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Thread: Hardware to mount X-brace to 91 850

  1. #1
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    Hardware to mount X-brace to 91 850

    Anyone have a list of additional nuts and bolts required to mount the x-brace to a 91 e31. I have done some searches, but no parts list. I remember seeing a DIY...

  2. #2
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    how about just checking out the ETK? It's all in there.

  3. #3
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    Wolf, the ETK doesn't apply here. On cars that came with the X-brace, there were threaded holes from the factory out by the pinch welds, to bolt the ends of the bars to ; they don't exist on early cars. The best way I know to add the X-brace is to weld a small chunk of angle iron to the bottom of the car and then run a nut and bolt thru it and the bar. Much better and stronger than trying to install a nut-sert fastener.
    How come the middle half of any project always takes the most time?

  4. #4
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    Yes been there done that.

    The difference is there 92+ cars have different torque boxes with the stamping and welded nuts required to install the brace fully.

    I have had a long think over it and at the end a threaded insert isn't going to do much as the torque boxes are spot welded to not only the floor, they are welded to the engine perch rails and the rockers, both are main structural pieces.

    As the torque boxes are fairly thin, it is their stamped shape that enables them to transmit forces to the frame bits described earlier.

    With that understanding, the only options are either welding brackets or square tubes to the torque boxes as spacers but ensure they are taken all the way to the frame rails and rockers. Other option is to buy the sheet metal from bmw, replace the torque boxes with the later ones and effectively updating your car to 92+ spec, which I've done.

    Now after all that, many members here have just simply sawn off the brace extensions and forget about the torque box fasteners. And to be honest, unless you autocross your car or have OCD like me you're probably not going to gain much extra.

  5. #5
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    Quote Originally Posted by Max Lumens View Post
    Wolf, the ETK doesn't apply here. On cars that came with the X-brace, there were threaded holes from the factory out by the pinch welds, to bolt the ends of the bars to ; they don't exist on early cars. The best way I know to add the X-brace is to weld a small chunk of angle iron to the bottom of the car and then run a nut and bolt thru it and the bar. Much better and stronger than trying to install a nut-sert fastener.
    IMO it does apply because it shows the adapters incl. bolts (#3 and #4) needed to mount the X-brace to the subframe.
    And regarding the extension I have to correct you. Some pre '92 cars (may be only ECE spec?) do have the frame extensions but a non matching threaded hole. My yellow 850 (03/1990) is one of them while my black one (03/1991) doesn't. Pretty strange indeed and I can't detect any logic in there.
    Since any welding and/or drilling is a potenrtial new spot for corrosion i decided on both cars to just ignore the X-brace extensions and left them unfastened. I didn't even cut them but have them "hang loose". Still a massive improvement.


  6. #6
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    Yup, there are definitely brackets and such that one will need from the ETK. I can confirm that.

    Mine 11/91 had wrong holes and no welded nuts inside. Yup, no logic there. The height of the stamping is also wrong. Too much schnapps on that shift at dingolfing I think.... You sent me pics from your yellow car when I was researching and I got even more confused haha.

    If my torque box stampings were at least at the correct height I would have just drilled new holes and use hi torque threaded inserts.

    Spot welds are not too damaging to surrounding paintwork/undercoating and easy to rust proof if it's done right. It's no worse than factory as I don't believe the E31 chassis was dipped...

  7. #7
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    Thanks.
    The x-brace and upgraded sway bars are parts of my suspension upgrade.
    I will eventually figure out the installation, but you pros have 'been there done that'. I will usually ask first unless it seems obvious. And even then...the easiest ones sometimes get you.
    Thanks for your input.

  8. #8
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    Quote Originally Posted by wokke View Post
    IMO it does apply because it shows the adapters incl. bolts (#3 and #4) needed to mount the X-brace to the subframe.
    And regarding the extension I have to correct you. Some pre '92 cars (may be only ECE spec?) do have the frame extensions but a non matching threaded hole. My yellow 850 (03/1990) is one of them while my black one (03/1991) doesn't. Pretty strange indeed and I can't detect any logic in there.
    Since any welding and/or drilling is a potenrtial new spot for corrosion i decided on both cars to just ignore the X-brace extensions and left them unfastened. I didn't even cut them but have them "hang loose". Still a massive improvement.

    Bit OT, is the front subframe of the e31 similar, or almost identical to that of an e32?
    Meaning would this cross brace bolt into an e32?

