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Benoit Leus
Grand Master
Username: benoitleus

Post Number: 371
Registered: 6-2009
Posted on Saturday, 29 September, 2018 - 00:45:   Edit PostDelete PostView Post/Check IP

I have a deep knocking/rattling sound coming from the rear suspension, each time I drive over a bump, pothole, etc...
I am inclined to believe it is air trapped in the hydraulic system, as it started after I had removed and reinstalled the LH rear hydraulic ram.

I bled the system, but no air bubbles seemed to come out, which was strange as there had to be following the removal of the hydraulic ram. As I had to do this on my own, I did it only for a short time (the time it took to fill up a jam jar with brake fluid) as I didn't want the reservoir to run dry.
Should I have bled the system for a longer time ?

Also, I read on the forum that it would be a good idea to clean the height restrictor valves. If they where full of crud, could this cause air to stay trapped in the systelm ?

Benoit
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Robert J. Sprauer
Frequent User
Username: wraithman

Post Number: 65
Registered: 11-2017
Posted on Saturday, 29 September, 2018 - 01:11:   Edit PostDelete PostView Post/Check IP

Did the rattling occur after the rams were removed?
Usually when air is trapped there is knocking after the car is shutdown and can last a few hours in my experience. If you have a rattle when going over road potholes and bumps there is another issue. It is always a good idea to periodically remove and clean hydraulic components. The restricter is simple in design.
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Benoit Leus
Grand Master
Username: benoitleus

Post Number: 372
Registered: 6-2009
Posted on Saturday, 29 September, 2018 - 01:23:   Edit PostDelete PostView Post/Check IP

Robert, it indeed started after the removal of the hydraulic ram.
Whatís peculiar, is that it can be heard very clearly iside the car (altough the sound seems to be coming somewhere from the RH rear suspension), but not from the outside (like for example a loose exhaust) which makes me think even more itís hydraulic.
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Robert J. Sprauer
Frequent User
Username: wraithman

Post Number: 66
Registered: 11-2017
Posted on Saturday, 29 September, 2018 - 02:15:   Edit PostDelete PostView Post/Check IP

I have left spanners behind that caused needless searching for deeper answers. Perhaps re-check shock hardware. Here's my Google album.
https://photos.google.com/share/AF1QipPnncFRTwsvZyCfz_ZCcq3WDnNF6-AF65Rampnoo39gisFrktz7PDsfVg5Tu01WVw?key=WTdPS05zeDg0WmNKaVFGMUNVRjVncVh3ZGJHcU1B
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Omar M. Shams
Grand Master
Username: omar

Post Number: 1676
Registered: 4-2009
Posted on Saturday, 29 September, 2018 - 02:29:   Edit PostDelete PostView Post/Check IP

When I had this problem I chased my tail for two years until I solved the problem.
The problem was perfectly new looking flexible hydraulic hoses that look lovely from the outside but act as restrictors form the inside. I changed those and the bleeding became possible. Once I bled the system all noises went away.
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Benoit Leus
Grand Master
Username: benoitleus

Post Number: 373
Registered: 6-2009
Posted on Saturday, 29 September, 2018 - 16:13:   Edit PostDelete PostView Post/Check IP

Iíve still got one question : if there is air trapped in the rear suspension hydraulic system, when would I hear the knocking sounds ? Because I only can hear it over small road imperfections (cobblestones, potholes, ...).
When disconnecting the height control valves and operating them manually by pushing the arm upwards the car rises perfectly without making any noise.
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Larry Kavanagh
Prolific User
Username: shadow_11

Post Number: 218
Registered: 5-2016
Posted on Sunday, 30 September, 2018 - 06:20:   Edit PostDelete PostView Post/Check IP

Hi Benoit, I reckon you should hear the knocking when neutral or park are selected or when weight is put in the rear as that's when the height control activates. I think that the most likely culprit is a clogged restrictor valve, more than likely the low pressure restrictor valve which return fluid from the height control passes through on its way back to the reservoir. It sounds like a plumbing knock and can cause vibration in the pipes near the restrictor valves and solenoid valve, when you rev the engine the knock would get faster and louder and if your finger was on the pipes you might feel the vibration.
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Martin Taylor
Prolific User
Username: martin_taylor

Post Number: 140
Registered: 7-2013
Posted on Sunday, 30 September, 2018 - 21:23:   Edit PostDelete PostView Post/Check IP

Get someone to bounce the rear up and down while you have a listen, sounds like the top of the shock could be loose where it attaches to the ram or the exhaust is knocking somewhere, it may be riding at a different height if you have had everything apart. If not set right the system can try to correct itself as you go over a bump, ie one side says down and the other says up, if the linkages are set correctly this should not occur however. Mine will clunk and bang if I havenít closed the door properly as it will correct after every bump on fast levelling which can get noisy. On slow it is silent.
See if you can move the shock inside the spring
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Omar M. Shams
Grand Master
Username: omar

