The Official: DIY OEM M3 Rear Conversion- Sedan

Alright after much trial and error and no official DIY on the OEM m3 rear bumper conversion i decided to give it a go. Here is a detailed DIY that i have put together to help out my fellow fanatics.

By no means am i a mechanic and any work done i did on my own free will and at my own risk. I will not be responsible for anything that happens to your car during your installation. I am just showing you the procedures that i did to convert my non m3 sedan rear end into an M3 rear bumper. Work on your car at your own risk!

Materials needed:

OEM m3 rear bumper w/ diffuser
Prefacelift bumper brackets
4-6 self tapping screws
Dremel
Drill
assortment of sockets and tools

heres a couple pics of the brackets you must use



These next few pics will show you what the bracket looks like in its original position. Notice the metal flap the is in front of the bracket and keep that in mind.






Those are 10 mm bolts holding the bracket in place. Remove these bolts and pull the bracket out and put it off to the side. You will need these later. Now you will see 2 studs hanging down from the rear quarter panel. Heres where the cutting starts.

Take your dremel, and remove the 4 studs (2 on each side) as they will get in the way of the new modified bracket.



Next the metal flap that sits in front of the bracket needs to be cut like this. This has nothing to do with the bracket itself but has to do with the bumper. These flaps will not allow the bumper to travel the distance it needs to and cause a nasty gap at the fender as u can see. Here is what u have to cut.




here you can see what i mean by the flap blocking the bumper, in this pic u can see where the bumper is now able to travel.




Now that you have that squared away, its time to modify the brackets. Reasoning for this is because the brackets need to be placed closer to the body of the car so that the bumper could be pulled in to line up with the fenders.

This is what you have to cut on the brackets.


This is what the new modified bracket should look like.



Now comes the tricky part. Place the bumper on the bumper shocks, take your new modified bracket, place it in the bumper sliders and position the bumper in the correct place. Make sure everything is lined up the way you want it and mark where the bracket is sitting. Remove bumper.

Now take your bracket and a self tapping screw, and mount your new bracket in your marked position. After you have 1 screw in place, put your bumper back on check and make sure the fitment is how you like. If fitment is off, remove bracket and reposition. If its in the right spot, than you can put your second self tapping screw in place.







Now that you have your brackets mounted you can place your bumper on and check fitment on both sides. What you are going to notice (especially on sedans) is that your bumper will be 1.25 inches short of your fenders as shown.





Well this bothered me too much, so before you bolt up your bumper pull it off one more time.

Now get into your trunk and remove the 2 side plastic trays and the long plastic sheild along the backside of your trunk. Than disconnect the negative terminal on your battery, u dont want your airbags going off now do u? Underneath you will notice 3 13mm bolts on each side. These hold in your bumper shocks as shown.




After those are removed you can just pull out the entire bumper shock assembly.



Next pull off the black plastic cap on the rear end of the shock, underneath you will see a white plastic plug.




Now measure 1 inch on the shock, from where it enters the housing. All u need is 1 inch even tho i measured 1.25 it is 1 INCH!
Now heres the fun part. You will need to drill into the white plastic plug into the shock to relieve the pressure

*****PLEASE WEAR PROPER PPE (PERSONAL PROTECTIVE EQUIPMENT)*******

Goggles should be fine and a long sleeve tshirt. Reasoning behind this is because when you penetrate the shock, hydraulic fluid will fly everywhere and i mean everywhere.

Once you have penetrated the shock, push the shock in to your desired length (1 inch) More fluid will gush out and this is OK!. Once you have your desired length, take a screw and screw it into the hole that you just created. This is to seal the shock and keep the pressure that is still in the shock.



Do that to both sides, and reinstall the shocks in reverse order.


Now that your shocks are shortened and installed, its time to put your bumper on for final fitting!. If you still short, remove the shocks and screws and push it in another .25 inches at most. If not than bolt up your bumper and your good to go!

If eveything went well you should have something that looks like this!


.

If you have any questions feel free to PM me whenever ill be glad to help!

I'd like to know also, this is a mod I plan on doing in the next few months

bump! i want to know!

when i did it i took off my stock bumper shocks and replaced them with the m3 carbon kevlar bar, i then took off my rear bumper sliders, driller holes in the rear quarters and in the bumper and zip tied the bumper on and pushed the bumper sides in, i pulled my fenders out a bit to get it to sit more flush but didnt do much..heres some pics

Are we talking oem rear or rep rear? I did an Oem rear

Originally Posted by E46 S54B32

when i did it i took off my stock bumper shocks and replaced them with the m3 carbon kevlar bar, i then took off my rear bumper sliders, driller holes in the rear quarters and in the bumper and zip tied the bumper on and pushed the bumper sides in, i pulled my fenders out a bit to get it to sit more flush but didnt do much..heres some pics

Understood the bumper shock part but have no clue what you mean about the rest lol please explain in more detail. Which bumper sliders? The brackets or the sliders actually on the bumper.

Originally Posted by codyfunk

Are we talking oem rear or rep rear? I did an Oem rear

Oem rear. Please explain. I'm getting exhaust routed Tommorow and want the bumper fitted right before I go in

I started tonight, will finish up tomorrow and give you guys info as I find it out. There are many ways I have heard to do this, so I am going to try them out. I have the oem Kevlar bar, extra bumper brackets and will shorten the bumper shocks if necessary

I would love to do this to my ci sometime

I had to cut the tips and use my 330 rear bumpers tips and kevlar'd the back side and cleaned up the front. The M3 is quite a bit wider afaik, the quarter panels come out about an inch and a half further than the coupes. not sure about sedans. I used all factory mounting materials though, bumpers, impact shocks, side brackets, etc. That's OEM, i dunno about replica's from our sponsors though.

