Differential swap xdrive50i to xdrive35d

theeld · 11-28-2018, 07:52 AM

On a whim I looked into other differentials for the e70 family. It appears the xdrive50i has 3.15 ratios as opposed to the xdrive35d 3.64 ratio. Anyone speculate as to whether these would bolt up onto the diesel? Would probably drop about 325 rpm on the diesel at cruising speed. Would put 70 mph at 1730 rpm, 80mph at 2030 rpm, which I think would make a nice difference, As I firmly believe the x35d is geared a bit too low, would probably make a significant difference in highway MPG.

Garnered from other posters:

"The 35i also got 3.15 w/ the 8 speed but the axle shafts are smaller so the dif is different. 50i and 35d use the same bigger axle shafts. F15 diesels w/ 8 speeds also use the 50i diff"

"I spent some time researching this to find the info above on the axle shafts. Here is some other info on the driveshaft part numbers. 35d, 50i, 50d, and 35i all have different rear drive shaft lengths. (1410mm, 1427, 1430 and 1445). However the front driveshafts are all the same length at 709 mm. I am unsure if the rear length difference is related to different transfer cases (ATC700 w/ 6 speed vs 45L). All rear dif after 6/11 appear to use the same locking number between the driveshaft and rear diff."

Naz24 · 11-28-2018, 09:51 AM

Diesel = low end torque. That's why. not sure it would be efficient to do that on the 50i

mitch808 · 11-28-2018, 01:55 PM

On other cars with AWD, that folks swap gearing, often the front rear ratios must match, other wise, you need to change the transfer ratio in the center gearbox. Not to mention, if there is any computer trickery that must be done... This can't be an easy swap on a car that relies to heavily on the ECU.

theeld · 11-28-2018, 03:02 PM

Quote:

Originally Posted by Naz24

Diesel = low end torque. That's why. not sure it would be efficient to do that on the 50i

Im proposing a swap from the 50i to the 35d, hence to take advantage of the low range torque.

135iTime · 11-28-2018, 06:15 PM

I would assume you should be fine if you swapped both the front and rear differential. If those ratios are the same the rest shouldn't matter. This is fairly interesting to me as well since I do a lot of freeway driving and it looks like used diffs are fairly cheap.

Juno01 · 03-26-2019, 03:35 PM

Has anyone decided to do this yet? I do a fair amount of interstate travel as well and I think the 3.15 would definitely improve fuel economy at 70+mph.

Performance around town worries me. It seems like the transmission doesn't kickdown as quick as I would like so even now and the car feels like a dog sometimes. It would be a lot of work to do the swap and have to revert back.

smass · 03-27-2019, 07:17 AM

Quote:

Originally Posted by Juno01

Has anyone decided to do this yet? I do a fair amount of interstate travel as well and I think the 3.15 would definitely improve fuel economy at 70+mph.

Performance around town worries me. It seems like the transmission doesn't kickdown as quick as I would like so even now and the car feels like a dog sometimes. It would be a lot of work to do the swap and have to revert back.

I was thinking about doing it but lost interest because I could not confirm the rear dif would be an exact fit. There are a bunch of different rear drive shaft lengths available based on which transmission, transfer case and rear end you have. Ultimately I want to do a full 8 speed swap w/ matching drive train. LCI 35d in Europe had that transmission. 50i parts cars should be getting cheap in the future.

Juno01 · 03-27-2019, 12:27 PM

Quote:

Originally Posted by smassey321

I was thinking about doing it but lost interest because I could not confirm the rear dif would be an exact fit. There are a bunch of different rear drive shaft lengths available based on which transmission, transfer case and rear end you have. Ultimately I want to do a full 8 speed swap w/ matching drive train. LCI 35d in Europe had that transmission. 50i parts cars should be getting cheap in the future.

From the limited research that I did I believe that the 50i rear is a direct swap. The housing on the 35d and 50i diffs have identical cast markings and look the same.
While swapping to a 8hp does sound like the perfect solution I think it could be very difficult to code it to the CAS and DDE. I know some folks that do this type of coding and they are very talented so I could wrong.

I'm going to continue to look into the diff swap, $500 or less for both front and rear isn't much of an investment imo.

Spyro235 · 03-28-2019, 12:00 PM

Quote:

Originally Posted by Juno01

From the limited research that I did I believe that the 50i rear is a direct swap. The housing on the 35d and 50i diffs have identical cast markings and look the same.
While swapping to a 8hp does sound like the perfect solution I think it could be very difficult to code it to the CAS and DDE. I know some folks that do this type of coding and they are very talented so I could wrong.

