323i vs 325i diff compatibility

cheerio · 03-05-2021, 10:49 PM

Hey all.
Just bought a 323i and it has a little bit of a rattle coming from the diff. From what I’ve heard this is caused by bad pinion bearings, is common on the 320i, and the 323i as well, which uses the same bearings.
The 325i’s diff seems to be much more reliable in this regard. I’m wondering if it’s be possible to get a 325i diff from a wrecker and install it... Does anyone know if they’re compatible, or are the diff mounts/driveshaft different between the two cars?
Thanks

Edit: Checked RealOEM, they seem to have 25mm different driveshaft lengths, presumably because 325i diff is longer. Any idea if it'd be worth swapping the driveshaft and diff together?

F31B48 · 03-06-2021, 12:13 PM

Quote:

Originally Posted by cheerio

Hey all.
Just bought a 323i and it has a little bit of a rattle coming from the diff. From what I’ve heard this is caused by bad pinion bearings, is common on the 320i, and the 323i as well, which uses the same bearings.
The 325i’s diff seems to be much more reliable in this regard. I’m wondering if it’s be possible to get a 325i diff from a wrecker and install it... Does anyone know if they’re compatible, or are the diff mounts/driveshaft different between the two cars?
Thanks

Edit: Checked RealOEM, they seem to have 25mm different driveshaft lengths, presumably because 325i diff is longer. Any idea if it'd be worth swapping the driveshaft and diff together?

I remember looking into this for my 323i. I think the driveshaft was different and both the output shafts as well. I ended up rebuilding my diff. The bearing/seal kit was about $230. I got it off Ebay from a UK seller. The bearings were all OEM.
Edit: i just checked the price on ebay. The same kit from the same seller is now $400. They'll blame covid no doubt.

https://www.ebay.com/itm/BMW-1-3-SER....m46890.l49292

cheerio · 03-06-2021, 07:29 PM

Thanks for the reply! Yeah, I was looking around a bit for bearing kits, they all seem to be around $400. Didn’t realise the price had come up so much :/

I was considering upgrading to the 325i intake manifold at some point for more power/torque, but if the 323i’s diff bearings fall apart at stock torque I’d hate to think how they’d wear with more load on them...
I’m also thinking that taking a driveshaft from a wrecked car might not be the best idea - what if it’s been bent out of balance?

By output shafts, do you mean the shafts going from the diff to the wheels? And was the diff rebuild very difficult? Any specialised tools needed?

F31B48 · 03-06-2021, 11:11 PM

Quote:

Originally Posted by cheerio

Thanks for the reply! Yeah, I was looking around a bit for bearing kits, they all seem to be around $400. Didn’t realise the price had come up so much :/

I was considering upgrading to the 325i intake manifold at some point for more power/torque, but if the 323i’s diff bearings fall apart at stock torque I’d hate to think how they’d wear with more load on them...
I’m also thinking that taking a driveshaft from a wrecked car might not be the best idea - what if it’s been bent out of balance?

By output shafts, do you mean the shafts going from the diff to the wheels? And was the diff rebuild very difficult? Any specialised tools needed?

Yeah output shafts from diff to wheels. When i was buying some shims from a diff shop to do the backlash, the guy there told me the issue with the small diffs is lack of lubrication to the front pinion bearing. He said even the 116i's and 120i's which have the same diff, wear pinion bearings. The later model diffs have a steel plate fitted to retain oil in the area of the front pinion bearing he reckons. He also recommended i reduce the preload on the pinion bearings, which i did. The only thing special you really need is a press to remove and install the pinion bearings.

I have changed my manifold to the 3 stage and flashed it to 325i spec. No issues yet. I think its been about 6 months and 10000km roughly since i did all that. No issues yet........ time will tell i suppose

cheerio · 03-13-2021, 06:14 AM

So I went and bought a diff, driveshaft and rear output shaft from a wrecked 325i. Price was comparable to the $400 it'd cost for the bearing kit, so after factoring in resale value of my 323i parts, it seemed like a no brainer.