Post Number: 1677
Registered: 4-2009
Posted on Monday, 01 October, 2018 - 01:13:   Edit PostDelete PostView Post/Check IP

Dear Benoit,
borrow Alex's GoPro and attach it to the bottom of the car and take a drive. You will see what is happeneing then.......
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Benoit Leus
Grand Master
Username: benoitleus

Post Number: 374
Registered: 6-2009
Posted on Monday, 01 October, 2018 - 05:46:   Edit PostDelete PostView Post/Check IP

I did the next best thing to using a GoPro and filmed it from beneath the car at standstill.
The sound quality is poor (blame the smartphone I used) so it's best to watch the videos in a quiet environment with the sound turned up or, even better, use headphones. When sitting inside the car the sound is much clearer as it seems to reverberate.

Video 1 : this was filmed inside the boot. What you see is where the LH rear suspension tower meets the boot floor. The suspension is pushed up and down no more than 1-2cm. You can hear a knocking sound. When sitting inside the car it's really loud and clear.

https://www.youtube.com/watch?v=MZpzHeJ1MRc

Video 2 : I disconnected the bottom bracket of the rear LH shock from the rear suspension arm as to make sure I isolated it from the suspension. The bottom of the shock is resting on a wooden block so the shock would still be lightly compressed when pushing the suspension up and down (1-2cm). Listen carefully and you can still hear the knocking sound.

https://www.youtube.com/watch?v=de9xhOrCgiQ

Video 3 : the bottom of the shock is not resting on anything so the shock isn't being compressed when pushing the suspension up and down. The knocking sound has disappeared.

https://www.youtube.com/watch?v=3YvNEkkyvaE

For me this leaves two options :
1) a faulty shock. The rear shock's (from Introcar's Prestige range) have already been replaced under warranty after a few months due to being noisy (though not in anyway as bas as now). So this would mean this shock has again developed an internal problem.
2) a problem with the top mount of the shock. I will remove the hydraulic ram and investigate this, but it seems unlikey as the noise is still present when the shock is not compressed and there don't seem to be any strange noises emanating from the area around the hydraulic ram.

Any suggestions are certainly welcome.
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Larry Kavanagh
Prolific User
Username: shadow_11

Post Number: 220
Registered: 5-2016
Posted on Monday, 01 October, 2018 - 07:32:   Edit PostDelete PostView Post/Check IP

anti-roll bar bushes or mounts possibly but that's a wild guess I'm afraid.
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Martin Taylor
Prolific User
Username: martin_taylor

Post Number: 141
Registered: 7-2013
Posted on Tuesday, 02 October, 2018 - 18:49:   Edit PostDelete PostView Post/Check IP

The top of the shock has to be loose, get a long piece of rubber hose, put one end in your ear, and put the other end up the inside of the shock tower to confirm. The noise is being amplified inside the cone like a speaker. A camera to look up there is only a few dollars on eBay but they never give any real perspective
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Benoit Leus
Grand Master
Username: benoitleus

Post Number: 375
Registered: 6-2009
Posted on Wednesday, 03 October, 2018 - 01:40:   Edit PostDelete PostView Post/Check IP

The saga continues :
with the LH rear shock still disconnected at the bottom I drove the car slowly over a small stretch of cobbled road. The knocking sound was still there, but not as loud. I then drove it with the RH rear shock disconnected at the bottom. The knocking sound was much louder now.
Finally, I drove the same stretch of road with both shocks disconnected at the bottom (for the full bouncy castle experience). The knocking sound had disappeared completely !

I can hardly imagine both shocks having failed in a similar way at the same time. So I guess that with the shocks connected, something in the suspension must be touching, causing the knocking sound.
I just can't figure out what would change in the rear suspension with both shocks disconnected so that the knocking sound dissapears.

Any suggestions are more than welcome as I'm getting rather fed up with laying under the car, poking at the suspension.
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Omar M. Shams
Grand Master
Username: omar

Post Number: 1678
Registered: 4-2009
Posted on Wednesday, 03 October, 2018 - 02:15:   Edit PostDelete PostView Post/Check IP

Do you have access to a pair of good used shocks to try them out? It is possible your shocks are "shocking".
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Benoit Leus
Grand Master
Username: benoitleus

Post Number: 376
Registered: 6-2009
Posted on Wednesday, 03 October, 2018 - 02:28:   Edit PostDelete PostView Post/Check IP

Unfortunately not, Omar.

