Just Some Info/to Be Aware Of - Rear Subframe

Hi,
Just thought I'd post a thread up regarding an issue Rick has found when removing a few subframes.
A particular one he came across was quite severe, as pictured below so thought it best to bring to peoples attention. Not sure if this has been mentioned before on here?
 
Seems to be a problem with corrosion between the back part of the chassis, and the plate that sandwiches between the subframe and rear chassis outriggers.  The corrosion on this car was so severe it had bent the plate and bent the subframe, causing the bolts to stretch and bending the captive nuts on the subframe.
This could potentially have caused the bolts or nuts to fail causing the subframe to come loose.
I have noticed this on the majority of vx's now, but it was so severe on this one so thought it best to photograph and make you aware.  Its like a white, powdery substance. Probably aluminium oxide but I'm not sure.  Only really way to check is remove your subframe and clean it. Bust as you already know, its a mammoth job. On the flip side of that though, what price do you put on safety?
 
Pic 1 - Showing Sandwich plate between subframe and chassis
 

 
Pic 2 - Shows plate being pulled away
 

Pic 3 - Oxidisation on Chassis

 

 

Pic 4 - Amount of Growth on chassis

 

Pic 5 - Shows amount of growth

 

Pic 6 - Amount of deformation of rear subframe and stretch where rear bolts are fastened

Thanks Liz,

 

Anyone who has the opportunity to remove their subframe should use duralac on each side of the sandwich plate to create an inert barrier. As an interim measure, ACF50 can be sprayed in the gap which will help retard any galvanic corrosion occurring between the two metals. ACF50 is used extensively as a galvanic corrosion barrier on aircraft.

There's a few spots on our aluminium chassis wagons that will crop up over the years as they get taken apart. Only recently found out that on the S1there's a bit where the heatshield mat gets damp on the back it creates similar white corrosion to that on the floors which have the rubber mats fixed down for years. Even so, every car made has issues of some kind - good to be aware but not shouldn't lose too much sleep or consider scrapping them all just yet. Could be worse, TVR outriggers for instance.

Similar happens where bolts and washers on suspension parts are, again ACF50 there does no harm on these areas

Thankfully I know mine are fine, I removed the rear subframe when the car was three and a half years old and it's never got wet since.

 

But I must admit to seeing some cars which looked like they needed some attention (new shims and anti-corrosion treatment) in that area 

Edited by vocky, 02 November 2013 - 12:06 PM.

Yep seeing more of this and def worth keeping an eye on that area what is more scary is the pitting and alloy that can corrode away. Not a hard job to resolve but time consuming to do right especially if doing the whole of the subframe DG

When I saw this I could not have put my car back on the road without addressing it and felt confident in the car.

Thanks for sharing the info. I've added this to the long list of work I want to do to my car whilst it is off the road for the winter. I assume I can get the shims from Vauxhall?

No need for new shims, they come up quite well with some rust removing solution in a bucket, then zinc etching spray paint, corrosion block and a fine wire brush worked well on the ally of the tub, got in all the little pits. Cleaned the subframe with crud cutter (or is it Krud Kutter?) and painted. Put it all back together using duralac as a gasket. finished off by applying duralac/corrosion block to any rivets etc that looked like they were being attacked and inside the box sections you can't get at.

 

 

Although mine was not as bad as the one above, it did look really bad until it was all cleaned up, had to straighten the plates a touch too.

 

 

Edited by Crabash, 05 November 2013 - 01:33 PM.

Thanks for that crabash. I've done a quick search but would like some confirmation, when removing the subframe the engine can stay in place right, just have to support the rear mount? Wishbones and brake lines off too?

To be honest I didn'ttake most of my car to bits, DG was doing all that while I was refurbing parts etc. But I would say even if it is possible you want to be in there and the more room you have the better, you will come across a lot more than this problem that you will want to fix while you have it in so many bits.

Was not really exspensive just time consuming.

I was already planning on taking the clam and rear suspension off as well as switching my back box over. So it would be rude not to clean up the subframe while I'm at it. All looking nice and tidy in the last pic. Was it just normal paint you used on the subframe or zinc too?

We thought a lot about what to do with subframe, including re-galvanizing it but in the end we went with krud kutter to clean the wax left by galv and etch the galv so it would take the paint, which was a high temp spray.

 

Oh and we also attacked any signs of rust on the subframe before cleaning and painting.

Edited by Crabash, 05 November 2013 - 01:44 PM.

I had one or two very minor pits on mine when I replaced the subframe.  As has already been said, new shims, and lots of duralac is a good measure.  I'm also looking into removal / replacing these sections on a bent chassis. 

 

There is also a corrosion issue on the box section that runs through the front.  The one that mounts the upper front wishbone point.  Those bits might be trickier to replace!

Thank you all. I have barely slept since the OP put this up.

They don't do this to me over on Netmums.

Thanks for that crabash. I've done a quick search but would like some confirmation, when removing the subframe the engine can stay in place right, just have to support the rear mount? Wishbones and brake lines off too?

check access to the top bolt holding the subframe on as certainly with the uprated vibra items you cant get the socket over it without removing the side mounts As steve has said a lot of other areas to focus on while there. Brake lines, clutch line etc. I replaced the brake line as you can see in the pic as the rust stopped just before going fully into sill. I had the tank off so a lot easier to work re hot dipping subframe was highlighted as a risk of warping by the main companies offering the service DG

The subframe can be electroplated just fine though but its cheaper just to find another. 

The subframe can be electroplated just fine though but its cheaper just to find another. 

 

I think it was more a case of the companies asked were not willing to give any assurance in our case.

This thread popped up at just the right time, as the engine was out so I thought I beter take a look.  As my car is at the higher end of the mileage range and is driven in all weathers, I was a little concerned about what I may find.

 

First pic (on its side) is the accretion growing out of the alloy - that should be a flat surface.

 

 

Second shows the distortion of the steel subframe face

 

Finally, the offending growth

 

 

It looks bad, but the face of the subframe is thin sheet between the hard points and there was no sign of movement, or the bolts being stretched. 

 

I'm now Duralaced up so won't be in the same position in another ten years!