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Installing the Lower Cross Brace on Your BMW
 
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Pelican Technical Article:

Installing the Lower Cross Brace on Your BMW

Time:

3-4 hours

Tab:

$25-$40

Talent:

****

Tools:

Flatblade screwdriver, metric socket set, ratchet, small ratchet, extensions, metric wrench set, pen and pad of paper, rubber mallet, Permatex High Temp RTV, torque wrench

Applicable Models:

BMW E36 3-Series (1992-99)

Parts Required:

Valve cover gasket or valve cover gasket set (for E36), spark plug hole gaskets (for E30)

Performance Gain:

No oil leaks from the valve cover

Complementary Modification:

Replace the spark plugs
101 Performance Projects for Your BMW 3 Series

This article is one in a series that have been released in conjunction with Wayne's new book, 101 Performance Projects for Your BMW 3 Series. The book contains 272 pages of full color projects detailing everything from performance mods to timing the camshafts. With more than 650+ full-color glossy photos accompanying extensive step-by-step procedures, this book is required reading in any 3 Series owner's collection. The book was released in August 2006, and is available for ordering now. See The Official Book Website for more details.

Many E36 owners upgrade their chassis with the factory crossbrace that mounts underneath the engine. This crossbrace was installed as stock equipment on all convertibles and the 1995 LTW, a lightweight version of the M3. The convertibles received this bar to stiffen up the chassis since their chassis are naturally less stiff than coupes or sedans because they have no roof. Installing the crossbrace on a standard E36 coupe or sedan serves a dual purpose: The crossbrace stiffens up the chassis and also protects the engine sump from road hazards.

 Quantity Part number Description
 1 51-71-8-410-212 Crossbrace
 4 07-11-9-915-093 M8x20-Z1 Allen bolt with washer
 4 51-71-8-175-003 M8 blind rivet nut (nutsert)

Installing a crossbrace is quite easy; the only difficult part is installing the inserts that attach the crossbrace to the front axle support bar. M3 cars manufactured after October 1994 already have these inserts installed. For all other cars, the holes are predrilled in the front axle support bar, but you will need to install the inserts.

The inserts corresponding to the crossbrace are called "blind rivet nuts", or "nutserts".The nutserts are installed into the front axle support bar and compressed against the sheet metal so they don't turn. They support loads from the attachment bolts.

First, jack up the front of the car and support it on jack stands (see our article on jacking up your BMW). Identify the four holes in the front axle support bar and remove any dirt or debris that may have gathered in them. Test-fit the nutserts into the holes. If they don't fit, chase the holes with a 7/16-inch or 11-millimeter drill.

Now, install the four nutserts into the holes. Use the procedure outlined in Photo 3. Check to make sure the nutserts are installed tightly and do not rotate in their bores. If they do rotate, pop out the insert and try again with a new one.

With the inserts installed, remove the support bar that runs just behind the rear of the engine sump. The crossbrace replaces this bar. Bolt in the new crossbrace and apply blue Loctite Threadlocker on the threads of the bolts as you install them. Tighten the larger rear bolts to 70 N-m (51.5 ft-lbs) and the smaller ones that mate with the nutserts to 27 N-m (19.9 ft-lbs).

There has been some talk in BMW circles about the benefits of welding the crossbrace in place. This is not a good idea, as it would require you to cut out the crossbrace if you needed to drop the oil pan to replace a seal or your rod bearings.

If you would like to see more technical articles like this one, please continue to support Pelican Parts with all your parts needs. If you like what you see here, then please visit our online BMW catalog and help support the collection and creating of new and informative technical articles like this one. Your continued support directly affects the expansion and existence of this site and technical articles like this one. As always, if you have any questions or comments about this helpful article, please drop us a line.

Figure
Figure 1

The factory lower support brace stiffens the chassis and provides undercarriage protection, especially for cars that have been lowered.

Figure
Figure 2

The E36 convertibles all have this brace installed as stock equipment from the factory. The crossbrace replaces the single cross bar installed as standard equipment on nonconvertible E36 models. The cross bar mounting points are shown with yellow arrows. The new nutserts need to be installed into the front axle support bar in the locations indicated by the blue arrows. As you can see, the crossbrace installed in this car has done its job--the bottom is scratched with scars from battles with the pavement. The bar also protects the bottom engine sump.

Figure
Figure 3

Installing the nutsert is the most confusing part of this relatively simple project. This photo sequence shows exactly how they work and how to install them without special tools.

A:
 Here's a close-up shot of the nutsert. The outer end of the nutsert contains threads. These threads will be used to install the nutsert and serve as the mating threads for the mounting hardware for the crossbrace. The lip on the other end butts up against the sheet metal in the front axle support bar.

B:
Apply red Loctite in two places on the nutsert--on the inside threads (yellow arrow) and along the bottom lip (green arrow). This will keep the bolt secure in the nutsert, and the Loctite on the lip will help keep the nutsert itself from turning in its hole. Note: Only apply Loctite on the lip of the nutsert right before you are ready to insert it into the front axle support bar.


