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Thread: Crack In Rear Firewall

  1. #1
    Senior Member vwdmc16's Avatar
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    Crack In Rear Firewall

    Ive been hearing this irritating knocking noise from the firewall area while driving, Its progressively gotten worse. It sounds like a piece of wood tapping the fiberglass on the fire wall.

    After much diassemblely I thought I found it in the rear frame cross brace. but the noise came back worse after a week. The real culprit is this thin crack that wraps around the corner of the seam between the firewall and rear shelf tunnel. When ever the body is twisted it moves about .010" and make that popping sound. its real noticeable when entering my driveway.

    Any one see a crack form here? my plan is to cut into the seam a bit to make it larger and then will fill it with some fiberglass mat fibers and epoxy resin.





  2. #2
    DMC Midwest - 815.459.6439 DMCMW Dave's Avatar
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    That's pretty unusual. Is there any other sign of crash damage, other glass repair, frame repair etc? Super-high mile car?
    Dave S
    DMC Midwest - retired but helping
    dswingle@DeLorean.com

  3. #3
    Senior Member vwdmc16's Avatar
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    There is some damage to the frame in the rear on the passenger side where the frame has a small twist to the bumper support. Perhaps its just taken all these extra years for it to crack enough to show movement. the frame was very rotted from east coast winters but I repaired that all before it got back on the road and had any real stress put back in it. She has 50k miles now

  4. #4
    accidental owner DMC3165's Avatar
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    I have an annoying "thud" that I hear every so often when making a left turn over uneven ground. I have been looking for it for six months+ I've looked high and low and even brought it into Grady's thinking it might have been a loose TAB. But never found anything wrong.

    After seeing this I'll be pulling my carpet back later to check. I can say that my car was involved in a serious accident years ago. Maybe that has something to do with it.
    Chris Piazza
    1GR8STRY
    Owner of 3165 by default

  5. #5
    President, DeLorean Industries
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    Quote Originally Posted by DMC3165 View Post
    I have an annoying "thud" that I hear every so often when making a left turn over uneven ground. I have been looking for it for six months+ I've looked high and low and even brought it into Grady's thinking it might have been a loose TAB. But never found anything wrong.

    After seeing this I'll be pulling my carpet back later to check. I can say that my car was involved in a serious accident years ago. Maybe that has something to do with it.
    Most likely you have a bearing shifting in a rear hub. This is becoming more and more common these days. While not fatal immediately long term this will wear down the bore of the rear carrier and require a sleeve insert when repaired.

    I started my career as a Ford Master Tech and was lucky enough to bring my annoying noise finding talents from complaining owners under warranty into the Delorean world. We use a chassis ear system or NVH tester to find components causing issues such as bearings, control arm bushings etc here at Delorean Performance.
    Last edited by Delorean Industries; 01-02-2012 at 09:32 AM.
    www.deloreanindustries.com Every Detail Matters

  6. #6
    Senior Member
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    Check the body bolts and remove the jack and wrench kit in the front compartment and see if the noise goes away. The crack in the fiberglass would seem to be from either a rotten frame that no longer supports that area properly or the result of an old accident. Push on the fiberglass under the center of the rear window. See if it is still attached to the glass. When it becomes unattached it gets really noisy in the passenger compartment. When fixing up the fiberglass, depending on the area and the damage, sometimes it helps to "glass in" a small piece of wood to stiffen things up.
    David Teitelbaum

  7. #7
    Senior Member vwdmc16's Avatar
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    Josh, I also have that rear bearing shifting problem too, my driver side was realy loose when I bought my car and I changed it but now the passenger is moving around alot, but it is a distinctively different noise

  8. #8
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    Hello Wolff and others!

    Sorry to resurrect this thread - I think I'm experiencing something similar. I don't know that I would call the noise a "knock" so much as a "creak". Maybe a very high frequency knock/click. It's very intermittent and irregular. It happens most over bumps and when the body is being twisted in various way (acceleration, starting up an incline)

    It has become more pronounced and annoying with my new suspension (not throwing any shade at Josh/DPI, this is an un-intended side effect )

    At first it sounded very much like a vinyl interior piece rubbing against another. But after I removed the rear parcel shelf trim board assembly (into which the parcel shelf light clips) and carpeted bulkhead (the rear interior "wall"), the sound remained and both got louder and became more like a fiberglass creakiness.

    I cannot replicate the sound outside of just driving around. It is difficult to pin point precisely where it is coming from but it seems to be the same area that you pointed to: the seam between the "firewall" (rear body) and the rest of the fiberglass body just inboard of the wheel well. You referred to this as a "crack" but I'm not sure it is a crack really, but rather a seam where these pieces of fiberglass are joined. Mine is sealed with black RTV. I scraped some RTV away and am able to pry slightly with a screw driver and very slightly separate the two fiberglass pieces.

    I have checked the body bolt's torque. There appears to be no fiberglass damage.

    Few questions for you, or anyone who might have ideas:

    -How did your repair work out?
    -If I have my wife drive around while I place a finger on the seam in question - I can feel the two pieces of fiberglass moving very slightly independently of one another. Is this normal?

    Thank you for any insight!

    James

  9. #9
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    Welp - unless I've fallen victim to the same red herring: I MAY have solved my creak. As you suspected all those years ago, it seems it was the crossbrace.

    I first loosened just the passenger side of the crossbrace and cleaned under it as best I could, and sprayed some silicone lubricant between the frame and body. Torqued down the bolt and I went to for a drive.

    The sound was far diminished but also moved to the driver side! I figured I was on the right track!

    I next removed both crossbrace body bolts. I used the side rear jack points to lift the body the TINIEST bit from the frame (all other body bolts are still in the place). I further lubricated between the painted metal of the frame and the fiberglass body.

    The metal holes which the body bolts go through (embedded in the fiberglass, seemingly) had some knurls on them which seemed would prevent the crossbrace from sitting flush. So I dremeled them down flat.

    I cleaned the surface of the body and crossbrace where they touch, and applied a thin coat of grease.

    I then centered the crossbrace, and torqued down the bolts a little at a time side-to-side, so they tightened evenly.

    I went for a spin with my wife to verify. Not a single creak!

    bonus: I've been driving around without the rear parcel shelf bulkhead interior piece - so when I get things all back to together she's gonna sound whisper quiet by comparison! Until the next rattle, creak, or vibration emerges!

    Fingers crossed it doesn't return like yours, vwdmc16!

  10. #10
    Senior Member vwdmc16's Avatar
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    Thats excellent!

    My car hasn't hasn't had the old noises comeback after I repaired the fiberglass.

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