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'.

Td5 D2 bodywork - Rear Bumper repair

The factory fitted rear bumper is a one-piece wrap-around unit made of lightweight moulded plastic on a strengthened GRP frame. There are two adjoining 'corners' mounted separately to the bodywork above the bumper unit either side of the rear door.

The design of the bumper incorporates two 'chins', a moulded checker-plate tread pattern section on the top surface and embossed 'Land Rover' lettering between the two chins.

Apart from being faded in tone, the bumper on Hx has some wear and tear issues which are effecting its fit and appearance.

This is the n/s rear quarter showing the scar from 
some collision that I honestly can't recall. Although only cosmetic, It has been strong enough to dislodge the bumper body from it's fitted position.

This view shows the gap that opened up with respect to the corner trim. The visible screw head helps locate the corner trim in position on the bodywork and it is not connected to the bumper body.

This view of the rear n/s top surface shows the start of the moulded checker-plate section, but also hints at the deformation or 'twist' in the outboard bumper section. It is also a good indication of the faded tone of the bumper surface.

Also shown is the seperate corner trim and the rubber bridging mat at the base of the door. These parts will need to be treated separately.

Compare the previous images to this one of the o/s rear bumper fitting. This is much better in terms of the fit and alignment with the bodywork, though it does display a couple of deep scratches and is visibly faded in tone.

On its top surface, the o/s does have a small crack on its surface that will need a repair.

REMOVING THE BUMPER.

Surprisingly for its size, the whole one-piece rear bumper is only held on to the chassis by two 19mm bolts. That means the corners of the bumper are really just 'floating' over the bodywork and are not directly attached to it. That arrangement probably leads to all the damage that can be done if the edge gets snagged while off-roading. I have seen many examples just get ripped away from the bodywork and that is probably why a serious off-road bumper is a good idea for the adventurous!

The bolts are located behind the inset light units and require the light units to be removed first.

The light units are held in position by a strong spring clip on the inner edge of the unit that is easily accessible from behind the bumper and once compressed the whole unit will hinge away from the outer edge allowing easy access to detach the electrical connector immediately behind the light unit.

With the light unit removed access is available to the 19mm mounting bolt.

This is the offside bolt and it screws into a 'captive nut' welded to a rear chassis mounted outrigger.

It can be seen how corroded its surface was and the nearside was the same. They both were extremely tight/siezed and required plenty of magic spray and a big breaker bar to get them to shift. Thankfully, neither the bolts nor the captive nuts sheared off! When it came to re-fitting I decided to replace the original 19mm bolts with suitable replacements from the spares bin. The torque wrench setting is 45Nm.

Once the two 19mm bolts are removed, the whole bumper is free to de-mount from the chassis. There may be a couple of plastic wiring harness clips mounted to the inner brackets of the bumper which need to be detached as well before the unit comes away freely (Hx does not have parking sensors). It is not heavy and can be removed without catching on the fitted tow bar plate.

The n/s mounting bracket welded to the chassis. The bolthole on the left is the attachment point for the bumper.

The o/s mounting bracket. The right-hand hole is used to attach the bumper to the chassis.

Surface corrosion is apparent, but more alarming by far is the 'open' ends of the rear chassis rails! 

The 'open' rear offside chassis rail.. the grey cabling is for the tow-bar electrics.

The 'open' rear nearside chassis rail....

mounted below it is the arm for the rear hydraulic step.

Can't believe the chassis is finished like this!

A real case of the old Land Rover 'that'll do' 

approach, 'they'll never see it anyway'!!

Another image from the Web showing the same area on another D2. I was keen to see if all D2's are built this way...!!

I know that the rear chassis cross member and outriggers are known corrosion kill points on elderly Discos and I'm now wondering if this is the reason.

A new rear chassis section is still available, and the chassis rail ends are also 'open'!

Starting to wonder why this is so?, I mean, joking aside, the designers can't simply have forgotten to close off the end rails...

The bumper mounting brackets can be seen at the very end of the chassis rails next to the open rails.

REPAIRING THE BUMPER.

Having removed the bumper assembly from Hx it was possible to study its construction and understand why it wasn't sitting properly when mounted.

The bumper unit has a plastic moulded outer surface that is attached to a reinforced GRP frame that incorporates the mounting points.