  9. #9
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    Quote Originally Posted by whiteghost1 View Post
    Bit OT, is the front subframe of the e31 similar, or almost identical to that of an e32?
    Meaning would this cross brace bolt into an e32?
    Yep. You can use it on the E32 as well as on the E34. I've mounted it on both already. Straight forward bolt on job as on the E31. In these cases I only did cut the extensions of the X-brace.
    One customer of mine has an E34 track car and upgraded it with the X-brace. Best upgrade ever to the suspension he says.
    Last edited by wokke; 09-18-2014 at 03:30 AM.

  10. #10
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    I was only talking about attaching the outboard ends re: the welded angle iron bracket.
    How come the middle half of any project always takes the most time?

  11. #11
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    For you guys that have added the X-brace, did you also get the new heat shields as well?
    Live, Love, Life, Amazing...

  12. #12
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    Quote Originally Posted by peezen View Post
    For you guys that have added the X-brace, did you also get the new heat shields as well?
    No heat shields renewed on my cars. I actually removed them because they were broke and sometimes rattled which drove me nuts.

  13. #13
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    Awesome, thanks Wokke!
    Live, Love, Life, Amazing...

  14. #14
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    Quote Originally Posted by wokke View Post
    Yep. You can use it on the E32 as well as on the E34. I've mounted it on both already. Straight forward bolt on job as on the E31. In these cases I only did cut the extensions of the X-brace.
    One customer of mine has an E34 track car and upgraded it with the X-brace. Best upgrade ever to the suspension he says.
    Just the man I was hoping would respond - cheers!

  15. #15
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    Has anyone fabricated an aftermarket X-brace for these cars?

  16. #16
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    Why would you want that? What are you hoping to gain over the factory x-brace?

    If the thinking is that a custom piece will make the rear extensions fit on a pre 92 then it's really a fool's errant IMO.

    This is because the post 92 torque boxes (i.e. the pieces of stamped metal that goes from the rear of the wheelwell to under the footwell, its used to spread engine torque and chassis loads to the rest of the chassis rather than just the engine cradle and firewall interface) are stamped differently to take advantage of the x-brace to transmit forces to the structurally stronger parts of the chassis rearward past the firewall.

    If this wasn't necessary then bmw could have easily made the x-brace's extensions so that it sits perfectly on the pre 92 torque boxes, all they needed to do then was to put a couple of weld nuts on it.

    But they didn't, it was a new stamping. I'm of the opinion that beancounters never approve new parts revisions unless it's necessary.

    My speculation is this - after the initial release of the car it was found out the front box is a bit weak (if you imagine the car as 3 boxes, engine, passenger and trunk), so they need a brace too keep the lower suspension points in their relative positions. Then they also found out the chassis is also a bit weak under torsional load between the front and middle box (picture a drag car lifting one front wheel on take off, though from suspension loads rather HP lol). So they extended the brace's design PAST the front box into the passenger box, effectively increasing the torsional rigidity between the front and rear suspension points. Voila, you have the shape of the x-brace we have today.

    <Edit> the extensions might also have a lot to do with allowing the use of thicker anti roll bars after 92 for the csi because the ARB mounts are OUTBOARD of the pre 92 crossmember or X without the extensions (cantilevered), in which case under load your ARB will be bending the ends of the crossmember or a sawn off X-brace and/or twisting the front box only. Still the rationale is largely the same as above. In any case I'm pretty certain in my head that this engineering change came from the development feedback of the csi. Very convenient timing. </edit>

    So, again it's just my opinion - either cut off the extensions and be happy that you fixed problem 1 or go the whole hog and fix both issues.
    Last edited by affa; 03-19-2018 at 06:34 AM.

  17. #17
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    Quote Originally Posted by affa View Post
    Why would you want that? What are you hoping to gain over the factory x-brace?

    If the thinking is that a custom piece will make the rear extensions fit on a pre 92 then it's really a fool's errant IMO.

    This is because the post 92 torque boxes (i.e. the pieces of stamped metal that goes from the rear of the wheelwell to under the footwell, its used to spread engine torque and chassis loads to the rest of the chassis rather than just the engine cradle and firewall interface) are stamped differently to take advantage of the x-brace to transmit forces to the structurally stronger parts of the chassis rearward past the firewall.

    If this wasn't necessary then bmw could have easily made the x-brace's extensions so that it sits perfectly on the pre 92 torque boxes, all they needed to do then was to put a couple of weld nuts on it.

