Engine undertray from hell (the 10mm nuts in the wheelarches are stuck!) 1.4i

SpdyHS

Member
As my thread title says, I'm in trouble! (petrol 1.4)

When I bought the car I did not check for the undertray, the car turned out not to have one. I have now bought one used, as well as a set of "undertray nuts and washers" from ebay (they seem to be correct).

However, the old 10mm nuts in the wheelarches are still attached to the car, but they are stuck. I can turn them but I can't get them released. Therefor I can't fit my undertray ?

Any ideas?
 
As my thread title says, I'm in trouble! (petrol 1.4)

When I bought the car I did not check for the undertray, the car turned out not to have one. I have now bought one used, as well as a set of "undertray nuts and washers" from ebay (they seem to be correct).

However, the old 10mm nuts in the wheelarches are still attached to the car, but they are stuck. I can turn them but I can't get them released. Therefor I can't fit my undertray

Any ideas?

Drill bit the heads off or get something behind it to hold the clip if possible


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Try soaking them with penetrating fluid for a day or two then clean the threads on the bolts fixed to the body then using a 6 sided socket carefully move the nut back and forward to loosen it then undo in the normal way, or try heat in you can..
 
.......
However, the old 10mm nuts in the wheelarches are still attached to the car, but they are stuck. I can turn them but I can't get them released. Therefor I can't fit my undertray ?

Any ideas?

Hi,

Take care here.
The thread is not a bolt - it is just a threaded section that is press-fitted and glued to the structure.
If you "break" the fixing of the thread it will just end up spinning and eventually come loose and fall inside the chassis.
If the nuts will not come loose, the best plan would be to remove the threaded section by whatever means you feel appropriate, buy some aluminium rivnuts and fit those in the chassis and then use some appropriate bolts to thread into the rivnut.

If you do manage to loosen the nuts, clean the threads of the both nut and thread and use some greaseto coat them to stop future corrosion.
Remember, if you pressure wash your car and clean the wheel arches you will remove the grease, so just blob a little back on the thread and you'll not have this issue the next time.

Hope this helps
Cheers
Jeff
 
Nut splitter might do the job? It's pretty easy to damage the stud if you go for forcing the nut, I did on my breaker fsi recently. For speed....
 
Anyone know of part number for the 2 small self tapping bolts towards the back of the undertray (nearest the rear axle). My best guess is these are maybe 5.5 x 19mm?

For info cant find any reference to these in workshop manuals or 7zap.
 
This might sound a bit daft but if the fixings are in good shape there is no real need for the two bolts.
The black one I've just sold both bolts had snapped but it never moved or dropped but I did make sure that the rest of the screws and fixings were good and secure.
 
Anyone know of part number for the 2 small self tapping bolts towards the back of the undertray (nearest the rear axle). My best guess is these are maybe 5.5 x 19mm?

For info cant find any reference to these in workshop manuals or 7zap.
I have used heavy duty zip ties with great success.
 
Had the same problem. My solution was to the spinning thread was use a nut splitter. Then I used an appropriate die to clean up the thread. Took a while with lots of wedging to stop the bolt turning. But eventually got the thread clean enough to accept nuts. I then wound on the “fixing nut“. To fully tighten it, I wound on two more nuts locking them together so I could tighten the fixing nut. When that was done I removed the two lock nuts.
In the unlikely event that your undertray is perfect you may need to adjust the hole size in it to accommodate the fixing nut. Then use a penny washer et voila Robert est votre oncle.
 
So - my issue is I had no thread - looks like the previous owner must have cut it off thinking it had seized :(

Instead I had a couple of self tappers screwed at the back of the undertray....I'll need to experiment it seems.
 
@cheechy are you talking about screws no 6 in the diagram that fit into the speed nuts in the cross member? Either the correct speednuts or paul makes 3d printed ones. Or the 2 threaded rods that secure the sides of the under tray to the front rails?
 
So on the whole I use the plastic rivets or wire ties where the front rails holes are. Usual black torx bolts around the front of the undertray.

I'm talking about the back of the undertray directly below the passenger area / dashboard - it seems there should be some kind of thread and nut assembly?
 
I've got the 3 No6 on the rear face but no nut. Now that I have had a really good look, the remains of the stud are there but it now just looks like a small dowel peg. No nut can be fitted, never notice it was threaded but only about 4mm in size.
 
If I was concerned about the stud I could repair it the same way I repaired all the sheared heatshield studs around the fuel filter when I hit a huge puddle in the recent floods and went boating...
 
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