Michael Benno

I've noticed recently that my rear suspension clucking or knocking sounds when the car is cold. It usual goes away about 5miles into my drive and is non-existent once it's warm out.

I recently checked and torqued the rear sway bar, dog bone lines, link rods and all the other suspension bolts I could access with the wheels off. I replaced the springs/shocks about a year ago and the I had not noticed the problem, previously.

I am curious to know if others have experienced this behavior where the problem goes away after being driven for a bit and what problem it may be pointing to. For example is this an issue of old an hard rubber on the rear shock upper bearings, or is this associated with one of the bushings in the weishach arm? Like I said, everything seems tight but I didnt check for bushing play.

Suggestions appreciated.

dr bob

Mike--

The most common cause of the noise you describe is inadequate torque on the lower link pin. Followed by incorrect installation of the cone washers. The cone washer condition is pretty obvious. The lower link pin torque isn't. The link pin gets a torque wrench on -both- nuts separately, as the pin is "locked" to the sleeve in the shock bushings as it gets tightened. That can fool you into thinking that correct torque on one end is adequate, when you really should verify the torque on both ends.

For those playing along at home, insufficient tension on the link pin offers a clunk when load changes, particularly between pulling and trailing throttle, and when changing the lateral load on the subject wheel. In minor cases it's "just" a noise, but in fact things are moving. So the car will be difficult to align in the rear, as the changing lateral position affects both toe and camber. In more severe cases, the change in toe will cause the car to abruptly change direction. Extreme cases will cause such an abrupt change in direction that you risk losing the rear grip if you happen to be in a high lateral load cornering situation when things move.

The Weissach rear geometry causes the rear toe to change on purpose in corners. A loose link pin can erase that benefit, causing the rear to suddenly track outward under high load. Code Brown pucker factor becomes active, never a good thing even with Driver Depends explosion-proof underwear.

FredR

Bob,

This is an interesting observation in that it seems to run counter to what I found assuming we are talking about the same thing.

I am puzzled as to what could lock the pin as there is fully sleeved metal to metal contact all the way through the assembly that the pin goes through- indeed I had to counter hold one end as I torqued up the other just as I expected I would have to so something does not quite add up there. If something was locking the shaft then what you say is logical but I cannot see how that could happen unless the pin was seized due to corrosion- just not the case after the pin has been out of the car.

Apologies if I am missing something but you have me a tad worried as I did not put the torque wrench on both ends and I had to use a breaker bar to counter hold the other end as I torqued up so I just cannot visualise why it should be necessary to torque both sides.

Rgds

Fred

Michael Benno

Thanks. I’ll check out he torque and washers this weekend

dr bob

Fred --

This is a housekeeping issue more than anything else. In some perfect world, everything lines up perfectly on the lower pin even with everything snugged correctly. The pin then "floats" with the shock bushing in the suspension arms. Meanwhile, the actual clamping can be a little more complex. The two suspension components (trailing/radius arm and the upright/carrier) and the shock bushing have alignment maintained by the cone washers for the carrier, and those washers and the shock bushing seem to grab the pin as they are drawn to alignment with tension on the pin. The pins on mine were assembled with anti-seize, and there was no evidence of damage when they were out for the shock and spring change. Still, on any given car there's always the chance that there will be binding that might affect the tension on the pin. So even though the tension should be identical, it's pretty darn painless to verify that both nuts and washers are securely drawn together. If there are any missing or incorrect pieces (washers...), the tension on the pin won't maintain the pieces in correct alignment even when torqued correctly. Doing both guarantees that neither end is allowing movement. For those playing along at home, the large flat washers on the ends must be the right pieces assembled correctly and tightened securely. The washer is clamped against the end of the machined section of the pin, so the stack height of all the stuff in between is maintained correctly. Some may remember when Carl offered the first revision of his rear tie-down hooks to replace the rear washer in the stack. The pin actually clamps the shock bushing, and rotates slightly relative to the other two suspension pieces with vertical suspension movement. So there's definitely clamping that holds the pin, and that gets more acute if there's any corrosion (bushing or pin) holding the pin to the shock bushing. Carl did some machine work to allow the pin and nut to float in his next-rev tie-down hook to eliminate the problem, by the way.


Bob

FredR

The only thing that struck me at the time was that this fastener is the only one I can think of where you have to counter hold the other end and it seemed a very strange concept. To help align the assembly I used a scissor jack under the lower arm and frankly I was quite surprised at just how easy it all went together. All I noticed was that as the torque increased the resistance to motion on the counter held end decreased but that is to be expected as the tension in the pin increases but for sure it never occurred to me to swap them over and check. Nothing in the WSM to this effect either.

As and when I have need to do this again I will make a point to put the torque wrench on both ends just in case.

Michael Benno

And the winner is @DrBob !

I was able to get the car up in the air with an oil change this holiday weekend and recheck the torque on all the rear suspension nuts/bolts. I was able to get a half turn more in each lower suspension pin nuts to reach the appropriate torque . Everything else was tight.

Drove the the car today and the problem seems to have gone away.

Thaks Bob for your suggestions, I would have never thought such a small adjustment would have made such a big difference