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The E30 has two types of differential, the small 166mm crown and the large 188mm crown. These are known as the small and large housings. The small housing diff has 6 bolts holding its back diff cover on, while the large diff has 8 bolts. The larger crown wheel is the prefered unit because of its added strength.
The 4 cylinder and early 6 cylinder E30's have the smaller diff, while the late model 6 cylinder E30's have the larger diff.
Fitting a 8 bolt diff to a early model E30 This is a simple bolt in job. Driveshaft and CV shafts both bolt up.
Compatable BMW Differentials The E28, E36 diffs are both identical internally. They can be fitted to a E30 by keeping the E30 back diff cover and swapping the output shafts to the CV's to the originals.
E28 Final drive ratios
Model |
Rear Axle Ratio |
| 518i, 520i | 4.10 |
| 520iA, 535i-E34-Auto | 3.91 |
| 525e | 2.93 |
| 525eA | 3.07 |
| 525e Cat | 2.93 |
| 525i, 535i-E34-Man | 3.64 |
| 528i, 320i-E36 | 3.46 |
| 528i (Sports Gearbox) | 3.25 |
| 535iM | 3.07 |
| 535iM Cat | 3.25 |
| 524td | 3.15 |
| 325 E30 | 3.73 |
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