Which to swap the gearbox or the diff

[Andrius.Z]

Hi all,

I have an E30 that at some stage had its engine replaced from M40 316i to M10 316, this was paired with E21 4-speed gearbox and a 4.27 small case diff.
I was able to get a 3.64 diff as the first and second gear was unusable and on the motorway at 100km/h engine was at 4500 RPM. That diff lasted about 10km before the main bearing shattered and locked the rear wheels in the middle of the motorway at about 80km/h. I got a second diff with a 3.91 ratio which is not a big difference from 4.27.

What would you guys advise - I have the option to get another diff 3.25 or I have the option to go for a 5-speed gearbox.

Would a 5-speed gearbox change much in terms of first and second gear, at the moment when I'm pulling off in the first gear it goes to 3000RPM in the first 10m.

It felt good with 3.64 diff before it tried to kill me

Thank you,
Andy

[It's Soda Not Pop]

This page has a list of gear ratios which might help you decide better.

https://www.bmwe21.net/?page_id=124

[moatilliatta]

5 speed minimum. Six speed if you want to add 25 lbs.

[TobyB]

Good luck finding a 6 that bolts to an M10. Good reason to go N52, though...

1st through 4th are almost the same on all non- sport M10 gearboxes, and there are very few 'sport' gearboxes out there. A 3.91 and a 5 speed's not a bad pair,
and a 3.64 and 5 speed works well on the motorway at 120kph, at the expense of a bigger gap between 2nd and 3rd.

whut I found,
t