Piston Slap: To Battle The Moonroof Rattle?

Sajeev Mehta
by Sajeev Mehta
piston slap to battle the moonroof rattle

TTAC Commentator Sobro writes:

Hi Sajeev and your goateed evil twin Sanjeev!

Beige. We all know it, we all love it, especially when it comes in Lexus Pearl White as my wife’s 2003 ES 300 does. This vehicle has had exactly one non-maintenance item replaced since bought new: the A/C compressor relay. My wife installed it since her office is near the Toyota dealer. And it was July. In Nashville. It was my research in the Lexus forums which led to this fix for the flashing LED in the A/C button.

Which brings me to my question.

The sunroof has started to clunk occasionally when hitting bumps, and the clunk is directly overhead of the driver. This sort of thing drives me nuts, so I’m glad I don’t commute in the wife’s ride. The Lexus forums have very little to offer, and what they do tend to start with “remove the sunroof”. Any ideas? Thanks!

Long time lurker, first time caller!

Sajeev answers:

Take it from someone working on moonroofs for 10+ years, you almost always remove the glass to do anything. The forums seem scant on info on a cursory glance but–ZOMG R U SAYIN’ ME AND SANJEEV COULD BE DAVID HASSELHOFF?

Wait, that’s no goatee on Garth! (sigh of relief)

So anyway, moonroof rattle: since you mention the glass itself opens/closes/seals like new (no wind leaks), I betcha the rattle comes from the shade or the wind deflector. Rule out the shade by pressing your palm against the shade and drive over a road known to cause the rattle. Start with light pressure and use more if the rattle doesn’t go away, to ensure the shade can’t possibly mask another problem with the track.

I have my doubts about the shade, as most Lexus’ products have a rather heavy and rattle-resistant shade, adding weight to silence a rattle isn’t likely. The (often spring-loaded) wind deflector is my bet. But other problems could be at fault: judging by the Sunroof Doctor‘s comprehensive repair kit.

What’s the fix? Get a factory shop manual (no exceptions) to ensure you don’t break anything. I’d venture a guess, but I’d prefer to remain lawsuit free after you install it wrong and the moonroof launches itself on the highway.

Sanjeev answers:

Wait, wait: you think anyone cares enough to actually want to sue you?

I’m too busy growing a goatee now, otherwise I’d tell everyone about that time you didn’t install a moonroof correctly and it flew off the car. If only people knew The Truth About Sajeev

Send your queries to sajeev@thetruthaboutcars.com. Spare no details and ask for a speedy resolution if you’re in a hurry…but be realistic, and use your make/model specific forums instead of TTAC for more timely advice.

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2 of 11 comments
  • Krhodes1 Krhodes1 on Oct 01, 2014

    Removing sunroofs is usually not particularly hard. Typically a couple screws on each side hold it to the mechanism, and it lifts right out. I've had a bunch of them out to replace seals and such over the years.

  • Wmba Wmba on Oct 01, 2014

    One of the three rubber bumpers at the front that forces the glass to push up against the roof's opening lip when closed fell out in my Subaru. Caused rattle. Opened roof to halfway position, did not notice rubber bumper missing. Closed roof, but it wouldn't go all the way. Hmm. Noticed black object in well under roof at front, extricated it, placed in only hole available, closed roof, rattle gone. Siliconed bumper in place at trip's end. You never know, might be as simple as that.

  • MrIcky I would like to compare the answers here against the answers in the recent civil forfeiture article- but I won't because research is hard. It's true though that currently a ticket has no punitive value on those with means and maybe an outsized punitive value on those without. That's not communism, that's just the way it is. Speeding tickets are too arbitrary anyway though: officer discretion, speed trap towns, excessively low speed zones in areas to increase ticket revenue instead of safety, etc. I could clearly see a case where expensive cars are selectively enforced over cheap cars because you only have so much time in a day to up the revenue. It's a gray rainy crap morning and I'm sure the government will do it wrong.
  • 28-Cars-Later Feels a bit high but then again... forget it Jake, its Clown World.In 2021 someone in Sewickley had an MY01 soft top in a manual with 54K otc which I am fairly certain was a 996 and not a Boxster - $20K. I already had my C70 at the shop being reborn and could have done the $20K but it would have been tight and just didn't make sense. Still...
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