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MG MGB Technical - Crack of Doom Repair

I’ve read of several techniques used to deal with the “Crack of Doom”, but I was just wondering what the latest, and best techniques are currently being used.
I know replacing the door skin is the answer, but wanted to hear if anyone else has come up with an easier method. Panel glue, welding…
Cleve

Many years ago i had a small crack about an inch or two long on my passenger door. i noticed a guy with awire welder I was driving past and stopped to see what he could do. In about ten minutes I pulled the car up and he welded it for me as easy as pie. and even ground the surface a bit. It was real fast and I gave him $20 for the job. It has never needed any other work. of course that was the eary 80's.
Bob Ekstrand

Just curious, why not back it up with a small piece of steel welded across the break?

BH
BH Davis

I have repaired perhaps 50 cracks of doom over the past 20 plus years. My method is to preform a piece of body metal the shape of the door skin. Approximately 8"x8". Then insert it up inside and hold in position. Drill several holes through both door skin and patch. , install self tapping screws to pull the patch up solid against the skin. Then with many predrilled holes in the skin I spot fill with MIG welder. Then remove screws and fill those holes. Grind smooth and I have never had a failure. I would guestimate that 20-25 holes total will be needed.The inside panel is formed to fit the complete profile somewhat like the letter "J". This gives support to the inner edge of the window opening also.
Sandy
Sandy Sanders

Sandy,
Do you do this with the door attached, or do you take off anything?
Cleve

Filthy Bugger ...
J



Cleve; Only on the real bad ones do you have to remove the 1/4 lite. It is not necessary to remove the door at all. What I usually do is to drill approx 20--1/8 in holes surrounding the crack. Place the patch in place and drill 6 or so more holes through both panels. Then using sheet metal screws pull the patch in place then fill in the other holes with plug welding. Remove the screws and fill them in also.
Grind smooth and refinish as needed. Do not forget to seal the inside from future rust.
Sandy
Sandy Sanders

As long as you remove the roor cause simple mig welding should be enough. I also used a bracing plate behind the skin that the door mirror screws into to give added strength. The cause of the crack of doom is a design weakness in the window opening of the skin, plus incorrect adjustment of the 1/4-light causing which allows scuttle-shake to be transmitted into the skin. If you haven't already have a look at http://www.mgb-stuff.org.uk/wn_bodyframe.htm and click on 'Doors'.
Paul Hunt 2

I did the passenger door by tapping in both sides of the crack and making a flat plate that slotted in between them it was curved to lie flush with the door skin and tapered towards the bottom to distribute the stress. It was then Mig welded in then the area was filled and sprayed. The plate was made from a bit of 18 gauge weldable zinc plated mild steel. This worked very well and was easy to do. When the drivers door went (after re-skinning !!!) the crack turned a corner and started heading towards the front of the car away from the mirror, which probably was stiffening that area. This one had to be done with a plate behind it, the welder make a complete *** of it, and took the dor off despite being told not to and it has never fitted as well since. As the first approiach works well and is less likely to go wrong I would use it, if you do, ensure that you, or the welder, unserstands they must build it up to the point where the gap between the 1/4 light and the return flange that tkes the weatherstrip is a strong as the rest of the door.I took the 1/4 light out both times, I have put athread on here to re-assemble the dor.
Stan Best

i tried an alternate way using Sandy's plate and 3M Auto-Mix Panel Adhesive (#2118). only had a 1/4" crack so i drilled the end to stop it. the properly curved pnl was drilled (prior to applying ad.) with small holes for sheet metal screws thru the mirror mount holes. i applied the adhesive and then secured with the screws for 24 hours. then i removed the screws; some adhesive had squeezed out the stress hole so i had smoothed it prior to curing. it just took some touch-up and seems to work qreat.
Drawback: the Automix takes an applicator gun, expensive if you can't borrow one. Product is fantastic
kelly stevenson

Hope this helps, the plate is at 90 degrees to the door skin and actually pushed through the split where it has opened up a bit as it is tapped in. What you see here is the door skin plus filler which hides the repair. This was done in 1996, I took this pic today. The plate, the semi flange plus the weld have made it strong enough not to crack.

Stan Best

JB weld and a new 4" x 4" plate molded to the underside of the panel. I drilled a small hole at the end of the crack to stop any further cracking. I was told that welding further weakens the skin. Was an easy fix and I further bolted the mirror to the new plate for added strengthening. 4 years later still holds OK.

Make sure you adjust the 1/4 light afterwards so it doesn't happen again. I tend to think that it happens most often when changing out the windshield and people aren't careful about aligning the 1/4 glass assembl afterwards. Mine showed up about 2 to 3 years after I changed out the windshield.

Luis
Luigi

This thread was discussed between 02/08/2007 and 06/08/2007

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