WBX Gearbox starter earth bypass cable

An alchemy of sparks, copper wire and earth

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itchyfeet
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Re: WBX Gearbox starter earth bypass cable

Post by itchyfeet »

irish.david wrote:At no point did i say that there wasn’t going to be localised galvanic corrosion due to normal corrosion that you’d see anywhere where dissimilar metals meet.

“The electrolyte is present in the form of salt crystals”

Salt crystals are not an electrolyte


I think the point that we disagree on is how much the effect of the DC current from the alternator flowing between the metals will have on the corrosion process. I don’t think it will have any noticeable effect and you do.

Dave

ok so open for debate on effect of dc current but whats clear is corrosion is a problem, if we can reroute the earth we can insulate the disimmilar metals and slow corrosion.
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Re: WBX Gearbox starter earth bypass cable

Post by ghost123uk »

Hey Paul, wouldn't you have to use plastic bolts as well?

I think it's because there's nowt good on the telly :lol:
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Re: WBX Gearbox starter earth bypass cable

Post by itchyfeet »

ghost123uk wrote:Hey Paul, wouldn't you have to use plastic bolts as well?

I think it's because there's nowt good on the telly :lol:

no not strong enough, you just have to reduce the contact of dissimilar metals, you can't remove it totally.

I'm told by my companies specialist on this (we make external products with aluminium and steel that get put by the coast and suffer also) that the dissimilar metals don't have to be in contact to corrode, close is enough, so the thicker the nylon washer the better, I think one on the nut side too will help ( reduces the volume of steel in contact only stud then in contact) then nyloc nuts.
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Re: WBX Gearbox starter earth bypass cable

Post by Aidan »

irish.david wrote:Galvanic corrosion is only an issue when there are two dissimilar metals that are linked with an electrolyte. It's a big issue for ships with metal hulls as the sea water acts as an electrolyte and and you get electrons flowing from the metal higher up the galvanic series to the one lower down. The solution for ships is to fit sacrificial anodes which are designed to corrode and be replaceable at set intervals, or an impressed DC current system to counteract the flow of electrons that causes corrosion.

The good news for your gearbox, galvanic corrosion isn't an issue as there isn't an electrolyte between the aluminium gearbox and steel body to allow ion migration between the two. The only issues you might have are where there is physical contact where you get the standard reaction between dissimilar metals, but most of these points are fitted with vibration mounts which act as a galvanic barrier and the others (such as the earth cable connections) are easy to take apart and clean from time to time.

Long story short, the corrosion on your gearbox is nothing to do with your earth connections.

Dave

sorry I have to disagree, the constant 12V potential in the presence of salt water film across disimilar metals causes corrosion, with the mag ali alloy case being the sacrificial and the steel plate taking the metal salt. This is aided by the reverse switch being permenantly live so when damp lallows a path for current and the resulting corrosion at the case join with the reverse housing is such a problem that vw intoduced an additional thick oversize paper gasket to reduce the effect in 1989 by which time they had seen lots of rotten cases

It is a major problem with the 5 speed boxes as the mount is only 1mm or so from the case so provides the perfect void for the salt water film and subsequents salts built up and enhance path for conduction, the stand offs on the 4 speed end case are more substantial but you will often seen quite bad local corrosion around the 4 studs and it is not from the studs but from the plate - I have seen dozens of rotten unusable cases becasue of the corrosion and get half a dozen requests for end cases for 5 speeds from other repairers every year they will concur with what I find

the earth strap is only located where it is for ease of assembly of the vehicle on the production line as it shares one of the mounting bolts when fitted to the chassis so meant one less thing to attach and thus saving 30 seconds per vehicle x 2.5 million vehicles equals a few lifetimes of assembly workers, wages and benefits and pensions

personally I'd just drill and clean up the body close to the starter and bolt through and fit a short strap direct from body to starter motor stud - obviously necessitates a 10mm round terminal and there isn't much spare thread, so it can be easier to go with the top bolt at the nut end and use the cable terminal as the washer, just be aware of the water pipes, and live cables and ensure no mechanical interference or uninsulated conductors

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Re: WBX Gearbox starter earth bypass cable

Post by ghost123uk »

itchyfeet wrote:
ghost123uk wrote:Hey Paul, wouldn't you have to use plastic bolts as well?

