'14 AGM 1SS/1LE Track build [COTW 11/17/14]

[X25]

Originally Posted by Stephen12ZL1

It has to be something with the Z/28 wheel and yes, I was running the Trofeos when the sensor retaining nut loosened. I was starting at 28psi the day it sidelined me at the track. Does it have to do with expansion & contraction of the metal in the wheel?

I got the valve stems replaced today. We checked the records, and indeed the stems were not replaced with new units during the last tire change. The Discount tire worker was also surprised, since he said they always use rebuild kits during tire changes. I am sincerely hoping that this was the cause of all this. I don't know what exactly happens during tire change, but if the valve stems are removed and re-installed, perhaps the plastic washer-like seals strip in the process.

I was told by Discount tire that the GM TPMS units do not come with retaining nuts, and that they just get the whole valve-stem replaced, which has plastic seals on it.

Here is the picture of the stem that was actively leaking. When the technician pulled it out, it actually ripped and split into two pieces. I am guessing it had a crack by that seal already, which is why it was leaking.


Here is another pic with the ripped piece moved further apart:


This plastic seal/washer seats very nicely into the cavity on the wheel. When installed, the TPMS sensor does not directly touch the wheel surface, but its very close to it. You can freely move the TPMS sensor, and it only moves the shaft in the center; it does not have any impact on the seal when you move it around. We also inspected every TPMS sensor from every wheel, and there was no sign of impact or damage on them. The shaft between the stem and the sensor was also not bent.


My thoughts:

• There is nothing to torque in this TPMS design, at least regarding the seal. The shaft is actually screwed to the TPMS with a preset torque, but even if that fails, it would not have anything to do with the seal. Stephen, I'm surprised your TPMS has a retaining nut. They showed me different types of TPMS devices, and the GM types are all same as what I pictured; they don't have anything to tighten for seal.
• The technician himself stated that they should have replaced the stems during the tire change. Would it still cause all for stems to become leaky? I'm not sure. To be fair, though, only one was actively leaking; the others required finger push to leak.
• Since I am still mystified, I will do the next track day using MPSC 2 tires with the exact tire pressures, monitoring the TPMS pressures the whole time during the sessions. If they survive it with no issue, I will be much more confident in thinking this was merely a mishap on Discount Tire not replacing stems that they should. If it happens again, though, then I will start wondering if it's the tires/pressures, and the design of wheel somehow making it easier to start leaking.

[Stephen12ZL1]

my sensors look like this with an 11mm/7/16" retaining nut below the schrader valve cap.

[X25]

Originally Posted by Stephen12ZL1

my sensors look like this with an 11mm/7/16" retaining nut below the schrader valve cap.

Thanks for the pic! I'm using OEM GM sensor. I don't remember what kind of stem they came with anymore (bought it from an online dealer as OEM part), but it had the rubber stem like this one:
http://www.ebay.com/itm/Buick-Cadill...pV4o91&vxp=mtr

Did yours come OEM with the metal one? The technician at discount tire said all GM cars come with the rubber stem that I've pictured before, but when I search, I find both kinds available. I wonder what kind of stem they originally come with..

EDIT: Here is a thread for OEM sensors. I suppose they indeed come with the rubber type (at least they did at the time of that posting of 2010):
http://www.camaro5.com/forums/showthread.php?t=66302


Here is another OEM sensor thread, this time from ZL1:
http://www.camaro5.com/forums/showthread.php?t=302085


It also seems Amazon's OEM sensors come with the metal version with the retaining nut:
http://www.amazon.com/ACDelco-209641.../dp/B005OVI6L0

[White_SS/RS]

Mine are OEM and all metal like Stephen's pic.

[Synner]

Without digging up numbers there are Cadillacs with metal stems. Both are available, I got metal at some point but it was a long time ago. The tire shop said the metal ones fail faster, I assume from the unions.

