Drove from Indianapolis back to Chicago yesterday in my wife's MB C280 (her tri bike doesn't fit in my 993). Clear weather with temps in the 80s, traffic not too bad (ie: few members of the "Anti Destination League"), "good" speeds.

Get in the car this morning, drive 3 feet and it's clear I've got a flat tire. This is surprising, because the car ran faultlessly all day yesterday.

Change the right rear tire, which is flat as a tortilla. In order to locate the problem (none is obvious upon initial inspection of tread, carcass, etc.), I reinflated the tire.

The problem is evident immediately. The valve stem is pumped up like a balloon and is leaking profusely. It only takes about 3 minutes to empty the tire.

Anyone ever heard of a similar failure (the body of the valve stem and not the valve mechanism itself)?

By the way, yes, it's clear to me how very, very lucky we were.

Regards to all.

 

David

It's not too common, but the rubber part of stems fail, from fatigue &/or old age (cracking) & sometimes from contact damage. That's why it's prudent (& very cheap insurance) to change stems whenever a tire is dismounted from the wheel.

Many (& I mean many) years ago I had a stem rupture on my Triumph GT6. The car had wire wheels & tube tires. It was raining, I was on a highway & rolled the car off the muddy embankment totaling it. You were obviously much luckier. Since then, I check the tire stems for any obvious damage whenever I check tire pressures..

 

Hi David:

Dan is right on target; its not common since the vast majority of tire shops will install new valve stems with new tires. Its cheap insurance.

That said, its possible that the stem was damaged or defective,(how long have they been on there?).

I'm glad you caught it before it became a real "problem",.....good job!

 

I always use metal valve stems on all of my cars.

 

I had the same problem before with three of my tires (two of them at the same time), so I replaced mine with heavy-duty metal valve stem.

 

yep... got metal ones on the cab... came that way. also, heard that @ speeds over 80mph metal stems or those metal tees are a must.

sounds like @ cruising speed your rubber stem ruptured when bending @ a higher speed.


i'd replace all the stems w/ metal ones if i were you... then, no probs!!!



bol!

 

Respectfully ... nonsense.

 

Thank you for your thoughtful replies. Where else but Rennlist, and on a Sunday, no less!

Dan's story of having his TR6 roll over was exactly the kind of thing that went through my mind when I figured out this morning that I'd been "giving it a bit of Wellie" all day yesterday, supported only by that #$^% valve stem.

Of course, the old rule "the tire's not new unless the valve is, too" has never been more true. I cannot, however, state with any certainty whether or not the valves were replaced when the tires were installed - a point I will never, ever overlook again.

ca993twin and RT7, can you guys tell me where to get metal valve stems? The NAPA site is very helpful and it seems you're suggesting the "clamp in" type over the "snap in" models, and this is very helpful. I suppose I can even figure out the right length on my own (clearly shorter is better). Are there "better" sources?

Also, the NAPA site offers several diameters of valves, suggesting that different wheels have different diameter valve holes. Seems 1/2" (.453", to be precise) is the most common. Is this the standard? Will these fit both the factory AMG wheels on the MB (it's the "Sport" model) and my 993's 17" "Cup" wheels? Where did you get your metal valves?

And can anyone tell me where to get the little stick-on aluminum wedgies which are intended to stabilize valve stems at high speeds?

As you can imagine, after this experience, I'm goin' fundamentalist on this, and both cars will soon be receiving metal valve stems and the support "wedgies" (is there a proper name for these?) as soon as you guys tell me where to get 'em.

As ever, thanks for your help.

Regards to all.

 

David
I think you're overreacting. The incidence of a catastrophic stem failure is extremely remote in street use, especially w/periodic inspections & replacements w/tire mounting. I'd be more worried about a meteorite through an open sunroof.

Consider that apart from the TT, Porsche (& virtually every other auto maker) installs rubber stems w/o any apparent liability concerns. Further, metal stems are not without problems. Regular inspections/replacements should be done of the rubber seals and the tightening nut should be properly torqued.

You should, however, always use metal valve covers with good o rings since valve leaks/bleeds are common, especially at high rotation speeds & a good cap will prevent pressure loss.

BTW, the stem supports are sold by Performance Products for about $5 each.

All just my $.02

 

I'll chime in and agree with Dan,......

Metal ones, while durable, are not failsafe and the rubber sealing rings at the bottom of the stem do deteriorate with age.

The rubber ones are just fine if they are replaced when new tires are mounted and new schrader valves are installed. Metal or rubber valve stem caps are both just fine.

The stem supports are a fine idea; Porsche used them for years.

 

The factory recommended valve stem support on the 80's Carreras that had wheels over 9 inches in width.

I had a stem failure on my '86 in Utah on the way to Steamboat some years back. Now where do you buy a 245-40-16 in St George Utah on a Friday afternoon? Tire Rack Fed-Ex'd one to the hotel, arrived Saturday morning, and we were on our way.

I have steel stems now.