But even then, the knocking sound seems to come from the same spot (somewhere close to the LH rear suspension tower), no matter if both shock or only one of them are connected. It's only not as loud when only the RH shock is connected.
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h_kelly
Prolific User
Username: h_kelly

Post Number: 260
Registered: 3-2012
Posted on Wednesday, 03 October, 2018 - 03:22:   Edit PostDelete PostView Post/Check IP

Hi, are you familiar with this site http://www.brabocars.com based in The Netherlands, might save you carriage/postage on future purchases.
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Christian S. Hansen
Grand Master
Username: enquiring_mind

Post Number: 927
Registered: 4-2015
Posted on Wednesday, 03 October, 2018 - 06:19:   Edit PostDelete PostView Post/Check IP

Benoit...
As a casual observer I can add that the silver lining in the issue is that you have at least isolated a set of circumstances that affects/eliminates the sound...the removal of both shocks entirely...so it would seem that the cause has "something" to do with those shocks...if not the shocks themselves, then their physical installation. Omar's suggestion, while perhaps not practical to implement, would however provide additional pertinent data. Have you tried switching them side to side to note any change of symptom?

As to having both shocks defective at the same time, stranger things have happened. It is similar to having two tail lights burn out "at the same time". The scenario goes like this: They did not really fail at the same time. First one failed and it was not noticed, or in this case did not cause any symptoms to alert you to the condition, then later the other fails and you become aware, but are surprised that "both have failed at the same time." I'm just saying. Been there. Done that.

.

.
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Martin Taylor
Prolific User
Username: martin_taylor

Post Number: 142
Registered: 7-2013
Posted on Wednesday, 03 October, 2018 - 07:15:   Edit PostDelete PostView Post/Check IP

Hook an ohmmeter to the disconnected shocks and check your rubber isolators are fitted correctly, is there any movement at all if you try moving the disconnected shocks from under the car?
Unless cornering the suspension is effectively parallel so disconnecting one side will simply transfer the damping load to the other side.
From your description it sounds like both shocks have a problem either in their mounting or internally but the left is worse than the right.

The rams provide a solid column of fluid so should not allow any movement to the spring perch once the height is set, however if there was air trapped as first suggested this would allow some spring in the ram itself, this movement would get worse with the shocks connected as it would slow the rebound in the up direction. Effectively a spring acting against a spring.

Bleed it again before taking anything else apart or check for upper spring mount movement relative to the body during your bounce test (this I could be difficult).

Failing that, depressurise the system and block off the rear levelling with a ball bearing and test again for noise, if the rams are fully collapsed there can be no movement in the upper spring mount. If the noise is still there it can only be shocks or shock mounts

All this should be easier than removing the rams (total last resort).
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Omar M. Shams
Grand Master
Username: omar

Post Number: 1679
Registered: 4-2009
Posted on Wednesday, 03 October, 2018 - 14:09:   Edit PostDelete PostView Post/Check IP

Bleeding the rear height control system is sometimes not all that easy .My way of ensuring full bleeding is to connect a very long tranparent tube all the way back to the reservoir and run the engine with the car in park and me jumping up and down on the back .When this is done over several minutes you get to see just how much air was actually still in the system .
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Martin Taylor
Prolific User
Username: martin_taylor

Post Number: 144
Registered: 7-2013
Posted on Wednesday, 03 October, 2018 - 16:22:   Edit PostDelete PostView Post/Check IP

After thinking about it, just do a pump down test with the brake pedal to depressurise the system, then lift the rear of the car a few inches, that will open both rear valves to remove all ram pressure, then do your bounce test on fully retracted rams. That should eliminate any ram noise and tell you if your shocks are ok
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Robert J. Sprauer
Frequent User
Username: wraithman

Post Number: 67
Registered: 11-2017
Posted on Wednesday, 03 October, 2018 - 21:38:   Edit PostDelete PostView Post/Check IP

Omar, the problem with your technique is the possibility of returning polluted fluid to the reservoir.
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Omar M. Shams
Grand Master
Username: omar

Post Number: 1680
Registered: 4-2009
Posted on Thursday, 04 October, 2018 - 01:05:   Edit PostDelete PostView Post/Check IP

Dear Robert,
yes you are right if indeed the system was not bled previously. Given that Benoit has bled and bled and bled - he should in theory only have clean oil. If he doesn't have clean oil then that oil is already in the system and what difference does it make if it remains there anyway?
Thanks

Omar
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Benoit Leus
Grand Master
Username: benoitleus

Post Number: 378
Registered: 6-2009
Posted on Tuesday, 09 October, 2018 - 01:08:   Edit PostDelete PostView Post/Check IP

Thank you, everyone, for all the suggestions and ideas. I've had my work cut out following up on them.
I'm afraid it's a bad shock again (after checking everything else), although it was replaced under warranty last may and has only done about 400 miles since.