Originally Posted by cd330

I started tonight, will finish up tomorrow and give you guys info as I find it out. There are many ways I have heard to do this, so I am going to try them out. I have the oem Kevlar bar, extra bumper brackets and will shorten the bumper shocks if necessary

Thank bro, I just need to know what you did with the side brackets. Take pics if you can. I know I Have to shorten the bumper shocks which I'm gonna have the exhaust shop do Tommorow. But I just need to have the bumper fitted correctly before I go in. Just let me know how you modified the side brackets and how you re mounted them. Thanks bro

Btw our cars are gonna be twins. Same wheels same rear end same amount of doors just diff colors. Except you'll have pdc and I won't

I think you have to buy different ones, I remember reading that last year when I did mine. I don't wanna say it but do a quick search on it, somebody had posted their process somewhere.

Originally Posted by AW330

Thank bro, I just need to know what you did with the side brackets. Take pics if you can. I know I Have to shorten the bumper shocks which I'm gonna have the exhaust shop do Tommorow. But I just need to have the bumper fitted correctly before I go in. Just let me know how you modified the side brackets and how you re mounted them. Thanks bro

Btw our cars are gonna be twins. Same wheels same rear end same amount of doors just diff colors. Except you'll have pdc and I won't

Not a problem. I plan on doing a full diy for future members. My understanding is you may need to shave down the top section of the side bumper brackets that mount to the body, as well as drill new mounting holes in the modified bumper bracket. So that the bracket sits closer to the body.

Since it is facelifted, the side brackets I am talking about are from prefacelifted.

You need these....

yea those sliders that are connected to the car i took off completely...i actually shortened one slider and put it on but the other slider broke while in the process on shortening it..

Originally Posted by cd330

Not a problem. I plan on doing a full diy for future members. My understanding is you may need to shave down the top section of the side bumper brackets that mount to the body, as well as drill new mounting holes in the modified bumper bracket. So that the bracket sits closer to the body.

Since it is facelifted, the side brackets I am talking about are from prefacelifted.

You need these....

Yeah I know my car came with the mtech 1 body kit. It is a facelift but all mtech 1 kits came with prefaclift brackets so those arethe brackets I have on my car. Its kinda weird my car has a prefacelift and facelift kinda thing going on. I was planning on doing a diy as well so maybe when you put yours up I can maybe add some additional info to make it even better! This site def needs a detailed diy on this. As for exhaust I have an idea that's different than everyone elses, I plan on keeping my spare tire well aswell.

Originally Posted by AW330

Yeah I know my car came with the mtech 1 body kit. It is a facelift but all mtech 1 kits came with prefaclift brackets so those arethe brackets I have on my car. Its kinda weird my car has a prefacelift and facelift kinda thing going on. I was planning on doing a diy as well so maybe when you put yours up I can maybe add some additional info to make it even better! This site def needs a detailed diy on this. As for exhaust I have an idea that's different than everyone elses, I plan on keeping my spare tire well aswell.

Yeah, that would be cool. The DIY is really hard to find that has any detail into it. We could do a combo thread

I am keeping my spare tire well as well. You can see my setup in that pic. The piping goes around the spare and curves around the back. On side mounts in the muffler mounting area/hanger, the other side bolts into the spare well.

Originally Posted by cd330

Yeah, that would be cool. The DIY is really hard to find that has any detail into it. We could do a combo thread

I am keeping my spare tire well as well. You can see my setup in that pic. The piping goes around the spare and curves around the back. On side mounts in the muffler mounting area/hanger, the other side bolts into the spare well.

Yeah I know, you have darons old setup and I've seen pics. I'm going to be doing kinda the same. Except I Have 2 single 2.5 in 2.5 out 4 inch Magnaflow mufflers. I'm deleting my second resonator. I'm going to try and route the passenger side exit around the other side of the differential casing, and the driver side routed down its normal path. The mufflers will prob be placed around the 2nd resonators position. If that doesn't work I'll just place the 2 mufflers where the 2nd resonator is and run the pipes just like you have them. Well see what works though.

But for sure on the dual thread. I feel many people could benefit from this.

so did you test fit the bumper at all today? How did you mess up one of the brackets?

Originally Posted by cd330

so did you test fit the bumper at all today? How did you mess up one of the brackets?

Well when I pulled my stock bumper off, on the driver side bracket the piece that holds the metal retainer which attaches to the fender liner was broken off. So now I can't attach the fender liner on that side. Than I tried to shave down the passenger bracket and I ended up cutting it too short. It ended up pulling the bumper too far in. I also could not find a good mounting spot with it. I ended up running out of daylight so I called it a night ( garage is filled with all my sisters furniture). I'm just gonna go get 2 new brackets Tommorow. I'll play around with the broken ones first and see what I have to do. Than attack the new ones. Im pretty sure that were going to Have to shave te 2 Studs that hang down from the body that mount the brackets. They are in the way for mounting the new modified brackets

Yeah, I had a problem getting my bumper off today as well. One of the filister screws was seized in to the top of the reinforcement bar. It ended up shearing off. I ended up getting the screw out, but it was a total nightmare and will have to be addressed tomorrow.

Looks like I am going to have fun with those mounting brackets as well

How are you going to shorten your bumper shocks? cut and re-weld? back into a wall? lol....