cfair

I've always thought the big cars should be quiet. I've had my '66 98 convertible for 35+ years. For a lot of that time I've been working on making it quieter, particularly on the freeway where wind noise is evident. My Dad bought it new and always said that car is best at 45 mph with the top down. I agree, but it's fun to see how nice it can be with the top _up_ too.

For most of those decades I thought the noise problem was the windows against their seals. I more or less ran out of stuff to adjust and in conversation with my interior guy, he suggested I chase top fabric noise.

I've had 2 or three tops on it over the years which kept out most of the water. I have no real complaints. The GM design is sound, but in more recent years, the reproduction tops seem to shrink faster and fit less well than they used to. Or at least how I remember the old ones. Last time around I had a Robbins top put on by Convertible service of San Gabriel, but had it replaced within a year or 2 since it was just too narrow. Like too narrow to cover the top rails. My upholstery guy went back east for a replacement and found a better one. Even the replacement is marginal for coverage over the top rails at the sides. Which leads to wind noise, especially on the freeway. Which drives me nuts.

Over the summer I had the door panels off the Starfire hard top and drove it on the freeway. I was amazed at wind noise coming through the doors. I always thought it was windows, but I learned wind noise comes through the door voids too. To reduce that, last week I was playing around with adding adhesive backed "P" seals from Trimlok just behind the door panels. The idea is to isolate the cabin from the noise source. I've got a couple of modern cars and I was really impressed with how well they seal, so I started looking around for stuff I could retrofit to the old cars.

The "P" seals helped the Starfire, so I got a sealing kick. Here's what I did to the Starfire and am waiting to do to the 98 convertible. Basically I stuck down the flap just underneath the edge of the door panel and let the bulb fill the void between the door edge (rear, bottom & front) and the car. You want the bulb just prominent enough to seal, but not sticking out so far that it impedes door closing. Something like this really helped on the Starfire, which is a lot quieter than the convertible by design:


Add a "P" seal to your Olds. Cadillac did stuff similar to this in the 60's, so we're not too far from factory. And hopefully not too obvious.

So this week I've been playing around with making the 98 convertible top quieter by adding Trimlok 1.75" flap seals to the top frame rails.

To start, I'm adding them where they can't be seen, but do seal out wind. Here's a factory convertible top frame rail with no seal, just a 1/4" bent metal edge pointing upward:

Typical GM convertible top frame. Functional, but not all that quiet by modern standards.

Here's what it looks like with the flap seal installed:

Trimlok 1.75" flap seal installed on frame rail. When the seal sits flat, it's invisible when top is up, but the 1.75" doesn't want to stay in place.
3" length flap seal is on order to get the non-factory seals to tuck in on top of the top pads without intervention every time the top goes up / down.

I should also add that at the same time I added a U channel/bulb seal between the rear trailing edge of the front fender & the front edges of the doors. This probably helped too, but I did it all at once so I don't know which made the biggest difference. For what it's worth, the fender/door bulb seal trick would work on most any GM car with the 3/16"'s factory gap. I cribbed this trick from my 2017 Audi which is sealed like a vault.

Here's what the front fender bulb seal looks like, not perfect, but not bad for a 15 minute test:

U channel grabs the rear fender edge putting the bulb seal between the rear of the fender and front of the door. This is mostly unseen, but helps quiet this old car.

The '66 98 convertible is now as quiet as I've heard in years. Wind noise is there, but substantially reduced. All for about $200 in materials and about and hour per area. I'm not affiliated with Trimlok, but am impressed with their stuff.

Couldn't be happier. I'm testing the effects of adding more flap seals tonight. I think the 1.75 flap length is version 1.0 of the sealing effort, since the flaps don't want to sit quite flat on top of the top pads. I'm not sure they need to be on top of the top pads, maybe eventually I'll just let them sit where they fall. I'm guessing I'll move to 3" flap lengths pretty soon after I get the stuff from Amazon.

Hope you all can benefit from the madness.

Cheers,
Chris

Greg Rogers

Good job!

JohnnyBs68S

Impressive modifications! Have you thought about adding an inner liner to the top like most modern convertibles have? I used to have a '70 C/S 'vert at the same time I had a '92 LeBaron 'vert and I always thought that the single layer top of the C/S was allowing a lot more noise in than the 2-layer top of the LeBaron. I've since sold the C/S and LeBaron and now have a T/A 'vert which also has an inner liner (2-layer) top which is very quiet, in fact more quiet by C&D's test than a T/A coupe (T-top). Indeed, sealing around doors and windows have come a long way from the '60s (as you are discovering), but I think further improvement could be found with an inner liner for the top.

Cutlass Fan

Interesting! I will try some of your tricks.

cfair

Funny you should mention a top liner. I’ve long noticed modern cars with a second convertible top layer.

My front section has custom liner with a 1/4” foam inside black bow drill cloth, emulating a late 70’s Eldo. Its great on the freeway.

But now the top noise comes from the behind the custom liner. So the end of that road is a liner for entire top. Which probably won’t allow the top to lie flush in the top well like it’s designed to.

My next step is a similar closed cell foam filled liner for the second section. I’m debating 1/8” foam vs 1/4” foam. 1/4 would be quieter, 1/8” has a better chance to lie flat in the well. The piece will probably be looped around the middle top rib attached with a strip of velcro at the rear rib. Nothing obtrusive, just a black liner.

If that works, then wind noise will come from the cloth “C” pillar aka the rear curtain. I have a feeling any lining in the left and right sections there will have to be removable. If lined, I think it will be too thick to lie flat in the top well. Especially on top of the rear wheel wells. I can live with removing panels, but it will complicate the top going up & down.

If the panels are removable, I can leave them out whe the top is likely to go up & down a lot and just live with the noise, then attach liners when it’s likely to be up most of the time. I’m debating attaching rear curtain liners with either snaps or Velcro, or maybe some of each.

At the edge of my thinking is using elastic fabric to pull insulation material out of the way when the top is down. I think I remember some modern tops cleverly using elastic to make fabrics mod where you want them as the top goes up and down. I think the elastic design is that it’s stretched out when the top is down and shorter/unstretched when top is up. Kind of like how springs keep a carb closed when your foot is not on the throttle.

Suggestions, thoughts and ideas most welcome. It’s great to hear what others are doing and thinking about.

Chris