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

[Jon K]

no - a kid @ my school has a turbo 535i with a 3.91 the RPM change is hardly noticeable. People get waaaaaaaaaaaaaaaaaaaaaaaaaay too concerned with rpm change when going to shorter (higher ratio) diff.

[Martin in Bellevue]

Yao, it is starting to sound like ya found that 540 sitting in the dead sea. The differential was hard to swap, the fuel lines were rusted. What else is corroding away on that thing?

[632 Regal]

I thought I would but with overdrive its not a big deal, if your final drive was 1:1 it wouldnt be a choice at all. Go Ebay for anything in them ratios and get what you get. the 3:64 will drive you nuts with the dead stop acceleration though, it will pull so hard youd think your gonna break something but its just the gearing making the big difference. In Germany on the Autobahn with a 3:64 your cruising speed would be in the upper RPM range, but you dont usually cruise in the 140-150 MPH range do you? If so than keep the stock unit.


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

[Evan]

Didn't I just send you to traffic court?

I'm looking at a used 3.64LSD from an 88 735

I'm researching rebuilds... if they're possible or feasible etc.

http://i6.ebayimg.com/02/i/08/42/21/4f_1.JPG

[632 Regal]

doesnt the 735 have the small differential?

[yaofeng]

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!

Maybe my impact is inferior. But I had to loosen it first with a breaker bar before using the air ratchet.

How do I like driving the 6 speed? I can only imagine. I am not there yet. Trying to get it done before winter closes in. I have too many things going on.

[yaofeng]

Yao, it is starting to sound like ya found that 540 sitting in the dead sea. The differential was hard to swap, the fuel lines were rusted. What else is corroding away on that thing?

I suggest you crawl under your bimmer to check the condition of your fuel return line and tell us what it looks like. Or you like to bury your head in the sand?

Does it look like this?
http://i21.photobucket.com/albums/b274/yaofengchen/BMW_95_540/DSC_3267.jpg

Or like this.
http://i21.photobucket.com/albums/b274/yaofengchen/BMW_95_540/DSC_3344.jpg

[Martin in Bellevue]

There is no corrosion like that on my 535. I've been under there a few times, & all the fasteners are clean. I replaced the fuel filter last week & checked all the lines; they're rust-free. When I put the 3.64lsd in the car, it was easy to work the fasteners with hand tools. When I put Bruno's subframe inserts in, that hardware was clean too.
I suggest ya check the hardware to the gas tank straps, remember Scott H, or somebody out East, seeing those fail, allowing the tank to sag.

[yaofeng]

There is no corrosion like that on my 535. I've been under there a few times, & all the fasteners are clean. I replaced the fuel filter last week & checked all the lines; they're rust-free. When I put the 3.64lsd in the car, it was easy to work the fasteners with hand tools. When I put Bruno's subframe inserts in, that hardware was clean too.
I suggest ya check the hardware to the gas tank straps, remember Scott H, or somebody out East, seeing those fail, allowing the tank to sag.

The fasteners have to be clean. They are stainless steel. I am talking about the fuel return lines held by the SS fasteners. Not the fasteners themselves. BMW doesn't even coat the 8 mm fuel return line. It is atrocious. They didn't do it on the E30, or any models for that matter. I bet they still don't do it on the latest and greatest models. You are lucky because you live in the salt free west coast.

Now take a picture of the fuel return line and let us see it. I don't believe a 17 year old bare carbon steel tubing can be rust free even in the west coast.

[Evan]

im under my car right now.. where is the gas tank?

[632 Regal]

front left side
im under my car right now.. where is the gas tank?

[Evan]

ok i found it.. it looks really small to have such a high capacity. how can they squeeze 18 gallons of gas into such a small box? Germans are INCREDIBLE