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Old 05-12-2021, 01:44 PM   #1
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Replaced rubber valve stems on Mercedes 3500HD-based Tiffin Wayfarer

Put over 2,150 miles on the Tiffin Wayfarer in 4 days this last trip. Glad I had my TireMinder TPMS system. Heard what I thought was the furnace kicking on in the back for about 20 seconds (loud blower sound) then my TPMS went nuts telling me I had gone from 80lbs down to 0lbs of pressure on my passenger outside dual. Without the TPMS I don't think I would have known until the inside dual overheated and gave way...

Turns out the valve stem gave up and split right at the rim. There is a brass insert and it sounds like the value stem usually gives way right where the brass starts/stops inside of the rubber stem itself. I've also ran into this issue before on a Dodge RAM towing a 5th wheel (twice) so I've been trying to resolve proactively on my Mercedes 3500HD based RV, but could never find a shop willing to do it.

These rubber valve stems from the factory are only rated around 60-65lbs and when you run them at 80lbs it isn't a matter of if they'll give way, but when. Took me forever to finally find a tire shop willing to replace the rubber valve stems for steel ones. They all acknowledged they had to be replaced, but on the Sprinter rims everybody hates to do it as the working area is so small it is very hard to properly tighten the value stem nut and to install extenders on to that; nobody wants to spend the extra shop time and effort to do it. Also, they are shorter than the rubber stems so some of the extension hoses and angled extensions have to be reworked/replaced to make up for the longer run required. Lastly, even those are a pain to then reinstall given the little clearance for their own tightening nuts at the valve stem due to the very narrow rim clearances where the stem mounts.

I know when Mercedes ships a chassis to a manufacturer, they are in compliance with the ratings. A bare chassis weighs nothing compared to the built-out rig. However, once an aftermarket manufacturer then adds enough weight to require the higher running tire pressures I'm flummoxed how they are not required to replace the valve stems that are rated for 80lbs that they themselves recommend right there at the factory.

Anyways, my issue is behind me, but thought I'd share.

Best,
-Mark
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Old 05-12-2021, 01:54 PM   #2
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There are two different types of rubber tire valves , one for cars , another for light trucks , I won't quote max pressures for these , but with the metal tire valves rated to 200 psi. those are the best to use.

Lets see if this link to Tire Rack still works .

http://www.tirerack.com/tires/tirete...jsp?techid=208

Well the link used to go straight to the valve info , not any more. I'll see if I can fix that.

EDIT : Well spelling correctly helps .

Yes , using a tire valve at it's max rating , isn't a good idea .
Safe travels.
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Old 05-12-2021, 07:41 PM   #3
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You might also consider the possibility that your tpms sensor contributed to the valve stem failure. Extra weight on the end of the stem, spinning around with centrifugal force. That's why they have the rubber insert stem keepers. Some tpms systems suggest using metal stems only, for this reason. In any case, you made the right move. What brand of valve stem worked?
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Old 05-12-2021, 11:35 PM   #4
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Quote:
Originally Posted by Grn_Mtn_Boy View Post
You might also consider the possibility that your tpms sensor contributed to the valve stem failure. Extra weight on the end of the stem, spinning around with centrifugal force. That's why they have the rubber insert stem keepers. Some tpms systems suggest using metal stems only, for this reason. In any case, you made the right move. What brand of valve stem worked?
My front tires had valve stem holders/grommets in the wheel covers to help the stems not flex. It was the outside dual stem that blew out though, which was connected to a set of valve stem extenders that were held in place by hard plastic grommets and bolts in one of the wheel holes to prevent any movement or flex. Because the valve stems on outside duals face inward vs outward, a number of manufacturers mount these extenders (that have bends in them) such that you can easily check your tire pressure and add air as though the stem faced outward. It was securely mounted.

That said you are right about TPMS sensors being a cause of valve stem flex if simply put on without stem protection or not on steel stems.

Best,
-Mark
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Old 05-13-2021, 06:37 AM   #5
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Quote:
Originally Posted by MarkMaxPayne View Post
Put over 2,150 miles on the Tiffin Wayfarer in 4 days this last trip. Glad I had my TireMinder TPMS system. Heard what I thought was the furnace kicking on in the back for about 20 seconds (loud blower sound) then my TPMS went nuts telling me I had gone from 80lbs down to 0lbs of pressure on my passenger outside dual. Without the TPMS I don't think I would have known until the inside dual overheated and gave way...