They all seem to be in good shape, diff isn't full of dark green muck like mine was, so things are looking promising. Hopefully installing them will go smoothly; I'll post an update when all is finished!

cheerio · 03-17-2021, 05:21 AM

Everything's installed and the awful grinding noise is no more!
Needed to
- Drain new diff
- Remove exhaust
- Remove heat shields
- Remove old driveshaft
- Remove old output shafts
- Remove old diff
- Install new diff
- Install new output shafts
- Install new driveshaft
- Reinstall heat shields
- Reinstall exhaust
- Fill diff with new oil

I didn't realise I'd need different fasteners to attach the output shafts to the new diff; the bigger diff uses bigger bolts, as the output shafts are larger diameter. Ended up having to buy the bolts and reinforcing plates from dealer at eye-watering price.

Also managed to strip the head on one of the driveshaft-to-diff bolts :/ It's slightly under-torqued now, should I be worried? I figured the other three are good, so I can inspect it every now and then and replace the bolts if the stripped one comes loose...

03-05-2021, 10:49 PM	#1
cheerio Private First Class 144 Rep 150 Posts Drives: E61 + E36 + E90 scrapheap Join Date: Mar 2021 Location: Melbourne iTrader: (0)	323i vs 325i diff compatibility Hey all. Just bought a 323i and it has a little bit of a rattle coming from the diff. From what I’ve heard this is caused by bad pinion bearings, is common on the 320i, and the 323i as well, which uses the same bearings. The 325i’s diff seems to be much more reliable in this regard. I’m wondering if it’s be possible to get a 325i diff from a wrecker and install it... Does anyone know if they’re compatible, or are the diff mounts/driveshaft different between the two cars? Thanks Edit: Checked RealOEM, they seem to have 25mm different driveshaft lengths, presumably because 325i diff is longer. Any idea if it'd be worth swapping the driveshaft and diff together? Last edited by cheerio; 03-06-2021 at 01:15 AM..
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03-06-2021, 07:29 PM	#3
cheerio Private First Class 144 Rep 150 Posts Drives: E61 + E36 + E90 scrapheap Join Date: Mar 2021 Location: Melbourne iTrader: (0)	Thanks for the reply! Yeah, I was looking around a bit for bearing kits, they all seem to be around $400. Didn’t realise the price had come up so much :/ I was considering upgrading to the 325i intake manifold at some point for more power/torque, but if the 323i’s diff bearings fall apart at stock torque I’d hate to think how they’d wear with more load on them... I’m also thinking that taking a driveshaft from a wrecked car might not be the best idea - what if it’s been bent out of balance? By output shafts, do you mean the shafts going from the diff to the wheels? And was the diff rebuild very difficult? Any specialised tools needed?
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03-13-2021, 06:14 AM	#5
cheerio Private First Class 144 Rep 150 Posts Drives: E61 + E36 + E90 scrapheap Join Date: Mar 2021 Location: Melbourne iTrader: (0)	So I went and bought a diff, driveshaft and rear output shaft from a wrecked 325i. Price was comparable to the $400 it'd cost for the bearing kit, so after factoring in resale value of my 323i parts, it seemed like a no brainer. They all seem to be in good shape, diff isn't full of dark green muck like mine was, so things are looking promising. Hopefully installing them will go smoothly; I'll post an update when all is finished!
	Appreciate 0 Quote

03-17-2021, 05:21 AM	#6
cheerio Private First Class 144 Rep 150 Posts Drives: E61 + E36 + E90 scrapheap Join Date: Mar 2021 Location: Melbourne iTrader: (0)	Everything's installed and the awful grinding noise is no more! Needed to - Drain new diff - Remove exhaust - Remove heat shields - Remove old driveshaft - Remove old output shafts - Remove old diff - Install new diff - Install new output shafts - Install new driveshaft - Reinstall heat shields - Reinstall exhaust - Fill diff with new oil I didn't realise I'd need different fasteners to attach the output shafts to the new diff; the bigger diff uses bigger bolts, as the output shafts are larger diameter. Ended up having to buy the bolts and reinforcing plates from dealer at eye-watering price. Also managed to strip the head on one of the driveshaft-to-diff bolts :/ It's slightly under-torqued now, should I be worried? I figured the other three are good, so I can inspect it every now and then and replace the bolts if the stripped one comes loose...
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