Rob Edwards

Kevin stopped by with his '87 S4 auto this afternoon, he's been chasing a clunk/cracking noise coming from the front end. We put the car up on the lift and his rack bushings are squishing out from the collars, but the bolts are all properly torqued. Everything else checked out ok on visual. Decided to stick a gopro to the control arm to see whether we could detect rack movement or binding that might explain the clunks. You can hear the 'cracks' between 1:00 and 1:15, but no visible rack movement:



The other thought was maybe tiny-bit undersized brake pad backing plates moving around, but it doesn't do it with every brake application, and there's no funny feeling through the brake pedal or steering wheel.

Thoughts?

Speedtoys

Does it do it with the brakes lightly applied? That will remove pads from the list.

Cant see the rack being braking related..

Drivetrain inspection time..mounts, bolts to mounts..??

the flyin' scotsman

sounds suspension related; watch the video of suspension extending/compressing as the noise is heard after the 1 min mark.

how are the motor mounts?

AO

The problem with those GoPros, is you don't get a good sense of the audio.

I guess it could be pad slap, but it sounds too tinny and doesn't seem to exactly correspond with the revving and braking.

What about something rattling around in the wheel wells? Cruise control. ABS. Outside temp sensor.

One other thought is a loose/broken flap hitting the condenser.

Rob Edwards

We put it up on my lift and poked and prodded- Kevin did motor mounts and OPG about 2 years ago, brakes got new Porterfield pads and bleeding last year, rotors are original. Tugged on the wheels, no play in the wheel bearings.

I agree the brake pad clank doesn't make sense, just grasping at straws. No matter what the rack bushings need to be R&R'ed, just didn't see any motion.

Speedtoys

I cant see again, how rack could make that much wet metal cracking noise, under those circumstances and not do anything when you turn the wheel.

Look for 'dusting' of eroded aluminum at the front and rear LCA mounts where things might be moving.

Compression of the springs..maybe a cracked spring near the upper or lower perches?

Mrmerlin

I would put a wrench on every bolt in the front end, check the MMs, also the upper mount to U shaped hat bolt, make sure the fingers are straight and that their is atleast 2 mm of clearance between the fingers, check the chassis to cross member bolts. the side bracket bolts the upper control arm to chassis bolts, the brake caliper bolts the wheel bearing play, sway bar link bolts

NOTE the lower shock mount bolt being loose could cause the air deflector shield to move just enough to cause this noise when the brakes are applied.

Also what was the last thing you fixed?

Dave928S

Sounds like something rotational to me ... like bolt holes have gone oval and two things bolted together move rotationally, one way and then back, depending on clockwise/anticlockwise torque direction.

Another thought is something sliding backwards and forwards, which would fit with the acceleration/deceleration ... TT?

Dave H.

yep loose LCA bolts would not be unheard of.

worf928

Listened to video (feels weird writing that.)

+1. I can easily imagine the clamp for the sensor/hose assembly coming loose, whacking the plastic splash shield and making that noise.

Edit: there seems to be a delay between the suspension movement and the noise. That's what makes me suspect something in the wells.

AO

updates?

Rob Edwards

Haven't heard from Kevin, was planning on taking a torque wrench to SF, will tighten every LCA bolt in sight.

GregBBRD

Most common 928 front suspension "crack" is a slightly loose lower sway bar to drop link bolt. Makes a hell of a noise as the suspension travels.

worf928

Since the factory used conical locking nuts on all of those bolts is it common that you find them replaced with normal nuts?

How else do they come loose?

Rob Edwards

Ironically I learned this just as I was trying to get Kevin to boil his brakes on the fun run last year, the GTS spat out the passenger side sway bar to drop link bolt in a hard right corner. Made quite a noise on its exit. Pretty sure I didn't have it fastened with a conical locking nut....

That'll certainly be something to check!