C:
With the Loctite still wet, place a nut and two washers onto the hex bolt and then insert the assembly into the nutsert, making sure that at least some of the threads protrude out the end (see Frame E). Lubricate both sides of the washers with WD-40 or other penetrating lubricant prior to installing them on the nutsert (orange arrow). Be sure not to get any oil on the area where you apply the Loctite. Let the entire assembly sit for a few minutes as the Loctite hardens. Only use high-quality bolts and washers for this installation. Do not use a bolt and nut more than twice to install each fastener; after that, they may yield and break off under the force of installation.

D:
Insert the nutsert into the hole in the front axle support bar. For the purpose of demonstration, I installed this nutsert into a spare hole on some shelving in my garage. Use an Allen wrench to keep the bolt from turning, and use a wrench to turn the nut clockwise. I prefer the GearWrench ratcheting wrenches with the reversible switch because they have a lip that secures the nut while you tighten it (blue arrow). When you start turning the wrench, it will require a lot of force as the nut begins to deform. After a short while, it will get easier. When you can't tighten anymore, simply back off the nut and then unscrew the hex bolt. The nutsert should be tightly installed.

E:
You normally can't see this when installing the nutsert. The nutsert will deform (red arrow) as you pull the outer threads closer to the lip. This will create a small sandwich of metal material, and the nutsert will eventually be very tightly compressed around the sheetmetal hole.

F:
Shown here is the back side of the nutsert. You normally cannot see this because it is hidden in the recesses of the front axle support bar. The metal has been deformed so there is now a lip on both sides, effectively sandwiching the nutsert between the sheet metal (purple arrow).

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Comments and Suggestions:
daruma3gakoronda Comments: I'm trying to fit this on an e30, which can be done with slight modification according to http://www.r3vlimited.com/board/showthread.php?t=214718. I can't seem to find the P/N for the rear outserts, which is M10. Any ideas on the p/N?
May 30, 2016
  Followup from the Pelican Staff: I don't have any experience with that modification.

I opened a post in our forums. A Pelican community member may be able to answer your question.
- Nick at Pelican Parts
 
GK12BMW Comments: I disassembled my x-brace on my Z3 for a job on the exhaust manifold. When putting it back together I had some trouble getting the one of the bolts back in. So i used some carefull force to get it back in. After a few turns I decided that this couldn't be right and after loosening the bolt I noticed that I damaged the thread of the hole because there were some metal shavings on the bolt. After a lot of trial and error I managed to get to bolt back in and torque it to spec. Will this influence the structural integrity? If I need to remove the x-brace in the future is there something I can do to solve this problem?
March 25, 2016
  Followup from the Pelican Staff: If the bolt threads are repaired, it should be fine. Remove the fastener and discard it. Then tap or chase the threads and install a new fastener. Give our parts specialists a call at 1-888-280-7799. They can figure out what part or repair kit you need.
- Nick at Pelican Parts
 
Chriscotech Comments: Before you buy the nutserts and worry about the trouble putting them in, check your cross brace. It is possible that some cars, other than M3s and convertibles have them already. I have a 1995 328i coupé that had factory nutserts, just like my 1996 Euro M3. The X-brace just bolts onto both cars. Maybe it's just an Australian model thing yes, 328is started in 1995 here. I was relieved to find that fitting it was a 10 minute job.
February 29, 2016
  Followup from the Pelican Staff: Thanks for the additional info. We appreciate it.
- Nick at Pelican Parts
 
94vert Comments: Hey. I have a 94 318 very. I hit a rock and dented my brace. Ouch. Now I want to install a new one. There are two nuts that just turn where the nutserts are. What would you say my best course of action would be? Thanks
January 23, 2015
  Followup from the Pelican Staff: If the rivnut is spinning in the frame, you will have to cut the fasteners out, then remove the rivnuts and replace them with new. - Nick at Pelican Parts  
Eric Comments: About getting out a nutsert that is spinning: I bought a 95 M3 with one of the M8 bolts missing and it turns out that the nutsert was loose. Drilling out the old nutsert was a little bit of a challenge due to the nutsert spinning while trying to drill. What worked for me was using a much smaller drill bit and working my way up to a bit that was bigger than the inside diameter of the nutsert but much smaller than the outside diameter. This allowed me to slant the bit, i.e. not straight in, get some traction and not overbore the 7/16" hole in the frame. BTW, my nutserts were exactly 7/16" inch bought Sep 2013. Followed your instructions here to the letter and worked great. Thanks. BTW, for others here are the relevant part numbers:

M8X20-Z1 Hex Bolt with Washer BMW# 07119915093
M8 Blind Rivet Nut nutsert BMW# 51718175003
September 29, 2013
  Followup from the Pelican Staff: Thanks for the additional Info. We appreciate it.
- Nick at Pelican Parts
 
alex Comments: I have a 92 325i. I took my car to a shop to install my xbrace and they said they cant install it because the automatic transmission brace/support is in the way. Is the support bar able to be removed for the xbrace?
July 23, 2013
  Followup from the Pelican Staff: That should be replaced by the x brace.
- Nick at Pelican Parts
 
