Found out what’s causing undercarriage composite to break apart

[AlanSubie4Life]

On my way out to run an errand, I did a brief survey of ~6 model 3s in the garage at work. I think I'm a little crazy.

Anyway, on a vehicle with VIN 11xxx (so it has all three bolts), this is what I found (for the rear bumper cover)!

Two out of three bolts were loose. They're about to fall out. I didn't tighten them - I guess if I encounter the owner at some point I'll mention it. So, I guess this is not a new problem.

As mentioned earlier, there is another vehicle with 2 out of 3 bolts missing (a car built with three bolt holes.)

All the other vehicles seemed intact and I didn't see any loose bolts on the rear bumper cover - but I found missing bolts on a couple of other cars for the undercarriage covers.

So seems to be a relatively widespread problem but for this small sample size affects only ~20% of cars.

 

[N54TT]

On my way out to run an errand, I did a brief survey of ~6 model 3s in the garage at work. I think I'm a little crazy.

Anyway, on a vehicle with VIN 11xxx (so it has all three bolts), this is what I found (for the rear bumper cover)!

Two out of three bolts were loose. They're about to fall out. I didn't tighten them - I guess if I encounter the owner at some point I'll mention it. So, I guess this is not a new problem.

As mentioned earlier, there is another vehicle with 2 out of 3 bolts missing (a car built with three bolt holes.)

All the other vehicles seemed intact and I didn't see any loose bolts on the rear bumper cover - but I found missing bolts on a couple of other cars for the undercarriage covers.

So seems to be a relatively widespread problem but for this small sample size affects only ~20% of cars.

Any of those missing bolts the middle bolt? If so can’t really say they are missing (fell out or missed install) without looking up or feeling if there’s a threaded hole for the bolt to even screw into. My car doesn’t have a threaded hole in the middle. We’re you crazy enough to do that? Lol

 

[AlanSubie4Life]

Any of those missing bolts the middle bolt? If so can’t really say they are missing (fell out or missed install) without looking up or feeling if there’s a threaded hole for the bolt to even screw into. My car doesn’t have a threaded hole in the middle. We’re you crazy enough to do that? Lol

I only said bolts were missing if there was a hole for them. In fact on the car with two missing bolts, the only bolt remaining was the middle one.

The early VINs always seem to have the middle bolt. Looks like it stopped being added sometime in Q3.

As you say, later vehicles have no middle hole.

Also, as someone mentioned earlier, you can see the imprint of previously installed bolts in the plastic of the bumper cover - so there’s actually no ambiguity at all about whether a bolt was installed from the factory.

 

[TEG]

The early VINs always seem to have the middle bolt. Looks like it stopped being added sometime in Q3.
As you say, later vehicles have no middle hole.

Data point: VIN 19xxx April mfg, has middle bolt.

I think soon after is when Elon mentioned something about reducing the number of welds in the car due to engineers saying it had more than necessary.

Perhaps that fastener point was also deemed excessive / unnecessary.

How Tesla is doing everything to get Model 3 cars out the door

...In an effort to drastically ramp up production, Tesla employees are now tinkering with the core designs of the Model 3 car and the production process, detailed by a New York Times report (paywall), something that experts say is unprecedented. Executives at Tesla decided that the car didn’t need so many spot welds holding the underbody together, so engineers found 300 “unnecessary” welds and reprogrammed the welding robots cut them from the production process...

 

[Avid]

Has anyone measured these fender shield retainer plastic "rivets"/"push pins"/"pop-its"? Hole diameter, stem length, flange diameter? I guess I'll go pop out one of the ones I have at some point and get a caliper on it if not...

They are 5/16 (7.94mm), used a drill bit to ascertain the diameter.

 

[Redrick00]

I only said bolts were missing if there was a hole for them. In fact on the car with two missing bolts, the only bolt remaining was the middle one.

The early VINs always seem to have the middle bolt. Looks like it stopped being added sometime in Q3.

As you say, later vehicles have no middle hole.

Also, as someone mentioned earlier, you can see the imprint of previously installed bolts in the plastic of the bumper cover - so there’s actually no ambiguity at all about whether a bolt was installed from the factory.

I just checked mine again, mfd 07/18 VIN 49xxx. Center hole does have threaded hole but no indentation mark of ever having a bolt there. On photo I’m pushing up on cover, when I let go it drops about 1/2 inch.

 

[Az_Rael]

Checking in with a 2017 model (VIN 1986). All three bolts present, but center bolt was loose.

 

[Redrick00]

I made video with front of car on lower side of driveway, about 2” lower than rear. I also taped up holes I drilled. Water ends up flowing to front side of composite cover. It also flows right through center once it’s soaked up.

 

[Stellavator]

So, could you run a bead of silicone along the top edge of the tail light housing to keep the water from getting down there?

 

[Redrick00]

So, could you run a bead of silicone along the top edge of the tail light housing to keep the water from getting down there?

I wouldn’t do that as water can enter from any side of tail light. It would take a whole tube of silicone to seal it. This is what it looks like with tail light removed.

 

[VT_EE]

I have a June build 30xxx VIN and have all three bolts on the rear underside cover. I couldn’t find any holes with missing bolts on the undercarriage and verified everything was tight. I did have a number of missing fasteners in the wheel wells, but had a Ranger remedy those.

 

[JPP]

Just looked at at my P3D+ VIN 75357 Sept. build....the center hole on the underside rear has no bolt and is a through and through hole with no obvious threaded nut behind it. Maybe drainage? The 2 side bolts are there and feel/look tight.

