Hi folks – hope everybody is having a good week. I need to install the rear window on the blue 914/6. Turns out it’s slightly allowed in the cockpit wud. Whoever would have guessed, right?

I saw Eric‘s write up which was super helpful just not sure what product people recommend these days.

Any tips on specific product/brand/sourcing it?

Thanks!

We stock it in various forms and kits

https://914rubber.com/search/?q=butyl

@Mikey914 - is it the same as for the front window? If so I have some from a prior order with you.

Yes they are the same thicknesses. Score

Reading up about this so online, the pro windshield install shops are using polyurethane even a foam tape dam for uniform thickness. They say it’s safer and a better bond than the butyl.

Any reason we should not use polyurethane?

Our cars flex more than modern ones with urethane-set windshields. There have been stories of glass cracking with urethane installations.

Some are also reporting that using buytl for the windshield is not legal. Any truth to that? I have seen multiple loose windshields set in butyl over time where they are only partially bonded and loose under the trim after many years.

Also, one of the reasons I'm making the side pillars and top of the windshield is that with urethane, it will often squish out to the inside and touch these. When removed you will find these pieces damaged from where it touched them.
I've done both. As far as legality, I think you will find that more of an issue of liability. The glass shops don't want the liability.

3M 1/4 inch

I did mine with urethane. The whole frit paint, glue and rubber seal deal. Its held up really well and was a lot easier to install then the butyl and chrome and clips.

I've never heard of urethane cracking glass. And I drive my car pretty hard, though my car is solid and does not have rust holes compromising the midsection - forcing strain through the roof to the windshield frame.

Zach

Thanks for the good advice!

The windshield on my project car was for the most part loose.

Oh shoot - looks like there are rubber mounts that I need (reading Eric’s write up).?

The rubber blocks just keep the glass from sliding down in the channel, which makes it difficult to install the trim. Any small rubber bit that’s about 1/8 inch should work. Just make sure it doesn’t sit too proud or the trim will bump into it and not lie flat. Here’s my install video…

EDIT: sorry…just realized this is for the back glass. Same idea though. Just without the trim:)

https://youtu.be/caoslhYlE1U

Thanks Ian!

Quick clarifying question - does the rubber bit used to prevent the window from sliding down/being too low stay in place once the butyl tape set up? I believe so but wanted to double check.

Thanks!

(hope everyone had a good weekend)

I installed a new windshield in my 73 with urethane many years ago. First railroad track l encountered cracked it in three places. I'll never use urethane on a 914 again!

I also installed a rear window with urethane too. What a mess!

Sorry to hear it - but that was super frustrating. I’m going with butyl tape.

So the rubber spacers stay in place post install? Two or three recommended?

Yes, the spacers stay in place after install. Two should be fine.

Thanks!

I just did this. I always use the 3M urethane primer, which helps the butyl stick. It's black so you don't have any body color peeking through.

You want rubber blocks at the bottom of the back glass too, it'll keep the window in position so it doesn't sag down and ride on metal.

Take extra care at the lower corners, it's easy to get a void in the corner which can leak.

Well I just did this to end and with everyone’s coaching here it actually went pretty easily. I had forgot that I used the 914 Rubber kit on another car front windshield so I sourced a 3M install butyl tape kit locally and surprise surprise it had three perfectly size spacers in it.

I did take extra care at the corners per your suggestion, thanks for that and to everyone else who provided some coaching.

In the glazing world, those spacers are called setting blocks. They support and isolate the glass from the metal chassis which isolates chassis stresses from impacting the glass along with the adhesive. Most every window installation configuration requires them.

3m knocked mine loose in the early 80s from auto crossing picked up 3m
and been in there ever since bought my car new in 75