Front end popping sound on 300SD
 

I've had this popping sound coming from the front driver's side wheel for about 3 years now. 2 years ago I rebuilt the front end and it didn't get any better. I took the car to a suspension shop and the owner was nice enough to let me stand under the lift with him as he checked every bolt and joint. He said that everything looked good and that I have nothing to worry about. When he was backing out he hit the brakes and the front end made the pop sound. He immediately said that it sounds like the spring isn't seated. He then noticed that the spring pad isn't entirely on top of the coil spring in the tower. This explanation makes sense because the popping became much worse after I swapped engines in the car. I can see how the spring might have moved a little bit with all of that weight taken off. The popping seems to be getting worse every day and only happens when I turn the wheel to the right at slow speeds going forward and reverse. It will also happen occasionally when I brake suddenly. I'm having a hard time believing that an unseated spring would be producing all of this popping unless that pad up there is starting to get torn up. One other point to make is that the steering wheel feels a little wobbly when it's about 10 degrees from maxing out to the right side. Any ideas? Thanks

What part manufacture did you use?

German stuff mostly. Febi, Meyle and Lemforder. I think that the guide rod bushings were Febi, and I've suspected that it's a faulty guide rod bushing making the noise.

That's highly likely especially from Febi (I'm sorry to have to say)

febi is not german made parts... it's a german company that has everything made in china...

My lower balljoints had the same symptoms once the boots tore and they started to dry out.

If you didn't use Lemforder balljoints, I would have a look at them. I seem to recall that my guide rod bushings only made noise under braking, not when turning, when they were gone.

You aren't alone in this experience, many people are getting burned on brands that were formerly thought reliable.

Lemforder, Phoenix, TRW and Moog* are the only names I would buy in aftermarket.

*: Some folks disagree with me on Moog.

I'm having a hard time believing it is a spring shifting as well. That beefy of a spring with that much weight, over light variance in terrain doesn't add up.

I would be more suspicious of the idler arm bushings. I'm betting the idler arm is often overlooked by suspension shops because it takes a certain geometry of the suspension to see excess movement, especially working solo. And your comment about wobbly when near max right seems to point there.

Guide rod mount failure is usually noticed when driving over variations, such as a speed bump. It is definitely noticed in the front floor boards. Plus, I don't recall any wobble due to them being worn.

Are you sure the pop is from the front end? I ask because a badly worn trailing arm bushing may cause a pop if the car is in the proper weight shifting circumstance, such as a maximum right turn. Are you noticing any unusual tire wear?

I replaced the idler arm as well as the following parts:

driver's lower ball joint
both upper control arms
driver's lower control arm bushing
both guide rod bushings
both tie rods
center link
steering damper

The tire wear is even for the most part. The drivers tire is a little more worn, but I credit that to more right turns and highway entry ramps on my commute.

The popping was the worst after I installed the new center link, and it went away when I installed the driver's side tie rod out of alignment. In other words, if i adjusted the toe out a certain amount, the popping went away.

The guide rod / braking rod mounts will make a pop / clunk sound when you get on and off the brakes when they go bad.

-J

The spring could not have been dislodged by an engine swap. Even of you jack up the car all the way, no weight on the wheels, there is a stop for the upper control arm so the spring does not come out. Perhaps it was not reinstalled properly if anything. Maybe the end of the spring was not aligned into the spring holder.

Guide rod mount could cause a clunking as well. I assume your ball joints are new and good.

The steering box/bushing can cause clunks and loose steering. With a new front end, you should not notice any wear on the tires if it was properly aligned. If the steering box is severly worn, you could still get wear on the tire/s even if everything else is good. This happened on my 300SD.

Some would disagree on TRW as well. There was discussion about how some TRW ball joints for import applications have a pressed rather than cast or forged lower cap. TRW might be repackaging low demand ball joints to improve catalog coverage.

Sixto
87 300D

Where is the steering box bushing located?

Inner or outer of the tire? Mine wore on the inner side. Every time I applied the brakes, the car would want to turn to the left; despite freshly rebuilt brakes.

Outer side of tire from right handed turns and on ramps I assume.

There are two. Both attached in-line with the steering column. One midway below the steering wheel in-board. One at the top of the steering box coming out of the firewall.

Edit: Some call it a flex joint.