (shark injector and monotronics expert.) You would see improved economy without the parasitic drag of the front drive line.

As far as the 6 speed conversion, looks like I will need a few specific parts. Trans mount brace, the correct section of drive shaft going to the rear as well as the shaft going from the transfer case to the front diff. due to increased length. As far as I can tell there were no changes made to the underside of the chassie of the e53 post facelift. So no worries about clearance fitment. I'll post as I learn more. Thanks for the replies.

Oh and just a side note, my brother who is an engineer for Hendrix Motorsports back in NC is on board with my project E53 X5 as it unfolds. He has some killer ideas for down the road......:thumbup:

If you're going into uncharted territory, here's a few links that *might* assist.

Performance Final Drives
Performance Gearing - are you ready for the ride of your life?
BMW X5 - NV125 : Automatic, Standard Transmission and Transfer Case Rebuild Kits, Cobra Transmission Parts 1-800-293-1848
NV125 Transfer Case, BMW X5 Parts
diffsonline.com - Custom Geared BMW LSD Differentials
Wavetrac® Differential - Application List
Sideshafts - Passenger Cars - GKN Aftermarkets & Services

If you purchase an E70 3.0Si, I wouldn't be opposed to trading differentials. :)

Best of luck in your search man!

It's a while since I've driven a 3.0i with five-speed manual but I remember the gearing being pretty sweet. The higher final-drive ratios may not make for better fuel economy and you will find that you'll be changing gear more often in hilly country or give-and-take driving. The factory goes to great lengths to optimise the gearing for each engine. If you can't afford the update 3.0i with the six-speed manual I'd just stick with the five-speeder as is. I think you could go to a fair bit of effort in changing the diffs and end up with something that's inferior. That my two bob's worth anyway...

Thanks for everyones input and the links posted. Its good to bounce different ideas off everyones head. You all offer good perspectives and opinions which I value.

After some hunting and pricing on a six speed trans swap I've decided for now to stick with the 5 speed manual and see how I like it. The cost involved doesn't make sense. I could step into an '04 and newer which I might just do. (3-4 grand on the high end to do the swap) I'm still crunching numbers and I have an independent dealer looking for me at auctions. He keeps tempting me with some nice 4.4's and I love the V8 power. But a lot of these at my target initial price range have just over 100k miles and the auto trans at that mileage could be iffy, but I guess its hit and miss with these to be fair. Let me know what you think.:dunno: