Starting M3 rear end/diff swap doityourself

[Jlastor]

Well, today I will finally start doing the M3 rear end swap. I will probably take about a week (hopefully not longer) to complete the job since I will be doing it in the afternoons after work. I will be using my dads "spare" car during this process.

I have searched everywhere trying to find a nice write-up about this swap but have not found anything. Only comments about people who have done it. I want to write this in order for everyone considering it, to have something to read before buying anything. This thread will most probably not be a DIY, but more as a guide to what you can encounter and what could help along the way.

Ok, lets get started,

What I have purchased until today (hopefully I wont have to buy any more parts):

-rear subframe (you have to make sure it comes with both rods, one shaped like a V and the other goes beneath the carrier, the carriers listed on ebay do not come with these rods)

-driveshaft

-axle shafts

-trailing arms, control arms, brakes (I wont use the M3 ones since I want to keep the installation as simple as possible, plus I dont want to bleed the brakes)

-rear sway bar, original M3 (bought it new through ECS for $69, limited time offer)

-rear sway bar links, bushings (might as well change them and since Im already there)

-front sway bar (got it free from a friend, and will be a nice compliment so have the complete M3 setup) I already had the M3 strut brace, also free from the same friend.

-front sway bar links (mine are in need of replacement anyways)

-guibo

-ALL new nuts, bolts, seals, etc. (basically I went to realoem.com and got everything that had a different part number. This was $553.00 in a local shop. I dont want a delay for not having a $0.58 nut, for example)

-new BMW lsd fluid (its supposed to be the best for this diff)

Hopefully I have everything I need. If something delays me, it could be a tool or need for help. I will have a friend, he has done this before on all his e30's, helping me throughout most of the process. The swap will be done using four jack stands, and inside a garage with plenty of light and area to work on.

The only thing worrying me a little right now is getting the 330 axle shafts out. My car has 93k miles and they could be pretty tight. Anyone has had to take them out? Any suggestions on this? I will be using a puller, but sometimes even with a puller they can be a pain.

Scope of work for today:

-get the car lifted (on jack stands)
-take wheels off
-remove sway bars
-remove exhaust
-remove heat sheild
-learn my way around the area I will be working. Check to see if I need any tool, or additional part.

So, no more talking for now. I will probably get started by 3pm eastern time and work all the way through 7pm.

Feel free to ask any question. My email is jlastor@acemergencypower.com. And if you ever come down to Puerto Rico let me know!

[danewilson77]

Nice!

[ryankokesh]

Subscribed!


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[Ryans323i]

Wow. Hope this goes smoothly. Take pics!


BTW, you have the coolest name, Juan Luis. I love it.

[cakM3]

Juan,

Be sure to take a lot of pics and document your process. I'm interested to see how everything works out for you :thumbsup

[M3TA5IN]

Good luck man, should be pretty sweet when you're done.

Audi just swapped in a 3.91 LSD in his e36. I got to drive it the other day :biggrin

[Hornung418]

I'm all for keeping things simple, but why are you not going to use the M3 calipers? Bleeding the brakes is child's play.

Good luck.

I'm on the moon.

[terraphantm]

I'm all for keeping things simple, but why are you not going to use the M3 calipers? Bleeding the brakes is child's play.

Good luck.

I'm on the moon.

Brake bias perhaps? I think the M3 piston is larger than the 330 piston, and retrofitting the front calipers requires the entire front end suspension off an M3 iirc.

[Hornung418]

Brake bias perhaps? I think the M3 piston is larger than the 330 piston, and retrofitting the front calipers requires the entire front end suspension off an M3 iirc.

Shouldn't matter. 3ers are designed with rear bias. If anything, performance should be improved? :dunno

I'm on the moon.

[iZHP]

Fantastic! Looking forward to the results :)

[az3579]

Shouldn't matter. 3ers are designed with rear bias. If anything, performance should be improved? :dunno

I'm on the moon.

If that was correct, then the rear brake pads would wear quicker than the fronts, which just isn't the case.

[Hornung418]

No, Front pads wear faster because the car is moving forward and where all of the weight is under heavy braking. e46s are rear biased. Improving the rear breaks increases stability under braking.

[terraphantm]

No, Front pads wear faster because the car is moving forward and where all of the weight is under heavy braking. e46s are rear biased. Improving the rear breaks increases stability under braking.

No E46 is rear biased. In all cases, the front piston is significantly larger than the rear piston, and the front rotors are usually larger than the rear rotors. In most cases this results in a brake bias of ~2.0:1 F:R, some a little more, some a little less. The most rearward biased E46 is the CSL/ZCP with a F:R bias of 1.76:1

The rear brakes would lock up very quickly if the brakes were 1:1, let alone actually rear biased.

[Hornung418]

My mistake, I didn't mean to say that the ratio was 1:1.XX F:R. Merely that if you send some of the bias to the rear, such as the CSL, you can gain a hint of stability and decrease stopping distance because the brakes are more balanced.

I still think that if you are going to swap the rear of an M3, why not do the rear calipers?? Just don't think it makes sense to go through all the trouble to do this and not use the rotors, pads and calipers.

[mimalmo]

You can do the M3 brakes as long as you swap the trailing arms and other associated hardware back there.

Those M3 swaybars you got from your friend won't fit your non-M.

[terraphantm]

You can do the M3 brakes as long as you swap the trailing arms and other associated hardware back there.

Those M3 swaybars you got from your friend won't fit your non-M.

Fronts would fit. Rears won't without swapping all the rear hardware afaik (or maybe the subframe alone is enough, idk)

A common "OEM" upgrade iirc is the front M3 bar and xi-rear.

[mimalmo]

Like I already said, he'll need the rear trailing arms and everything else back there in order to do the rear brakes. They fit, it's just the mounting points that are different.

The rear swaybar absolutely will not fit. The front M3 sway bolts on but since you have to use the non-M rear sway, you end up with a very stiff front and a looser rear which if I recall correctly, induces understeer.

[Jlastor]

Hey guys! Thanks for the comments!

Well, Im not doing the rear brakes (although I have the trailing arms, calipers, and rotors) to keep swap as simple as possible. But also because I would have to get new pads, new rotors (the ones I have are rusted), and I dont know the condition of the e-brake. But that will come in the future, just want the diff swap for now.

For yesterday's work, I was able to get most of the things out of the way. I also inspected everything down there and was glad to see that the swap should go along well; no surprises for now.

I will be posting pictures as soon as have some real progress.

The only bad news is that I will not be able to work on the car probably until next Monday since I forgot that Im the best man for my friends wedding this weekend. So I have several activities tomorrow and the rest of the weekend. The good news is that to make up for the lost time I bought myself a set of ebay headers and a Shark Injector lol. But I will install those after the diff swap in order to really feel the difference of only the diff.

Thanks!!

[Sinister]

Can't wait the see progress pics!!! I have a full rear sub frame sitting in my garage right now. Waiting on more funding for extra parts (adjustable control arms, reinforcement kit, etc) and some rear diff service items. Good luck!

http://sphotos.xx.fbcdn.net/hphotos-ash4/305638_10100584575852310_20903873_48828619_1090782 863_n.jpg

[danewilson77]

Sinister in the hizouse. Good seeing you. Good luck on the swap.

Subscribed!

[Hornung418]

Nice!! I've got my eye locked on one as well. Are you going to keep it 3.62? I'm converting mine to M5 3.15 R&P.

[terraphantm]

Nice!! I've got my eye locked on one as well. Are you going to keep it 3.62? I'm converting mine to M5 3.15 R&P.

Since he's got a 6-speed, the 3.62 wouldn't be that bad. His top gear revs would actually be lower than yours with a 3.15

[az3579]

Since he's got a 6-speed, the 3.62 wouldn't be that bad. His top gear revs would actually be lower than yours with a 3.15

About 2800 or so at 70. Seems a little high, but not too much higher than stock. Definitely doable!


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[Hornung418]

The whole thing that I think is pointless is the fact that you're missing that extra grand of revs. The gearing is stupid short. 3.15 would allow for better driveablility.

[terraphantm]

The whole thing that I think is pointless is the fact that you're missing that extra grand of revs. The gearing is stupid short. 3.15 would allow for better driveablility.

Eh not really - unless you redline each gear every time when cruising normally, slightly shorter gears will not pose a driveability problem. My car came w/ a 3.62 from the factory - I find myself shifting around 3000-3500 in most gears. I don't find myself having to shift excessively or anything like that. Also keep in mind that the 323/325 5MT verts also came with 3.46s and those cars were plenty driveable. Cruising revs were a bit high for my tastes... but that's with a 5-speed. Now as far as maximum acceleration goes - yes your maximum speeds in each respective gear will be reduced. But you'll accelerate at a quick enough rate that it's not really an issue. 0-60 may be slower, but 30-50, 50-70, 70-90, etc... should be quicker. 1/4 mile will also be slightly quicker. So that's really a nonissue there.