First thing noticed was some of the plastic connectors holding the assembly together were snapped or missing. They are the generic 'rivet' style and some replacements were sourced from e-bay. I managed to remove 3 connectors from the lower surface and re-use them on the top surface. When refitted to the chassis, the lower surface connectors are exposed and easier to replace then the upper surface ones.

There are two metal strengthening brackets that reinforce each end section of the bumper as it wraps around the bodywork. One of these brackets was clearly bent out of shape causing the distortion to the fit of the bumper.  

Unsurprisingly the bent bracket was behind the nearside wrap around section which is the area identified earlier (see beginning) as not fitting properly.

This is the bent n/s bracket to the left alongside the normal o/s fitted one.

A better view of the twisted bracket.

The newly straightened bracket....

 alongside the o/s bracket again.

High hopes that this will cure the slight 'twist' when fitted back on HX.

SURFACE SCRATCH AND CRACKS.

This crack is on the upper o/s surface. Whilst 'picking' and cleaning it out, it was noted that it seems to have been repaired earlier. There are signs of previously applied filler around the crack and on the reverse side, there is a small GRP plaster in that area. 

For the repair, I used a small piece of Alu plate stuck across the back of the crack with some contact adhesive. Suitable packing and a G-clamp helped to maintain its profile while drying. I left it overnight to dry and set, ending up with one of the packing pieces stuck to the Alu plate. In future I will remember to place a piece of plastic between the repair and the packing piece to avoid this happening again.

I then started to sand back around the crack on its upper surface. I used a fine grade sandpaper wrapped around a pencil eraser to flatten the area before applying a smudge of filler into the crack and sanding it back again.

Nearly ready for painting. Just a final rub down and a wipe with meths to clean the surface.

PAINTING THE BUMPER.

I recently bought a can of 'Satin black' Pro-Cote from Toolstation. I figure this will provide a better looking finish then the Matt black, but it remains to be seen.

Working outdoors leaves me at the whim of the weather. I have to wait for a dry calm day. Even a gentle breeze is to be avoided.

Made use of a wheelie-bin as a handy stand for spray painting. All the surfaces are accessible for spraying.

It's a good idea to practise the spraying movements that will be needed before starting to spray.

The repaired crack. This also shows up the faded mottled tone on the bumper surface..

The scuff marks on the n/s of the bumper, again showing the faded and mottled tone.

The embossed 'Land Rover' lettering on the centre of the rear bumper. Can't say I ever really noticed this untill I saw a photo on the Web of a D2 with these letters picked out in red. I did think of finishing the letters with a gloss varnish or even a lacquer coating just to give slightly more definition to them nut still remaining stealthy ....

Was doing this work in the middle of a heatwave, yet had to wait a couple of days for the right conditions for outdoor spraying. Ended up spraying after a passing thunderstorm in complete calm at about 8pm.

Bit of a heatwave going on around here so it was still very warm outside.

I used the Satin Black Pro-Cote spray and working quickly and methodically laid down repeated coats to build up the finish. Eventually the can began to empty and started to splutter. I took this as a sign to stop!

Hmm... Satin Black gets the immediate initial thumbs up. Will reserve final judgement till its mounted on Hx. Already I can see me buying another can of Satin Black to touch up the bumper and spray the other trim pieces to match....

CORNER TRIM AND BRIDGE PLATE.

Must mention the remaining bits of the rear bumper assembly...

There are two L-shaped plastic corner trims mounted to the bodywork each side of the rear door. Here is a photo from the web...

Rave is curiously silent about them so I had to do some digging around.

First thing was to figure out how they are attached to the bodywork. With the bumper removed, there is only one visible screw attachment point. I started to think that the body of the trim was somehow 'bonded' to the bodywork.

On Hx, the o/s trim screw mounting has snapped and the front end of the trim is loose on the bodywork. Given that I uncovered previous repair work to the bumper in this area its probable that the corner trim also sustained some previous damage. It may even have been replaced.

Photo shows o/s snapped mounting on Hx. The corner trim is loose at this point. The bumper has been removed and the curled up gaffer tape is a mystery. I'm guessing it's role is cosmetic or vibration dampening and it will be replaced..

The n/s corner trim on Hx. This side is strongly attached and the strip of black gaffer tape is intact.

