Differential Upgrade 540i Automatic

[Evan]

What are the pros and cons of upgrading my differential?

Should I buy a 3.25 or a 3.64 or some other LSD diff?

Is this a DIY job and what's involved?


Thanks,
Evan

[632 Regal]

dont know your top gear ratio but I popped in a 3:64 and was quite surprised at how low the rpms are at speed. like 3k at 85 (guessing)

[grave77]

thats low, the original was 3.15 right? then how low was the RPM at the same speed before the swap?

[yaofeng]

What are the pros and cons of upgrading my differential?

Should I buy a 3.25 or a 3.64 or some other LSD diff?

Is this a DIY job and what's involved?


Thanks,
Evan

Can't comment on performance changes on those different numerics. But I can tell you what is involved in replacing the final drive having only recently replaced mine during the 6 speed conversion.

There are 24 M10 allen head bolts you need to remove from the two drive shafts. Each one is tightened to at least 70 ft-lbs, my guess is much more. My air impact wrench didn't do a thing. I also recommend cleaning the allen bolt head as much as you can before proceeding. Mine were covered with grime. I stripped two bolts, because I didn't clean them. It took me three hours to cut the head off using my Dremal tool.

After the drive shafts are removed, you need to loosen the propeller shaft (six nuts). Then place the transmission jack under the final drive. Loosen three M14 bolts and down it goes. Don't forget to disconnect the speedo pick-up.

Did I mention the exhaust? Don't know if you need to remove the exhaust. I guess you do. The exhaust on my 540 was removed in June and it has not been bolted back up yet.

[Evan]

How many pounds of torque does your air gun have? Mine is about 435 ft/lbs so i don't think many bolts would be a problem.

How do you like driving the 6spd?

Thanks for reply!

[632 Regal]

the side shaft bolts: most were removed on one side by Sal, my now 9 year old son. One he couldnt remove was stripped and I had to use a chisel to spin it loose. Definetly clean the holes!

the exhaust didnt need to go anywhere when I did mine.

[632 Regal]

If you find one make sure it is the large unit like from an S38 or 540 or 740 etc, the common small units are just that, too small. My lawn tractor has a similar small ring gear.

What are the pros and cons of upgrading my differential?

Should I buy a 3.25 or a 3.64 or some other LSD diff?

Is this a DIY job and what's involved?


Thanks,
Evan

[Evan]

530i 5 speed (M60) 3.07 3.46
530i Automatic (M60) 3.15 3.46
530i 5 speed (M30) 3.64 3.91
540i ->3/04 2.93 3.25
540i 4/94-> 2.81 3.25


according to bruno, I have a 2.93 and i should go for a 3.25

Dinan sells a 3.64LSD for $3.5 million dollars installed

[Evan]

I do a lot of highway driving... will I regret the change?

[632 Regal]

dude, thats a chart, no big deal. I freaked about a 3:64 thinking id loose first gear and have 5000+rpms at 100, simply not true. The city acceleration with a 3:64 is much better, boosted mileage and didnt hurt anything on the open road.

I would say to go for at least a 3:23 but better is a 3:42 or 3:64.

530i 5 speed (M60) 3.07 3.46
530i Automatic (M60) 3.15 3.46
530i 5 speed (M30) 3.64 3.91
540i ->3/04 2.93 3.25
540i 4/94-> 2.81 3.25


according to bruno, I have a 2.93 and i should go for a 3.25

Dinan sells a 3.64LSD for $3.5 million dollars installed