Rear wheel wells each seem to be missing 2 fasteners (hole is in liner and sheet metal). Front wheel wells have holes in the liners for 2 additional fasteners, but no matching hole in the sheet metal to fit them in to.

 

[R1Fast]

Just looked at at my P3D+ VIN 75357 Sept. build....the center hole on the underside rear has no bolt and is a through and through hole with no obvious threaded nut behind it. Maybe drainage? The 2 side bolts are there and feel/look tight.

Rear wheel wells each seem to be missing 2 fasteners (hole is in liner and sheet metal). Front wheel wells have holes in the liners for 2 additional fasteners, but no matching hole in the sheet metal to fit them in to.

Same findings here, exactly. Vin 099xxx built 09/18. Rear cover bolts are tight and center is a hole with no hole in the frame/sheet metal so it looks like a drainage hole.

Strange about the front liners, must have been a design change on the more recent builds. Otherwise I wasn't missing any fasteners except one on the drivers side fender liner bottom-left (@ 8:00 position).

 

[AlanSubie4Life]

Re: fender liners. Agreed on the latest builds having two fasteners missing in the front and two missing in the rear wheel wells.
-> there is no place for them to go on the front wheel wells
-> on the rear wheel wells there are holes for the fasteners

Also, forgot to mention that two weeks ago when taking delivery, I checked the bumper cover bolts for a nearby Model 3 (to make sure this missing middle one was normal - which it is, as discussed, these days), and that Model 3 was missing BOTH of the remaining bolts! I didn’t look to see if there was evidence that they were ever there.

I feel like these bolts must be getting installed by a misconfigured robot, to be done so poorly. I don’t see how a human could do so badly.

For all the people checking their bumper bolts, remember the check the composite covers’ bolts/washers, front and rear, while you’re at it. The middle ones are hard to see but it is possible. There are at least 8 for the front cover and 8 for the rear cover. I say “at least” because there are a variety of other attachment bolts you’ll find - some are the 10mm heads but they are recessed, so it is hard to see their function/what they are attaching, and some are star heads. If I ever lift the car or even get it on ramps I’ll try to figure out what they’re all for and get the correct counts.

 

[R1Fast]

A little off topic, but I wonder if it would be worth pulling the composite piece and spraying it with plasti-dip or some type of waterproofing material to strengthen it a bit. The composite alone seems like an odd material choice for an area so exposed to the elements, and a light coating of waterproofing might help with it breaking apart.

 

[SMAlset]

A little off topic, but I wonder if it would be worth pulling the composite piece and spraying it with plasti-dip or some type of waterproofing material to strengthen it a bit. The composite alone seems like an odd material choice for an area so exposed to the elements, and a light coating of waterproofing might help with it breaking apart.

Seems to me that would add more weight and keep any water from escaping.

 

[AlanSubie4Life]

I have news on the rear undercarriage cover (not the rear bumper cover). I put the back of the car up on ramps to get this information.

• There are 12 10mm bolt/washer combo attachment points for the cover. There is actually a spot for a 13th in the middle, but my car didn't have that (the threaded hole and the cover hole didn't align too well - and it looked like a bolt had never been inserted).
  
• There are multiple drain holes. They are located at the lowest points. Water is not going to accumulate on top of this cover.
• There are several other attachment points at the edges of the cover near the wheel wells, with rivet like joins to metal bars which run above the cover. There are also attachments on each side to the wheel well composite shield.

Attached are a few pictures. If someone has the middle bolt on this cover, please let us know and provide a picture. I especially wonder if the early builds had this bolt? (I'm not talking about the bumper cover middle bolt which we've already discussed.) I'd like to have this last bolt inserted, because it seems to snug the cover up against the bottom of the car by a fraction of an inch. But it might take some forcing to get it past the cover due to the misalignment.

The summary is: This undercarriage composite is quite robustly attached (assuming all bolts are present), and it seems very unlikely that it will sustain damage unless it is not properly attached, or something hits it and damages it.

I definitely don't think car washing or it getting soaked is going to be an issue at all; it's just too well attached & well drained. The effect of snow and ice is a little less clear, but it also seems unlikely to be an issue unless it is a very bad icing situation, or you're driving in deep snow and throwing up a lot of it. It looked to me like the snow being thrown off the wheels would tend to be diverted from landing on top of the cover.

So, as far as the OP goes - I continue to think the damage most likely occurred because the cover was never properly attached. Or, it sustained damage somehow inadvertently, due to road debris.

Definitely no need to do anything to it, other than to make sure it is attached - it's been solidly engineered to remain attached to the vehicle, as far as I can tell.

 

[SMAlset]

Thanks for the extra undercover work there @AlanSubie4Life .

 

[FlyNavy01]

I just checked my July build (~55k VIN) and it has all 3 bolts in place and tightened.

Although that might be because I just got the felt underbody liner replaced by service two weeks ago for a hole that ripped in it after driving through a puddle (just like the separate thread mentioned above) so no way to tell if the techs just noticed missing bolts in the plastic part while replacing the felt part and installed the missing bolts while the car was on the lift.

 

[AlanSubie4Life]

I just checked my July build (~55k VIN) and it has all 3 bolts in place and tightened.

Thanks. Narrows down removal of center bumper cover bolt hole to July/August timeframe, as I am aware of an early August built car which does not have the middle threaded hole for the bumper cover.