Stripped thread in rear knuckle?

[JJDubya]

The fun never stops! I was taking my time this weekend installing H&R OE springs, SS brake lines, pads, ATE fluid etc. on my 2012 S4. Regarding the rear springs, following many of the DIYs here, some suggest removing the damper to get extra clearance when loosening the subframe. The large 21mm bolt that attaches the damper to the knuckle is a monster... but came out relatively smoothly (it didn't come out by hand, but with little effort using a socket). I had already disconnected the control arm and the sway bar and the suspension was at full drop. There was only a little tension on the damper, but it apparently was enough that, as the bolt was backed out, it marred the threads.

I'm not sure what to do. It is Sunday and I doubt I will find an M14 x 1.5mm tap locally (I believe this is the correct size). I suppose there is a chance I can salvage the threads with a tap. There is no way the bolt will go back in (even without the damper in place). I tried taking a picture to post, but it was difficult to get a clear shot down the threaded hole. I thought about just cranking the bolt back in an hope it cuts threads, but I think that would be a mistake.

I looked up the part online (entire knuckle) and it is $500. I don't want to do have to do that.

Questions:

1. How does one remove the damper without this happening?

2. Anybody think I can save this with a tap? About 4 threads on one side about 20mm in were damaged as the bolt was backed out.

3. Can anyone confirm the bolt size (I know, long shot)... AllDataDIY doesn't show sizes.

[JJDubya]

I can answer my own questions #1 and #3 above:

#1 Raise car by frame rail/pinch weld and support with jackstands at subframe. Remove two plastic fasteners at center of wheel well liner along centerline of damper to expose the two upper damper mounting bolts. Slightly raise the knuckle from below (i.e., with floor jack). Remove two upper 16mm bolts and damper will be free at the top.

I swapped the spring on the other side without ever removing the lower damper bolt.

#2 The bolt is indeed an M14-1.5. Verified with a matching nut (previously I just measured the diameter/pitch with a caliper).

I now hope a tap will repair the marred threads on the other side. I will find out in the morning.

[wwhan]

.......
Questions:

1. How does one remove the damper without this happening?

2. Anybody think I can save this with a tap? About 4 threads on one side about 20mm in were damaged as the bolt was backed out.

3. Can anyone confirm the bolt size (I know, long shot)... AllDataDIY doesn't show sizes.

That bolt is is common with a lot of late model Audi rear shocks.

1.) I use a floor jack under the knuckle where the lower shock bolt goes, to relieve the vertical tension, when putting in and removing the bolt.

3.) Rear Shock Securing Bolt (http://www.scuderiacarparts.com/part/audi/rs5-coupe-quattro-2012/N10500802/bolt-hex-hd-with-shoulder-self-lock/113-331-14243-412527-101222.html), M14x1.5x90, Audi # N10500802
ECStuning (http://www.ecstuning.com/Audi-B8_S4-Quattro-3.0T/ES468320/)

[JJDubya]

Perfect, thanks for helping me confirm the bolt specs. Of course, I damaged the threads on the knuckle, not the bolt.

Regarding using the floor jack to relieve tension, it never is obvious when the tension is off. I went by "feel"... the bolt was relatively easy to turn with the ratchet, so I thought I was safe. I guess not.

I'll report back once I try to chase the threads on the knuckle with a tap (there is one in stock at the Fastenal nearby).

[wwhan]

Perfect, thanks for helping me confirm the bolt specs. Of course, I damaged the threads on the knuckle, not the bolt.

Regarding using the floor jack to relieve tension, it never is obvious when the tension is off. I went by "feel"... the bolt was relatively easy to turn with the ratchet, so I thought I was safe. I guess not.....

Just use your fingers directly on the socket over the bolt, you will feel no tension, when it is right.

[PitchS4]

I am confused why you did not just remove the upper damper mount? It is 4 16mm bolts with lite torque spec (40 ft/lbs IIRC) and 10x easier to R/R then dealing with that massive bolt. The few DIYs I read before I did my springs called for doing it that way. None of them mentioned messing with the damper to knuckle bolt.

[JJDubya]

Believe me, I'm kicking myself for removing the lower bolt. I was trying to avoid lowering the subframe so I didn't run the risk of altering the alignment and thought removing the damper would help (The STaSiS DIY doesn't mention dropping the subframe...). I couldn't do it without a more compact spring compressor and I ended up dropping the subframe anyway... so, yeah, kicking myself.

And, I think there are only 2 16mm bolts at the top -- which makes it even easier than you suggest. Lesson learned. Now I have to fix the damaged threads.

[PitchS4]

Believe me, I'm kicking myself for removing the lower bolt. I was trying to avoid lowering the subframe so I didn't run the risk of altering the alignment and thought removing the damper would help (The STaSiS DIY doesn't mention dropping the subframe...). I couldn't do it without a more compact spring compressor and I ended up dropping the subframe anyway... so, yeah, kicking myself.

And, I think there are only 2 16mm bolts at the top -- which makes it even easier than you suggest. Lesson learned. Now I have to fix the damaged threads.

I hear you that sucks man. Are you able to possibly get a longer bolt that you can put a nut on for added security? I can't remember if the knuckle is drilled through.

Lowering the subframe isn't a huge deal as long as you do it 1 side at a time. And I was going to need an alignment anyway with the springs so I didn't think much of it.

[wwhan]

I hear you that sucks man. Are you able to possibly get a longer bolt that you can put a nut on for added security? I can't remember if the knuckle is drilled through.

Lowering the subframe isn't a huge deal as long as you do it 1 side at a time. And I was going to need an alignment anyway with the springs so I didn't think much of the alignment.

It's a blind hole. I have had that bolt out many times.

The upper 16mm head bolts were always a pain, because of the odd angle the fender liners.

[JJDubya]

Chasing the thread with an M14-1.5 tap worked. I could only get 1/8th of a turn at a time and had to "peck" at it, but finally got the threads repaired.

Perhaps this thread can serve as a PSA for those installing springs: leave the lower damper bolt alone.