DIY: How To Swap a Differential (plenty of pics)

[99blackbird]

Originally posted by Tn325I
Pictures are worth much more than a thousand words when your trying something new.....

Hey! That's the excuse I can give my girlfriend for keeping all my porno mags.


Great write-up man. I'm leaning towards changing my differential and this is a big help.

[Tommy R]

Thanks, guys. Happy to help. I've gotten lots of good info from this site and thought this would be a nice way to "repay" the favor. Expect more soon... Bushing swap, custom cat-back, etc....

Tommy

[U1arunit]

Great write-up Tommy! I will be swapping mine out this coming friday and this is just what I needed. :

[Tommy R]

No sweat, Mark.

Hey Butch, where did you see that tool? I definitely think that piece would be worth $40! :

Tommy

[Bernman]

That tool is made by Stahlwille and carried the part number SF 1067. The only site that I have ever seen it is http://www.zdmak.com though I can not find it there any longer. I would be willing to bet it is still available if you asked them. They have a bunch of other cool tools on that site as well

*edit* Found it on page 2 of the BMW tools at ZDMak

[badmonkey]

Nice DIY write up. But seriously, you probably spent more time snapping pics than it takes to swap diffs

[Tommy R]

Originally posted by badmonkey
Nice DIY write up. But seriously, you probably spent more time snapping pics than it takes to swap diffs

Nope, my friend Zac took the pics.

A diff swap is a simple job, true, but is daunting to someone who's never done it before. Considering it only added about 10 minutes to the job to grab the pics and maybe an hour to write all the details, I figured it'd be worth it. I figured folks who haven't done it before would appreciate it.

Tommy

[poynter]

thats weird, mine doesnt have the torx bolts...they are just regular bolts....

[Tommy R]

Originally posted by poyntofdesign
thats weird, mine doesnt have the torx bolts...they are just regular bolts....

Interesting. Are you the orig. owner? Can you grab a picture of it?

Thanks,
Tommy

[xvxax]

TommyR,
I want to thank you for making this writeup. I've been searching and searching all over to gather information on the differential swap I am about to do this weekend. Thanks for making me laugh along the way, too. I appreaciate it,
Peter Tyson

[Tommy R]

You're welcome, Peter, but what is up with your website?? I wasn't about to proceed beyond the front page!

Tommy

[xvxax]

Woah, that is really messed up. I didn't put that there but I can imagine that I have a virus. I wouldn't put some nasty website as my homepage. Thanks for the heads up.
-Peter Tyson

[Tommy R]

No sweat... I don't think I'd want that as my website, either!

Tommy

[kutch]

How did you determine which diff to install? By year/ gear ratio? Because there are many different ratio LSD units, right? I'm just trying to determine which would work best in my 98 328is 5-spd. It's not like I'm looking for 4:11s to better the 1/4 mile, I'm really interested in just having a LSD rather than the open diff... I don't need a ratio so high that my gas milage goes out the window...any suggestions on what to look for and price ranges?
Thanks, Kutch
kutch_L@juno.com

[snk328is]

How did you determine which diff to install? By year/ gear ratio? Because there are many different ratio LSD units, right? I'm just trying to determine which would work best in my 98 328is 5-spd. It's not like I'm looking for 4:11s to better the 1/4 mile, I'm really interested in just having a LSD rather than the open diff... I don't need a ratio so high that my gas milage goes out the window...any suggestions on what to look for and price ranges?
Thanks, Kutch
kutch_L@juno.com

You can get a used 3.15 LSD from a '95 M3 for around $400. If you want a higher ratio, you're looking at spending a few hundred bucks more.

TommyR, thanks for doing the write-up! I don't think I've come across one quite as thorough and well-documented. I have a 3.15 LSD sitting in my garage waiting to get swapped in for the stock open 2.93. This write up will help tremendously!

[Tommy R]

Happy to help...

Tommy

[4Life]

Just recently installed the 3.23 into my 328is, my acceleration feels good even with my heavy 18's on. And I am loving the LSD, accerating without the one wheel peel is so much better.

[lilsnoboardr22]

im looking for a 325is differential to do a m50 engine conversion on my 318is did you sell it already? becuase if you didnt i am interested

[snk328is]

I just wanted to bump this thread (it's an awesome thread!) and add a few tips that I have for first-timers (or second-timers) because I just did this swap (2.93 Open -> 3.15 LSD) yesterday.

1. You don't have to get the Lisle External Torx socket set from Sears for $20.

I had already bought the set and was visiting Autozone to buy the steering wheel puller (which you also probably won't need, it turns out), when I happened upon an E12 socket sold by itself for $3.99. The socket walls were thinner than the Lisle socket, which made the fitment alot better than the Lisle E12 socket. I believe the Lisle socket is an impact socket, which explains why it has thicker walls.

2. Use some pipe tubing to get more leverage on the 3/8-in. drive ratchet for the external torx sockets.

Your average 3/8-in. drive ratchet won't give you enough leverage to easily break the torx bolts, especially when you're on your back under a car on jack stands. By using a length of pipe tubing slipped over the ratchet handle, you can break the bolts loose more easily. FYI, this trick works on many other tough bolts so it's always good to have one handy.

