Galvanising front and rear subframes
 

My recently purchased 2.8QS needs a complete front & back control arm and shock absorber set and seeing as both subframes are quite rusty on this almost 20 year old car I was also thinking of getting them sand blasted and galvanised.

Have any of you done this?

I don't want do do powder coating as its not as permanent and protective as galvanising.

Any opinions?

Interesting idea. The only challenge I see with it is that the bushes are pretty much unobtanium now, and you'd need those out to hot dip it otherwise they would just burn up. IIRC I bought the last full set of S8 bushes with the last subframe I stripped, but the 2.8 bushes may still be around somewhere. If you can find them and are willing to spend the cash then go for it.

Generally I just blast and re-paint with something like Rust-oleum combicolor when the bushes are intact. I agree powder coat is definitely not tough enough for a job like this - it tends to flake off the sharp edges and welds quite easily.

I looked into galvanising when I had my subframes replaced a while ago but decided to go with a coating of POR-15 instead.

I really like the idea of galvanising the subframes. I managed to get hold of a pair of very good condition front and rear subframes last year. Both have very little corrosion and are ideal for galvanising.

I managed to get hold of a full set of bushes actually quite easily. The fronts (8 of them) from Audi main dealer and the rears (4 needed but 2 different part numbers) from ECS Tuning in the US. Except to pay good money for them though. I think mine were around £700 for them all.

Removing the old bushes is also a challenge. Especially the front ones as they cannot simply be pushed through. I managed to get hold of the genuine Audi tools for removing the bushes but I still had to do some improvising.

When I get done with my rear suspension refurb in the spring I'll start to look at getting the frames galvanised or some other suitable coating. I want something that involves "dipping" as the frames are hollow and painting the inside would be difficult.

You bought the last set then +++ I know when I asked recently there were three left. Fat lot of use that is!

According to my info the pn for the bush is 4D0399415K and its shared between phaeton and found lots of them on ebay?

My plan was to buy the 2 subframes from forum sponsors then get them galvanised and then give it to my mechanic, this would avoid the car being in bits for probably weeks.

These are the 2 subframes I bought as spares. As you can see they are in pretty good condition already. I was in no rush so I held out until I found some that came from a dry climate.

I can't remember where the front one came from but it was somewhere in Europe. The rear came from southern Italy, a nice dry climate.

All the UK ones I looked at seemed pretty rough.

Wow thats a good tip, to buy some from a warm country. Those look like they were taken off a 3 year old car or less!

Tread carefully with hot dip galvo, it's hot, really hot and can cause deformation. I'm fairly familiar with the sub frames can from memory they have holes everywhere and that's good as it'll explode if there are any pockets. Also anywhere that is a tight fit before will be tighter after dipping, it's quite a thick coating.
Lastly choose your galveniser wisely, some are rough even for ships, Crediton are OK depending on when they last changed it out as they are a bit agricultural toward the end it can be lumpy and thick.
We would send stuff to Liverpool from Devon

Thats the A8 V8 bush. The S8 version is L and I think that's used on various Bentleys too. The A8 V6 bush is F - not sure what else that might be found on, maybe the V6 Phaeton?

The subframe will probably need dipping in something to strip it in the first place to get all the paint off the inside too. Sandblasting won't work for that, and I suspect molten zinc may not respond well to paint. I'm not sure what sort of hellacious paint stripper you'd need to get the factory coating off because its amazingly tough. Except where its rusty :rolleyes:

I'm a fan of POR15 too. I'm planning on painting the '65 Chev frame with it eventually. Very tough and it can be sprayed or brushed depending on preference.
You can also get zinc rich primers such as Galmet, for addition corrosion resistance.

Also not a fan of powder coating. It has one significant flaw, once it chips, it may as well not be there as far as corrosion is concerned!

If you're concerned about the heat, instead of hot dipped galvanising, you could use a sacrificial annode? Works for bridges and ships (and one fancy looking opera house in Sydney).

