Hood (bonnet) torsion spring mechanism failure E9&E3

Hey There fellow car nuts.

On the topic of hoods/bonnets that do not stay open; this is a topic that is raised a few times each year, so I thought to make an FAQ about it.
This is often due to deformed or broken parts in the system. There are 3 separate issues with the mechanism that leads to failure of the function.

The E3 and E9 are close in design but not identical.
Here are some combined notes, with pictures from various other members.

The hood mechanism failures are due to 3 different reasons, so it doesn't mean that you should replace the whole assembly if it doesn't work properly. Full replacement sets have been available from BMW, but stock ran out around 2015 or so.

Getting it functional again (without simply replacing the whole mechanism) can normally be done by replacing only the failed subcomponent.

Most commonly the problem is associated with the welds breaking between the thin tube and it's left and right half arm parts. This is easily fixed with a fresh weld, or better: with a new steel tube with it a bit thicker wall section. The original tube is very thin, and therefor prone to break. If you choose something a bit thicker, it's also easier to weld in.

pic of failed part from @Stevehose from this thread: https://e9coupe.com/forum/threads/hood-support.23738/post-175119:

1656582381454.png

welded up:
1656582441985.png




Secondly, the small L-brackets used on E9 are flimsy and under-designed. As a result the 'finger' often bend out. Some members have made them themselves in a thicker steel. The E3 is different; stop is integrated.
1656581156474.png

replacement made by a member @pickman:
1656589864611.png


Link to thread on replacement parts: https://e9coupe.com/forum/threads/hood-torsion-bar-repair.34893/post-326659

Another failure is this soft metal part that locks one spring end; it deforms fover time as it's made from a soft lead based metal. A nice comparison of the deformation is shown in the pics below with a old and new E3 part next to each other.

E3:
1710411957196.png
The e9 part fails in a similar manner:
deformed metal e9 hood hinge block.jpg


Replacement parts status (status March 2024)

  • The E9 part is available through BTS teile (see below). BMW is sold out.

www.bts-autoteile.de


Halter an Motorhaube 02, E9
Halter an Motorhaube 2000 CS, C, CA 1600-2, 1600ti, 2002, 2002 ti bis Modell '71 E9 2,5 CS - 3,0 CSi BMW OE 41 61 5 480 146
www.bts-autoteile.de
  • The E3 has been purchased by a member here at a BMW dealer in March 2024 for under 10 usd.
  • As an alternative for the E3 part a 2002 part may be used as a replacement: white, top is E3, red, botttom is 2002. Picture from @dang on the 2002 forum.
1656581929186.png


E9 parts, assembled:
1656582312714.png





And it's also possible to fix that part yourself, if you're handy & inclined to do so :

1674487383324.png
1674487419089.png
1674487400359.png
1674487415669.png

 
Last edited:

Krzysztof

Well-Known Member
Site Donor
Messages
1,651
Reaction score
791
Location
Poland
Great topic.

Will the stops from E3 (reinforced with the tab) work also on E9?

Wondering why they were not the same.
 

eriknetherlands

Moderator
Site Donor
Messages
2,768
Reaction score
2,004
Location
Netherlands, Eindhoven area
I do not think so. Otherwise it would have been known I guess.

Let's see if I can remember to update this thread, as I recently chopped up and rewelded my own system. Got plenty of pics of that while in progress.
 

eriknetherlands

Moderator
Site Donor
Messages
2,768
Reaction score
2,004
Location
Netherlands, Eindhoven area
Some pics showing how to fix the whole thing:

Measuring before cutting apart the elements. Trying to keep the arms intact, so i cut the tube where needed to separate them. The arms themselves also had cracks in them.
20231109_152352.jpg 20231107_121657.jpg 20231107_131758.jpg

New tube (size 2*26*1062); shaped the ends with a slot for the spring that locks in the oblong hole in the arm.
20231111_192212.jpg 20231111_194316.jpg

Welded:
20240129_211505.jpg

Cut apart the rivet holding the 2 arm halves togehter; i wanted to do this to be able to completely re-zinc them. This required me to sand off the rivet head. To be able to assemble the hinge again, I drilled an 4.2 mm hole and then cut an M5 thread into the remainder of the rivet, effectively making a book screw out of it. Next I needed to make a new M5 screw for it; I choose one with an flanged allen head, at it resembled the best the original rivetted head.
Note how also a thin shim was placed between the 2 arm halves.
20231112_124641.jpg"20231112_125258.jpg20231112_125428.jpg 20231124_140045.jpg

Redesigned the weak hinge part into 7076 grade Aluminium:
20231111_194405.jpg 20231116_003950.jpg 20240115_155922.jpg

Installed, with 2 new hooks kindly provided by a generous forum member @pickman
20240115_213638.jpg
1706546933633.png
20240115_213550.jpg


link to more build details: https://e9coupe.com/forum/threads/fixing-that-little-rust-spot.18521/post-391912
 

Attachments

  • 20240127_171346.jpg
    20240127_171346.jpg
    417.7 KB · Views: 14
Last edited:
Top