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A Tire Story

November 30, 2011, 07:15:01 pm

For several months, I have had an intermittent, and small/slow, leak from my Left Rear Inner (LRI) tire.  It has been erratic, some times going several weeks with no loss, then show 3-5 PSI low.  I could always find a rationale that would allow me to add the lost air and "press on"!

After our first severe cold front, with a temperature drop from 65 down to 40 degrees, and having planned an "exercise run",  I checked the tires. I was surprised that the LRI tire was at 60PSI instead of 90PSI.  The matching LRO was at 85 (down from 90).

Using the Michelin Rule-of-Thumb of 10 degrees drop equates to 2 PSI drop in the tires would account for some of that change, but not the whole 30 PSI change.

I added air and checked daily. It held pressure for 3 days, and then dropped again. 

Our Local RPM Truck Tire Dealer suggested changing the valve core as the first repair step.  This time the tire held for 2 days and then dropped from 90PSI to 55PSI.  So today I went back to RPM Tire, asked that they replace the valve stem. 

There was the problem: the grommet sealing the valve stem inside the wheel was in tatters and was falling apart inside the wheel.  No other cause for air loss was found.  These stems were new 20 months and 15,000 miles ago when new tires were installed.  The Tire Dealer and I are both surprised but sure don't doubt the evidence.

Moral (for me): 1) check those tires every running day; 2) don't rationalize irrationally!

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Re: A Tire Story

Reply #1 – November 30, 2011, 07:39:19 pm

I had the same leak, same tire and the fault was the valve stem as well.  But I had other issues when the repair was performed.
 
What did you do to your coach today.
Rear Axle Studs - Rockwell

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Reply #2 – November 30, 2011, 08:41:40 pm

I was checking the driver's front tire in the middle of nowhere but after removing the gauge, the air continued to leak. I always carry the small, silver valve core R&R tool but the stem was a little too far recessed and the 4 way tool hit on the aluminum wheel. I had steel stem caps with the rubber gasket inside in my tool box. Sealed nicely until I could buy the valve core tool without the extra stuff on the side that would clear the wheel. At $1.50, it's a good tool to have with you along with some extra cores and steel caps. View tool and supplies at: Valve Core Remover | Valve Stem Repair Tools | VA602

Some imported truck/bus style tire gauges seem to either damage or cause the core to stick. The kind you buy at Harbor F.

Never hurts to check the end of the stem for bubbles with a tiny bit of water/soap mix.

Pierce

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Reply #3 – November 30, 2011, 11:39:40 pm

We have had DP coaches for a bit over two years. We have had two tire problems. Both were valve stem issues. In both cases, leaks developed at the grommet where the stem connected to the wheel. I am convinced the problem was caused by adding pressure sensors to the stems that had relatively old grommets. Grommets and cores seem to be exceptionally vulnerable parts of tire systems.

We travel in cold weather and did not have good results with a TST TPMS system when temperatures dropped below freezing. I now use a tire gauge with a flexible hose and a dial gauge that holds the pressure reading until released. All valve stems are capped with steel caps that have rubber seals in place. I check all the tires before a trip and set pressures according to Michelin charts and ambient temperatures that I expect on the upcoming trip. I check tires with a "thump" and/or an infrared thermometer at most rest stops. A problem is likely to cause a different response to the "thump" or a different temperature reading.

I have found that cold pressures are very consistent and vary primarily based on ambient temperatures. I check in the morning before the sun shines on the tires. There appears to be a gradual and consistent loss of pressure with time. Any loss of pressure on a single tire as compared to other tires is indicative of a problem that should be addressed.

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Reply #4 – December 02, 2011, 03:17:21 pm

The old handy dandy " air-thru valve caps" will cause problems with road grit and grime getting in while checking air. Checked the tires the night before a morning departure, all was good, next morning L/F flat $150.00 later nothing found in the tire air-thru cap leaking, tire guy said he sees it all the time.

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Reply #5 – December 02, 2011, 07:51:17 pm

I appreciate all the replies and glad to know I am not alone with this problem.  I quit using my TPMS several months ago because it seemed to be more trouble than it was worth with false alarms, signal drop outs, etc.  I had not thought of the sensor's weight leading to grommet failure but that is certainly plausible.  I do check my tires every running day, and with an IR Temp "Gun" at stops on the road.

If I have a problem with another stem, I will get all the wheels broken down and put in new stems.

Again, thanks to all!

Dan Spoor 2003 U-270

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Reply #6 – January 26, 2012, 08:06:26 pm

A follow-up to this story.

A month after the valve stem repair, I had a similar slow leak on the other side, the RR Inner.  Tire dropped 15 pounds more than its running mate, and again, on a cold night. 

I got both right-rear wheel/tire valve stems replace on a semi-emergency basis, and then today, went back to RPM Tire on I-35, Exit 271 in Jarrell (North of Georgetown, near the new Flying J), and had all of the remainding tires re-stemmed (is that a word?).  I give the RPM location because they are not widely advertised, are a competent shop, and reasonable ($30/tire).

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Reply #7 – January 26, 2012, 09:33:31 pm

In working on my Pressure Pro to see if accurate to my gauge the manual indicates that you should have metal stems not rubber.  Assume you have metal.  Tks DAN

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Reply #8 – January 27, 2012, 08:54:35 am

Yes, all steel solid valve stems with solid steel valve stem extensions on the inner dual tire (I know, Extensions are sort of a "No-No").  The failure is in the valve stem grommets which are inside the wheel.


The ones that failed were on the inner wheel, and the appearance of those on the outer wheels were that they would fail soon.  All were new at the same time, about 2 years ago.  For 1 1/2 years, all had Pressure Pro Sensors on and I am believe that extra weight on the stem is the culprit.  I may be wrong but now I have all-new stems and no PP.

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