I'm going to continue to look into the diff swap, $500 or less for both front and rear isn't much of an investment imo.

Please keep us updated. I get great mileage at 70mph(currently on a commuting tank, have 31.3, 300 miles into the tank), because it sits right at 2k rpm I think. Starts to drop off pretty quick over 2k rpm, and the motor certainly doesn't need to rev at 2300 rpm just to turn 80mph. I am wondering about trans tuning though- how would this effect the trans shift points? Does it use RPM shift points, RPM+load taken into account, or does it also account for speed? If it accounts for speed, I see it might run into issues where it's short shifting instead of letting it run, because it's not prepared for the extra load/ lower RPMs.

This sounds like a WONDERFUL mod, and honestly, if someone reported that they did it and it worked, I'd start looking for the parts to do it myself immediately. I can't be the experiment on this one, as I sold my second car to daily/ tow with the D. I run mostly highway mileage, and the only con I can see to this is increased stress while towing, but with such an abundance of torque, I don't think it'd be an issue anyway.

rodnex · 04-01-2019, 03:19 PM

I can confirm the 3.0i Diff fits on the Diesel.
Don't know about the V8, if they kept the same housing

Juno01 · 04-01-2019, 04:29 PM

Quote:

Originally Posted by rodnex

I can confirm the 3.0i Diff fits on the Diesel.
Don't know about the V8, if they kept the same housing

Are you referring to the front diff? According to the OP the 50i and X35d have thicker axle shafts, presumably for the rear. From my research i believe the diesel and v8 have identical rear diff housings.

rodnex · 04-01-2019, 05:24 PM

I've swapped both diffs front & rear.
I've got super short 4,44 gears now on my 400bhp Diesel.

Rear diffs are actually all the same, small 185mm model.
Even though the shafts differ, but the diffs are same. 3.0i fits to 3.0d / 3.0d fits to 35d etc

Front diffs... I did my google image & ETK research and was pretty sure the 3.0i Diff will fit.
And yes, it did!

If the V8 housing won't fit the Diesel oil pan... You can still swap the shaft & pinion into the old housing.

smass · 04-01-2019, 09:31 PM

Quote:

Originally Posted by rodnex

I've swapped both diffs front & rear.
I've got super short 4,44 gears now on my 400bhp Diesel.

Rear diffs are actually all the same, small 185mm model.
Even though the shafts differ, but the diffs are same. 3.0i fits to 3.0d / 3.0d fits to 35d etc

Front diffs... I did my google image & ETK research and was pretty sure the 3.0i Diff will fit.
And yes, it did!

If the V8 housing won't fit the Diesel oil pan... You can still swap the shaft & pinion into the old housing.

Was coding required to correct speedometer? Were you able to use your original drive shafts?

Thanks

Juno01 · 04-02-2019, 12:26 PM

Quote:

Originally Posted by rodnex

I've swapped both diffs front & rear.
I've got super short 4,44 gears now on my 400bhp Diesel.

Wow, 4.44 final is crazy low lol! Do you have the zf8hp70?

Quote:

Originally Posted by rodnex

Rear diffs are actually all the same, small 185mm model.
Even though the shafts differ, but the diffs are same. 3.0i fits to 3.0d / 3.0d fits to 35d etc

I don't understand. How can I use a rear diff from a vehicle that has smaller axles? Output flanges are the same? 185mm refers to what exactly?
When I look at images of the the v8 and the x35d diffs on ebay i'm not seeing any difference in size or shape. Images of the 3.0i definitely don't look like the v8 or x35d. Not saying you're wrong just something is not adding up here. Don't want to make a purchase and have it be the one that doesn't work.

Quote:

Originally Posted by rodnex

Front diffs... I did my google image & ETK research and was pretty sure the 3.0i Diff will fit.
And yes, it did!

Yeah I was thinking the same, good to know now for sure.

Quote:

Originally Posted by rodnex

If the V8 housing won't fit the Diesel oil pan... You can still swap the shaft & pinion into the old housing.

But then there's preload, crush washers, etc. Probably pretty straight forward just not something I care to take on at this time.

sunny_j · 04-02-2019, 12:31 PM

Quote:

Originally Posted by rodnex

I've swapped both diffs front & rear.
I've got super short 4,44 gears now on my 400bhp Diesel.

