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Discussion Starter #1
In the 3 yrs I've had the car there's always been a knocking from the rear. It's a dull metal thud that happens over bumps, when accelerating and when ever else it likes.

In pursuit of this, I've so far replaced all the rear bushings (trailing arms, t bar and anti roll bar), replaced the rear and middle exhaust sections and made sure it's all tight, replaced the prop shaft centre mount, changed the diff oil and don't carry anything in the boot.

And it still knocks, I've tried to live with it but it's driving me nuts.

Any suggestions welcome as I've ran out of ideas!

Thanks
 

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Can you reproduce the knock pushing down on the back of the car or shaking the car from side to side as hard as you can?
 

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Discussion Starter #6
Thanks guys

Donut was fine as were u joints, I had the whole prop off when swapping centre mount.

Shocks and springs seemed okay when I stripped the suspension, shocks checked and springs cleaned and repainted. I also fitted new rubber tops for the springs.

Yes I can feel as well as hear it.

No knocking from up and down but there is a knock from side to side, not sure it's the same knock though but may sound different as I'm not in the car.
 

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are the shims good (or even there?) on the T bar? (photo shows where they are missing)....if these are missing you would get a side-to-side bang, I would think.....
Shocks upper mounting bolt tight?
Perhaps a real bad rear wheel bearing?
 

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Discussion Starter #8
Thanks but no, replaced those with super flex ones.

Thought about a wheel bearing but it seems to be from the middle of the car as appose to a corner, plus it's not related to the speed.

Having another look at this diagram, the only thing I haven't replaced is the bump stops for the rebound straps, so could it be these or the rebound straps themselves. The straps are in good condition but do they need to be set in some way?

Rear suspension (diagram) | Classic Alfa Romeo spare parts and accessories

Thanks
 

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not not really, I don't see the bump stops or straps being the source of any knock......the straps generally don't need to be touched...... unless you have put in very short hard racing springs, in which case the straps would need shortening to compensate for axle shaft max travel.

.....was the rear knock always there (ie. before you did any suspension work)...?
 

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Discussion Starter #10
No I haven't changed the springs, all standard.

Yes the knock has always been there. Could it be to do with the differential, is there anything in there that knocks as that's where the noise seems to be coming from?

Or the prop, I though I'd cracked it when I found that the centre mount rubber was split but only to find it was the same when I fitted a new mount. I know I have a knock from where the front of the prop meets the gearbox but you can only hear this if you pop the clutch, but this is down to a worn bit (can't remember the name of the part) in the gearbox. When I had the prop off I phoned Classic Alfa who advised that this was common but it's a new gearbox if I wanted it fixing properly and duly packed it with grease as recommended. I thought the sound could be transferring down the shaft but I don't think so.

Any other straws to clutch at? ;-)
 

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You say it makes the sound when you accelerate and/or go over a bump. Do you get it when you brake?

It sounds to me like something in the boot moving around e.g. the spare wheel clunking around, but its obviously not that as you have checked the boot.

But what about inside the fuel tank? I don't know how the in-tank pump is attached but could that be moving around? Or something else in there that a PO has dropped and not retrieved?

Is the petrol tank fully secured - bolts all tight, foam gasket good?
 

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Discussion Starter #12
Not sure about when braking, will test for that.

I took everything out of the boot, including the spare.

The tank is secure too, I suppose there could be something loose in there but it's not that sort of sound, if you know what I mean!?
 

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was the "BIT" in the gearbox, the so-called "onion" on the output shaft, that fits into the prop bushing?......though that would cause more vibration rather than a knock..the red outlined piece in this diagram:
Alfa Romeo Bulletin Board & Forums - View Single Post - how to change flex disc 86 spider
(since posting that I have heard that some experts can weld that up without pulling the box apart!)

what about the UJ's.......? you don't say you checked those?...they might knock on acceleration...
 

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Discussion Starter #14
Yes that's the one, it's not bad, certainly hasn't caused any damage to the prop.

The uj's were fine I think, I didn't specifically check them for play but they moved freely. I might double check them though.
 

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noises are so difficult to pin point.

What I would maybe do (since you say there is a knock when physically shaking the car side to side....that has to be a clue here, in my eyes) is, if you have a helper, put the rear of the car on ramps (so suspension is in roadgoing status) then get him (her?!) to shake the car and you listen or better still feel everything under there with your hand.........

a long shot, but on the german alfisti website a guy had aproblem after refurbing his whole rear suspension (wasn't a clunk per se, but was a knock)........only thing he did not replace were the stepped bolts on the trailing arm lower bushes..these turned out to be worn and clattering inside the steel shaft of the bush. It is not something one thinks wears normally...like I say a long shot, but you might be able to feel movement there when your buddy shakes the car??

failing that a cam and mike under the car, drive like hell and put it on you tube;)
 

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I'd be curious if you findout, I have had whole load of stuff replaced, springs, shocks, bushes, I get a knock when going over bumps, i even resorted to bubble wrap between the parcel shelf arm and the parcel shelf. Have you checked the gearbox mounts?
 

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Discussion Starter #18
thanks Silverback6 but im talking about my S2 which has a different set up to the Alfetta
 

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I was thinking about this earlier, as I drove into work in my Spider, accompanied by various rattles and groans (some of them from the car, not just my own joints...).

I wondered if anyone has experimented with placing an old phone with video function under the car whilst driving, to see if anything makes contact or moves unexpectedly? Or, if not a phone, one of those mechanics cameras in a flexible tube? http://www.ebay.co.uk/bhp/flexible-inspection-camera
 

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Oops my mistake!! I read the title on the “GTV Transaxle electrical connectors” and then went to your problem??? (Must pay more attention)

Good luck with it!

Cheers
 
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