Fine Tuning: Gear Ratios / Rear Differential LSD

sd-mk2 · Post by **sd-mk2** » Sat Mar 19, 2016 7:57 am

Hey guys,

I'm at the point where i want to start looking at my cars gearing. Im very very green on this topic so your patience is greatly appreciated.

My car is a stock 1981 528i, from what i can tell this car has a decent amount of power, it hauls ass once i get going on the freeway, but is a dog off the line. Not that Im using this car for red light drag races but I think a sportier ratio would be a huge difference in the cars performance and feel. Im assuming BMW set this car up to be a daily driven tame car that can do well at high speeds. Im also assuming there were different configurations for this transmission depending on the car / model. Im also under the impression that there is an LSD out there that fits my car.

My question is:
What different configurations are there for my transmission? What does it take to make these adjustments? Which set up is recommended for a car that gets windy road use / spirited driving?

My rear differential is whining pretty loud so I'm gonna get it checked out, if its in need of repair i would like to just swing for the LSD. Which model am I looking for and which one pairs well with a gearing setup I need. (I should say, gearing setup that would work best for the kind of car I have)

This post feels all over the place and I apologize in advance, it is clear i do not know what I'm talking about and would love to be educated on this topic.

thank you!

Jorge

Mike W. · Post by **Mike W.** » Sat Mar 19, 2016 10:09 am

Diff choices are pretty limited, however your car should move off the line pretty well with a manual, but will be slow with an auto. Stock it would have had a 3.45. Early 530s and some Bav's which used the same sideloader had 3.64, hard to find now. Some euro 635s came with 3.07 with a close ratio 5 speed, but that's going in the wrong direction for you. There may also have been some 3.25s on euros, but again, not what you're looking for. Plus since E12s use a mechanical speedo a change in diff ratio will throw the speedometer off.

sd-mk2 · Post by **sd-mk2** » Sat Mar 19, 2016 3:52 pm

hmmmm.... so what in the name of Jedediah Springfield do I do next?

Identify my specific setup and get the appropriate pairings / options I have available to me?

PatinaBeforePolish · Post by **PatinaBeforePolish** » Sat Mar 19, 2016 5:58 pm

I've not done it but I understand fitting an e28 subframe and differential is pretty straightforward with more ratio choices and better availability of limited slip units.

Mike W. · Post by **Mike W.** » Sun Mar 20, 2016 12:01 am

PatinaBeforePolish wrote:I've not done it but I understand fitting an e28 subframe and differential is pretty straightforward with more ratio choices and better availability of limited slip units.

I too have heard it's not too difficult and more ratios are available, the E30 325i diff is 3.73 but keep in mind you would need E28 brakes, you might be able to use E12 shocks/springs with a spacer and your speedo will still be off.

sd-mk2 · Post by **sd-mk2** » Mon Mar 21, 2016 6:04 pm

Just out of curiosity. Most of you guys have kept the stock ratio configuration?
I know some of you guys have some fairly sporty e12s, just curious if Im trying to do a common upgrade or a difficult one

onovakind67 · Post by **onovakind67** » Mon Mar 28, 2016 10:01 am

PatinaBeforePolish wrote:I've not done it but I understand fitting an e28 subframe and differential is pretty straightforward with more ratio choices and better availability of limited slip units.

I've got an E28 subframe under my Bav and it works very well. If you get the right diff cover it bolts right in on the stock mounts. There were a few mods necessary, like the sway bar mounting brackets and brake line configuration, but it was a couple of days in the driveway and it was in.