Pete Comments: Why not use nuts and bolts? Is it inaccessible to hold the nut w/ a spanner?
June 21, 2013
  Followup from the Pelican Staff: The bolts go into the subframe. There is no access point to hold them. You have to use a riv-nut. - Nick at Pelican Parts  
Pabs Comments: No this was before compressing it. I wasn't able to compress it since it wasn't able to grip to the holes. I'm sure I drilled it straight but you never know I might have made an error. I was just curious. They are in solid now of course with the weld and compression.
April 17, 2013
  Followup from the Pelican Staff: At times they will spin before and while compressing. You just have to do your best to hold them still. The rivnut is designed to be installed with a nah held tool, a rivnut gun. - Nick at Pelican Parts  
Pabs Comments: Just a question. I have a 95 318is. I went to install this today and when I used the 7/16 drill bit it bore it out but then the hole was too big for the nutsert and it didn't hold; it kept slipping out. I ended up holding them in with the Locktite red thread locker then I actually welded the edges of them to the subframe and they held great. I installed the crossbrace and tightened it to proper torque with no problem. Any reason as to why the 7/16 was too large? Just curious.
April 14, 2013
  Followup from the Pelican Staff: Is there a chance you didn't drill the hole straight? When you say it slipped out, this was after compressing it? - Nick at Pelican Parts  
kp29 Comments: Today I went to install the x-brace nutserts in my '96 e36, and I found that a 7/16" bit was insufficient to chase the cross member holes. Not even really close.
So I measured the diameter of the nutsert shaft with a dial caliper and they're 1/2". Why do your instructions for nutsert installation say to use a 7/16" bit when that is not large enough? Has the nutsert design changed?
December 4, 2012
  Followup from the Pelican Staff: The design might have changed. Thanks for the additional Info. We appreciate it.
, - Nick at Pelican Parts
 
HarryN Comments: Hey Pelican Staff, I have a slight problem: I lost two of my nutserts in the process of tightening them down to get the lip to seat the nutsert onto the assembly. Now, we each have different amounts of strength and what one can feel as tight, another can feel as "almost" tight. That was my issue. In the process, I now have to drill out a couple nutserts might as well remove them all and start over. My question is two fold:

1. When is tight, considered tight?
2. What is the best way to remove a nutsert after it has become stripped/damaged? Drill? What size drill?

Thanks!
August 6, 2012
  Followup from the Pelican Staff: The nutsert should not spin in the hold, there is a tool that will help install them correctly, and drilling them is the best way to remove them.Give our parts specialists a call at 1-888-280-7799. They can help you find the right tool.
- Nick at Pelican Parts
 
KVJ-1 Comments: There is a way to make inserting nutserts less painless: http://www.understeer.com/xbrace.shtml
April 14, 2011
  Followup from the Pelican Staff: Thanks for the additional Info. We appreciate it.
- Nick at Pelican Parts
 
Alvin Wong Comments: It seems like the stock crossover brace on my E36 automatic transmission is also a transmission mounting point of some sort. Would it be possible to remove it and install the X-Brace in it's place? I was always under the impression the E36 shared the same crossmember regardless of transmission, but when I went under my car to look it was different and definitely looked like it was bolted to the transmission as well.
November 11, 2010
  Followup from the Pelican Staff: The cross brace does not bolt to the transmission. If it did, then that would be a direct connection from the transmission to the chassis. The drivetrain (transmission and engine) are suspended using motor and transmission mounts in order to isolate vibration. I'm sure if you look closer, you will see that they are close, but not connected. - Wayne at Pelican Parts  
Rob Comments: Does the E34 5-series have attachment points for this crossbrace? I ask because the bodies of E34 and E36 are fairly similar.
November 3, 2010
  Followup from the Pelican Staff: I haven't heard of anyone putting this bar on the E34, but it probably can be done with some adaptation and a little ingenuity! :) - Wayne at Pelican Parts  
bostongrun Comments: I just checked it during my oil change and it still holding months later.
April 9, 2010
  Followup from the Pelican Staff: Thanks for the feedback. Glad we could help.
- Nick at Pelican Parts
 
bostongrun Comments: Those "nutserts" are a real pita, It seems simple but you often stretch the internal thread of the nutsert when you are installing it so you really have to exert abnormal torque twisting the screw in thus loosening the nutsert itself again the nutsert spins freely in the hole. I had two nutserts ,one on each side, left holding firm. I used a generous ration of JB Weld squished right into the area between the XBrace and lower member, let it dry to 24 hrs and violla it holds even better than the nutserts. For safety sake I looped four large industrial zip ties around the whole thing to act as safety straps in the event the JB came loose but after carefully monitoring it. I don't think that will happen; it's rock solid. If I need to remove it, I will use a propane torch, JB weld reliquifes at 600 df. It's not pretty but it tight!!! Don't forget the safety straps hd zip tieson the front to keep it from scraping in the event it comes loose!!!!
December 23, 2009
  Followup from the Pelican Staff: Thanks for the Info. We appreciate it.
- Nick at Pelican Parts
 

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