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MG MGB Technical - Cracked Windshield Again!

I restored my 74 B about 14 years ago. Last summer after Gatlinburg the windshield cracked as the car sat quietly in the garage. A few months ago I had it replaced by University Motors who pulls the frame assembly and sends it out for the new glass installation. Now it cracked again sitting in the garage. The crack is across the lower corner on the drivers side.

I have read most of the archived messages but can't really find a good explaination of why this would occur. Before I put another one in I'd like to identify the problem. My only guess right now is that when the windshield mounting points on the shell are not perfect, tightening the mounting bolts stresses the windshield. I figure when I do it again I will put the vertical frame members on and measure the distance across them at the top and bottom. I think I can then compare them with the assembled windshield and see if they match up or if shimming is needed. Sound reasonable???

Thoughts????

Cheers!
Jim
Jim Budrow

You may want to try setting the frame in the pockets without the packing and checking that the ends of the side posts are parellel with the pockets in the frame. If they aren't you may be putting stress on the frame when tightened down as the bolts will be trying to bend the bottom of the post to match the pockets.
John H

Check you *have* all the packing pieces and shims. Should be one thick spacer plus as many shims as needed. However these should stay in the car when the screen is removed, unless someone has taken out the Posidrive screw between the two bolts as well as the two bolts. This screw holds the spacer and shims (between spacer and body) in place when the screen is removed. With the frame dropped in but no bolts inserted you should not be able to move it back and fore across the car.
Paul Hunt 2

has the correct glass been put in your frame as there are two types
yours should have the bottom corners cut out which could explain the bottom corners cracking
the other is that the bottom rail is bent slightly putting pressure on the glass
ste
Ste Brown

I too had a windshield spontaneously crack recently after a windshield rebuild and mine was a NOS triplex glass....which certainly leads me to believe the stress must be coming from the frame so definitely following this thread with interest for all suggestions offered.
Frank Mooring

My 73 had the screen without the bottom cut-outs, as did the first replacement. The 2nd replacement (both breakages from flying stones) has the cut-outs, and I believe that way round is 'safe', even though there is precious little overlap between seal and glass in those corners i.e. an increased possibility of leaks. From the Parts Catalogue the same item was used throughout. There were five different complete frame assemblies from inception to August 76 - two for the USA and Sweden and three for the rest of the world. From September 76 there was only one assembly. The side pillars of the frame changed at chassis No. 172700, 187210, 306515 and 360300 up to August 76. The bottom rail changed at the first two but not the second two. I suppose the glass could have changed at any of those, but it couldn't have been (based on my car) before Dec 72 (when Clausager indicates a pillar change, but not glass). With the change to rubber bumpers Clausager specifies a change to the "windscreen assembly". From Sep 77 individual frame part numbers aren't given. Clausager does mention "An otherwise unspecified change to the roadster windscreen glass and glazing strip in April 1977 is thought to concern the introduction of slightly thinner glass". If that's correct the glass without the cut-outs should be fine for a 74, and in fact may even be stronger. Maybe the cutouts in the glass were made to cope with the possibility that the pillars might be squeezed together a bit if the correct shims weren't used.
Paul Hunt 2

Jim,

If the wrong screws, which hold the frame together, are used in the wrong location(s) it could be your problem. Without knowing how far frame was disassembled previously or if someone put longer screws in wrong location, it/they may be hitting the glass through the glass to seal gasket. Need to be very careful with length of screw used/using on frame assembly with glass.

HTH

Fred
Fred Wright

Does the longer screw go to the outside and the 2 short ones inside?
D Enghauser

yes long on out side
moss sell both screens and when i taked to david james at windscreen clinic there are at least two frames
my top rail was bent so he sent me a new one up which had a completely diff arc on it to the first so there is still a poss that the bottom rail has been bent or the side pillars are attached at an inward angle
ste
Ste Brown

It will be some time before I can get around to actually replacing the windshield but this gives me plenty to check and think about - so no feedback for a while, sorry. Thnak you very much for your excellent insight!

Regards,
Jim

Jim Budrow

This thread was discussed between 02/08/2007 and 04/08/2007

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