BX corrosion stinker - any views or advice?

DLM · Post by **DLM** » Sat Jun 11, 2005 8:31 am

Here's the text of a question I PM'd to Jon - and the reply. Any other views are VERY welcome but I know I've got a bit of a nasty job on my hands.

Hi Jon.

I'm in the middle of working on my BX for an MOT and after various minor repairs, have discovered a real stinker of a corrosion problem.

Where is the rot on the BX? Not in a nice place. While cleaning up around a weeping rear cylinder gasket (in the wrong orientation - easily fixed) I found there was rather a lot of mud around sundry areas, including the rear arm pivot bolt - looking almost so bad as to restrict movement.. I started removing it, then moved upward and flaked away a particularly large gollop of mud on the curved box section located just above the pivot bolt.
Bad move - there was about 2 to 2 and a half inches of corrosion in the outer corner of the box section - *****!
There's peelaway of the edge of the vertical face by about 1/4" across most of that length, cracks along the corner, and a definite hole emerging. The lower face looks unrotten. I've not had the courage to attack it with a screwdriver yet. And of course it's mere centimetres away from the rear subframe mounting point. A quick look from inside with the rear subframe mounting screws exposed didn't reveal a lot more, as the deadly spot is "back up the tunnel" from there.

It's not a great thing to discover on a car with just-expired MOT and tax - and it's also in a tricky spot for repair (if that is possible) as the front-to-back brake and suspension pipes run just below it.

A couple of questions, if you don't mind me leaning on your knowledge of the BX and access to people like Louis Barbour and others who have long experience of MOTing BXs :

(1) Is this likely to be legally fixable?
(2) Might an uncorroded section from a donor scrap BX be inserted?

Jon's reply:
Hi,

Ok, I have never seen one rusty here, and I phoned Louis who said he had only once, its in an area that tends not to get spotted because, as you say mud collects there. Infact, it usually gets picked up if the car is being repiped front to rear, not so common nowadays as all cars 89> had plastic covered pipes.

To repair this well is really not going to be easy, its going to be necassary to drop the subframe one side to gain access. Chop out corrosion, and seam weld a nice plate up there. As long as the plate is fully seam welded (as it is within 12 inches of a structural component) that would be fine for MOT purposes.

Stewart (oily!) · Post by **Stewart (oily!)** » Sat Jun 11, 2005 9:03 am

My old GTI went under there, we managed to get an L section plate in and seam weld it, it passed a test but to really get at it your idea of removing the subframe sounds best, that is the spot where I have really blasted Waxoyl into my newer one.
Stewart

DLM · Post by **DLM** » Sat Jun 11, 2005 11:23 am

For anybody considering a Waxoyl blast to cover this area, there are 2 points of access - the drain holes for the box section, and limited access to the frontward part of this section from above via the access point for the rear subframe bolts.

DLM · Post by **DLM** » Tue Aug 09, 2005 6:29 pm

Many. many thanks to Jon for his welding work to resolve my problem: a sizeable chunk of rear chassis leg had to be cut out and plates patched in, and a hole in the sill on the driver's side had to be covered as well. Both repairs were primed and undersealed.

Jon suggested that while the rear floor and boot of the car is beautifully rust-free (thanks to an extensive rear shunt repair before I owned it), the rust could well have been caused by rippling of the overlapping plates in the chassis leg, as a consequence of the previous damage. One to look out for! I'll be watching the other chassis leg like a hawk.

I have to confess to responsibility for the sill damage, done as a result of a jack slipping because it wasn't fully inserted into the central jacking point.

Also, many thanks for the rear caliper masterclass. The car now pulls up rapidly like a dream (the sort in which you fall out of bed). Let me know if you ever find the mysterious disappearing caliper piston, Jon.....

So, I'm back driving Graculus again (the great green bird of Noggin the Nog mythology) after a hiatus of a couple of months, and doesn't it just feel good! I celebrated by putting nearly a couple of hundred miles on it straight away.