Convertible Suspension Refresh: Mixing Spring Brands Based on OEM Part Numbers?

[thrashandburnn]

Hello All,

I am currently in the process of refreshing my entire suspension setup on my '87 325i convertible. I have reached the point where it is time to replace the springs. I have decided to go with a bit of a more OEM+ path vs the typical H&R/Billstein combo. I live in Massachusetts, so the last thing I need is to hit a pothole the wrong way and lose my oil pan.

I have decided to go with the factory M-Tech suspension based on a 1991 325i MT2 VIN (WBABB1318MEC04986). So far, the OEM front springs (31331131330) are unavailable online or from the dealership. I have already acquired the rears (Part No. #33539057349), as those were still available. Cross-referencing that part number, I have come across various aftermarket/OEM supplier parts that match up to the factory part number. They are as follows:

- Bilstein 36-226917 OR Suplex 06024 (Seems to be the correct option)

So question number one is, do either of these parts seem correct based on the OEM part number?
Question number two is, Would it be okay to pair the Bilstein or the Suplex springs aftermarket rear springs based on the OEM part number?\ The rear springs I bought are Lesjofors 4208423 based on part #33539057349.

I know this probably seems stupid to a lot of you, but I've been trying to find answers for months, and I'm finally at the point where I need to consult the wisdom of the R3V Wizards.

Thank you in advance!

Sam

[82eye]

did you make sure you had the vert springs ? regular m-techs won't work for the rear. you need vert specific springs.

[thrashandburnn]

did you make sure you had the vert springs ? regular m-techs won't work for the rear. you need vert specific springs.

Yes, the VIN is for a 1991 325iC

[82eye]

Yes, the VIN is for a 1991 325iC

it'll work then. vert springs can be hard to source. all the e30 springs were supplied by h & r if you have trouble sourcing.

[thrashandburnn]

it'll work then. vert springs can be hard to source. all the e30 springs were supplied by h & r if you have trouble sourcing.

So then it should be okay to run Bilstein or Suplex in the front while running Lesjofors in the back? I've only found the basic vert-specific lowering springs on the H&R website. Not what I'm looking for.

[Mike36]

Is your car an Mtech II?

[thrashandburnn]

Is your car an Mtech II?

No, Base 325iC

[reelizmpro]

I wouldn't try to order M technic springs based on RealOEM numbers these days. Firstly, M technic springs have been NLA for many years. As E30's are 40+ years old, what BMW does is consolidate and supercede old PN's with new ones and the new one is likely a standard spec part. The reverse can also be true, the new standard spring could actually be an M technic spring although I think this is unlikely. If you cross reference the numbers they come back to many base model cars so don't be surprised if you don't get what you thought you were getting.

I remember a while back, people were saying early 318i's had M3 front springs because the PN was the same on RealOEM. This doesn't mean the springs that came on the early 318i originally are the same as E30 M3. It only means, this is what they spec for both cars currently.

BTW, the rear springs you ordered do not come back as M technic springs in RealOEM even with the M tech vin you provided. Only the front springs are listed as M tech.

[thrashandburnn]

I wouldn't try to order M technic springs based on RealOEM numbers these days. Firstly, M technic springs have been NLA for many years. As E30's are 40+ years old, what BMW does is consolidate and supercede old PN's with new ones and the new one is likely a standard spec part. The reverse can also be true, the new standard spring could actually be an M technic spring although I think this is unlikely. If you cross reference the numbers they come back to many base model cars so don't be surprised if you don't get what you thought you were getting.

I remember a while back, people were saying early 318i's had M3 front springs because the PN was the same on RealOEM. This doesn't mean the springs that came on the early 318i originally are the same as E30 M3. It only means, this is what they spec for both cars currently.

BTW, the rear springs you ordered do not come back as M technic springs in RealOEM even with the M tech vin you provided. Only the front springs are listed as M tech.

Ah I See the deilemma here, I figure its worth a shot though right? Also, I thought only front springs were M-technic specific? Rears should be the standard, at least for convertibles no?

[reelizmpro]

Right, only one way to find out. I looked into the rear springs and RealOEM shows there are M tech rear springs as well.

33539058543 is listed as an M tech rear spring for 325i convertibles EURO spec.

[thrashandburnn]

Right, only one way to find out. I looked into the rear springs and RealOEM shows the M tech rear springs as well.

33539058543 is listed as an M tech rear spring for 325i convertibles EURO spec.

Just so I'm on the same page, the rear springs I need are 33539058543 and for the fronts would it be 31331131333 or another part number that I have to be digging for? I know I can't be 100% certain but at this point it's a risk I'm willing to take.

[82eye]

based on the year you'd be looking for 31331131027. considering they are all euro market i'm not sure how you're sourcing them here.

[thrashandburnn]

based on the year you'd be looking for 31331131027. considering they are all euro market i'm not sure how you're sourcing them here.

So I can’t use LCI MT2 springs on the front? Seems like that part number is fro pre-LCI cars? My goal is to have the same suspension setup as cars with the 704 M Technic suspension

[82eye]

So I can’t use LCI MT2 springs on the front? Seems like that part number is fro pre-LCI cars? My goal is to have the same suspension setup as cars with the 704 M Technic suspension

all the part numbers are euro specific if you look at realoem. if they are available it will be from that market. ordering or sourcing them from here may not work out so well. some set ups are very specific. the fronts change on certain years if you have a/c etc.

really sounds like a crap shoot. if the supplier doesn't have the specific one wanted you will get sent one with a superseded part number by default. which will not likely be what you are looking for.

edit : h&r made all the springs. all the m-tech really were is a sport spring. h&r have a few you could choose from to end up at the ride height and handling you are looking for.

[reelizmpro]

I came up with many different "M tech" part numbers based on different setups and if it's euro spec BMW won't sell it to you. Safe bet is to run H&R cabrio specific springs. Yes, you can buy thicker pads or even stack old pads.