The only real concern IMO is the cruising RPM and fuel efficiency. 3.62 in 6th is almost the exact same ratio as a 3.07 in 5th. No biggy.

Now if you have a supercharger, then gears that short would be useless. You'll burn through 1st and 2nd anyway. But a 330 is deficient enough in torque that it could make good use out of a shorter diff.

[LeontiyZHP]

I havent read much about this, but what is the benefit of doing this? What would be improved? Any reads on this?

Are you done with te swap?

[Hornung418]

I'm lost here. Is the goal to get a Limited Slip Differential or get a short ratio Final Drive?

Each one has their benefits but for a car that comes with a 3.07 diff from the factory wouldn't you want to retain stock performance at the cost of MPG, and still have an LSD? Even if I had a 6 speed transmission, I'd opt for the M5 r&p simply because there are not enough revs in the car to enjoy the 3.62.

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[derbo]

I'm lost here. Is the goal to get a Limited Slip Differential or get a short ratio Final Drive?

Each one has their benefits but for a car that comes with a 3.07 diff from the factory wouldn't you want to retain stock performance at the cost of MPG, and still have an LSD? Even if I had a 6 speed transmission, I'd opt for the M5 r&p simply because there are not enough revs in the car to enjoy the 3.62.

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The benefit would be the LSD in my opinion. As far as enjoying a 3.62, you can definitely enjoy it even with a lower redline! I know for myself, turn 2 at infineon is in 3rd gear but however I am around 3000RPM going uphill and the ZHP feels like it got hit by an invisible wall. :(. Adding a 3.62 would set up the 3rd gear a little higher and allow me to push right up that hill in the prime torque powerband. By changing the gear ratio, the car would feel more alive and ready to pounce whenever you hit the gas. You will have to shift more due to lower mph redlines at each gear and it would suffer at MPG due to higher RPMs are normal freeway speeds. Top speed suffers as well but hey, how many of us reach 155mph on a normal day anyways? The car will have about a 18% increase in acceleration.

I know a 3.46 gear ratio with a 6spd increases 12% acceleration from a 3.07. :)



But awesome to the OP. I love to have myself an M3 LSD. I'll probably do one down the line. If not, its 3.46LSD here i come.

[terraphantm]

I'm lost here. Is the goal to get a Limited Slip Differential or get a short ratio Final Drive?

Each one has their benefits but for a car that comes with a 3.07 diff from the factory wouldn't you want to retain stock performance at the cost of MPG, and still have an LSD? Even if I had a 6 speed transmission, I'd opt for the M5 r&p simply because there are not enough revs in the car to enjoy the 3.62.

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LSD and shorter ratio aren't mutually exclusive.

A shorter ratio does not *reduce* performance. It will reduce the top speed in each gear, but overall acceleration should improve (0-60 may suffer slightly due to an extra shift, but there are plenty of cars out there that don't hit 60 'til 3rd anyway). Absolute top-speed will not be effected since the 330 does not have near enough power to max out 6th gear with a 3.07.

I don't really see why you think it'd prevent you from enjoying the car either. For cruising around - just increase your shift points by a couple hundred RPM (so if you used to shift at 3000, shift at 3500 after the swap). For maximum performance, I think the shorter gears will make it more fun. Part of what makes a fast car feel fun is that kick you get in the back of your seat. And I do remember when I had my 330 that the gears felt unreasonably long; it felt like it took eons to max out 3rd gear. So if I can get a little better use out of my gears, I would.

Now if i had a 5-speed, I wouldn't do it. The cruising revs become too high. 4000+ RPM at 80mph would get old. Shortest I'd go with a 5-speed 328/330 is probably 3.23 (like the E36 M3)

[Sockethead]

Back in the day when I was drag racing, I ran a 4.57 in the rear with a 4 speed and 1:1 4th gear... Going through the gears with 400+ HP was awesome but 3500 rpm at 55 mph was annoying. I switched to 4.11 and that was acceptable even with a 1:1 fourth gear. After I blew up my good motor, I stuck a stock V8 in the car and I was still blowing the doors off of most other cars, even big block Chevy's and Mopars that were using a stock gear in the back...those gears made that much of a difference in acceleration
A 3.62 & a 6 speed should be fine... and believe me, the first time you go through the gears, you're going to have a huge grin on your face. :biggrin The increased acceleration will make you think that you just added a shit load of HP to the car.

