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clunk from the back 
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Joined: Sun Oct 19, 2014 10:10 pm
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Post clunk from the back
I've got a clunk at the rear end, nearside I'd say. It sounds like metal on metal, kind of like a lump hammer hitting a vice. It only happens on compression bumps (like sunken manholes) or when coming down off speed humps. I've checked all my ball joints (I have Mk1.5 rear suspension - 8 ball joints, 4 brackets), damper bushes and the various other ball joints on the rear uprights and tie rods and all seem okay. I can't find anything loose and no obvious signs of chipped powder coat or suchlike to indicate things hitting other things. It been getting gradually worse since I got the car 2.5 years ago.

Anyone got any thoughts?

I'm currently thinking its the gearbox mount - the square Metro one with the triangle of metal suspended between rubber lumps. There seems to be big gaps all around the triangle and whilst I can't get the middle part to touch any of the outer parts by rocking the engine it does come close. Next step is to take the weight of the engine/box on a jack and shove a lump of rubber (maybe from an old hose or suchlike) into the gap, maybe held with cable ties and then see if the clunk goes. If so possibly a new mount or maybe the liquid rubber treatment. have others had a similar clunk? Did those that did the liquid rubber thing do it to cure a clunk or just to reduce engine movement?

(VVC/PG1)


Thu May 18, 2017 10:22 pm
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Post Re: clunk from the back
I recently had to do the top engine mounts ( near the cam cover) which helped with a clunk. Also having fitted new dampers, found that they were adjusted wrong, which meant there wasn't enough travel which led to a loud clunking noise over speed bumps. It's a quick and easy job to adjust the springs, even if it's just to eliminate them.


Thu May 18, 2017 11:41 pm
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Joined: Wed Jan 23, 2008 11:31 am
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Location: Rowley Regis, West Midlands
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Post Re: clunk from the back
I get an occasional clunk on compression bumps, never have worked it out.
I suspected the spring hitting the frame, the washer bottle hitting the tray the vents sit in or the actual dampers.
Never thought of the mounts, let me know how you get on.
Juls


Fri May 19, 2017 9:59 am
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Post Re: clunk from the back
Should have said, it has definitely appeared to get worse since my Stoneleigh broken steady bar issue which is another reason I'm thinking about the engine mounts. While the engine was rocking back and forth with no steady bar it must have put some unusual stresses on the mount rubbers...


Fri May 19, 2017 12:38 pm
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Post Re: clunk from the back
Attachment:
Gearbox mount new.JPG
Gearbox mount new.JPG [ 38 KiB | Viewed 524 times ]


Looking at this image of a new gearbox mount I'm starting to think I may be on to something. The bottom of the central metal part on mine is only about 3mm off the metal frame and the lower rubber blocks are very thin compared to this image. I know they'd squash a bit under load but mine look worn down rather than squashed.

A new mount is over £100 on Rimmers and I can't find any used ones right now so I think I'll be trying out some liquid/setting polyeurathane sometime soon. While I'm at it I'll do the same to the other mounts too although I noticed that Rimmers have the right hand side mount for only £20+vat at the moment as a clearance item...

When others have done the poured poly thing have they taken out all the old rubber or just poured it in around the old rubber?


Fri May 19, 2017 1:16 pm
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Post Re: clunk from the back
A while back I fixed a fully goosed void bush on a CRX with a cheap version of tiger seal - it worked brilliantly. Just tip it in around what is already there. You might want to somehow hold the centre bit in the position that it should be, as opposed to where it has sagged to.

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Fri May 19, 2017 2:28 pm
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Joined: Mon Aug 18, 2014 6:07 pm
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Location: Devon
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Post Re: clunk from the back
sanzomat wrote:
Attachment:
Gearbox mount new.JPG


Looking at this image of a new gearbox mount I'm starting to think I may be on to something. The bottom of the central metal part on mine is only about 3mm off the metal frame and the lower rubber blocks are very thin compared to this image. I know they'd squash a bit under load but mine look worn down rather than squashed.

When others have done the poured poly thing have they taken out all the old rubber or just poured it in around the old rubber?


I think if the rubber is in reasonable condition I'd leave it in and pour around, if it's jiggered I'd make a basic jig to hold the insert in place and pour the whole thing. I expect the noise will go up without the voids, but it should be stronger.


Fri May 19, 2017 5:27 pm
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Post Re: clunk from the back
You can always drill some holes after moulding if it needs to be softer.


Sun May 21, 2017 2:37 am
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Post Re: clunk from the back
Doing the gearbox mount made no difference to the clunk but while driving with a passenger the clunk was absent which set me thinking, especially as the clunk is on the passenger side. It turns out that with the ride height set as 145mm at the rear (sill to ground) my shock is almost fully extended. Adding the driver drops it down a bit and then a compression bump means that the shock hits its internal stop on the rebound - clunk! With a passenger there must be enough starting compression to not use all the travel on the rebound.

So, it seems a fix for this will be to lower the ride height so there is some travel left but that would mean dropping it to something like 135 and to get the front the recommended 15mm lower, 120 at the front which seems low. I thought the recommended rear height was 150 but that will have the shock fully extended at rest which doesn't sound right to me. Have I got the wrong shocks?? maybe the kit was supplied with Libra ones?? Are they shorter??


Sat Jun 17, 2017 8:28 am
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Post Re: clunk from the back
I thought the Spyder shocks were shorter than the Libra


Sat Jun 17, 2017 11:08 am
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Joined: Wed Feb 09, 2011 1:12 am
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Location: Derbyshire
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Post Re: clunk from the back
my libra protech rears are about 575mm i think spyder ones are shorter but do not know how much protech sell extended top eyes that may give you the travel you need without replacing whole shock if they match the thread on the end of the piston of the ones you have


Sun Jun 18, 2017 10:42 am
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Post Re: clunk from the back
Mine are 530 overall so if measured from centre of bush to centre of bush would be 500mm.

Mine are GAZ so Protech top mount extenders won't help much :roll:

How close are your Libra shocks to fully extended at rest at the correct ride height?


Sun Jun 18, 2017 3:38 pm
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Post Re: clunk from the back
forgot to put where measured centre of bush top to bottom fully extended 578mm travel 110mm to bump stop gtm rdm web site used to say 70mm of travel under bump and 70mm drop at wheel so due to lever ratio 55mm each way at shock these measurements are for early type protech with the narrow lower section to clear the early spec wheel offset the later ones that Don stephenson helped protech design as on jamie z cars rear car are a longer shock so may have a bigger piston stroke but have clearance problems with the early type wheels the protech parts may fit your shocks if the thread is the same this will give a longer shock but will make the operating range at a higher ride height i have gaz spring seats on protech shocks i have some atr rears with same length fully extended but have 170mm travel is it worth trying swoping rears side to side to see if the one from o/s makes same noise when fully extended on n/s


Sun Jun 18, 2017 7:26 pm
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