MGB Windscreen Rebuild


5/21/2020

Sorry in advance for the wall of text. I have been threatening to write this up for a while now, and then I got a Special Request from a reader for how to do this. I promise I will come back and clean it up and add pictures and all that cool Web stuff, but for now its gonna be a Wall! Of! Text!

Windshield jobs can be one of the most unpleasant jobs on an MGB, especially if it hasn't been touched in years and the fasteners are all rusty and frozen. If its been gone through recently, with careful thought for the future, it isn't that bad. You won't know til you try, so let’s get tore in as they say…

Have a look at the exposed edges of the glazing seal around the glass. If it is at all crispy or stiff, order a new one. Order two new grommets for the windscreen posts, they are ridiculously cheap. If the frame to body seal is still good, leave it alone. If its covered with paint overspray or splitting at the edges, order one of those, too. Order a new set of the four short screws for the bottom brackets. If your top screws are ugly, order new ones of them, too. Acquire a long-ish #10-32 machine screw that will be used later on.

You are going to need a 9/16" socket and ratchet, or even better, a gearwrench, a 7/16" open-end, a long #2 Pozidriv screwdriver, and a rubber or soft dead-blow hammer. If you have a cotter pin hook (one of the most useful tools in the world) have it ready. You will need a small ratcheting tie-down strap. You might need a #2 pozi socket and a hammer-powered impact driver. If you are going to replace the lower body seal, you will need a selection of screwdrivers and prying tools to get the frame back in. The new seals are very stiff and make reinstallation of the frame much more difficult. You will need a tube of glass bedding compound and a caulking gun. This is a horrendous, goopy product that never hardens and is going to keep your water out for years to come. You will need something to remove excess bedding compound. I recommend 3M Adhesive Remover. This is great stuff to have around the shop anyway. Did I mention this job is messy? It is.

If things are really nasty inside the frame and fasteners and brackets are rusty, you will need a #21 drill, a #10-32 tap and a tap handle, and a really narrow drill. I have a cheap pneumatic drill, smaller than most electric drills, that can really get into tight corners. You may also have to order some brackets and screws once you get it all apart, depending upon what gets sacrificed on the way in.

With your 7/16" wrench, loosen the two bolts holding the center rod bracket to the top of the dash. You will have to one-flat-at-a-time it, since there is no room to get a ratchet in there. You won't be able to unscrew them all the way, they are quite long. Just take them up as far as you can for now.

With your 9/16" gearwrench, remove the four bolts holding the frame posts to the body. They are way up at the side of the dash, but you can usually shove things out of the way enough to get a gearwrench in there. 

If you still have the under-dash panels, they will need to come off. Depending upon the interior panel design, you might want to unscrew the outer kick panels with your #2 pozi screwdriver. Often, the top tabs have been previously removed by angry mechanics. If you need to remove any dash support brackets to get your arms up there, feel free to do so. You should be able to work the wrench between the outside edge of the dash and the body, pulling on the lower dash edge itself might be necessary, but they are somewhat flexible.

The dash panels and outer coverings were never precision pieces and sometimes there just isn't room to get your wrench and fasteners in between there. That sucks. In those rare cases, you will need to remove the six 1/4" nuts & washers holding the upper edge of the dash to the top of the scuttle, along with the more obvious small screws and brackets at the lower edge. This sucks. I use a long springy extension with a 1/4-drive ratchet. They are way the hell up there. You will likely see blood at some point. There is lots of pointy stuff back there. I'm sorry for your loss...

Once you get the dash panel loose, you can pull it towards you just enough to get your bolts out. You don't have to remove the dash or anything in it, just get your bolts out and shove it back in place for now.

Have a handy picnic table or something nearby, along with a sacrificial blanket or furniture pad. It will get dirty. No, that’s not true. It will be ruined. One guy can get the windshield out, but its always better with a friend. Each of you grab a side and pull up and forward to loosen the corners. Once loose, go back and continue to unscrew the two center bolts, which you should now be able to remove. Grab the frame again, lift up and forward and the frame will rotate right up out of the car. Abscond with it over to your table.

Pull the two grommets off of the posts and peel back the body seal to expose to two screws hiding in the seal channel. If you are reusing your seal, only remove it enough to get at the screws. If your seal is going to be replaced, go ahead and peel it all the way out. It’s fun! 

