The Getaway...Crom's build and adventures

Crom's Automotive Hospital Laboratory -Surgical Pathology Report

Please read with much sarcasm



Report Date: February, 24, 2017
Patient Name: OE Denso Valve Core #2
Patient Name: OE Denso Valve Core #3
Date of Manufacture: 2016
Country of origin: JAPAN
TMPS Sensor manufacturer: DENSO
First entered service date: FEBRUARY 16, 2016
Patient Medications: REGULAR DOSES OF EARTH'S ATMOSPHERE IN THE FORM OF COMPRESSED AIR

Date of Death, Valve Core #2, JUNE 30, 2016
Age at time of death: 4 months, 15 days (136 DAYS)

Date of Death, Valve Core #3, NOVEMBER 22, 2016
Age at time of death: 9 months 7 days (281 DAYS)

Attending: DR. NICHOLAS J. CROMWELL
Procedure: POST-MORTEM EXAMINATION

Preoperative diagnosis: VALVE CORES WILL NOT HOLD AIR
Clinical History: NONE
DIAGNOSIS: TBD
GROSS DESCRIPTION: The valve core body is constructed of several individual integrated components. Each component plays a vital role in the regular operation of maintaining a hermetic seal, and allowing the regular injection of compressed air to maintain proper inflation of tire. Understanding the role of each component, and the designers intent, was essential for me in determining why each patient died in the same manner.

Schrader 20055 TPMS Nickel Plated Valve Core​

Dismemberment of Schrader Core body
​

After surgically dismembering the valve core body, its composition can be described as follows:

1. A machined head being threaded on the exterior.
2. PTFE (Teflon), a dynamic sealing surface
3. A drawn sheet metal shell, most likely nickel plated brass
4. A plated brass pin which travels internally, and along the axis to the core body, operable from the top
5. A plated brass cup with a sealing washer, operated by way of pin
6. Not shown or labeled in the diagram is a stainless steel spring inside the shell.

A cutaway example, note the TPMS cores are nickel plated brass
​

Prior to dismemberment of dead core, it was observed that the head would spin freely and move effortlessly vertically in relation to body shell.

Core 1 is good, Cores 2 and 3 are dead, and the subject of this examination​

In order to determine if this was normal I found a live subject to compare. Juxtaposition of live and dead cores reveals that the live core's head will spin in relation to the body shell, however, there is stiff resistance. The head will not move vertically in relation to shell.

I looked up United States Patent #3712328, which defines in great detail the normal operation of a Schrader valve core.

Buried inside I found my answer to what went wrong in section 1 of the patent claim. I will quote it and bold the relevant part

It was only then I realized that the head and the metal shell are mechanically attached by crimping (compression).

In both my patients, the head was detached from the body and free to float there only retained by the pin; it was the crimp that had failed. I will get to the why it failed later, but for now I know what went wrong.

The Machined head is crimped on to the shell body​

Next I turned my attention to Schrader International. The reason for this is, ostensibly the cores in the Japanese Denso TPMS sensors are in fact made by Schrader.

Schrader has a nice library of information, and one such publication is a Valve Core Brochure.

Notable statements:

• Serviceability No Valve Cores are to be reused under any circumstances after removal from the Valve Body. Always install a new Valve Core when servicing the system for air, fluid or gas applications.
  
• Opening Pressure: This is the typical air pressure necessary to overcome the resistance of the spring that keeps the valve closed, allowing air to pass through.
• Minimum and Maximum Travel: This is the recommended distance the pin can travel without damaging the valve core. This information can be found on specific Schrader drawings.

The first bullet point is quite interesting for those who like to pull cores when airing down!

The third bullet point has grabbed me as a highly probable reason why my two cores died. It is quite possible that when using the Terraflex tire delators, that I simply screwed them on too aggressively, therefore, effectively stretching the core beyond it's limits causing the crimp to give out. I will continue to search for the specifications for the Schrader TPMS cores, but as of yet have not located it.

After much research, that is my final hypothesis for the valve core deaths.

