How to Replace MGB Window Seals

There are several reasons why you may want to replace the window-to-body seals on your MGB. They may have deteriorated over the years, or you may be painting your car and do not wish to have dull gray old seals ruining the new job, or maybe you’re just a glutton for punishment.

Whatever the reason, the parts are inexpensive, and with the following tips, the job is relatively straightforward. The windshield seal is in the same league with replacing the C clips on the rear brake cylinders. For those of you who have done this job you will know what I mean—for those who have not, your day will come!

The tools needed to replace the windshield-to-body seal are a razor blade (to cut the seal to length), a screwdriver, and a putty knife. The windshield must be removed from the car in order to replace the seal. I have not found it necessary to remove the dash in order to remove the windshield, and would suggest that you experiment with various wrenches before resorting to dashboard removal.

Start by placing the windshield (curved side up) on a table at a convenient height. If you are right-handed, start on the left side, where you will see two screw holes in the bottom of the frame. Lubricate the T seal with liquid soap and slide as much of the seal as possible into where the two screw holes are. (The area is hard to describe, but you’ll know it when you see it.) You will find that you will only be able to keep about three inches of the seal in the slot of the frame before it starts pulling out. Working with about three inches at a time, place the lower portion of the T section of the seal into the slot of the windshield frame.

While holding the bottom T of the seal in the frame with one hand, push on top of the T section with the putty knife. Push hard, otherwise the T section will not go into the frame. Keep moving from left to right, putting the bottom of the T into the frame slot, forcing the top of the T in with the putty knife. When you get about eight inches away from the right end, carefully cut the seal to length. Make a straight cut, like the factory cut, and not on an angle, as you will be tempted to do. When you get to the very end, use the screwdriver instead of the putty knife to finish the job. After the seal has been completely installed, make sure the rounded part of the rubber is fitting correctly into the groove on the windshield frame. If not, push it into place with the putty knife.


Reinstalling the windshield is difficult, and an extra set of hands will come in handy. What makes the job difficult is that the new seal is curled and acts like a spring, pushing the windshield off the body. Letting the assembly sit a couple of days will help compress the seal, as will clamping the ends of the windshield to the body of the car. Do not put any sealer on the windshield until the job is done. If you do, you will have a mess that will be impossible to clean up. Wait until everything is installed, then lift the seal and squirt the sealer in.

Contrary to what the shop manual says, the first thing to do is to attach the two bolts in the center of the windshield. This will provide the pressure to keep the seal from turning under itself. It helps to push out the edge of the seal from inside the car with a thin object such as a wooden paint stirrer—be careful not to scratch the paint!

The two bolts on the right and left, that hold the windshield to the body, can be extremely difficult to attach. It’s necessary to push down hard on the top of the windshield frame, while at the same time wiggling it to line up the bolt holes. At first, it might seem as if the bolt holes do not line up with the holes in the body. If this is the case, take a screwdriver and push the fiber washer inside the fender around a little. With luck, you should be able to get the whole job done in about 2 1/2 hours—half an hour for the seal and a couple of hours to reinstall the windshield. But remember, it helps to let the windshield sit for a while to take some of the spring out of the new seal.


The side window seals are straightforward. Roll down the window, drill out the old pop rivets and install the new seals. The vent window seals take about 45 minutes each from start to finish, and it is not necessary to remove the side windows as stated in the shop manual. There are five bolts that hold the vent window assembly in: two are at the top of the door right under the window, and two more are reached from the outside edge of the door above the hinge (the access holes should be covered by plastic plugs); the last bolt is at the very bottom of the door.

Once all the bolts are removed, the vent window assembly should pull straight up. To get it high enough to replace the sill, you will need to move the roll-up window out of the way, but you do not need to remove the window completely. Near the outside edge (the edge apposite the hinge), at the bottom inside of the door, you will find a bolt that holds the window channel. Remove this bolt and slide the window over. Next, take the vent window assembly and twist it slightly—this will dislodge the roll-up window. (The roll-up window uses the lower portion of the vent window assembly as the channel in which it slides up and down.) You should now be able to raise the vent window assembly enough to remove the old seal, and the new seal goes in exactly as the old one came out. When reinstalling the vent window assembly, make sure everything lines up so that the doors close without any stress on the exposed portion. After this, you can proceed with car window tinting or even adding a layer of protection such as an xpel paint protection film.

'How to Replace MGB Window Seals' have 3 comments

  1. January 13, 2016 @ 3:00 pm Norm Davis

    Ihave just completed the fitting of the windscreen frame to body seal my advice to anyone contemplating this is simply DONT


    • June 27, 2018 @ 3:12 pm Dennis Wagoner

      This is my most hated MG job. Thirty minutes is very optimistic. Be patient. You stuff less than 1 cm at a time. I would never try to do this with a putty knife. The best tool I have found is a PAINT CAN OPENER available from Lowes or Home Depot. Cut off the fingers of an old glove or wrap your palm. As stated the side you start from depends on whether you are right or left handed. Stuff from front of windscreen only. The rear holds the seal and is the most important, if distressed it might pull out. Silicone the channel at the ends helps. DONT FORGET, unless you want water on your legs you must seal the posts at the body seals with calk, new seals will do nothing for you. 3M Strip-Calk part NO. 051135-08578 is ideal. You can also soap and pull but this is a job for two people with very strong hands. If possible let it sit in the hot sun for awhile before you install. A string under the seal can help to unfurl the seal. A towel can be used but might pull the seal out. Paint can openers are also good to pull the dress rings off the front headlights pulling from the bottom.


  2. August 29, 2022 @ 11:14 am Doug Fox

    My biggest problem in installing my 74.5 MGB roadster windshield was figuring out how to trim the seals for the final fit. I am sure I left too much of the lower seal extending out under each each side rubber end which led to a cracked glass as I attempted to manipulate the assly down far enough to catch the 4 mounting bolts. That means I will be doing the job over and would love to find out how to do the final trimming of each of the rubber components which surround the windshield before I make my second attempt. All of the ‘help videos’ I viewed were helpful but none addressed the correct procedure needed to final cut the clearly oversized individual rubber components. Help in this regard would be greatly appreciated! Doug


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