b25, getrag 240, 4.10 diff

[Rhyse30]

A few month ago the timing belt went on my b20. Unfortunate but quite glad since i now have an excuse to put in a b25. After searching everything over the past few weeks/months, I'm still not sure on some points.

I can use my 1989 320i gear box right? Its pretty close to the 325i sport gearbox?

Will i need to change the diff? As far as i know it still has the original diff, which would be 4.10??

I have a 325i gearbox available if that would be better to work with the 320i diff?

Will this be ok? Or just a big hassle to drive? I don't do much motorway driving (with some exceptions)

Basically I just want to know if this is a combination ok to use and what are the down falls? 1st gear useless? High revs in 5th on motorways? fuel consumption heavily affected?

As you can tell, still fairly new to this so any comments appreciated.

Cheers

[gromgsxr]

Im using a 320i box with the 4.10 small diff its not all that bad first and second are fairly short but acceleration is good totally usable but 70 on the motor way is about 3200 rpm in 5th im still using the standard 320i clutch as well. I'm happy with the set up

[Grrrmachine]

I wouldn't recommend keeping the 4.10 diff. I use a 320i box in my Touring with a 3.64 diff, and despite it being a heavy bodyshell 1st gear is pretty much useless in the wet, so a 4.10 will be absolutely horrible.

[Rhyse30]

Ok, thanks for the feedback. Would it be any better with the 260 box instead of the 240? just while I try and get my hands on a better ratio diff?

[jmc330i]

The 320i box will be fine. If you use a 325i box you will still need to change the diff to a more suitable ratio.

Unless the 325i box is free, I'd use your 320i box and source a diff (3.64 - 3.91). You could run your 4.10 until you find a suitable diff, but 1st gear won't be much use so you'd effectively be driving a 4spd 325i
The acceleration will be fun for a while, but will quickly become tiresome when you look at the revs and fuel it'll be using.

[Brianmoooore]

The 320 box and 4.1 diff. will be exactly the same attached to a 325 engine as they were to the 320, and changing to a 325 box would be little different. 4th, 5th and reverse are identical in both boxes, 1st is almost the same (less than 3% difference), 2nd on the 320 box is almost identical to that on the 325 'sports' box, and 3rd on the 320 box falls midway between that on the standard and 'sports' 325 boxes.
The 4.1 diff. is unnecessarily high for use with 325 torque and power, and much better fuel consumption will be achieved without any great loss of acceleration by changing to a 3.76.

[Rhyse30]

Ok. I'll keep an eye out for a more suited ratio diff then. Thanks for the feedback. I'll be swapping a b20 for the b25 from a donor car so I have both options for the gearbox. I might stick with the 240 box if its a little more sporty. If I change the diff, what else will i need to swap a small case to medium case diff? Will I need to swap the propshaft and output flanges I currently have in the 320i?
Thanks

[Rhyse30]

Sorry, *different driveshafts not output flanges*

[jmc330i]

The diff will just bolt in. The driveshafts are the same, the difference is taken up with the output flanges. The prop may need slight adjustment but thats a simple job.

If you've got a donor 325i, you will already have a suitable diff.

[Rhyse30]

Unfortunately the guy I bought the donor car from took a few bits off before selling. The diff was one of those things and he put a small case 4.10 on. Not to sure why. But the car was cheap enough I had to buy it for the engine. I'll try and source another diff in the meantime. Cheers for all the help.

[maggspower]

Full e30 spares service here, including diffs

I'm in Pontypool.