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I have been dealing with this issue for the last few months: when driving over small bumps and cracks at low speed. I get a small thunk from the front suspension. Oddly enough, it goes away when lightly applying the brakes. I went ahead and replaced the endlinks, and no luck. I have had the car up on Jack stands 3 times, and have inspected every bushing. The compression arm bushing is intact and not ripped.
When driving on a road with small bumps and cracks, if I drive with the brakes slightly depressed (I.e riding the brakes) the noise goes away entirely. However, I don’t think the noise is coming from the brake components themselves because everything is tight. It happens on both the driver and passenger side front corners.
Has anyone ran across this issue with similar symptoms? How did you address it?
From what you described it pretty much has to be braking components. I would get the front up on jackstands and aggressively pull the wheels around in various ways (top edge, just grab and shake the car violently, same with the front edge) and try to reproduce the sound. My gut feeling is either the inner or outer tie rod ends, and that applying the brakes is actually causing the tires to have just enough drag on them that they toe out ever so slightly and prevent the rod ends from slapping back and forth. You should be able to reproduce the sound by grabbing the front or rear of the tire and trying to turn the car quickly left/right at the tire (on jackstands).
You also might have some very slight feathering on the front tires if this is the case.
After reading the comment from Cleric670, I jacked up one side of the car, and with one side on the ground, I attempted to turn the unloaded wheel to the left and right to reproduce the noise. I was shocked at the lack of play, and really bummed out because I was CONVINCED at the time it was not the compression rods. The rubber looked good on the aft bushing, and the forward ball joint didn't have any cracks or leaks. At the same time, I checked the brake pads and found that the hardware was properly installed, and I could not recreate the noise. While inspecting the rear of the car for anything that might produce the noise (although I heard the sound in the front, I wanted to think outside the box), I noticed the rear swaybar endlinks were absolutely shot (I could move them with two fingers). With all this information, I went back to forum posts. I eventually found obender66's comment on this post, which gave me the idea that the ball joint in the compression rod was bad. I believe that his method of diagnosis would be useful on cars that aren't quite as rusty underneath. Using a flathead screwdriver for leverage, I looked really hard at the ball joint boot, and found the smallest of separation in the bottom of the boot. This, and the linked post was the loose evidence I used to conclude that it was the compression rod ball joint.
I sourced all of the parts from RockAuto. So others can look on this post and order exactly what I did (between the AWD, RWD, Coupe and Sedan options it can be tricky to find the exact part you need), here are the parts I used for my RWD 2005 G35 Sedan:
Rear Right Swaybar Endlink: MOOG K750047
Rear Left Swaybar Endlink: MOOG K750044
Left Compression Rod: MEVOTECH CMS301002
Right Compression Rod: MEVOTECH CMS301003
The rear swaybar endlinks were a lot easier to replace, as both sides of the endlink had a nut on the back so that a wrench could be used. I stripped one of the nuts (rust), so I had to use a Dremel to cut away the nut as I had to do on both of the front swaybar endlinks (because there is no nut on the back to hold on to, just a little tab which was a very poor design choice). The install was very easy.
I started on the driver's side (left) compression rod afterwards, and it was almost nightmarish. Using
video (there are other videos as well), I started by jacking up the wheel knuckle to relieve some tension. I was gifted (early) a Milwaukee 1/2 High-Torque Impact Wrench, which made short work of the rusty bracket bolts that hold on rear of the compression rod.
As an aside, I don't think you would be able to do this job without an impact wrench; I have a suspicion that the ball joint would just spin and you would have to get creative using a vice grips (as shown in this DIY post). In order to remove the forward (ball joint) part of the compression rod, I actually removed the jack from under the knuckle, which put enough pressure on the stud to hold it in place while the impact took the nut off.
The aft compression rod bushing was the nightmare-fuel. Under normal conditions (as in the video above), once you remove the two nuts holding the front and rear of the compression rod, you should just be able to hit it with a hammer to knock it loose. As described in this post, what can occur (and what happened to me) is the inside sleeve of the bushing can rust-weld itself to the frame and the stud. No matter how hard you hit this compression rod, it's not going anywhere. I attempted to use a jaw puller to remove the bushing, but this did nothing more than ripping the bushing away from the rod (which, after removing the bracket shown in the DIY post I found the bushing to be slightly ripped anyway). This is what it looked like:
From here, I used a drill to completely detach the rubber from the stud and compression rod, which allowed me to remove it and get better access. A flat head and hammer removed the leftover rubber from the metal. Using a Dremel with a metal cutoff wheel, I made three cuts through the metal sleeve of the bushing, but taking care to avoid heavily marring the stud. As mentioned in this comment, removing this stud is almost a death sentence for the car. The goal of these cuts was to cut out a piece large enough for the stud to pass through the metal sleeve sideways. The rational behind this was that I would be able to apply enough lateral force to break the rust on the base of the metal sleeve, and from there I could pull it out. Here was the result:
As you can see, the stud is tapered. I actually made a bunch of very small cuts, taking out a piece at a time until I reached this stage. From here, I made my best effort to cut as close to the body of the car as I could to try and make the base of this metal sleeve week. I would cut for a bit, spray with penetrant, hit with hammer and chisel, spray, and hit again. Eventually, I was able to get the sleeve moving, and it was a matter of back-and-forth movement to break the rust and remove the sleeve. Here is what it looked like afterwards:
and the stud:
There were a few cuts in the stud, but nothing that would compromise it too heavily. I used some sandpaper to remove the rust and debris from the stud, and then I used some copper-based anti-seize on both the stud, as well as the top and the inside of the new metal sleeve so that next time this job is easy. The installation of the new compression rod was fairly straightforward: I put the new conical bushing into the hole for the ball joint, fastened the ball joint with a new nut and new cotter pin, then jacked the knuckle up to align the rear bushing, followed by a couple mild blows of the hammer. while the car was on the ground, I tightened everything per the FSM (59-79 ft-lbs for the ball joint, 80-93 ft-lbs for the aft bushing, and the other two bolt holding the bracket to 45-51 ft-lbs).
After a quick drive around the block, the noise from one side was completely gone. Today, I replaced the passenger side compression rod with the same method described above which removed all noises. But, how does braking cause the noise to go away? Here is my hypothesis:
Under normal driving conditions, the compression rod does not have much pressure on it. When the vehicle drives over bumps, the compression rod prevents negative caster. The shock is reduced by the aft bushing, and the ability to turn is accomplished by the ball joint on the compression rod. When either of these two fail, it can cause a clunk or bump at low speed. Either the bushing or the ball joint is no longer adequately absorbing the shock as the wheel moves forward in well (negative caster). When the brakes are applied, tension is applied to the compression rod, which eliminates the shock of the bumps in the road.
The real challenging part of all of this, is that it is almost impossible to see this with the vehicle on jack stands. A clue could be a torn ball joint boot, or a very slight tear in the bushing, but none of this would seem like it would be enough to cause the noise.
Glad you got it all figured out. My rule of thumb when something fails on the front of a G35 suspension is to REPLACE EVERYTHING!
That stud will be fine even with a few nicks and dings. Copper-kote is some amazing stuff, use tons at work and it will definitely make life easier in the future when/if you take it apart again. Personally for auto use I use the aluminum anti-seize because it has better resistance against salt than the copper one does. I only ever use copper if I NEED that +200 degrees of heat resistance (exhaust pipes esp. catalytic converters).
It's very hard to troubleshoot suspension issues on a multi-link unless you have a 4 post lift because you have to have the suspension loaded while you're prying on things.
11-02-2020, 09:13 PM