Here is where it gets interesting. With a small pick tool or wire, clean the crosses out in the screws as much s as you can, and spray some penetrating oil in there.

DO NOT use a Phillips screwdriver! You will mess the screws up! You have been warned! These are Pozidriv screws and your only chance to get them out is with a good-fitting Pozidriv driver. It looks like a Phillips, but it ain’t. The geometry is different and they don't cam out they way that Phillips drivers are designed to do. See the additional small cross between the drive flanks for identification. Google it.

Anyway, get your #2 Pozi driver in there, give the end a couple of light taps with a hammer, push it down into the screw as hard as you can and try to unscrew the screw. Maybe you will get lucky and it will come out. If not, now is the time to try your #2 Pozi socket and impact driver combo. Get it all set up, apply some unscrew-y pressure and give it a good whack with your hammer. One of two things will happen. Either the screw will come out, or you will strip it. If you strip it, don't panic, the fight isn't over yet. It’s just the end of Round 1. We can come back to it. Repeat the whole process with the other three screws.

If you stripped any screw heads, take your little drill and #21 drill bit and drill right down the middle of the crossed driver divot. It should center itself. Keep going until the head comes free. Don't go nuts and drill all the way through, just take the screw head off.

By now you should have the bottom screws removed or at least dealt with. Flip the windscreen over and go after the top screws. You only need to take the outer three off of each end. Screws 4 and 5 can just chill.  If things are rusty and ugly, use penetrating oil and a heat gun and go at it slowly with lots of heat/cool cycles. The outer screws go directly into the aluminum frame, so you don't want to break these off if you can help it. If you do, its a real pain to drill them out and keep straight as the drill would rather wander over into the soft aluminum instead of doing its job and chewing out the hard, rusty steel. Better to take your time and let the oil and heat free them up. The next two screws go through holes in the aluminum frame and then into a steel bracket, pinching the aluminum of the side post between. They usually come out, as there is less water involved up there. Same routine to remove the screws, drill the heads off as a last resort. These go in a bit further, since you must drill the heads off as well as the part through the aluminum extension but don't go nuts and drill through the steel bracket and into the glass...

With all ten corner screws removed, take your rubber or deadblow hammer and bonk the frame sides outwards off the glass and glazing. Just pull them straight sideways. Ignore any ropey goo in there. Have a look at the lower brackets. If they are rusty and horrible, order new ones and hose down the old ones with oil, since they have to come off eventually. If they are functional, hooray! Even if we need to remove some screw gubbins we’ll call it a win. 

Now, remove the slotted nipple (yeah, its a wire wheel spoke nipple) from the bottom of the long threaded center rod. If the rod unscrews from the upper bracket, that's fine too. Reemploy your well-practiced hammer skills and bonk the upper and lower frames off of the glass.

If you have any drilled fasteners to remove, let’s get it done now so we can get to the fun part. Take your same #21 drill and continue off of the same center point that removing the screw head left. You are going to go straight through the center of the threaded hole like. If you did it right, you left nothing but threads around the hole. Heat that thing up with a propane torch, squirt some oil on it and you might even be able to pull the thread remnants out by hand. You'll need a 10-32 tap to chase them out through. Sure, the original thread is actually a 2BA, but at that thread depth only an aerospace machinist can tell the difference. 10-32 taps are way cheaper. Clean out all ten holes. Hooray! You saved your brackets!

Now is time for your tube of automotive glass bedding compound, not adhesive, not silicone. Sometimes called Silastik or some such quaint British term. Its a thick, viscous, black and sticky goo and it never hardens. If you can get it, I also like to use a British product called Waxoyl. Its some other sort of waxy goo in a mineral spirits carrier that also has some sort of rust-inhibiting ingredients. Beats me, it sure works on making windshield repairs future-proof. I've taken apart screens I put together 15 years before and all the screws were fine and the goops were still goopy, so I'm sticking with my methods.  I have seen a 3M product called Rust Fighter, which seems to do a similar job. In a pinch, you can probably get away using never-seez on the screws at least. The idea is to never have to fight this job again. Say you catch a rock and bust your windshield. With the correct products and fasteners in there, you'll never have to fight them again and you can probably completely rebuild a windscreen in about an hour.