[X25]

Originally Posted by Synner

Without digging up numbers there are Cadillacs with metal stems. Both are available, I got metal at some point but it was a long time ago. The tire shop said the metal ones fail faster, I assume from the unions.

I called Discount Tire, and asked about types of stem. They said my sensor only accepts the plastic stem (I provided the TPMS sensors originally). He also said the metal type is usually more problematic, especially when you hit a curb since they don't flex much.

At this point, I'll chalk it up to them using the old stems and closely monitor pressures, using tires at the same pressures.

If it happens again, I'll switch to the other type and try again.

[Synner]

No place I know recommends the replaceable stems, they suggest new units. It was a whole sensor with integrated stem I bought with a GM part number. You should be able to find it on here if you need it.

[X25]

Originally Posted by Synner

No place I know recommends the replaceable stems, they suggest new units. It was a whole sensor with integrated stem I bought with a GM part number. You should be able to find it on here if you need it.

Why would you just not use a rebuild kit? The rebuild kit for my TPMS type is that plastic stem. Looks like the other type will have it in metal. Either case, it will be like new; why change the sensor itself, which lasts 10 years?

[Stephen12ZL1]

my factory sensors are of the metal variety in the Amazon pic posted above. My 2009 GMC Sierra had ones like you posted with the rubber valve stem. I am still using the factory units and have had tires replaced without messing with the sensors. They may have changed the plastic washer/gasket when the tires were swapped...I did not ask and they told me nothing.

[X25]

Originally Posted by Stephen12ZL1

my factory sensors are of the metal variety in the Amazon pic posted above. My 2009 GMC Sierra had ones like you posted with the rubber valve stem. I am still using the factory units and have had tires replaced without messing with the sensors. They may have changed the plastic washer/gasket when the tires were swapped...I did not ask and they told me nothing.

I think you should ask them to change it every time they change the tires (TPMS rebuild kit). I sincerely hope that the fact that they were not replaced had a lot to do with my leaks.

There is another track day next Saturday on 3/5. I will try same pressures, anxiously monitoring TPMS pressures at the track, and will see if the issue reproduces.

[X25]

Made a quick maintenance run, and the car is now ready for next Saturday's (3/5/16) track day - of course if the weather permits!

I've finally replaced ZL1Addons' regular rock guard with the longer/wider version. It will hopefully make the difference between needing clear bra on the sides v.s. not needing one. I am not sure about the impact to aero, but I will just ignore that line of thought


I'm still very fond of my brake ducting layout. Short of my patched area of ducting fail, I did not have an incident yet. It's not direct, but there's no rubbing. I'd bet the drop in pressure due to turns would be miniscule.


Replaced the diff fluid for the first time since switching to Eaton's unit. The fluid was in vegetable oil color (what Redline 75W90 NS has as the original color), but it was cloudy. The drain plug magnet also picked up quite a bit of material. So, I believe it did break-in. The fact that color of the fluid stayed intact tells me that the fluid never overheated (even though I didn't wait too long to change it); so I suppose diff cooler works!


EDIT: I just went over all the pic links from current page (36) through 31, and fixed those image links that only work on select browsers. It seems Google has changed the image format to webp for the browsers that support it. I've used FireFox to view those pages to force Google site to show JPG versions, and fixed whatever pic that did not show up.

[Stephen12ZL1]

looking good! Wish we could get on track together at some point...west coast is too far away!

[X25]

Originally Posted by Stephen12ZL1

looking good! Wish we could get on track together at some point...west coast is too far away!

That would be fun! Most of you guys are in East coast, making it practically impossible for me to meet up at the track.

I'm still yet to even meet up with White_SS_RS, who's in Spokane, WA. We should make that happen : )

[X25]

Just received the thermostat. I'm surprised that GM sources it from Japan. I'll check where the SS thermostat was made as well, when I remove it. It shows 70 degrees C, which makes it 70x1.8+32= 158 degrees F!