3. Make sure you measure/compare your input and output flanges.

I was quickly able to determine that the input flange was not going to be compatible (4-bolt vs. 6-bolt), but for some odd reason I just assumed that the output flanges would mate to the drive shafts. Big mistake. I had already gotten the new diff bolted onto the car - which was a monumental task by itself because I was doing the job by myself - only to find out that the output flanges did not mate up with my drive shafts! After 10 minutes of cursing, I calmed down and found out that I was able to get the output flanges out with the diff still in the car. I highly recommend that you do this *before* you put the diff back in, though.

4. Make sure your jack has a large diameter jack plate (the part that actually makes contact with your car) if it's going to be of any use to lower/lift the diff.

My jack from Sears has a jack plate that's about 3 inches in diameter. This is utterly useless when you're trying to balance a 90 lb (or smtg) hunk of metal. You need something that's at least as wide as the jack plate on one of those race jacks. I only used the jack for supporting part of the weight of the diff as I lowered/lifted it in place. Even if I had a buddy, he would have had a very hard time keeping the diff balanced on the jack I used.

All in all, it took me 7-8 hours to complete this job by myself. Dropping the exhaust/sway bars and putting them back on took about 3-4 hrs total by themselves. The UUC rear sway bars can be a real bitch to put in. I struggled with it the first time and it was still a bitch the second time.

As for the diff, it was a really easy job. It's just very hard to manage all the weight by yourself. I only used the jack to support the diff from time to time, but for the most part, I muscled it off/on the car. I'm pretty sore from all the awkward lifting I did yesterday.

The car accelerates faster, and I can definitely get on the throttle a lot faster on corner exit now (tested on a closed course ). I can't wait to try it at an auto-x!

[AaronT]

Outstanding thread, thanks! I need to print all of these type of DYI threads out and make a book....

[clumpymold]

Outstanding thread, thanks! I need to print all of these type of DYI threads out and make a book....

Book? I've got two 3" binders completely full and alphabetically organized into sections and then chronologically ordered.

Then I've got my Bentley. But I've noticed that I hardly ever refer to these write-ups when I do the installs/replacements. I read them once and then it's usually pretty easy to figure out.

[phillyB///M3]

Sweet write-up. Something in my Diff. is screwed up so I will be dropping in a 3:38. This makes mentally prepping for the job alot easier! Good job Tommy!

[KTL]

Great write up. Those who take the time to nicely document the procedures (with good pictures to boot) always get a from me.

Some things i'd like to add......

What kind of lifespan do the LSD units have? Meaning, what kind of mileage can you get out of them? The friction plate kind can eventually wear out. Now if the LSD is of the Torsen torque-biasing kind (like a Quaife) then they "never" wear out. I'd just hate to see someone get a used LSD that was worn out.

If one chooses to replace the Torx head bolts, no need to reinstall the same Torx head kind. As long as you use the right shank length, thread length & thread size and the right property class (these screws are most likely 12.9 class) then you should have no problem replacing the screws with allen/inhex head screws instead of the Torx kind. Just use a quality brand. McMaster-Carr (www.mcmaster.com) and Metric Multistandard Components Corp. (www.metricmcc.com) sell high quality metric fasteners.

Tommy & others, I know this has been asked before, but please post the type of fluid you used for the differential.

Thanks,

Kevin

[Tommy R]

Great write up. Those who take the time to nicely document the procedures (with good pictures to boot) always get a from me.

Thanks. Happy to help...

What kind of lifespan do the LSD units have? Meaning, what kind of mileage can you get out of them? The friction plate kind can eventually wear out. Now if the LSD is of the Torsen torque-biasing kind (like a Quaife) then they "never" wear out. I'd just hate to see someone get a used LSD that was worn out.

Given the nature of an IRS car, the clutch packs should hold up to a LOT of miles of street use. Put some race compound rubber on there and start lapping or autocrossing, however, and I'd expect a rebuild after a few years, depending on several variables. These cars have clutch diffs from the factory, BTW.

[Tommy & others, I know this has been asked before, but please post the type of fluid you used for the differential.

I've run Redline 75W90 N/S, I believe. Though running regular vs. N/S apparently doesn't net much of a difference in performance or longevity.

Tommy

[KTL]

Thanks Tommy.

Reason I asked about the lifespan is because of the early wear-outs i've heard of regarding factory Porsche ZF limited slip units. The later G50 units (mostly 993 units from what I understand) have poor longevity friction discs and wore out in 20-30K miles!

So I figured i'd ask about the BMW LSDs. Are they manufactured by ZF as well?

Thanks for the info. on the fluid. Sounds like the same deal with Porsche LSDs. They don't seem to experience chatter like other makes, so the friction modifier (for those who don't know, 75W90 has it, 75W90NS does without the fm) is not necessary. But I imagine the standard stuff is the way to go since it has the fm that most LSDs like to see, which reduces chatter and smooths the locking characteristics of the diff.

Thanks again!

I just love how easy it is to change out the diff. on these cars. Can't wait to tackle mine someday.