S30 Rear Strut Assembly Knocking - Nissan : Datsun ZCar forum :Nissan Z Forum: 240Z to 370Z
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post #1 of 7 (permalink) Old 01-06-2017, 01:36 PM Thread Starter
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S30 Rear Strut Assembly Knocking

Hey everyone,

New member here, I just recently picked up a 78 280Z as a first car for my brother and have been working on the suspension for the last couple months. After replacing the shocks and springs on all four corners with kyb's and voigtland springs, along with new end-link bushings, tie rods, and a set of T3 rear lower control arms, I started getting this knocking sound coming from the rear when driving over any uneven surfaces.

First thing I did was take the whole rear suspension apart and put it back together again to make sure I hadn't left anything out when doing the initial install and the noise is still there. The rear knocks when I push down on the car's rear end repeatedly and sounds like its coming from the upper part of the assembly where the strut mounts are. To add to the symptoms, with the car off the ground I can also get the noise by grabbing the assembly and pushing it back and forth, in which the entire assembly will wobble with enough force. That the assembly can wobble that much worries me but I'm not sure if that's normal or not because the only cars I've ever worked on had leaf springs in the rear.

Any input would be hugely appreciated because this is starting to stress me out....
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post #2 of 7 (permalink) Old 01-06-2017, 02:10 PM
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Originally Posted by q6tran View Post
. To add to the symptoms, with the car off the ground I can also get the noise by grabbing the assembly and pushing it back and forth, in which the entire assembly will wobble with enough force.
"The assembly" is pretty vague. Of course "the assembly" wobbles when you are shaking "the assembly". See the problem?

You do know that the gland nut is designed to compress the shock body in to the strut tube? If the nut bottoms out on the tube top instead of the shock body then the shock body will be loose in the tube. The shock shaft should not move side-to-side in the strut tube if the nut is fitting properly.
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post #3 of 7 (permalink) Old 01-06-2017, 02:35 PM Thread Starter
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Sorry, if I was being unclear, but the point of me asking that was that I was unsure if it's ok to have play in the assembly if I try to shake it. I was grabbing the strut assembly (#4 in the diagram).

I did the shock install a while ago so I don't remember if the gland nut is bottoming out on the shock body or the tube. But I do remember that the hole for the gland nut is bigger than the diameter of the shock shaft so the noise could be from that. If this is the issue do I need to address it immediately or is it something that can wait?
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post #4 of 7 (permalink) Old 01-06-2017, 03:45 PM
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It's unclear where the "play" is. That's my point. Is it loose at the top, bottom, or middle?

Some springs are short enough that with the car off of the ground the spring is not compressed at all. So if you grabbed the spring you could get movement. But it's been seen also that the bushings between the hub and control arm can degrade, allowing movement there. And then there's the potential movement between the shock body and the strut tube. Between the top of the strut and the bottom. So there are a lot of places that can have unwanted looseness.

There should be no knocking or looseness when the car is on the ground. From top to bottom it's all tight with right parts installed the right way. You might need to get some bright lights under there and see what's loose. You don't want to let it go too long because it can cause damage.
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post #5 of 7 (permalink) Old 01-06-2017, 04:20 PM Thread Starter
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The noise and play is coming from the top of the assembly. I'm pretty convinced now that the knocking is coming from movement of the shock body inside of the strut tube.

I remember the gland nuts that came with the kyb's were too small so I used the originals and the holes for them are bigger than the diameter of the kyb's shock shaft.
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post #6 of 7 (permalink) Old 01-08-2017, 11:26 PM
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Did you get the correct rear struts for a 280Z? What part number are the KYB struts?


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post #7 of 7 (permalink) Old 01-09-2017, 09:21 AM
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Originally Posted by steve240Z73 View Post
Did you get the correct rear struts for a 280Z? What part number are the KYB struts?
I know this doesn't totally fit with your description of the symptoms but....

I too had a knocking sound when I slowly drove over uneven ground. I too had just rebuilt the rear suspension.

I got rid of the knocking by greasing the stabilizer bar bushings. I think the new poly bushings were too tight and the bar was binding as it twisted over the uneven ground.

Herb in Florida
1978 Datsun 280Z ( Dec 77 build)
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