Rear diff lock actuator...

[Chris5-7chev]

Ok hands up all those who 'googled' sacrificial anode thanks to Mr Sideways suggestion?? I did even though heard of it
before but never really understood it, so apparently this will work in air as well as water.
Does this mean anything alloy under the car is likely to corrode faster than the steel parts all around it?
Any other examples? all I can think of are ally wheel cyls. in drum brakes which seemed to deteriorate fairly rapidly.
If only Mr T had made our actuators in steel, we'd all still have working lockers maybe.
Some nice motors there Lars, like the 100.

Chris S.

 

[Towpack]

A sacrificial or galvanic anode would not work on a car as it does on a boat or outboard motor for obviuos reasons. The only effective way to stop the electrolytic corrosion of alloy car parts is to insulate them from the parts made from ferrous or any other metals at the other end of the galvanic scale, as the builders of alloy bodied/steel framed vehicles do.

 

[IRLGW]

I always use Durlac ( isolating paste) when bedding different metals (in this case will use it when rehousing the actuator to the diff etc). It comes in a tube but we wary of getting it on any painted surface or anywhere you dont want to be marked. You can apply it directly to the metal and then use a sealant/gasket as normal if required.

http://www.marinesuppliesdirect.co.uk/d ... -428-p.asp

http://www.silmid.com/Products/Surface- ... 00500.aspx

 

[Cptsideways]

Sacrificial Anodes are difficult to make to work on a car, (generally) but Toyota somehow managed it!

If someone did the analysis on the material I guarantee a difflock housing is made from exactly the right stuff.

some info on it I dug up

Choosing Between Aluminium and Zinc
Zinc has been in use as a sacrificial anode for longer than Aluminium and is considered the traditional anode material. However, aluminium has several outstanding advantages as a sacrificial anode material and is fast becoming the material of choice.

The efficiency of an anode material depends on its electrochemical properties. There are two electrochemical properties that are of relevance: the first is the material?s open circuit potential and the second its electrochemical capacity and consumption rate.

The open circuit potential is the potential the anode material develops when immersed in an electrolyte. For Aluminium it is 1.05V to 1.07V while for Zinc it will be 0.95V to 1.0V. Thus Aluminium can develop 50V to 70V more than Zinc and this makes a significant difference in their respective current delivery capabilities with Aluminium capable of delivering more current.

Secondly Aluminium anodes can develop 2500 amp-hr of current for every Kg of material that it sacrifices while the comparative figure for Zinc is 780 amp-hrs. Higher the current capacity lower is the consumption rate. Thus 3.4 Kgs of Alumnium gets consumed for generating 1-amp of current for 1 year while the corresponding figure for Zinc is 11.2 to 11.5 Kgs! Thus a lesser mass of Aluminium anodes will protect a given surface for a given period of time as compared to Zinc anodes. This l

 

[Lars Bo Kjeldstrom]

This turns out to be quite interesting now Now I understand better what happens to these alloy parts ....

Once I experienced that the casing on the winch motor came apart and the crumbles landed on the floor of the landcruiser house (garage!)...lots of fresh air for the motor ....We were several guys who got a replacement for free (it was about 2 years old), so appearantly an unlucky combination of materials?

Also the "thing" on the backplate of the rear brakes, where the cable enters, is continuously deintegrating and siezed up. This is one of the few points where the 100 will fail you if not maintained

If this is correct would it then be a good idea to get the alloy parts eloxy-plated (if thats the right term?) like my portable saw mill

-and thanks Chris for the kind words...I will pass them on to the car ...I thought "sacreficial anode" was a cool expression, hence the new name for diff lock actuator in my post....

 

[Andrew Prince]

I guarantee a difflock housing is made from exactly the right stuff.

Really? Surely the neatest solution from an engineering perspective is to avoid galvanic corrosion first and foremost? I "guarantee" that Mr T did not intend the actuator housing to be a sacrificial anode - very easy and cheap to have located a small billet of ali somewhere for that purpose if the design required there to be potential differences all over the body due to different metals being used.
There must be a reason that Mr T chose a non-steel material for the actuator body, perhaps ease of casting and lightness and therefore cost versus cast steel. But to guarantee that it's the right stuff? Perhaps for the accountants tallying up the pennies when the design was costed

 

[Cptsideways]

I guarantee a difflock housing is made from exactly the right stuff.

Really? Surely the neatest solution from an engineering perspective is to avoid galvanic corrosion first and foremost? I "guarantee" that Mr T did not intend the actuator housing to be a sacrificial anode - very easy and cheap to have located a small billet of ali somewhere for that purpose if the design required there to be potential differences all over the body due to different metals being used.
There must be a reason that Mr T chose a non-steel material for the actuator body, perhaps ease of casting and lightness and therefore cost versus cast steel. But to guarantee that it's the right stuff? Perhaps for the accountants tallying up the pennies when the design was costed

The right stuff for the wrong reason

 

[BobMurphy]

The right stuff for the wrong reason

Look on the bright side . . If you're stuck with flat batteries on a dark night, just bridge across the Actuator and the Axle and light your LED torch.

Bob.

 

[Chris]

I understand sacrificial anodes (no I didn't have to Google it, I just paid attention in physics classes) but I am not completely convinced that this is the only force at work. However, I don't feel that strongly that I want to have a punch up over it. But - let's say we'd taken a DLA and hung it on a piece of string under an 80 seventeen years ago. Are we saying that by simply not being connected (bolted) to a dissimilar metal, that it would look like the day it came out of the box? I think not. Some of this has to be simple surface corrosion too. Aluminium (oxide) is a very stable compound but hardly wear resistant and the DLA is in quite a vulnerable position. As I said, whilst I do support the whole dissimilar metal and electrolytic action with salt solution trapped behind the motor and axle, it's not the only cause of early demise, is it. Not all of them go. Mine looks in very good condition and it's just as old as most of the others (1994) so the passing of time isn't the only factor, clearly.

But having said that, they don't do bad really. All they need is a really good coat of paint or lacquer when you put the new one on and I'm pretty sure that it will then outlast the rest of your truck.

Chris

 

[Julian]

If it is bi-metallic corrosion, it would be accelerated by exposure to salt
It is a pretty regular occurrence in the boating industry and can be combated by something as simple as lanolin

Or
http://www.intek-uk.com/duralac.htm

 

[Chris5-7chev]

Physics lessons?? not easy to "pay attention" couldn't hear what the teacher was saying, the corner shop and local
canal where just too far away...........
Lots of knowledgable people here especially Capt S.,

Going to replace it soon, can't wait to clean it in a glass bead cabinet.
Chris S.