No, not strong enough,.

It's tomorrow morning now, so the impetus has faded. It was a joke :wink: :roll:
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Re: WBX Gearbox starter earth bypass cable

Post by silverbullet »

Time that a good end case went to a foundry for remanufacture then.

Galvanic slight return:

Every single time you start up your engine, the entire drivetrain sweats, (inside and out) as the temperature passes through the dew point.

Heat, moisture, evaporation, salts, DC voltage.
20+ years of this treatment and now its only getting driven occasionally and parked on grass for days?

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Re: WBX Gearbox starter earth bypass cable

Post by California Dreamin »

Aidan...starter mounting bolt to chassis led..exactly where I put mine and where I would recommend others to use.
You can never have enough earths lol....beneath the coil on mounting to the engine (flat braided copper cable) problem is, over the years the smaller cables turn to dust or fray directing even more load through the remaining engine to chassis earth cabling.

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Re: WBX Gearbox starter earth bypass cable

Post by CovKid »

And the earth should (as you pointed out elsewhere) at least equal the type used for positive cables/leads. I reckon mines OK but since all the upgrades I did this year, I'll be fitting a new one anyway. Now wheres that soldering iron..... :roll:

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Re: WBX Gearbox starter earth bypass cable

Post by California Dreamin »

I'm all for big fat cables, however, the leisure battery really doesn't require anything like those on the starter battery. The ones on the starter battery supply anything between 140 - 190 amps (for a Diesel) on cold start. The leisure battery on the other hand is unlikely to ever see more than 40 amps TOPS....through the split charger when flat.
I would suggest that 60 amp cable would easily suffice.

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Re: WBX Gearbox starter earth bypass cable

Post by CovKid »

Well yes, but I think leisure batteries a different topic.
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Re: WBX Gearbox starter earth bypass cable

Post by California Dreamin »

CovKid wrote:Well yes, but I think leisure batteries a different topic.
Indeed ..... who was it posted the picture of a leisure battery hmmmm?

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Re: WBX Gearbox starter earth bypass cable

Post by itchyfeet »

Thanks for all the comments.
I'm looking for a solution that anybody can and will do and so I think drilling holes and removing paint may put some off so I'm going to try the bypass to the origional earth and see how it works.
Yes it's a longer path than drilling a hole but the origional fixing is m8 threaded and looking at the condition I'd say its been corrosion protected somehow.

So I ordered a 915mm m10 to m8 ring in 25mm2, it's a 10mm diameter and I will route over the box
I also ordered m10 nylon penny washers, these are 30mm diameter and 2.5mm thick
Because I think the nuts may not hold a torque I orereded m10 nyloc nuts.
all in about £15.

Will post a couple of pics when fitted.
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Re: WBX Gearbox starter earth bypass cable

Post by CovKid »

Leisure battery??? Thats my starter battery. :roll:

California Dreamin wrote:
CovKid wrote:Well yes, but I think leisure batteries a different topic.
Indeed ..... who was it posted the picture of a leisure battery hmmmm?

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Re: WBX Gearbox starter earth bypass cable

Post by California Dreamin »

itchyfeet wrote:Thanks for all the comments.
I'm looking for a solution that anybody can and will do and so I think drilling holes and removing paint may put some off.


Will post a couple of pics when fitted.

No drill holes! there are several suitable pre-drilled holes on the chassis leg parallel to the starter motor location...definitely no need to drill anything. Yes, scrape around the hole to bare metal, but once the new earth strap is fitted a quick daub of paint seals it. To be honest, any new location will require a good scraping back to brite metal, whether its painted or not.

I'm sure your method is fine but like I say...don't be put off fitting an earth from starter mounting bolt to chassis... it definitely doesn't involve drilling holes.
Strap is 14 - 16 inches I think (will have to measure mine) 8mm eyelet to chassis & 10mm eyelet the other end to starter mounting bolt. Electrically, this is an ideal place for the strap, however, it will be subjected to 'engine movement', hence the importance of using a flexible braided earth strap or multi-stranded flexi wire (braided 'tinned' is best)

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Re: WBX Gearbox starter earth bypass cable

Post by itchyfeet »

Don't suppose you could run to a pic of where you joined yours please Martin?
Would be interesting to see alternatives positions that work without drilling.
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