Doing some transmission work on my Mercedes. The pan is secured with aluminum bolts and new ones come in the filter kit so no problem. The valve body is also secured to the transmission with aluminum bolts, ten of them for at nearly $3 each. They can't be reused as I assume they get stretched, but why use them in the first place?
Why aluminum bolts?
- Thread starter atikovi
- Start date
Are you sure it's aluminum? A lot of German application bolts have a silver anti-corrosion coating on them.
Unless it's non-magnetic titanium, which at $3 it isn't, it's aluminum.
It's probably more of a galvanic corrosion between the magnesium case with aluminum bolts vs steel bolts
could be stainless.
torque to yield one time use bolts.
You never really know with the Germans, what with their patent system and royalties from patents as well as the necessity of keeping proprietary systems proprietary so that the reason is esoteric in nature.
Just another way of saying will never know why those people did it that way but they had their reasons..
Not stainless either.
The bolts ARE aluminum.
All of the German auto manufacturers are using one-time-use aluminum bolts in their engines and transmissions. BMW is famous for this. I could be wrong but I personally believe that this is directly responsible for the German vehicle's propensity to develop fluid leaks.
All of the German auto manufacturers are using one-time-use aluminum bolts in their engines and transmissions. BMW is famous for this. I could be wrong but I personally believe that this is directly responsible for the German vehicle's propensity to develop fluid leaks.
then most likely explanation was torque to yield... with their own fuggin patent and licensing reasons.. or as my brother the automotive engineer says, in Germany those individual engineers get to patent their little design and get royalties, so that is probably the best explanation. Not too mention since this crap is most likely proprietary you end up buying it from them, as well and maybe needing a special tool.. Does it need special tools or did you luck out on that end?
of course it wouldn't be impossible to substitute standard bolts assuming they dont have proprietary thread design... ( since its the futzing German's you can almost bet it is. LOL ).
FWIW is it a ZF transmission. ZF builds most of that stuff in Kraut industry..
dnewton3
Staff member
The only thing I can think of is the topic of dissimilar metals.
Alum bolts into alum cases makes for less concern than steel bolts galling or otherwise fouling the case threads.
Alum bolts into alum cases makes for less concern than steel bolts galling or otherwise fouling the case threads.
You must use stainless steel with aluminum. That's $$. I'd be surprised if the bolts in question were TTY but it's possible. Some ZF units have TTY.
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Aluminum (alloy) doesn’t have a well defined yield point like steel. It would probably fracture. Corrosion resistance is the likely reason for use (and weight) and the one-time use is probably because they are afraid of galling, broken threads and rounded bolt heads.
Only some ... For example with ZF. Steel bolts - 10 nm. Aluminum bolts - 4nm +45 degrees
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they used to have ZF's so My Bad.
not that Mercedes building their own is actually any better, not when it comes to the service side of things.
Benz has the same Germanic propensity for propriety parts, service info and specialty tools
Esoteric stuff.
most automatic transmissions have steel based helical type inclined plane fasteners in aluminum cases.
You big bang theory guys will know what I mean.
I changed the pan bolts because they came with the kit. The ones that came out looked fine compared to the new ones so I kept them for spares. If they hadn’t come with the kit I would have reused them. I think they use them because of the dissimilar metal corrosion thing. The probably make you replace them because they’re easier to damage than steel. 08 c300 7sp. I reused the bolts in my Audi zf6hp fwiw.
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Could it be to avoid zinc plated fasteners? I have heard of industry/regulatory initiatives to eliminate zinc plating.
Welcome to the subtle joys of MB ownership. It's designed to make you feel better about your tranny service.