It’s time to clean your frames up. You should already have all of your screw holes sorted out, so just clean off any dried up stuff that might remain from previous work. Factory compound was a pale tan or gray, and there is usually a bunch of it stuck in the posts. Just scrape it off with a Popsicle stick or what have you. You don't have to use go nuts and scrub it clean, just remove any old crud that might interfere with reassembly.

Now is also a good time to inspect the rest of the frames. If any of the brackets and doodads pop-riveted to the frame are loose, fix them now. It’s possible to replace pop rivets with the glass in place, but there is a really high risk that the remains of the old rivet will end up working around inside and cracking the glass. Fix any loose visor brackets, visor anchors and make sure the center rod brackets are good and tight. If the tonneau snap at the bottom of the post is missing or damaged, do it now.

OK! The hard part is done! The rest is easy, if a little messy.

Take your caulking gun and your bedding compound and put a thin smear inside the channel of the glazing strip, where the glass will sit. This is not so much for sealing purposes as to give some ability for the glass to move around. You can use Waxoyl here instead if that makes you happier. Waxoyl will be slipperier and the bedding compound will help hold the glazing in place as you wrestle the various pieces. Find the joint on the glazing where the ends meet and put this on the glass at the top center. Work the strip all around the glass, noting the four relief cuts on the back should correspond to the locations of the brackets on the frames and be even side to side.

Brush some Waxoyl in the channel of the upper and lower frames and slip them onto the glass/glazing combo, making sure they are perfectly centered side to side. Don't just eyeball this, actually measure it. With the upper and lower frames held on, screw the nipple back onto the center rod to hold the frames together.

Taking up your side posts, brush a good layer of waxoyl on the steel brackets, especially in the screw holes. Take up your caulking gun and lay a big, thick bead along the vertical channels, around the inside corners and across the mating surfaces where the frames will butt up together. You are not trying to fill the entire gap, but you do want enough that when assembled, the glazing strip touches the compound all the way around. Wrap some around the top bit of the aluminum where it will meet the upper frame and bracket. You can go ahead and shoot some around the upper frame/bracket area as well.

You can now take the side posts and offer them up to the windscreen. You will need to go at an angle, starting at the top with the long aluminum section sliding between the upper frame and its bracket, sliding them together until the side of the glass/glazing can slip into the channel and the lower bracket can be winkled into place in the lower frame. Don't worry about lining up holes yet. Once both sides are in about the right place, it’s time for your small ratchet strap. Wrap it around the frame the long way, with the ratchet on the inside of the frame, not touching the glass.  Slowly start pulling the frame together, using the strap to just apply a steady squeeze. The bedding compound should start to ooze out of all the little gaps as you go. Take your time, and make sure that the glazing strip is going into the channel straight, hasn't caught its little lippy edge inside the channel and isn't getting pinched at the corners. Make sure the lower frame end goes into its little notch in the front face of the post. If things stop moving, either you are close to being together, or something is hanging up or crooked. Be careful, go slowly and you won't have any problems. 

Once you get the frame all closed up, dig out your one long #10-32 screw and your cotter pin hook. Use the hook to fish around and line up the holes in the bottom corners. Pick one, doesn't matter which.  Thread your long screw into one of them, no more than 3-4 turns. Use the long screw to pull the bracket into place so that you can get the other screw started and screwed up snug. Remove your long screw "tool" and replace it with the second screw.

For the upper corners, try to get the outer screw started first, since it goes directly into the post. For the next two, your cotter pin hook and long screw are your friends. The idea is to thread into the inner steel bracket no more than 3-4 threads and then pull it snug up to the bottom of the aluminum. You should then have enough threads on your new screw to reach the bracket and get started. Snug it up and then replace your "tool" with the other new screw. Keep in mind that these screws are specific lengths for a reason. Resist the urge to use a longer fastener to get things started. Its real easy to forget about the extra length and just drive it right through the glazing and into the glass. I know.

Hooray! You should have two short screws in the bottom corners, one long and two medium screws in the top corners and lots of goop everywhere. Snug up all the corner screws, check the center rod and start cleaning!

