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Stainless Steel & Aluminium galvanic reaction ?


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I read this a while back from the Elise pages:

http://www.elise-faq.info/content/bodywork/corrosion.php

Obviously on an aluminium car it's a bit more of a problem than on the Esprit.

Thing is I'm working with the rear hub atm which looks to be of aluminium (or at least I've been led to believe it is). If I put the new bolts back in stainless steel am I chancing my arm against this corrosion ?

I wont be screwing into any ali but the stainless is in dorect connection with it.

I always use copper grease all over my fixings to aid them in rotation and prevent them from fusing and corroding but will this help in this case.

Washers against the hub arn't a big deal becasue they will be painted both sides.

The main issue is the bolt shank against the ali bore as the thing sits in place, it should be sealed inbetween the washers from any water ingress but will that stop it ?

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I read this a while back from the Elise pages:

http://www.elise-faq.info/content/bodywork/corrosion.php

Obviously on an aluminium car it's a bit more of a problem than on the Esprit.

Thing is I'm working with the rear hub atm which looks to be of aluminium (or at least I've been led to believe it is).  If I put the new bolts back in stainless steel am I chancing my arm against this corrosion ?

I wont be screwing into any ali but the stainless is in dorect connection with it.

I always use copper grease all over my fixings to aid them in rotation and prevent them from fusing and corroding but will this help in this case.

Washers against the hub arn't a big deal becasue they will be painted both sides.

The main issue is the bolt shank against the ali bore as the thing sits in place, it should be sealed inbetween the washers from any water ingress but will that stop it ?

You probably don't want stainless steel in suspension bolts. Stailess steel is weaker than Grade 8 or Grade 5 (Grade 8.8 or Grade 10.9 metric system)...

Travis

Vulcan Grey 89SE

My Lotus Photo and Projects Album

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I'll post a picture up tonight of the job. main reason why i use stainless everywhere is I do a lot of home maintenance and tinkering and I cannot stand rust / corrosion.

I thought the sheer strength of stainless was comparable to mild steel if not better ? If the bolts are tight then there is a lot less load on the bolt and the break would have to sheer it straight across which is highly unlikely I would have thought - not 100% which is why I ask. I've busted plenty of mild steel bolts but never any stainless ones.

I may leave the lower stud (one that holds the damper to the hub) original but I can't see much wrong with the rest such as the radius arm to hub carrier and the links to chassis.

Either that or I'll get some new bolts and galvanise them.

Either way just found out the upper link has a reverse thread on so that's got to stay as well now <_<

Any info is appreciated.

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strength is a misleading term. bolt ratings are more a reflection of how much the metal flexes. mild steel won't flex as much and tends to shear. you can't use the same torque settings if the ratings aren't the same. ratings are standardised though, so trust the numbers.

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I have noticed a great deal of variation in SS alloy mixtures between countries and between companies. As a result, do not trust any general rule about fastener strength (e.g. SS is ALWAYS softer than mild steel, etc.). Ask for the manufacturer's MSDS test results from your hardware supplier. These should be trustworthy.

In some cases, a great variation in SS fastner strength appears to be how much metal the manufacturer puts around the countersunk head (especially in the case of allen-head screws). Some Asian firms I have used (these supply Japanese motorbike tuners) have very skimpy bolt heads . . . the head height is shallow and the head diameter is 10-15% diminished. Perhaps this is for weight reduction in racing. Regardless, you can easily internally strip such a screw head though in doing so the strength of the threaded section is uneffected. Drilling the screw's head out, removing the static piece and using vicegrips is unscrew the threaded bit is the only easy way to service the assembly.

In nearly all cases I use low-temp Loctite as a preventative measure for galvanic corrosion in alloy assemblies, copper grease in frequently serviced items (e.g. rear wheel bearings), and ceramic grease (wildly expensive) for extreme high temperature conditions. In the end I think the Lotus factory used none of these measures. I had to drill out half of my rear wheel bearing allen-head fasteners to replace the bearings. The same thing happened on the from main seal housing. Any quality SS part with some measure of corrosion protection in better than the untreated steel fastners Lotus usually use.

But maybe I worry about these things too much.

AP

Edited by andrewp1989
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I just read a good article about it with normal stainless coming to grade 2 compared to grade 5-8 of carbon steel...good job I stopped here, they showed what happened with suspension and brake system with standard stainless bolts <_<:D

*ping*

Washers and nuts are probably safe, I'll just paint the heads when they're in place with that fantastic paint of mine :P

I'll just have to suffer the rest and keep it clean.

Thanks for the info, learning all the time !

Edited by Jonathan

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Just thought I'd mention it, stainless steel does not have any reaction with aluminium, full stop. Mild steel, galvanised steel and porrly coated/ treated steel however does cause a reaction that is called electrolytic corrosion. I know this to be true because I work with aluminium, galvanised steel & stainless steel all the time and have done for the past 17 years. To prevent this accelerated corrosion between glavanised steel and aluminium, you use stainless steel fasteners. If you have two metals touching then you have to isolate between the two with something that doesn't react. I don't know if copper slip or other similar copper based product reacts with any of these other metals so I won't comment on it.

I have to admit that I have not come across the term of galvanic corrosion before. Is this something different to electrolytic corrosion or is it simply another term for the same process?

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