Aluminum Valve Stem Caps

bavbob

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OK, I fully admit I am a moron. I bought my sons aluminum "BMW" caps for the valve stems for the 2007 328XI they bought, a gift. My son got a flat and the car has run flats. He came home and I cannot get any of the caps off. Besides replacing the tire, I am now looking at a TPS sensor replacement. We hit each cap with PB blaster to no avail. The aluminum has fused to the brass stem. Anyone have any insight as to how to get these off or are we stuck with at some point, replacing all the stems and TPS sensors?

I put a little anti-seize on the ones on my car at least.....hindsight is 20/20
 

autokunst

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I don't know how to get them off, but my wife can share your pain. She did the same thing with her Jeep and we ended up having to buy (4) new TPS sensors. She now uses plastic caps.
 

day66

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I’ve had a similar issue - I ground a flat down one side of the cap to loosen it - you’ll mark the threads on the valve stem, but you can still get a valve cap on afterwards.
 

day66

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A second thought, it might be worth trying pouring boiling water on them first, the heat might just make the aluminium expand enough to loosen the cap.
 

Arde

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How about hydrochloric acid? It should dissolve the aluminum and make the brass shine.
Option 2 is a new son, as full new wheels are too expensive.
 

boonies

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what about vinegar? With the car off at the upholstery shop I have been puttering in the garage and used vinegar to strip the rust off some old tools and it is quite effective and not very aggressive, so risk of damage is low. You can always move up to something more powerful.
 

dave v. in nc

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Would cold on the brass (keyboard blaster/compressed air), while hot (boiling water/wood burning tool/something?) on the aluminum make one shrink and one grow?
 

bavbob

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Muriatic acid did not work, stems are rubber so cannot use heat. I will try the freezing method.

I just feel like such an ass but at least I caught this when the car was local. Usually my son has the car 400 miles away at college. My biggest fear is having your BMW towed to the middle of nowhere and being at the mercy of Goober Pyle.
 

JFENG

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Bob,
what bad luck, and on a rainy day no less. When are you going to build that 2nd 4-car garage?

I didn't know BMW used rubber valve stems with TPMS. I only recall metal.

You can still grip the rubber stem just below the cap (where there's still brass under the rubber). Just use a layer of something to prevent the plier teeth from cutting the rubber.

(a) give the caps a couple of good sharp taps with a metal object to try to break any galvanic corrosion bond
(b), (c), fugedaboudit
(d) cut the caps off (aluminum is pretty soft stuff), clean up the threads with a dental pick

do you have a dremel tool (I can bring you one with lots of different cutting bits)?

John
 
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