Td5 D2 - Rear Chassis Corrosion

A couple of years ago, (Oct 2015) I was replacing the rear air bags on Hx and became aware of just how corroded the rear chassis surfaces looked!..

Rear o/s rail above,  n/s rail below...

All the factory applied coating had or was in the process of flaking away. Hx was 15 years old at this point and clearly had issues! It was alarming to see the extent and I feared the dreaded tin worm was alive and hungry and the situation could easily end up like this..

Corrosion in the seams and pre-drilled holes...

Two photos of unchecked corrosion on/in the rear chassis rails. Alarmingly, these rails have corroded from the inside out and along the welded seam. Thankfully, Hx is not this far gone!

SPOILER ALERT.

Research around the web revealed some very worrying facts.. Corrosion in the rear chassis rails of D2s is very common! 

It appears that one of the 'improvements' over the D1 was a lighter chassis made from thinner plate. There was never any internal corrosion proofing and externally there was only a thin layer of black paint applied. 

The bodywork on a D2 is much better protected against corrosion then on a D1, yet the chassis is less protected...? Another example of Land Rover's "that'll do approach".

There are plenty of pre-drilled holes in the chassis rails that allow moisture/salt/mud thrown up from the wheels (or wading!) inside to gather and trigger corrosion from within.

Added to this is the open rear end of the rails and the 'c-section' construction of the rails themselves with the internal unfinished side of the welded seam aiding the onset of corrosion by offering a nice damp niche for corrosion to get started...

Two views of the 'open' end of the rear chassis rails on Hx (June 2017). This was only revealed when the rear bumper was removed. 

Corrosion in the rear chassis is a problem with 'elderly' D2s. There lies the problem - Age related degeneration. Sections of the rear chassis are still available at a premium price to enable repairs to be carried out and the chassis life extended. But it is a hefty price to pay...

 A complete rear chassis repair section .... or...

sections of single rear chassis rails (n/s) ..

The three Web photos above (Robisonservice blogspot) showing the replacement rear end rails during fitment. This involves removing the fuel tank, tow-bar and ancillaries, then cutting out the effected chassis rails and cross member before fitting / welding / bolting the replacement sections onto the remaining chassis.

FIGHTING A LOOSING BATTLE.

So what can be done to stave off the enevitable fate? Is it too much to have a fully galvanised chassis?

The best approach for the concerned owner is to be aware of the issue and to regularly check all around the vehicle for corrosion/damage and learn the location of potential corrosion points. This mainly means the rear chassis rails aft of the suspension mounts, any of the 'outriggers' and the inner rail surface near the cat if fitted. (the heat cycle can fatigue the side of the nearby rail)

There are lots of aftermarket anti- corrosion coatings available ranging from chassis and cavity spray coatings to numerous scrape and paint coatings for treating visible surface corrosion.

In the past, I have always gone the scrape and paint route for any visible surface corrosion. Experience has taught me though that it's the corrosion you don't see that will get ya! And of course, once you start treatment, it's a on-going commitment!

So, on Hx, I started getting underneath and having a good look and scrape around. The rear chassis surfaces caused the most concern. After scraping all the loose factory coating and surface rust away as best I could, the first treatment was to use 'Kurust' which promised to convert surface rust to stable iron-oxide. In doing so it halts the existing corrosion process but it is not that effective in preventing 'new' corrosion re-appearing.

Kurust is easy to apply by brush. It has a white milky appearance and is about the same consistency as milk. It promises a lot but comes with the condition that it must be over painted itself to maintain the surface protection it initially offers. I found it to be very effective and left the treated surface with an attractive blue/black finish.

Hx rear chassis with Kurust applied but not over painted five months after application....

Well, after about 5 months (Mar. 2016) I finally got around to spraying over the Kurust on the chassis rails with Pro-Cote Matt Black. The finish was nice and it looked good peeking out under the rear wheel arches. I had thought about using a bitumous 'stoneguard' type under sealer but declined.

There were some areas that I had treated with Kurust that I never did overcoat even to this day. Other treated areas are beginning now to show spots of new surface corrosion peeking through the finish.

Coming up to date (June 2017), during the refurb of the rear bumper, (and after seeing the 'open end' chassis rails) the decision was taken to paint the rear chassis in the immediate area of the bumper with 'Flag' smooth metal paint. This is similar to the 'Hammerite' brand, is solvent based (avoid water-based) and a lot cheaper.

The previous coating of the rear chassis (Kurust and Pro-Cote) was beginning to show some pitting but nothing serious and I'm very confident a thick coating of Flag metal paint will treat it good for at least another 2 years..

Rear chassis on Hx (June 2017) showing surface pitting on the coating of Kurust/Pro-cote 15 month after application. 

Looking inside the open rails, you can just see the ends of the right-angled strips that are welded inside the corners of the chassis rail to strengthen/reinforce the 'thin' walled rails. These strips can, by their attachment, provide crevices and gaps for rust to get a grip...

Roughly the same area treated with Flag smooth metal paint (June 2017). The hydraulic rear step arm is visible at the bottom of the photo and the rust colourred area on its upper surface is original and completely untreated left as a kind of experimental 'control'.

Hopefully, I will be sufficiently enthused to get down under and Flag the rest of the rear chassis, axle and suspension arms, in fact everywhere that I had previously treated with Kurust.

A GALVANISED CHASSIS...?

It seems the only sure way to guarantee corrosion is kept away is to galvanise the chassis. This basically involves a total rebuild, crazy money and massive conviction. Even then, it's recommended not to galvanise an old chassis but to purchase a brand new one. And they are available 'hot dipped' for around £3k.

I recently bought a can of  'Cold Galvinating Spray' to experiment with. It offers the same protection to bare metal as the 'hot-dip' process. To be 100% effective it has to be applied to clean fresh metal. Finding such on a 15 year old chassis is a big ask, but it can be applied over a 'prepared' surface and it can also be over painted.

It's main use is for repairing a hot dipped chassis when holes are drilled in it and the Galvinating protection is broken through.

I did intend using it on the rear chassis behind the removed bumper but felt a good thick coat of Flag metal paint would be more practical.

There is better access to the chassis rails forward of the rear axle. They appear to be in much better condition and could be a good candidate. 

I read a really good article about galvanising and thought I downloaded it, but sadly its lost to the Internet. It was a question and answer article that helped convince me to have a go..

RUSTPROOFING THE RUNNING GEAR.

Here is a photo of the rear axle on Hx (Oct 2015). All the loose flaky factory paint coating was removed and surface rust rubbed back. As an experiment, some Kurust was then applied to the o/s and the Diff casing. That is the dark coloured patch on the Diff casing shown above. The n/s of the axle was left untreated. 

After six months the axle looked like this. After another rub-down the rest of the axle and the sway arm was coated with Kurust. Time for an update me thinks.....

Photo above taken June 2017 which is about 15 months since the 'rusty' areas were coated with Kurust, (but never over-coated) I can see the need to rub down the surfaces again and either retreat with Kurust or go straight to Flag metal paint....

FURTHER READING ..

robisonservice.blogspot.co.uk

The online blog of J E Robison Service., it is full of good stuff with two in-depth blogs dealing specifically with the D2 rusty chassis issue. (grabbed some photos from there!)

www.galvanic 200.com>docpdf>20

A 9 page Q+A all about Cold Galvanising from 'Bio-Direct'.