Running a 5speed getrag 260 with the original 4.10 rear the car came with

[NYSE30]

So my car is an '89 325is automatic. I have the 5speed getrag 260 and all the supporting parts for the install. Thinking of leaving the factory rear diff in the car for now which I'm thinking is a 4.10 LSD because its an IS model car. Am I wrong about the gear ratio? Is it an LSD? Also is it too big of a ratio to run with the 5 speed swap? The car will be used for cruising(not a daily driver) and some spirited back road driving. Should I swap out for a factory 5 speed diff? My car is a one owner car I bought from an older family member that babied the car so I know the diff is in great shape so I kinda don't want to give it up for that reason.

[LJ851]

If you don't do much highway driving it is fine. I left mine in when i converted to manual for a while, but i do a lot of highway daily so i went to 3:73.

[NYSE30]

Thanks for the quick reply. Drawback would only be gas mileage I'm assuming? And of course more wear on the motor cause its spinning higher while cruising at any mph compared with a 3.73 rear?

[LJ851]

I never checked my gas mileage. I suggest using it because it is already there and see what you think. It is not a massive difference.

[NYSE30]

That sounds like a plan. The car would benefit on acceleration from the taller gear as well which should make it feel a little faster and fun lol. Thanks!

[dustyperez]

It's a fun little setup I remember exact same thing last summer . But it's definitely not for highway driving

Sent from my SCH-I545 using Tapatalk

[LJ851]

That sounds like a plan. The car would benefit on acceleration from the taller gear as well which should make it feel a little faster and fun lol. Thanks!

Yes, one way to look at it is that it shifts all 5 gears lower so you don't start out in first gear, you start out in like .7 gear, then shift into 1.7 gear, etc. and end up in 4.7 gear.

[Sea Aych]

I did literally the exact same swap as you. '89 auto to manual and left my 4.10 in (it's a very tired LSD).
It's a LOT of fun when shooting around curvy and city roads, and highway mileage isn't toooo bad. It's noticeably worse than with a 3.73 and makes a little more noise at highway speeds because of the higher revs, so not the most comfortable for that kind of driving.
That being said, second gear makes it pull like a jet, which is nice

[ColdAsLife]

I swapped from Auto to Manual as well as turbo'd my late model at the same time. 1st and 2nd were absolutely useless. Maybe it'd be fun having a stroker NA ITB motor with a 8k redline and a 4.10 otherwise its just not very practical IMHO.

[srvE30]

I never checked my gas mileage. I suggest using it because it is already there and see what you think. It is not a massive difference.

It's a subtle loss in gm. 1-2 miles less. But worth the 3.73 from what I understand.

[Killacortes]

Not sure how guys are getting that worse of mpg. Im running the same set up in my 89 325is and I get great mileage and that's around 40 miles a day on the highway 5 days a week. The difference is only 300 rpm compared to a 373 on the highway. Keep the 410 its alot more fun.

[efficient]

I got 210 mpg city in my 325i with a 3.73 lsd manual.

[blownm20]

i run a 4.10 in my 325is. its not annoying to drive it pulls alot faster and highway is pretty much like driving an eta

[Killacortes]

Wow 210mpg? Whats your secret. I get about 22 mostly highway

[efficient]

Wow 210mpg? Whats your secret. I get about 22 mostly highway

is that good for a full tank? i do smash here and there but i try to drive conservatively
lol my motor is refreshed stock chip/afm/and 17lb injectors. i used to have an acura so i think thats pretty poor imo