A Popsicle stick cut off square is good for gleaning goop out of the glass to glazing area and a razor blade can scrape the majority of the glass clean. You will be reduced to rags and paper towels with 3M adhesive cleaner to get the goop free of all the joints. Don’t try to remove all evidence of the bedding compound. If a crack or joint still has compound, that means its filling a gap that would otherwise let in water. Just wipe off enough that you won’t be smearing it over when washing the car. Use glass cleaner to clean the final haze left from the compound.

If you are reusing the old body seal, it should still be in the lower channel. Use a short screwdriver tip to work the bead back into its groove where you pulled it back to access the screws.  Pop two new grommets back onto the posts, using some more bedding compound at the joint with the body seal. Installation of the frame is the reverse of disassembly, as the manual says.

If you are replacing the lower body seal, I don’t envy you. I don’t know how the factory did it. I have tried pulling, pushing, boiling it soft, loosening it up with a few drinks, etouffee, you-name-it. The least-crappiest way I have found is to use a small flat-bladed screwdriver to work it into the groove one screwdriver-width at a time. Working from the front and leaving the seal a little long, shove the inner edge of the t-shaped lip into its groove, hold the outer lip out of the way and shove the front edge of the tee into the groove. Repeat. A lot. Once you work a section in, release the outer lip and it can snap up into the front of the frame. Walk your little screwdriver along and eventually you will make progress. Taking breaks to uncramp your hands, it takes a good 20 minutes, at least. Bring a friend, take turns. Once you get it all into the channel, unfold the lower flap and trim the ends so that they are long enough to just fit under the “foot” of the posts. Don’t leave them too long, its just more material to compress.

To install a windscreen with a new lower seal, its a bit more work. You are going to do the same “rotate into place” installation, but you are not going to accomplish it all at once. That new seal is going to take a while to compress and relax enough to smash down like the old one. Shove the frame as far down into the sockets as you can. Using your cotter pin hook, pull the front lip of the seal forward so that it starts to lay down on the top of the scuttle. As you work the frame down into place, you will probably have to chase that lip back and forth a few times before it gets the idea. As soon as you can manage it, get the two bolts started through the center bracket down into the captive nuts in the dash top panel. Now you know why those bolts are so long. Start tightening them down and you will feel the bulb of the body seal start to compress. Well before you are anywhere near down, they will start feeling what I call “scary”. Don’t try to run the screen down. Take a break, have a beer, go to bed. Let that seal relax. Come back later. Shove the posts down some more, tighten the center bolts some more. When the posts get down to the point they are smashing the grommets, you are almost there.

Now, let us regard the post bolts. Notice that the big thick washers have a flat. Have a look at where they are going and be aware of where that flat is pointed. You will never get the bolts in if the washers wander around and you end up trying to wrestle a bolt in with a washer fighting against you. The washer will win.

You will need to do about three things at the same time, so bring a friend. You need to pull the frame post down, line up the bracket with the hole in the body and start the bolt into the hole straight. I have had good luck using a medium screwdriver as a pivot in the lower hole, prying upwards to pull the frame down while your buddy applies pressure on the frame from in front of the door. Get the upper bolt started into the frame post and turn it a couple of threads in by hand while you yell at your friend to keep pushing. Take a break. Do the same thing on the other side. Take another break. This time, get your friend to pull the frame top forward, pivoting on the upper bolts, and you should be able to get the lower bolts started in their threaded holes.

That’s the hard part done. If you want to let the seal relax some more, it will make the final adjustment easier.

Roll the door glass down and carefully close the doors to check the alignment of the frame. You may need to slide fore or aft, or adjust the tilt, all of which is possible now that you are no longer fighting the new seal. Fully tighten up the four outer bolts, making sure the washers are still pointing the right way and are not hung up sideways. Do a final tighten of the two center bolts. 

You have successfully resealed/replaced an MGB windscreen. You are one of the Few, the Elite, a certifiable Total Badass™. Your Total Badass™ Certificate will be along in the mail shortly. If your Total Badass™ tattoo ends up scoring you free drinks or something it was all worth it. 

Exit through the Gift Shop.

Bradley Restoration

Andrew Bradley, Proprietor

14093 Riverbend Rd.

Mount Vernon, WA 98273

(360) 848-6279