I've had some driveability issues with my '05 S600 so I figured I'd put a new accelerator pedal in it, A2203000004. From reading on here I knew it took a 10mm socket, so I put one on a 3/8" ratchet, teased the plug out that hides the nut, then started loosening. And loosening. And loosening. Took the ratchet off and saw that the nut had made NO progress up the stud. Aw hail no! So the stud must be spinning. Had the car up on jack stands for some other work, so crawled under to see if I could see the back side of the stud/bolt. No dice, because it's right above where the driver's side catalytic converter is, and there's heat shield all over that area, which didn't look easy to remove. Plus it probably wouldn't be a bolt anyway, but rather a swaged or welded stud.

No problem, I sez, I've dealt with this sort of thing before, like carriage bolts in wood where the head wants to spin. But if you use a pry bar to pry the pieces apart, putting some tension on the bolt, the "teeth" in the head will usually bite enough to let the nut break loose. So I got a 1" wood chisel, wedged it under the base of the pedal assembly, and pried up with one hand while ratcheting with the other. Still nothing. Here's a picture:
Any ideas on how to get this dude off? I plan to try again with a pry bar, just didn't have one at hand before. Would get more pressure on it, but I'm also worried about pulling the stud out of the floor. Does that look like a locknut to you? I think it is. Is that factory, or would someone have added that?
I thought about using a microtorch to melt the nylon out of the nut (with a fire extinguisher handy), but 1) it would probably just run down into the threads, and/or 2) it would probably re-solidify before I could get a socket on it. And make the inside of the car stink.
I could cut the base loose from the stud with a Dremel or similar, then when I get the stud/nut by itself I could hold the stud with a needle-nose Vise-Grips while turning the nut with a wrench.
Has anyone else run into this? The new pedal assembly is in the mail, so I don't have one to look at, but I'm guessing the throttle position sensor at the top isn't easily swapped by itself? Asking in case replacing that in situ was an option.
Thanks,
Mike

 

My only suggestion is to make certain that you are actually turning the nut...

 

I had a similar problem when installing a Sprint Booster on my W211.
Turned out I was using the wrong size socket and that's why it kept spinning.
Maybe try a metric socket one size smaller than the 3/8".

 

Or make sure that it is a hex nut, and not a male spline or something similar.

 

All good suggestions, thanks. I'd read here that it was a 10mm nut so I just grabbed a 10mm socket and went at it, but maybe it wasn't actually engaging. I'll give it another go tomorrow when it's light out.

 

I just changed mine the other day. Definitely a 10mm socket is needed to remove the nut from the stud on the floor. There's no real way to get any other type of tool in there....like pliers or wrenches.

I had resistance almost the whole way off the stud when removing it.

Keep trying.