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Bulkhead(?) rattle


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Hello Everyone,

There is a very suspicious loud rattle noise coming from the rear when driving on a rough surfacegoing from the garage to the lift in my S4s. It doesn't appear when steering quickly, it's really more related to the road bounces apparently, even at a very low speed.

I am not sure if it developed recently as I haven't driven the car much yet (so far I have spent much more of my time in the boot or under it than in the driving seat, but anyway :D)

I was a bit concerned something broke loose in the engine compartment or suspension (nothing obvious though), and then I stumbled on the infamous plywood bulkhead shrinking story \o/
I will have to check that as it corresponds so well to my symptoms, but I was wondering why it was advised to remove and shorten the clamping plate from the inside, at the back of the seats (and having to cut the carpet/soundproofing) instead of just adding a few washers (or another plate) between the engine bay bracket and the plywood?! ("washers/spacer" pictured in green in the included drawing). Is there a specific reason?

Thanks in advance!

PS:

A few references:

https://www.thelotusforums.com/forums/topic/40761-clunking-behind-passenger-seat/

http://www.lotusespritworld.com/EGuides/EModifications/BulkheadPlate.html

 

BulkheadMountingPlate_+washers.gif

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Having done this a number of times, I'll give me view:

- firstly, the bolts are welded to the engine mounting bracket so cannot be withdrawn independently from the plate. Plus the plate is shaped not flat

- secondly, the thread engagement is not overly generous, so if you are boosting the bracket backwards it becomes difficult to refit the clamp plate

- thirdly, the thread run down a long way without the shoulder bolt so it that combination that guided the solution

Admittedly, it seems a bit harse to cut the carpet and soundproofing, but only back in place behind the seats it is not really noticeable.

DSCF0037.JPG

1996 Esprit V8, 1998 Esprit V8 GT, 1999 Esprit S350 #002 (Esprit GT1 replica project), 1996 Esprit V8 GT1 (chassis 114-001), 1992 Lotus Omega (927E), 1999 Esprit V8SE, 1999 Esprit S350 #032, 1995 Esprit S4s, 1999 Esprit V8 GT (ex-5th Gear project), 1999 Esprit V8SE ('02 rear)

1999 S350 #002 Esprit GT1 replica

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  • Gold FFM

I did this modification to my car, and it changed nothing.

Looking at the edges of the plywood bulkhead where it fits in the car, I could see no sign of any movement whatsoever. But I still have the creaking and knocking going on, it's as if two components are stuck together, and then release, giving the noise, and it's definitely behind the seats. So, I'm now looking at the tailgate as a possible source, including the canopy. I've yet to do any testing but will revert if or when I have any news. Ideally, I would remove the tailgate and go for a drive, and I may still do that just to prove the point.

  • Like 1

Margate Exotics.

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27 minutes ago, ian29gte said:

........  Ideally, I would remove the tailgate and go for a drive, and I may still do that just to prove the point.

For me, it was precisely a drive minus the rear deck that pointed to the bulkhead

DSCF0031.JPG

1996 Esprit V8, 1998 Esprit V8 GT, 1999 Esprit S350 #002 (Esprit GT1 replica project), 1996 Esprit V8 GT1 (chassis 114-001), 1992 Lotus Omega (927E), 1999 Esprit V8SE, 1999 Esprit S350 #032, 1995 Esprit S4s, 1999 Esprit V8 GT (ex-5th Gear project), 1999 Esprit V8SE ('02 rear)

1999 S350 #002 Esprit GT1 replica

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Thanks a lot Everyone!

 

4 hours ago, mike_sekinger said:

the bolts are welded to the engine mounting bracket

Oh, OK, I thought the bolts were welded on the seats/carpet side!! Shucks!

3 hours ago, ian29gte said:

I did this modification to my car, and it changed nothing.

Shucks!! I must say it is not very reassuring

 

3 hours ago, ian29gte said:

it's definitely behind the seats

Yes, I think it's behind the seats too. I put my hand onto the bulkhead between the seats and I felt a slight vibration as I was hearing the clung.

3 hours ago, ian29gte said:

 I'm now looking at the tailgate as a possible source, including the canopy

I kind of checked it by moving it downwards and upwards quickly and heard nothing. But of course it's not a proper test in real conditions.

My idea before I read about that bulkhead story was to ask someone driving the car while I had a look from sitting in the boot :D

As for the bulkhead test, apparently a pillow stuck between the seat and the bulkhead is a temporary fix. It would confirm whether it is really the bulkhead or not.

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Mike, that plate with bolts welded, is interesting. I think that when we removed @OwenGT3 's bolt, they were just bolts and separate tubes etc. I'm fairly sure of that as we cut the nuts off, and the bolts shot into the engine bay as we did each one, if they'd been part of a single  welded-together component they'd have been easier to find. I wonder if that plate is a later upgrade, or possibly for cars that have the stiffening tubes not present on earlier cars. I know there's no point in checking my car as it's so unique (read as, it's been modified so much).

