Renewing self locking screws on steering knuckle(82 300 SD) - PeachParts Mercedes-Benz Forum

paulh300sd · #1 10-14-2008, 02:42 AM

The factory service manual indicates that one should renew the self locking screws when re-attaching the caliper or steering arm to the steering knuckle. I have looked extensively through the forum to see if I could find any information about this and did not run accross anything. I came accross a ton of information on front end work, but did not see any mention of renewing the screws as the factory manual prescribes. I was wondering how important this is. Would a certain type of loctite do as well or is it really necessary to replace the screws? I have never worried about this on other cars. Can one buy these screws online (where)? I would be grateful for any expertise about this. Thank you.

SD Blue · #2 10-14-2008, 12:01 PM

When I bought my car, the steering arm was loose on the passenger side and had worn to the point of mandantory replacement. I found the arm on a salvage unit but went to the dealer for the bolts as I was unsure of being able to reuse a self-locking bolt in such a critical point.

Most likely, most will say just clean the threads and reapply Loctite. However, if the bolts are worn, and I am assuming this is why they were removed, then the only source for new ones might be the dealer. I know this isn't a clear cut answer but this is probably a judgement call on why the bolts were removed and the appearance of wear.

patbob · #3 10-14-2008, 03:04 PM

I don't think you're going to get much more than a "use your judgement" or "do as the FSM says" answer on this. Bolts, nuts and lockwashers corrode, rust and get chewed up. Bolts can also stretch, locknuts fail to lock as tightly, and lockwashers collapse and fail to grip. There are very few parts on a car that you want to have fall off at freeway speeds. Inspect every nut. bolt and lock washer you take off your car as you work on it, replace them if they are definately bad, or if you are in doubt, even if the FSM doesn't say you should. If the FSM says you should replace them as a matter of course, it will certainly be safer and more reliable if you do. Not doing so is a decision you have to make for yourself based on the condition of the bolts, and whether you think it is safe to reuse them or not -- none of us can, or should, make that decision for you.

When I did my front end work, I reused the caliper bolts, but replaced an UCA because the stud and nut of the ball joint was too chewed up for my comfort. When I was replacing a broken bolt on my chipper/shredder last weekend, I also replaced the four 20 year old locknuts (but not the bolts) I had to remove to get to the broken bolt. I figured it was cheap ($0.90) insurance against the engine falling off.. and that wasn't even a failure that was likely to hurt anyone.

So.. use your judgement.

jt20 · #4 10-14-2008, 03:08 PM

ditto

paulh300sd · #5 10-14-2008, 11:11 PM

Thanks much for the feedback. The bolts actually seem to be in good shape (I removed them to get the steering knuckle off so I could replace the ball joint), but nevertheless I was leaning towards going to the dealer for new bolts to be safe, but just wanted to double check if it was really worthwhile.

Brian Carlton · #6 10-15-2008, 07:53 AM

Quote:

Originally Posted by paulh300sd

Thanks much for the feedback. The bolts actually seem to be in good shape (I removed them to get the steering knuckle off so I could replace the ball joint), but nevertheless I was leaning towards going to the dealer for new bolts to be safe, but just wanted to double check if it was really worthwhile.

Whether you reuse the old cap screws or purchase new screws, the most important part of that task is the proper torque on the screws. You can't just wing that deal.........because you're in a difficult place and have no way to "calibrate" your arms for the task.

micalk · #7 10-15-2008, 09:39 AM

Self-locking bolts for most MB applications are likely available from the dealer. I know that I've also ordered them from various online MB parts sources as well when ordering things like rotors or suspension parts. They came with the Bilstein shocks I just installed. The interesting thing is that the bolts for the front shocks came with the blue threadlock pre-applied, but the rear shocks came with wavy split-ring washers and standard bolts.

As for reusing the bolts, I'm sure you'd be fine with applying blue loctite to the bolts and reusing, as long as the bolts are in good shape.