Hatch garnish loose only at driver's side edge

That lubricant seems to be a New Zealand specific product.

The hatch opens pretty well once it is lifted up a few inches, but there does not seem to be enough oomph when fully compressed to make the hatch start moving. Which is peculiar, since if anything that should be when these gas struts have the most force.

 

Turns out "Shin Etsu" makes a lot of different products which might be the one Honda sells. Here is one of their summary documents:

https://www.shinetsusilicone-global.com/catalog/pdf/grease_e.pdf

Does the Honda product have a Shin Etsu product number on it?

Their G-501 product seems like the perfect thing to put on little plastic gears in actuators.

 

Bought some Shin Etsu grease from the closest Honda dealer. Today cleaned the hatch rubber weatherstrip thoroughly with water, then treated it with the Shin Etsu grease. Cleaned the metal parts of the hatch that touch that rubber thoroughly as well. Put a tiny bit of the grease on the rod of the struts, worked the hatch up and down. I know, this grease is not the same thing as that gel, but it is a Silicone grease and if any sort of lubricant would help, pretty much any should for a short time. Moving the hatch up and down scraped what looked like 99% of the grease off and formed a little grease donut around the shaft at the extreme (closed) end of travel. Wiped that off, it was just going to collect dirt.

End result - no improvement whatsoever. The point at which the hatch will start to lift is actually so high that I can look underneath and see that no part of the hatch is touching the weatherstrip. Guess the Stabilus lift supports just failed, or at least one did. Also it was quite warm today (80 F!), so that rules out "doesn't work because of the cold". Will contact RockAuto about replacing them.

I took a very close look at the hatch hinges, with an eye towards lubricating them, and I don't think any product I have is going to do a thing. The gaps between the "barrel" (which rotates) and the supports on each side are very small. A lubricant would have to wick through that small space as thin liquid and then convert into some other state so that it wouldn't leak right back out again. These hinges don't squeak or scrape or make any "I need to be lubricated" sounds, and the hatch moves pretty easily, other than the weight. Seems pretty unlikely that after 17 years they would suddenly develop so much drag that it was a problem.

 

The only option under the Stabilus's manufacturer warranty was RockAuto shipping a second set of the same product, and I would have to pay for shipping the defective one(s) back. Since the product failed so quickly I don't trust it. Why would I want another? So I ordered a pair of strongarms instead. If one of the Stabilus lifts is still OK when it comes off it will be kept as a spare.

 

Same numbers on the tube I bought.

I don't know what these hatches are actually supposed to be like, that is, as designed by Toyota. We bought our 2007 used, and the hatch would pop up several inches and then need a little nudge to open the rest of the way. It would go up pretty slowly and I didn't worry about it breaking the roof welds. When the lift supports started to go it needed more user supplied lift to open, especially near the top of travel. Right after the Stabilus replacements went in it would pop open and continue upward gaining enough speed that it was prudent to keep a hand on it so that it didn't break the roof welds at the end of its travel. Now it just sits there after the hatch is released, it has to be lifted the better part of a foot before it will rise, and it takes a couple of pounds of force (applied to the metal, not the garnish), then it goes up the rest of the way, but much more slowly than when these parts were first installed. Whatever pressure the Stabilus is set to, resulting in slow or fast rise, it should certainly stay the same for more than 6 months!

FYI, at least some of the Stabilus lift supports are user adjustable - if you have the right tool:

This adjustment seems pretty dubious to me though. One can let out some of the gas, but it is not quantitative at all, and if one goes too far, it is time to buy another lift support. Seems to me that if there is a valve in there one should also be able to rig up a system to put in a defined amount of pressure, just like a tire. These things are filled with nitrogen, and I certainly don't have the equipment for that, but tire shops sometimes offer that service. I wonder if they could adjust lift support pressures? Guess it would depend on how high the pressure is in these things. Searching... Claim is 29 to 241 PSI

How Do Gas Springs Work? | Our Blog | Lift Supports Depot

Tire shops should be able to go up to maybe 100 PSI, although they wouldn't have the right fitting for this.

 

I can, just increase the force. At the initial stages the lift support is working at a very inefficient angle, almost perpendicular to the lift direction, so it takes a lot more force to move the hatch. But given enough force, it will move. More force is consistent with the hatch flying up quickly once it got moving.

This Stabilus lift support's description says:

• Rust-resistant piston rod extends product life
• Smooth operation in all temperature extremes (between -20°F (-30°C) and 176°F (+80°C))
• Consistent lifting force through 50,000 cycles
• Linear spring characteristics for continuous application of force across the entire range of movement

Unclear to me if that last one implies that it is supposed to act like a perfect spring (F=-kx), or if it is supposed to provide the same force at all extensions. I think more likely the latter. Who knows what force vs. extension relation was present in the stock lift supports, it could be linear with different slopes over several extension ranges.

In any case, not all claims match the reality. We might have opened the hatch 100 times since they were installed, and the lifting force clearly changed. So the third one was optimistic by a factor of 500.

 

I don't think so? Looking at the car from the side it appears to me that the line along the strut when the hatch is closed passes a couple of inches below the center of rotation of the hatch hinge. That results in the geometry of the attachment, which is supposed to be the hatch in its closed position (approximately, it isn't to scale). The smaller circle with its radius shows the strut from the part on the body to the part on the hatch. The larger circle and its radius shows the line from the center of the hinge to the point where the strut attaches to the hatch. It looks to me like the strut will be increasing in length continuously, at least near the closed position. The force in the closed position is mostly wasted since it is almost normal to the larger circle, only the smaller component tangent to that circle will exert a lifting force.

 

Consider the force needed to move the hatch. If the hatch was hanging straight down, or was balanced straight up, that force would be tiny. When the hatch moves to a position where its center of mass is at the same height as the hinge the force needed to lift it will reach its maximum. So let's start with the hatch latched. It releases and at that point the force from the strut is more than the force from the center of mass so the hatch starts moving up. However, before it goes too far up the center of mass has moved out enough that it balances the force available (it really is a terrible angle for the strut, pushing mostly sideways instead of up) and the hatch stops. A person then lifts the hatch a little bit more, and that moves the center of mass past its maximum (maybe) while simultaneously improving the angle on the strut (definitely). At some point the strut "wins" and then the hatch will open the rest of the way without any more help.

Complication: no idea where the center of mass is. It doesn't have to be at the same position as attachment point for the strut.

If a replacement strut has more oomph than the one just described, enough to overcome gravity on the hatch at all positions, it will never stop once unlatched and will just open all the way by itself. It will probably also hit the top of motion hard, which will be bad for the roof welds. That seems to have been the case for these Stabilus struts when they were first installed. Now that they are failing, they don't hit the top of motion with much speed. Although they do still get there.

The prediction is that if a set of struts pops open all the way like that, attaching a small weight to the hatch, for instance, tied to the base of the wiper arm or attached to the license plate, would bring the motion back into the "stops part way up" realm. Just as an experiment, not suggesting leaving the weight there permanently.)