Turns out the valve stem gave up and split right at the rim. There is a brass insert and it sounds like the value stem usually gives way right where the brass starts/stops inside of the rubber stem itself. I've also ran into this issue before on a Dodge RAM towing a 5th wheel (twice) so I've been trying to resolve proactively on my Mercedes 3500HD based RV, but could never find a shop willing to do it.

These rubber valve stems from the factory are only rated around 60-65lbs and when you run them at 80lbs it isn't a matter of if they'll give way, but when. Took me forever to finally find a tire shop willing to replace the rubber valve stems for steel ones. They all acknowledged they had to be replaced, but on the Sprinter rims everybody hates to do it as the working area is so small it is very hard to properly tighten the value stem nut and to install extenders on to that; nobody wants to spend the extra shop time and effort to do it. Also, they are shorter than the rubber stems so some of the extension hoses and angled extensions have to be reworked/replaced to make up for the longer run required. Lastly, even those are a pain to then reinstall given the little clearance for their own tightening nuts at the valve stem due to the very narrow rim clearances where the stem mounts.

I know when Mercedes ships a chassis to a manufacturer, they are in compliance with the ratings. A bare chassis weighs nothing compared to the built-out rig. However, once an aftermarket manufacturer then adds enough weight to require the higher running tire pressures I'm flummoxed how they are not required to replace the valve stems that are rated for 80lbs that they themselves recommend right there at the factory.

Anyways, my issue is behind me, but thought I'd share.

Best,
-Mark
Aluminum wheels and metal valve stems are the best solution.

Why are you running 80 psi in your tires? Every inflation chart I've seen indicates pressures in the range of 55 to 65 psi for the maximum axle weights on my 2020RW Tiffin Wayfarer. I run 60 in the front and 65 in the back.
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Old 05-13-2021, 09:04 AM   #6
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Quote:
Originally Posted by f14av8r View Post
Aluminum wheels and metal valve stems are the best solution.

Why are you running 80 psi in your tires? Every inflation chart I've seen indicates pressures in the range of 55 to 65 psi for the maximum axle weights on my 2020RW Tiffin Wayfarer. I run 60 in the front and 65 in the back.
The sticker inside my driver's side door from Tiffin says to run them at 80 psi. Yes, the Mercedes factory sticker states a much lower rating, but that was for a bare bones chassis before the RV manufacturer built out on top of it.

Best,
-Mark
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Old 05-13-2021, 10:29 AM   #7
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Quote:
Originally Posted by MarkMaxPayne View Post
The sticker inside my driver's side door from Tiffin says to run them at 80 psi. Yes, the Mercedes factory sticker states a much lower rating, but that was for a bare bones chassis before the RV manufacturer built out on top of it.

Best,
-Mark
Hi Mark,
I think you are misreading the Mercedes label. If your sticker is like mine, the pressures shown are for a fully laden (max axle weight) condition. Notice the cylinder images indicating a load. The owner's manual explains the label. Thus, unless you are overloaded, these are the minimum pressure you should run. I add a few pounds for changes in altitude but you most surely no not need to run at 80 psi. That makes for a rough ride, decreases the surface area of the tire that is in contact with the road (decreased traction), may result in uneven tire wear, and is higher than the valve stem rating. 80 psi is the MAX inflation pressure for the tire, not the proper inflation pressure for the tire.

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Old 05-14-2021, 07:53 AM   #8
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Quote:
Originally Posted by f14av8r View Post
Hi Mark,
I think you are misreading the Mercedes label. If your sticker is like mine, the pressures shown are for a fully laden (max axle weight) condition. Notice the cylinder images indicating a load. The owner's manual explains the label. Thus, unless you are overloaded, these are the minimum pressure you should run. I add a few pounds for changes in altitude but you most surely no not need to run at 80 psi. That makes for a rough ride, decreases the surface area of the tire that is in contact with the road (decreased traction), may result in uneven tire wear, and is higher than the valve stem rating. 80 psi is the MAX inflation pressure for the tire, not the proper inflation pressure for the tire.
Yes, I am ignoring the chassis sticker. The NTSB requires that all RV manufacturers add a supplimental label that supercedes that of the chasis manufacturer without obscuring the original. Mine is located inside the front driver's door below that provided by Mercedes. Tiffin's label for my 2018 is attached. It says 80 psi... I'll reach out to Tiffin and see if that is simply the max.

Best,
-Mark
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