Diagnosis: Death caused by owner.

To guard against this type of failure in the future, I bought myself a nice valve core tool and a 100-pack of nickel plated cores

Tire valve medicine



New live cores
​

Here endith my pathology report for TPMS valve core deaths.

 

Lol. Nice write up.

My mud flaps.

 

Well done Dr Cromwell. If the head detaches from the body the patient dies! We will include that in the journals. Thank You

 

Very good. We had the same idea! lol

Looks top notch! I hope mine look as good as yours and Dave's when I'm done.

 

Pardon me for quoting the most important part of your post. An important TL;DR to me!

I used the ARB deflator initially until I learned about the Terraflex deflators. One of my concerns about the ARB was the fact that it seemed it might be a bad idea to be repeatedly pulling the cores.

Really interesting to see that the Terraflex or Staun deflators could also induce a failure mode too! Seems the best practice then is really simple - once the air starts flowing stop tightening the Terraflex.

Awesome failure analysis Nick. Thanks!

 

@SC2SC I thought you might like this write up with your background. Also tons of good info in this thread!!

 

Not hard..... Utility knife, fresh blade, cutting surface, straight edge and a paint can for the radiused corners. I used 11in wide by 20in tall.

Used factory hardware to mount and a SAK awl for the holes...... I used a couple of molly bolts to attach to the fender well, but I'm probably going to change them.... Maybe try a rivnut.

 

@Crom where did you source the valve cores depicted?

Also- how low did you air down for the reported failure? Just wondering if lower tire PSI resulted in the failure- or if it was the mechanical connection/metal fatigue alone that caused failure.

Edit: found the cores on Amazon.

 

It was purely mechanical failure.

The core deaths were caused by me when attaching the Teraflex tire deflators. They are screwed onto the valves and depress the core pin to let air out. There is no regulator to limit how far you can screw them on. I'll be more careful in the future and I'll be employing the same technique that Ken listed above.

Today I'm gonna swap all four cores for new.

 

Good to know, thanks!

 

Refrigeration systems use Shrader Valves for the service ports. We would constantly see failures right out of the box before we even installed them (hydro tested before install). Sometimes it was a matter of seating the core and others had to be replaced. It's a mass made part, some bad ones are going to make it through the filter. @Crom hit it with carrying the tool and some spares.

 

Welcome.

Good to know, thanks

 

Got more maintenance done today.

• Went commando with roofing sealant and gun. Attacked air/water leaks at shell door. Stupid design flaw with shell mounting hardware on door.
• Replaced 4 valve cores with new, just because
• Aired up all tires to 40psi
• Replaced quick disconnect air fitting in bumper. Old went bad and won't self seal anymore.
• Performed power steering fluid flush. Super easy job.

Will update this post with mileage record in near future.

 

My roofing sealant job was successful. Sealed on Saturday, and rained on Sunday, and big f'ing deluge today!

I also noted a curious characteristic of my truck, don't know if universal for all second gens, but probably is. That is my 1GR-FE engine has a vibration / harmonic at 1500-1700 RPM. I detected it while parked and idling the truck, slowly increasing RPMS, engine was not yet warmed up. Useless information? Maybe. Where I see this as having any useful value is when chasing down vibrations. It might be worth the time, to feel the engine's effects before blaming tires / drive shaft / gears, etc.

After doing the PS flush on Saturday, I took my family out to Mount Helix.

Stellar views in every direction, this one to the west, and the Pacific Ocean.

Nice amphitheater to play in.

 

Sick build bro!

 

How long did it take you to get to where your at?

 

High clearance bumper??

 

​

 

Thanks.

My first off road adventure with the truck happened within 24 hours of delivery in May 2009. The truck build started in June 2009, when I had my buddy melt on some sliders.

So I guess that's almost eight years now.

Yes.

Virtually all of the modifications to the truck are listed on the first page of the build. take a look, click on whatever you want, ask any questions you want. Hope you find useful.

Welcome.

 

Who built the rear bumper and swing arm for tire?