Small split in rear window

Paul Newton-Smith said:
I have a small spit in yhe plastic rear window. How do I stop it getting any bigger? Can it be filled in any way?
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Best option is to replace the window, but here's some possible options and some guidance.


Hutchinson's Repair Kit
Gorilla Patch & Seal
Falingo Tape

How I'd repair a small split on your Z3​

If, for example, you have a 20 to 50 mm split:

  1. Do not lower the hood.
  2. Work somewhere reasonably warm so the old PVC isn't brittle.
  3. Carefully clean both sides of the window. Avoid aggressive solvents.
  4. Bring the two edges of the split together naturally. Don't overlap them.
  5. Cut a strip of Tenacious Tape approximately 20 to 25 mm wider than the split on each side.
  6. Round the corners of the patch rather than leaving sharp square corners.
  7. Apply it to the inside of the window first.
  8. Smooth it outward without stretching the PVC.
  9. For additional reinforcement, I would put a second clear patch over the outside.
  10. Leave the roof up and tensioned while the adhesive establishes.
The objective is not really to "glue the crack back together". The tape acts as a flexible reinforcing bridge so that movement of the hood doesn't immediately propagate the split.

Important point with the Z3​

Your Z3 is unusually repair-friendly because the original rear screen uses a zip-in replacement system. Replacement procedures show the existing window being unzipped and a new screen zipped into the soft top.

So I'd regard tape as:

Tiny split (<30 mm) → Tenacious Tape is worth trying
30–75 mm split → repair may work but I'd regard it as temporary
Long split / brittle yellow plastic / multiple cracks → replace the window

There are complete replacement screens currently available. One OEM-style Z3 plastic window with zipper is listed at £249, while another clear Z3 Roadster replacement is approximately £118.49 plus postage from the US.

One specialist replacement also confirms that its window fits all 1996–2002 Z3s and uses the Z3 zipper arrangement.

What I'd use on your 1999 Z3​

Buy the Gear Aid Tenacious Tape Clear PVC first. For roughly £11 it's worth attempting before replacing an otherwise decent original screen.

I would not use superglue, Araldite, ordinary silicone, duct tape or windscreen adhesive on the clear PVC itself. The Z3 rear screen needs to remain flexible.

If you tell me roughly how long the split is and whether it's in the centre or starting from an edge, I can tell you whether I'd repair your particular window or replace it.
 
I was able to buy an oem replacement window through the local dealership. They replaced it as well.
 
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