dgmattingley

I just got my car back from the alignment shop after installing rennline solid side mounts, rennline monoball shock mounts, and erp rear control arm bushings, along with RS wheel carriers and tie rods and rennline camber plates up front.

Everything feels great behind the wheel, but I'm surprised at the amount of knocking noise from the rear over bumps. I assume this noise is coming from the rear mounts, but is this normal? The knocking is not dependant on speed, and it is not the sway, which is factory RS. The shocks/springs are PSS9. Thanks for any input.

JPS

My JICs have done that forever. Sort of sounds like when a truck or van has a load in the flat part and it bounces just a bit. Speed bumps seem particularly surprising. I don't have the wheel carriers and tie rods. I did just install the Tarrett toe links and that seems to have ever so slightly magnified it, but that could be in my head.

trophy

9 times out of 10 the Monoballs in the rear shock mounts are slightly loose. It took me forever to find the issue, with the roll bar in my car it sounded like someone was hammering on the bar with a ball pein hammer.

Pulled of the strut tops, tightened them and all is ok.

dgmattingley

Thanks. How do you tighten the monoballs? Mine sounds like someone hitting their knuckles on the rear fender.

Bill Verburg

No, it's not normal.

First thing i'd look at
loose nut on the shock top, you need an allen wrench and a pass through socket to tighten these.

993KT

Did you get the rennline rear spring perch? Did you use the spacers that came with the rennline solid mount, and how did you set up the boot? I am about to do this same and wondering if there is enough clearance between the spring perch and the solid mount. Maybe the noise is related to that?

dgmattingley

I used the rennline spring perches and their spacers and had the same suspicion. When the assembly was out of the car I could twist the mount and make contact with the perch, even with the piston nut torqued down. The torque spec is quite low, so I'm doubtful that the lock nut is the culprit.

trophy

The mount has the mono ball held in place by a large thrust style bolt the top of is is 32 to 36 mm. Mine were not torqued down completely, it also had thread locker holding it in there. Took it off and loosened it off, cleaned out the threadlocker and torqued it down. Sound went away. Just make sure these is no dirt, old threadlocker etc between the bottom of the bolt and the monoball, needs to be clean, as any contamination may not allow it to torque down, and cause the knocking.

Bill also has a good point, these can cause the nock as well.

il pirata

From another thread. Also assume you are at RS height (or lower) in which case the rear sway needs to be below the suspension not on top.


09-16-2012, 07:17 AM #27
guards red
User



Join Date: Nov 2007
Location: Reading, Berkshire UK
Posts: 237

Hi,

I'm afraid the issue is also a little more complex than the width of the spring, the RS spring mount/perch will fit the spring for width (notwithstanding the issue of the final winding being flat), however the issue you will most likely encounter is articulation of the strut in the monoball. The monoball in the RS mounts (with spacers) protrudes much further from the bottom surface of the mount than do the Rennline mounts. This allows a gap between the bottom of the RS mount and the spring perch which means the strut can move in an arc as the suspension moves up and down.The RS spring mount is concave on top which works fine with this extra length, however as the Rennline ones don't protrude the perch will sit flat on the bottom of the Rennline mount meaning the strut cannot move. See this pictures on Jackal's website (RS Top Mounts) for reference.

Hope this makes some sense.

Regards
GR

dgmattingley

Yes, sway links are below arm and there is ample clearance.

I think you hit it right on the head regarding the movement of shock within mount. I removed them and found that shock was articulating within the mount, allowing the bolt heads on the bottom of the mount to strike the spring hats, clearly marring them. I removed the spacers, reassembled, and the articulation was eliminated, with the mount now basically flat and parallel to the hat, with no articulation. Went for a drive and noise is gone.

Roche993

Good job, Don. Glad you found it.

ToSi

Which spacer did you remove? the one circled in red below?

Does the hat now contact the underside of the mount??

dgmattingley

The picture isn't loading for me, but I removed the flat spacer that sits between the hat and the monoball. This spacer is listed as 'optional' in the rennline instructions. The mount now sits closer to hat, but does not make contact as it now doesn't articulate. There is still a small gap between hat and monoball. Hope this makes sense.

993KT

I am glad it works out, but I still don't understand how taking out the spacer will change the amount of movement. If the spring perch is closer to the top mount, wouldn't they make contact even more?

dgmattingley

There may be some slight contact still, but the mount cannot crash down onto the hat since the gap is smaller and the articulation is eliminated. There is about a credit card width of gap between mount bolt heads and hat. I tried two spacers but that was only going to make it worse, it could still make contact and would crash even more.

I compared with the oem mount, and without the spacer seems to be the most similar in terms of how everything fits together. Will call rennline today just to see what they think.