Technical Problems with the last bolt !

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Technical Problems with the last bolt !

chr1s

Panda Lounge TA 2012
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May 13, 2004
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I am removing my rotten fixed rear axle / rear sub-frame, to fit a new one, but the last bolt holding the sub-frame to the chassis turns very stiffly and won't come out.

Everything was going so smoothly. I am trying to remove the sub-frame without disassembling the brakes etc., by detaching the swing arms before removing the sub-frame.
The exhaust is lowered, spare wheel removed, shocks removed, springs removed, swing arm bearing bolts removed, swing arms dropped out of sub-frame and brake pipes detached from the fixed rear axle. Three of the last four bolts, through the suspension mounts, have come out with no problems, but the fourth one turns very stiffly and won't come out.

The bolt has come out by about 10mm, but was very stiff all the way. Now turning it further doesn't seem to make any difference. Of course whatever it is screwed into (captive nut ?) is internal to the box section, with no access holes.
When I turn the bolt, it is a constant stiffness. If a captive nut had come loose I would have expected it to be very loose, or to feel tight then slip then tight, etc.
The bolt and whatever it is still attached to will move/rattle slightly when wiggled by hand.

Any suggestions on what's happening, and how I can sort it out ?
 
The end threads of those bolts protrude through the captive nuts inside the chassis, leaving a few exposed.
Any moisture that gets inside will tend to corrode the threads.

If I were you, I'd wind it all the way back in, then drill a small (6mm~1/4") hole in the side of the sub-frame as close to (and level with) where the end of the bolt is as possible.
Then you can spray some penetrating fluid inside and hopefully get some on the threads.
Let it soak for a good few hours, and re-spray every half-hour as well.
Then squirt some oil in as well, engine oil will do.
Then undo the bolt, if it gets tight, wind it back in and squirt more oil in.
Keep doing this and you should get it out.

Don't put too much torque on it, if the captive nut breaks loose, you're looking at a lot more work (chopping and welding).
 
Hi


For what it's worth, from my experience with seized bolts and Multipla's,you've got 2 options.


1) If the protruding end of the bolt is rusted as suggested above, then before you look at drilling the subframe and soaking the bolt, I would try undoing the bolt by a turn, and then tightening it half a turn, then undoing it by a turn and so on. This might be enough to clear the rust from the bolt, without putting too much stress on the captive nut, which you don't even want to go there!


2) if you've got the other bolt out, I would get a replacement bolts from a local supplier, and I would cut the head of the stiff bolt so that you can remove the subframe from the car, leaving the stud section of the cut bolt removed. From here you can see what is stopping the bolt coming out, and deal with it, without having to work through a subframe. At this point, you can also use heat which is your friend with seized nuts and bolts.


I hope this helps, a bit.
 
Thank you both.

Having thought about this some more, after reading your posts, I think I must have already damaged the thread on the captive nut and/or bolt. This is my only explanation for why it turns without screwing in or out.
The two rear bolts came out with no sign of rust, but the one front bolt which is out has signs of rust from the tip down most of the threaded part, so this agrees with your diagnosis.
I'm still deciding how to proceed, but if it turns without too much effort I may try to get WD40 onto the threads and then screw the bolt in (perhaps with some gentle upwards pressure at the same time). If the bolt won't screw in, due to knackered threads, then I may have to cut the head off the bolt, remove the sub-frame; drill out the remains of the bolt and try to re-tap the thread !
 
If, as you say, the problem bolt turns without coming out any, it sounds to me as though the captive nut has come away from the subframe. If that's the case, JA's suggestion (2) is likely the best approach.
 
Hi
Having read the extra posts, I remember with my front bolts that the shaft of the bolt had gotten rusty and swollen which made it difficult to turn in the subframe. This might explain the difficulty to turn that you're experiencing.

I hope this us the case for you as I don't think that you'll be able to retap if the captive but has broken away from the subframe.
 
Hi,

While I realise this was a few months ago now ill post this anyway to help anyone who had this problem and how to fix it.

Like the OP I had problems with the last bolt on the subframe and no matter what could not get it out and it was quite clear the captive nut had came loose.

My solution.

1. Cut head off bolt to get subframe clear.
2. Approx. gauge where captive nut was from inside the car.
3. Use holesaw to cut hole in floor from inside the car which revealed the piece of box section which held the captive nut.
4. Using holesaw cut hole in box section of chassis (again from inside the car) to reveal the "captive nut" which is actually a threaded piece of thin wall tubing welded onto a piece of flat plate which must is, I assume slid into the box section at the factory and if your subframe bolt is rusty like mines was the additional force required to loosen it causes the box section to distort and therefore the piece of flat plate to turn.
5. Weld (i used stick welder) plate from inside the car through the 2 holes you made earlier.
6. Give yourself a pat on the back and a thumbs up :)

Heres a few pics I took and hope this helps anyone else who has this problem.
1.jpg
2.jpg
3.jpg
 
Years forward, I am at the same stage but can't access the photos. I am hoping that seeing them might give me a clue as to where to start drilling/cutting. Thanks.
 
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