Do you think there's any value in adding some body seam compound (Tigerseal etc) around the outside of the tube so that if the wood firewall attempts to move there is a rubberised buffer (steel tube in rubber like a bush)?

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34 minutes ago, Giniw said:

Oh, OK, I thought the bolts were welded on the seats/carpet side!! Shucks!

I just had a second look at the photo on LEW and apparently the welded side is on the seats side?

http://www.lotusespritworld.com/images/maintenance/BulkheadMountingPlate/BulkheadMountingPlate_01.jpg

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Sorry - I've created some confusion.  The bolts are welded on the carpet side for sure, but clearly cannot be withdrawn independently from the plate.

DSCF0034.JPG

1996 Esprit V8, 1998 Esprit V8 GT, 1999 Esprit S350 #002 (Esprit GT1 replica project), 1996 Esprit V8 GT1 (chassis 114-001), 1992 Lotus Omega (927E), 1999 Esprit V8SE, 1999 Esprit S350 #032, 1995 Esprit S4s, 1999 Esprit V8 GT (ex-5th Gear project), 1999 Esprit V8SE ('02 rear)

1999 S350 #002 Esprit GT1 replica

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My take on this was as you all said,  But .... before I shortened the tubes (spacers)  I just put some bolts through with a plate (no tubes on)  pulled up really tight ..... end of problem ..   Ran it for number of weeks like that then refitted with tubes 1/4'' shorter ...Job done.........or so i thought.... a couple of months later... clonking !!!!! again...   took tubes out again , pulled up tight as before .... too tight sheared one....  re-evaluated .... fitted M10 instead of M8 bolts pulled up tight ...  Had no problem for several years then one day more of a creak than a clunking,  checked  bolts,  they were slightly looser than previous so re-tightened .  have not had any further problems in that area since.. ..  

PS..   also have found other body to chassis mounts on customers cars with slack in them.. It is important they are all tight or it will allow flex and exaggerate the problem in the area discussed   

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@ian29gte > Once you know for sure it's  nothing alarming I guess it's OK to wait a bit, but I must admit I worried about that and that kept me from bringing the car to the MOT, just in case it was a disaster waiting to happen in the engine bay!

@CHANGES > Thanks, I will also check where are those body to chassis mounts bolts if the bulkhead tightening do not address that dreadful clong.

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On 20/09/2017 at 17:15, ian29gte said:

Not yet, that will be something to do on Saturday!

I had a look at the car earlier today and actually the carpet and the soundproofing are not glued (any more? :D) to the plywood on the (UK) near side so it was an "easy" access. Not that the other side is really easy to put a span on it, but it's doable (I still had to stop before I finish!)

Anyway, I just realized that those fixings were actually the body to chassis mount so I find it suspicious that a pillow would change anything?!

Clipboard03.png

 

 

On 20/09/2017 at 14:58, ian29gte said:

The bolts in mine were not welded in.

Neither mines. I suppose it's only on the late V8 and/or GT3 which are welded.

 

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I didn't remove the bolts on mine when I had the interior stripped but on the cabin side they were nuts and large washers. Maybe there were several variations on how this was done in the factory?

Not worth starting anything now...🍺

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I finally took off the first plate yesterday, and on a second thought I think it can't be the plywood bulkhead tapping on the chassis mount since the plate was firmly screwed on the bulkhead with the six screws, and on the other side the chassis mounting is tightly screwed onto the tubes from the plates.

So really I can't see how the chassis mount would tap the plywood.

However, the hole in the chassis mount is oblong vertically and a bit horizontally too.

So I am wondering if the clunk noise is not just the mount sliding from an extremity of the oblong hole to the other? That would be reduced by just tightening the screw further (actually my washer was a bit twisted! and the second screw is not even the original one — overtightened by the previous owner?), and that would be reduced even further by shortening the tubes so that the chassis mount is in contact with the plywood and the friction coefficient is higher, resulting in less sliding in the oblong hole.

So, now I am wondering if just a rubber insert between the chassis mount and the plywood could be an even better fix than shortening the tubes? (the friction coefficient between the plywood and the chassis mount can't be that high anyway)

What do you all think about that hypothesis?

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  • Gold FFM

When you say 'chassis mount', presumably you are referring to the two tabs hanging off of the chassis cross- tube that the bulkhead bolts use?  If so, I have to say that in my opinion, they're shit: Too thin to be of any real use as a support, and possibly orientated incorrectly, anyway.

It really needs something far more substantial welded to the chassis cross-tube.

2015-04-01 17.54.03.jpg

Margate Exotics.

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Well yes those tabs are thin and won't help much to restrain in a longitudinal load but I suppose they maintain the GRP body for the side loads?

Unless I am wrong, they are listed as the body fixings to the chassis in the parts manual (see the picture I posted in https://www.thelotusforums.com/forums/topic/91272-bulkhead-rattle/?tab=comments#comment-742759)

And here is a little video showing the fixings (just a little bit different in side of the main frame as he counts 3 pairs and the diagram only shows 2 pairs, but maybe it was different in the Giugiaro cars):

 

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