Rear diffs are actually all the same, small 185mm model.
Even though the shafts differ, but the diffs are same. 3.0i fits to 3.0d / 3.0d fits to 35d etc

Front diffs... I did my google image & ETK research and was pretty sure the 3.0i Diff will fit.
And yes, it did!

If the V8 housing won't fit the Diesel oil pan... You can still swap the shaft & pinion into the old housing.

rodnex, I would love to hear about the mods you've done to the X5d

Juno01 · 04-02-2019, 03:13 PM

Quote:

Originally Posted by smassey321

Was coding required to correct speedometer?

I think speed is measured from the wheel sensors. So changing the diff ratio won't affect the speedometer but changing the overall tire diameter would.

You could still do coding to make your speedo accurate. Most if not all BMW speedometers are very optimistic from the factory. Both my 335d and x35d are 3-4 mph off at 70 according to gps.

rodnex · 04-04-2019, 09:51 AM

Quote:

Originally Posted by Juno01

Wow, 4.44 final is crazy low lol! Do you have the zf8hp70?

Nope. I've got the ZF6 but with the short diff ratio it works like a ZF8 with 2 last gears missing

Quote:

Originally Posted by Juno01

I don't understand. How can I use a rear diff from a vehicle that has smaller axles? Output flanges are the same? 185mm refers to what exactly?
When I look at images of the the v8 and the x35d diffs on ebay i'm not seeing any difference in size or shape. Images of the 3.0i definitely don't look like the v8 or x35d. Not saying you're wrong just something is not adding up here. Don't want to make a purchase and have it be the one that doesn't work.

185mm is the diameter of the ring in the diff. Unfortunately BMW decided to place those mid-size diffs in the X5. E.g. the 5-series has a 215mm ring and is way more durable and can take more torque/ beating.

Quote:

Originally Posted by sunny_j

rodnex, I would love to hear about the mods you've done to the X5d

I will start my own thread the next coming days.
But I'll tell you a few things...
Single hybrid turbo, straightpiped, no MAF, no EGR, no Swirlflaps, XXL Intercooler, short diffs, Quaife LSD at the rear, X5M brakes all around, airride, etc

9vapors · 04-04-2019, 12:44 PM

This sounds cool, looking forward to your thread!

Deftronix · 04-07-2019, 01:54 PM

Quote:

Originally Posted by rodnex

Nope. I've got the ZF6 but with the short diff ratio it works like a ZF8 with 2 last gears missing

185mm is the diameter of the ring in the diff. Unfortunately BMW decided to place those mid-size diffs in the X5. E.g. the 5-series has a 215mm ring and is way more durable and can take more torque/ beating.

I will start my own thread the next coming days.
But I'll tell you a few things...
Single hybrid turbo, straightpiped, no MAF, no EGR, no Swirlflaps, XXL Intercooler, short diffs, Quaife LSD at the rear, X5M brakes all around, airride, etc

Please do. Would love to see the details of the build

yco · 04-18-2019, 06:06 AM

not sure its a good idea.. if the goal is to make some economy just change the car mate not the diff..

Spyro235 · 04-18-2019, 09:20 AM

Quote:

Originally Posted by yco

not sure its a good idea.. if the goal is to make some economy just change the car mate not the diff..

Deleted and tuned I've gotten 32mpg USA, on a hilly 600 mile tank. Show me another luxury SUV that isn't slow as sin, that can do the same.

yco · 04-18-2019, 04:41 PM

Quote:

Originally Posted by Spyro235

Deleted and tuned I've gotten 32mpg USA, on a hilly 600 mile tank. Show me another luxury SUV that isn't slow as sin, that can do the same.

what was the total cost of changing the diff?