As it happens I once used to work as an apprentice in an aerospace electroplating company and once in a while we would get company's boses mates ask for their jag suspension parts to be cadmium plated.
We would first degrease them, then sand blast, then rinse and then leave in highly concentrated hydrochloric acid for 10 minutes (the stuff was so strong it would go through you if it dripped onto your body) and then it would get plated.
Hot dip galvanising is a totally different process but preparation should be the same.


I rang about for a few quotes and the cheapest I got was £900 for the single front subframe which is nuts!

I will ask my contacts in Poland maybe they can find a place that does it really cheap, but already this idea is starting to look very expensive and long winded.

£900, wow! I didn't expect that. Well that is a real shame. I had almost convinced myself to get one done this summer and was actually looking forward to seeing how it turns out.

It's still cheaper than getting hold of a new one (rear) but that's a big chunk of cash. I was kind of thinking £400 or so. Guess it just shows I know nothing about galvanising.

Does Cadmium plating still exist? Extremely toxic isn't it?

We used to get blokes asking for "Cad plated" bolts when I worked in that industry.
What that usually meant was bright Zinc plate. But sometimes they specifically wanted yellow Zinc.
There was a belief it was a better coating. I was never sure if it was due to being fractionally thicker, or less reactive with the additional chemical treatment to turn it yellow, or whether it was just the placebo effect?

Galvo process is a caustic bath, rinse, pickle, rinse, flux, galvo dip.
From memory the zink bath is around 500c

We know the areas they tend to go, and as they seam to rot from the inside out we can repair these before going to dipping to help prevent and distortion where it might be a bit thin.

And £1000 yeah right oh. We get charged on weight, A farm gate is heavier than a subframe and you can buy one of those for about 200 quid brand new, galvanised.

Yes Cadmium plating still exists and yes it causes bone cancer, hair loss to name a few.

On its own cadmium plated components are light gray and you passivate them in chrome which causes them to go yellow. A 10um coating can whitstand 10 000 hours in a 60C salt bath which translates to many many years of normal use in a car without any corrosion as long as there's no mechanical damage to the coating.

Here are some pics of the jag parts before and during plating. Once again this was a one off favour for the company i used to work bosses mate:

https://i.imgur.com/Sj3p5QZ.jpg

https://i.imgur.com/WXXGWY4.jpg

I've spoken to another hot dip galvanising company who said they would not do the subframes as the holes in them are too small to allow for air to escape as soon as they are dipped in the 450-500C vat which would cause an explosion or deformation.

They also said the best course of action is to sand blast it then get it powder coated to a rough finish and then paint it with some proper boat paint for best result.

They also said that its the temperature shock which can warp and cause the subframes to crack and that ovens that poweder coats use heat up gradually to completley avoid this risk...

so it looks like a no go unless someone else has a better idea?

I'm sure I mentioned that.

The holes issue is not a problem as long as there is a hole. I use a 6mm dia hole in 42.2 o/d heavy tube ships hand rails, drilled on the underside of tube right where its welded to the last stanchion. That hole is big enough to let the air escape as it expands. So the big holes in the subframe will be fine. Distortion however is another thing all together and I don't know how you'd control it. Still think a basic steel jig to check after, it would be interesting to try one. You can buy brnd new glavo chassis for a land rover be interesting to know how they manage it.

Marine paints need a full application to work, I have Jotun primer I use at home. It's thick and needs thinning to use, also goes off quick throw the brush away job. It's a zink rich primer and I rate it. Pop round with a jam jar or 2 and I'll fill them for you.
Top coats are all different, under the waterline ships use an antifouling paint, that would useless to you. Above waterline it rots fast, anyone that has been to sea on a ship will all say the same, its a constant battle. International, hempel, jotun all do good emamel topcoats but I really don't think it'll help the rotting from inside out.
Do what they do with Land rover chassis, waste oil and diesel mixed.