    But they didn't, it was a new stamping. I'm of the opinion that beancounters never approve new parts revisions unless it's necessary.

    My speculation is this - after the initial release of the car it was found out the front box is a bit weak (if you imagine the car as 3 boxes, engine, passenger and trunk), so they need a brace too keep the lower suspension points in their relative positions. Then they also found out the chassis is also a bit weak under torsional load between the front and middle box (picture a drag car lifting one front wheel on take off, though from suspension loads rather HP lol). So they extended the brace's design PAST the front box into the passenger box, effectively increasing the torsional rigidity between the front and rear suspension points. Voila, you have the shape of the x-brace we have today.

    <Edit> the extensions might also have a lot to do with allowing the use of thicker anti roll bars after 92 for the csi because the ARB mounts are OUTBOARD of the pre 92 crossmember or X without the extensions (cantilevered), in which case under load your ARB will be bending the ends of the crossmember or a sawn off X-brace and/or twisting the front box only. Still the rationale is largely the same as above. In any case I'm pretty certain in my head that this engineering change came from the development feedback of the csi. Very convenient timing. </edit>

    So, again it's just my opinion - either cut off the extensions and be happy that you fixed problem 1 or go the whole hog and fix both issues.
    Thanks for the info and explanation! The only reason I asked about an aftermarket brace is because I cannot find a brace stateside.

  18. #18
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    I bought mine direct from bmw a few years ago. May be it's nla now but it was only 130 or something like that... the new torque box panels are about 30 bucks a side. Good luck!

  19. #19
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    I lucked out and found an X-Brace on Ebay earlier this week. It arrived today and its in great shape. Waiting on a few pieces of hardware so I can install it soon. The seller put another one on Ebay a day or two ago, but it has already sold.

    IMG_20180922_144434972.jpg
    IMG_20180922_144420945_HDR.jpg

  20. #20
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    my first post! I have an 850i built 11/91, have done rear sub frame mod and installed 17mm csi bar, also test fitted the front cross brace and Csi 27mm bar. could do with a part number for the "torque Box" mentioned in these threads in order to secure outer ends of x-brace, just want to see the drawings, but realoem doesnt show the floor panels. Thanx for all the information and pictures on the forum, it has been great help in restoring my vehicle so far

  21. #21
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    I have not found time to climb under my car to mount the X-brace I bought recently. Here are a couple of links to other threads on the brace. There is an adapter, part #3, and I bought a couple of them recently. I have also seen where someone took what looks like a piece of square tubing, cut the top side off, welded a nut on the inside, and then fitted and welded this mount onto chassis so that the long rear leg of brace could be bolted on. I have not confirmed it yet, but there may be a gap of an inch of so between the long rear legs of brace and where it meets the chassis which is why the square tubing bracket was made to fit leg to chassis. i just cannot find that thread.

    https://webmail.roadrunner.com/do/re...7c314479c1580c

    https://webmail.roadrunner.com/do/re...272f058c374e53

    https://webmail.roadrunner.com/do/re...ae3c354e468b8f

  22. #22
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    Question on installation of X-brace on early E31. Will I need to set rivet nuts in subframe to mount the two adapters item # 3 in drawing, part 31111140576? I have the adapters but I have not found time to climb under car. Thanks,

  23. #23
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    Quote Originally Posted by malcolmstevenso View Post
    my first post! I have an 850i built 11/91, have done rear sub frame mod and installed 17mm csi bar, also test fitted the front cross brace and Csi 27mm bar. could do with a part number for the "torque Box" mentioned in these threads in order to secure outer ends of x-brace, just want to see the drawings, but realoem doesnt show the floor panels. Thanx for all the information and pictures on the forum, it has been great help in restoring my vehicle so far
    I found the thread where Bryson fabbed up some brackets to fit the rear xbrace arms to chassis: https://www.bimmerforums.com/forum/s...E31-Guys/page2

  24. #24
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    I finally mounted the X-brace on my car today at a new DIY shop where a lift is available. I did not realize that I needed shorter anti-sway bar links so I will have to go back tomorrow with some adjustable links. I also spent some time making up cardboard templates so I can fab some brackets out of 1.5" square tubing like Bryson made for his car so rear arms can be bolted down at the ends.

    I am thinking about stitch-welding the brackets onto floor of car and I am wondering if DMEs need to be unplugged when welding on the car. I sure don't want to damage them from welding current. Thanks,

    IMG_20181101_163539662.jpg

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