11-28-2018, 07:52 AM	#1
theeld Private 12 Rep 72 Posts Drives: xdrive35d Join Date: Jan 2006 Location: Cedar Rapids, IA iTrader: (0)	Differential swap xdrive50i to xdrive35d On a whim I looked into other differentials for the e70 family. It appears the xdrive50i has 3.15 ratios as opposed to the xdrive35d 3.64 ratio. Anyone speculate as to whether these would bolt up onto the diesel? Would probably drop about 325 rpm on the diesel at cruising speed. Would put 70 mph at 1730 rpm, 80mph at 2030 rpm, which I think would make a nice difference, As I firmly believe the x35d is geared a bit too low, would probably make a significant difference in highway MPG. Garnered from other posters: "The 35i also got 3.15 w/ the 8 speed but the axle shafts are smaller so the dif is different. 50i and 35d use the same bigger axle shafts. F15 diesels w/ 8 speeds also use the 50i diff" "I spent some time researching this to find the info above on the axle shafts. Here is some other info on the driveshaft part numbers. 35d, 50i, 50d, and 35i all have different rear drive shaft lengths. (1410mm, 1427, 1430 and 1445). However the front driveshafts are all the same length at 709 mm. I am unsure if the rear length difference is related to different transfer cases (ATC700 w/ 6 speed vs 45L). All rear dif after 6/11 appear to use the same locking number between the driveshaft and rear diff." Last edited by theeld; 11-28-2018 at 03:03 PM..
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11-28-2018, 09:51 AM	#2
Naz24 Lieutenant Colonel 1628 Rep 1,727 Posts Drives: W205 AMG C63 / E70 X5M Join Date: Mar 2014 Location: North/Central NJ iTrader: (1)	Diesel = low end torque. That's why. not sure it would be efficient to do that on the 50i __________________ 2017 C63 2012 X5M SOLD: 2015 M3; 2007 X3 M Sport; 2014 X3 M Sport 35i; 2004 X5 4.4i; 1994 325i
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11-28-2018, 01:55 PM	#3
mitch808 Captain 107 Rep 994 Posts Drives: 2012 X5 35i Join Date: Mar 2014 Location: Seattle iTrader: (0)	On other cars with AWD, that folks swap gearing, often the front rear ratios must match, other wise, you need to change the transfer ratio in the center gearbox. Not to mention, if there is any computer trickery that must be done... This can't be an easy swap on a car that relies to heavily on the ECU.
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11-28-2018, 06:15 PM	#5
135iTime Enlisted Member 25 Rep 33 Posts Drives: 135i, '12 X5 35D Join Date: May 2017 Location: Midwest iTrader: (0)	I would assume you should be fine if you swapped both the front and rear differential. If those ratios are the same the rest shouldn't matter. This is fairly interesting to me as well since I do a lot of freeway driving and it looks like used diffs are fairly cheap.
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03-26-2019, 03:35 PM	#6
Juno01 Enlisted Member 0 Rep 41 Posts Drives: X5 35d Join Date: Nov 2017 Location: Erie iTrader: (0)	Has anyone decided to do this yet? I do a fair amount of interstate travel as well and I think the 3.15 would definitely improve fuel economy at 70+mph. Performance around town worries me. It seems like the transmission doesn't kickdown as quick as I would like so even now and the car feels like a dog sometimes. It would be a lot of work to do the swap and have to revert back. Last edited by Juno01; 03-26-2019 at 03:41 PM..
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04-01-2019, 03:19 PM	#10
rodnex Private 22 Rep 57 Posts Drives: E70 3.0si, E70 3.0d, E70 X5DUS Join Date: Sep 2017 Location: Island iTrader: (0)	I can confirm the 3.0i Diff fits on the Diesel. Don't know about the V8, if they kept the same housing
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04-01-2019, 05:24 PM	#12
rodnex Private 22 Rep 57 Posts Drives: E70 3.0si, E70 3.0d, E70 X5DUS Join Date: Sep 2017 Location: Island iTrader: (0)	I've swapped both diffs front & rear. I've got super short 4,44 gears now on my 400bhp Diesel. Rear diffs are actually all the same, small 185mm model. Even though the shafts differ, but the diffs are same. 3.0i fits to 3.0d / 3.0d fits to 35d etc Front diffs... I did my google image & ETK research and was pretty sure the 3.0i Diff will fit. And yes, it did! If the V8 housing won't fit the Diesel oil pan... You can still swap the shaft & pinion into the old housing. Last edited by rodnex; 04-01-2019 at 05:29 PM..
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04-04-2019, 12:44 PM	#18
9vapors Major 648 Rep 1,252 Posts Drives: CB X5M Join Date: Jun 2018 Location: Des Moines iTrader: (0)	This sounds cool, looking forward to your thread!
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04-18-2019, 06:06 AM	#20
yco i'm just saying 5725 Rep 2,634 Posts Drives: E71 X6M '10 (sold) Join Date: Jan 2018 Location: Istanbul & Kyiv iTrader: (0)	not sure its a good idea.. if the goal is to make some economy just change the car mate not the diff..
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