[Jlastor]

First of all sorry for the delay. I ended up paying (with beer, lol) a mechanic friend of mine to do the job. I could have been able to do it, but something told me to get someone who had previous experience in case anything came up, and something came up.

I finally got the car back last week, and have been driving around before writing in order to tell you guys my opinion on driveability/performance.

Basically the the swap CAN be 100% "bolt off and bolt on swap", but that will depend on what you are willing to change. I will write what happened in my case, if you have done this before and disagree with what I had to do in order to get this swap don correctly feel free to comment.

I will divide this into two sections, the swap, and my opinion on driveability.

Note:
My car is a 2003 zhp 6MT. Parts came out of a 2003 M3 convertible SMG. Just in case.

Ok,

The swap:

1- Driveshaft, diff, carrier, and suspension all bolts back up perfectly. As if intended by BMW to perform this swap.

2- Exhaust (I have UUC by Corsa TSE3-L, with stock resonators) fits pefectly. If you have either stock or aftermarket you will not have a problem. I say this because someone told me that maybe I would have to delete one of the resonators in order for the exhaust to clear the larger carrier/diff. No problem here :)

3- As you may be wondering, yes I had issues with axle-shafts/trailing arms. Good news is that you have two options on getting this solved. First of all, when I was doing my research everyone told me that I would not have to change the trailing arms, only the axle shafts. Well, that is incorrect. When we tried that method we found out that the M3 axle-shafts would be about 1.5 inches too short and would not get to the diff. We started wondering how could this be since the trailing arms are supposed to be "identical" in measurements (as I was told). We took one of the 330 trailing arms down to compare it with the M3 ones that I had. THEY ARE DIFFERENT! I mean, they can be swapped without issues but the M3 ones will get the M3 axles the 1.5 inches in to the diff.

So, thats when we started to figure out what our options were. I initially said, "well, I'll have to spend more money on more parts" since I would have to service the M3 rear brakes. But my mechanic and I insisted that somehow members in other forums had been able to do it without changing the trailing arms. Well, they are correct, kinda. You can use your stock 330 trailing arms, but you will need to reuse your 330 axle-shafts. That way the shafts get to the diff perfectly. By now you may be thinking that the bolt pattern on the shaft and flange are diffrent, you are correct. Only 3 bolts match.

Ok, so we have two possible solutions, either you change the trailing arms and axle shafts (and that would require getting new abs sensor, new brakes if the ones you got are worn and rusted like mine, new hub, new bearings, etc. All this to do a proper job.) or reusing the 330 parts. If you go with the 330 parts you would have the take the axle-shafts to a machine-shop and mill three additional holes to get all six bolts to "bolted" tho the diff flange.

I decided to simply go all out on this and got new rotors, pads, abs sensor, hub and bearings. And damn M3 parts are expensive! Twice or triple the price vs non-m parts. BTW - abs sensor changes, not getting into details, they just change.

My mechanic told me that most probably the people who say that they did not change the trailing arms, probably they took the car to an indy shop and the shop either used the 330 axles with 3 bolts, or drilled additional holes. But they definitely did not use the M3 axles. The 330 axle flange are forged, and it would not lead to problems if drilled properly and then use the M3 reinforcements.

4- I had originally said that you also need some rods (as illustrated in realoem.com). I bought them and they are not needed. They cost me $220 for both of them and you do not need them. They are only for structural reinforcement. I did properly weld two brackets to the body of my car in order to use these "rods", part numbers 33312229295 and 33312229899, since I had already paid them. And its probably a good mod.

All in all, it is not a cheap alternative as previously thought. I mean, I paid $500 for the diff, drive shaft, carrier, axle-shafts, trailing arms, and calipers. Then about $700 for all new screws, bolts, diff fluid, sway bar, rods, bushings, etc. Since I decided to do the M3 brake service about 500$ more on all that. Plus, all the beer, food, tools, and stress to get this done properly.

Total, $1,700 with free labor. You could spend upwards of $2,000 with labor. If you go the cheap way with 330 trailing arms and drilling the 330 axle shafts you could be just below $2,000, but not by much. And all that is because I got a great deal on the diff, carrier, etc.

It is probably cheaper and easier to get your stock diff an aftermarket LSD and gearing. But that is up to you. My best way was to do it like I did, since I was able to pay most of the things in cash and not all at the same time; gave me time to pay some parts first, then a couple of weeks later other parts.