I just send a mail to Introcar and am awaiting their response.

For those who are curious on how it sounds whend driving, I made a sound clip :

https://www.youtube.com/watch?v=vQYYbNAYcKg
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Patrick Francis
Prolific User
Username: jackpot

Post Number: 250
Registered: 11-2016
Posted on Tuesday, 16 October, 2018 - 07:38:   Edit PostDelete PostView Post/Check IP

Hi Benoit
I think I have had everything apart and renewed in my brake system and rear suspension, and I still get gremlin noises. I would be very interested in knowing if the noises stop when you put the new shocks in.
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Benoit Leus
Grand Master
Username: benoitleus

Post Number: 379
Registered: 6-2009
Posted on Wednesday, 17 October, 2018 - 02:38:   Edit PostDelete PostView Post/Check IP

Introcar send me a replacement shock and the noise has completely disappeared. So what I thought couldn't be the cause (a replacement shock going bad within 400 miles), happened anyway.

Patrick,
you might try to do what I did : disconnect the bottom of the shocks, rendering them inoperative. Wrap them in a piece of cloth or towel, so the cannot bang against the suspension, causing a new noise.
If your gremlin noises have disappeared, you will know it's the shocks.
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Patrick Francis
Prolific User
Username: jackpot

Post Number: 265
Registered: 11-2016
Posted on Wednesday, 17 October, 2018 - 18:35:   Edit PostDelete PostView Post/Check IP

Thank you Benoit.
I will try that.
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Patrick Francis
Prolific User
Username: jackpot

Post Number: 267
Registered: 11-2016
Posted on Wednesday, 24 October, 2018 - 21:22:   Edit PostDelete PostView Post/Check IP

Hi guys
I have cured a rattle at the back. It happened to be the horizontal torsion bars that go along the top of the boot between the boot hinges.
There are two sponge rings that should separate them which I repositioned and also used two tie wraps to hold the bars together slightly.
Now to the next rattle!
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Patrick Francis
Frequent User
Username: jackpot

Post Number: 341
Registered: 11-2016
Posted on Monday, 22 June, 2020 - 08:10:   Edit PostDelete PostView Post/Check IP

Hi All
I was not sure which post to put this into, because there are a lot out there dealing with rumbling and knocking noises.
Anway, this is my story in case it may help somebody:

About a couple of years ago there started a rumbling noise that was emanating from the back of the car.

It would happen only occasionally and only on uneven surfaces.

I kept examining different bushes, and components in the rear. Checked for loose items in the boot, a loose spare wheel, loose exhaust etc etc.

AS this slowly got worse and more annoying, and only on certain surfaces, and only a couple of rumbles at any one time, I put our mechanic in the boot and drove around until I had made it rumble a few times, but he said he couldnít hear anything.

He then got in the back seat, and we went for a drive, when he said that the noise was actually coming from the front of the car! All this time, and still, it sounded from the driving seat to be coming from the rear!

So now from the front seat position, the noise was still intermittent, and difficult to locate, but we were convinced that it came from around the LHS (passenger) footwell area.
I changed 3 suspicious bushes on the front suspension, but passengers would confirm that they could still feel the rumbling by their feet. Very annoying....

I read on the forum that it might be one of the 4 big subframe bushes (£365 each!!), so I dropped the subframe slightly and checked them.Fortunately, they seemed ok. I torqued them and went for a ride hoping that they had maybe been loose - no such luck.

I then used my microphone listening set that has 6 microphones that can be clipped anywhere and listened to individually.

I clipped microphones to every part of the front suspension in turn. Also to the exhaust, subframe, spring, bottom shock absorber mount, bodywork, around the turret inside the engine compartment, but could not hear anything that coincided with the rumble

The last place I clipped a microphone was to the top stud and nut of the shock absorber and "eureka", I finally heard a rattling which coincided with the rumbling.

I checked the rubber bushes which seemed tight, and so I thought I might have to replace the shocks at £220 each.

I remembered, though, how well both front shocks had performed during the last MOT test.

the rubber bushes seemed relatively tight and compressed.

Finally, I swapped over both front top shock absorber bushes and added washers to compress the rubber more.

Et voila, noise gone!!

Always go for the most obvious first!!!!
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richard george yeaman
Prolific User
Username: richyrich

Post Number: 1153
Registered: 04-2012
Posted on Tuesday, 23 June, 2020 - 21:18:   Edit PostDelete PostView Post/Check IP

Great news, I am sure Carlos is relieved no more trips in the boot.

Richard.

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