The mystery of their attachment was solved after finding this image on the Web....

The screw attachment point can be seen on the lower left. What this image reveals is the three push-fit plastic retainers used to mount the trim to the bodywork. 

They are the same type normally found behind the door cards and are not forgiving of removal. They seem to slot into the base of the trim and I reckon the leading pin on the o/s has already snapped or worse the locating lug on the trim has snapped. It would seem that the way to remove the trim is by pulling and levering them out. 

It would be better to remove them to spray them black. I originally thought about spraying them to colour-code with the bodywork, but I now feel the potential hassle of dealing with snapped pins and lugs is just not worth it... If needed, they can be re-sprayed black 'in situ'. And I strongly feel that they will need re-spraying.

The bridging plate is a flat piece of trim that bridges the gap between the rear bodywork beneath the rear door and the upper bumper surface.

It runs across the full width of the door aperture.

The profile of the rear bumper provides a big flat surface for rainwater to just pool onto and then evaporate leaving an inevitable build up of green algae on its surface. This will wash off easily enough and should not be allowed to get out of hand leading to slips and gooey grime everywhere!

I had hoped that it was attached by concealed screws as I planned to remove it and spray it black as well. It is attached by hidden rivets along its lower edge that would need drilling out to remove so I reckon it's another 'in situ' refurb...

One of the concealed rivets holding the bridging plate onto the bodywork. The shiny black surface is the newly painted rear chassis.

PAINTING THE CHASSIS

Before re-fitting the bumper I took the opportunity to rub down and paint the exposed rear chassis that was revealed once the bumper had been removed. In the past I had already treated the accessible areas from below, but took the opportunity to re-coat those areas as well.

For the painting I used 'Flag' smooth black metal paint. Pretty much the same as Hammerite. I modified a brush by sticking some packing tape around some of the bristles to make it more of a 'stipple' brush for getting into the tight spaces. This proved very effective and is a technique to use again to stop the bristles spreading apart. For jobs like this I tend to use cheap sacrificial brushes and discard them when finished.

I was keen to coat inside those open chassis rails but limited in the access to their insides. A good thick coating was applied over all the accessible surfaces many of which won't even be seen when the bumper is replaced,

Some photos of the newly painted rear chassis. It is not easy to convey the glossy black finish in a photo. I wonder how long the shine will last?

THE RE-FITTED BUMPER

Re-fitted the bumper to Hx today 23/06/17.

I managed to reposition the locating screw on the broken corner trim and was able to secure the trim to the bodywork better. The bumper went back on easy enough but I had to ream out the n/s locating bolt hole to allow the bumper body to sit slightly 'higher'.

There are two foam packing pieces that somehow fit behind the wrap-around ends. I only have one piece of foam and its fitted location was not seen while dismantling. 

Looking at the end gap to the bodywork, I figure it has something to do with sealing that gap and maybe even dampening any vibrational drumming.

Well pleased with the Satin Black finish. It makes the bumper look brand new but inevitably that shows up the rest of the faded trim tone!!

The work never ends..

Got to love a freshly painted surface that repels the rain drops..

THAT MYSTERIOUS FOAM PACKING.

When I initially removed the bumper section from Hx it was noticed that a shaped piece of foam 'filler' literally fell away from the offside 'wrap-around' end of the bumper body. 

It's original position was deemed to be filling the gap between the bumper end and the bodywork. Perhaps its function is to suppress drumming or to channel road spray or both?

The foam is 'closed-cell' and I reckon its also waterproof given its exposed location. It remains flexible to mould itself to the contour required. It has a peculiar shape and in the last photo, the pointy end is fitted downward on the vehicle. It appears to have been stuck to the bumper surface (not the bodywork), and I'll be re-attaching them with some mastic or contact adhesive.

The nearside foam packing piece is missing, but it was possible to see where it was fitted by the residue left on the inside surface of the bumper. I noticed that it was not fitted right at the very end of the bumper body but more inboard.... A replacement will be sort.

I decided to use a cut down piece of 15mm copper pipe insulation. It has the required properties (waterproof, flexible, compressible) and hopefully will be a tight interference fit.

I tried to find a photo from the net showing the foam piece in place on a similar bumper, but it seems that their absence is a pretty common thing..