Now to another subject equally important, and equally questioned.

Is if worth it? LOL! Its absolutely awesome!!!

Some of you guys have questioned whether the 3.62 gear ratio is too short for our cars. In my opinion, NO. My car drives perfectly fine for daily use. I cant feel a difference from stock when driving around the city. First gear is not that short and gear changes come with enough time between them. I mean, yes you do notice a difference, but its not that big of a difference. At highway my car is at around 2,600 rpm at 60-65 mph. At 70 mph Im at 2,990 rpm (lol, it just not 3k but almost there). At 75 mph its just above 3k rpm. And I even think my cars has better MPG's in the city.

Took the car for a 2 hour drive the weekend and it was a blast!! Had my dog with me so I did not have many spirited driving on the way to my destination. But on the 2 hour drive back, my wife took the dog on her car, and did a lot of different driving styles.

Is the 3.62 good for drag? I dont think so. I dont like drag so I dont care. But at WOT first gear is short. LSD does a fantastic job though.

How about in track like conditions? It is superb for track. Someone here (cant remember the username) was talking about Laguna Seca, it should be the best mod for that track. The car just goes on any gear, very alive. Third gear is a blast! The handling of the car is SO MUCH BETTER!! The new M3 front and rear sway bars I installed also help here!

My two hour drive was to a track day. I only did a few laps since all I wanted was to test the diff. I have new tires which I did not want to wear too quickly.

On the way back, as I was saying, I would put the car in 6th gear and drive at 65mph (2,700 rpm), then if I need to change lane all I would have to do is press the gas a little and thats it. The car felt like it was on 4th gear. So amazing how the car responds. Then I slowed down a little to 55mph downshift to 3rd, and WOT the car flies!!

Back to the city, and the car now responds like a normal car. If you have ever driven a R53 Mini Cooper S (the 2005 that had a tranny with shorter gears) you know that that car has really short gears, very fun btw. My car is not like that. As I said, my car drives more like stock, yeah with shorter gear but not that dramatically shorter.

Would I recommend this mod to anyone? ABSOLUTELY!!!

If you want a zhp that feels more alive this is the mod for you! If you want the advantage of an LSD on the track, this is the mod for you! If you ever wanted a e36 M3 but went with a newer car, this is the mod for you! There is no excuse (other than financial reasons) for not doing this mod.

I will be installing headers and shark injector soon. I have them here with me but want to do one thing at a time in order to feel the difference each mod makes.

After all this writing I cant remember if Im missing something. Feel free to comment and I will gladly help. If you want to email, text or call me I will leave my info here. If you call me and I dont answer please send me a text, because sometimes I cant answer. But I always answer text, and then call you back.

email - JLAstor@acemergencypower.com or juanluisastor@gmail.com
cel. - 787-221-8777

Hope this helps anyone!

Juan Luis

[Beau B]

Thanks for doing the write up on this, I have been wondering about this since all my bushing in the rear are shot. Does the M3 subframe have any benefits over the stock 330 subframe? beefier etc..? Lastly where did you find such a good deal on the M3 rear end?

Beau

[Jlastor]

The subframes are different and need to be changed. The M3 diff does not fit on the 330 subframe. I got a very good deal on these things because a friend of mine bought the same guy the s54 engine. So my friend offered $2k for engine and rear end and I gave my friend $500 lol. But the seller was kinda in a rush to get $$ quickly to buy another car.

[Beau B]

I was just trying to decide between just using the stock 330 subframe with an aftermarket LSD, or switching out the entire subframe over to M3 to give a little beefier rear end..

Beau

[Jlastor]

Id consider price first. Id look up for prices on aftermarket LSDs with a higher gear, 3.46 for example. I did not get that price since I got the M3 stuff for cheap. But I would recommend getting prices first since it is easier and faster, on the installation part, to keep the 330 diff. But if you can, the M3 rear end is a great mod, at least for me.

[06ZhP]

My mechanic told me that most probably the people who say that they did not change the trailing arms, probably they took the car to an indy shop and the shop either used the 330 axles with 3 bolts, or drilled additional holes. But they definitely did not use the M3 axles. The 330 axle flange are forged, and it would not lead to problems if drilled properly and then use the M3 reinforcements.


Did you guys ever try to swap the output flange from the zhp diff and install it into the M3 diff?

[terraphantm]

The changes you described can be attributed to having a shorter open diff... How does it feel around corners / when sliding?