Rear susp knock

robsad

True Classic
listers, I just put my rear suspension together on my 74 however there is a slight knocking on both sides when the rear of the car moves up and down. I can lift the rear of the car up and down and I can see the centering cone at the top mount moving up and down. First, everything is new back there - the pillars with new wheel bearings, new KYB excel shocks, new top mounts and new control arms. I originally put Vick performance springs on and noticed the knock so I replaced those with original springs but the knock is still there. I also put the Bigfoot strut plates on but my shock towers didn't need them and I'm tempted to take those off to see if that makes a difference. Also as per Matts specs, I used the spring perches for 80 - 88 cars when installing the KYB shocks on an earlier car. I'm sure the top nut and cone is put on correctly and I couldn't tighten the nut any tighter. I had Koni struts on the car prior to the rebuild and had no issues. I've run out of ideas and I hope some of you can lend some advice.
Bob

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Bob, have you been able to replicate the knock by bouncing the back of the car (when parked), or is it only while driving? If it is only when driving then check to make sure the CV joints aren't hitting the axles, due to the rear lower engine mount sagging. If you can make it happen while parked, then raise the car (on stands), go underneath and use a long pry bar to try and wiggle every joint, bushing, mount, suspension part, etc, looking for movement or play that should not be there. It takes considerable force to move things so don't be afraid to give it a good lever. Try and move things in all directions. Usually the offending component shows itself.
 
Bob, have you been able to replicate the knock by bouncing the back of the car (when parked), or is it only while driving? If it is only when driving then check to make sure the CV joints aren't hitting the axles, due to the rear lower engine mount sagging. If you can make it happen while parked, then raise the car (on stands), go underneath and use a long pry bar to try and wiggle every joint, bushing, mount, suspension part, etc, looking for movement or play that should not be there. It takes considerable force to move things so don't be afraid to give it a good lever. Try and move things in all directions. Usually the offending component shows itself.
Jeff,
Yes, I can make it knock when parked. Keep in mind that every component is new - The knock was not there
Before I replaced everything. I'm starting to think it might be the top mounts. These are new "heavy duty" top mounts from Obert.
 
listers, I just put my rear suspension together on my 74 however there is a slight knocking on both sides when the rear of the car moves up and down. I can lift the rear of the car up and down and I can see the centering cone at the top mount moving up and down. First, everything is new back there - the pillars with new wheel bearings, new KYB excel shocks, new top mounts and new control arms. I originally put Vick performance springs on and noticed the knock so I replaced those with original springs but the knock is still there. I also put the Bigfoot strut plates on but my shock towers didn't need them and I'm tempted to take those off to see if that makes a difference. Also as per Matts specs, I used the spring perches for 80 - 88 cars when installing the KYB shocks on an earlier car. I'm sure the top nut and cone is put on correctly and I couldn't tighten the nut any tighter. I had Koni struts on the car prior to the rebuild and had no issues. I've run out of ideas and I hope some of you can lend some advice.
Bob

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The difference between the '79 and older <===>'80 and newer strut operating rods IIRC is that the older has a two-step profile at the top and the newer has a one-step profile. Since the upper spring perches have to match the operating rod, best to doublecheck that aspect.
 
The difference between the '79 and older <===>'80 and newer strut operating rods IIRC is that the older has a two-step profile at the top and the newer has a one-step profile. Since the upper spring perches have to match the operating rod, best to doublecheck that aspect.
Dan, problem is I haven't seen a separate listing for different top mounts for different years. There seems to be only one type of top mount available. Since this problem wasn't there with the old original springs and top mounts this must be the problem. Not sure how to proceed now.
.
 
Dan, problem is I haven't seen a separate listing for different top mounts for different years. There seems to be only one type of top mount available. Since this problem wasn't there with the old original springs and top mounts this must be the problem. Not sure how to proceed now.
.
Did you use keep the old upper spring perches? If so, that may be your problem.... the ‘74 rear spring perches are not compatible with newer shocks and must be replaced with the 80-88 spring perches.
 
Is this a sound you could have just once when moving the car, so the parts "settle in their place" or something always knocking if you are shaking the car?
 
Eric,
I did use the perches from the 80 - 88 cars and the knock is still there.
Well shucks - I knew the easy answer was too much to hope for.

It is odd that the centering cone is moving visibly, as it should have zero play.

I did the shock/spring/perch replacement on one of my ‘74s a few years ago, didn’t have this problem but also don’t remember the exact arrangement of washers and bits at the top of the struts. So either your KYBs are different than the ones I used, or there’s some spacer or the like needed to take out the play you’re seeing.
 
I have had a similar issue if the strut top nut was not tight, or assembled correctly.
To help find the source touch the different components, or junction of components while the car is bounced to make the noise.
 
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