MGB Register Forum

Hi all,

Having spent much of the last couple of years distracted by work, I’m beginning to assess jobs that need doing on the car. (Near the) top of the list is hunting down any rust that might be spreading out of sight and renewing the anti-rust protection that I think was last done in 1989.

I’ve been aware since I bought my car that there is a mottling / incrustation / something behind the dashboard around the old flasher unit that I’d like to identify. I’ve attached an image.

Three thoughts occur to me.

1) It’s some old converted rust that someone treated a long time ago (although it doesn’t look like that to me), , or other form of preservation effort that I need to be mindful of.

2) At some point someone made modifications and that residue was left over (Why would the disused Lucas flasher unit not have been removed in that case)?

3) At some point there was a catastrophic leak of the break fluid. It wasn’t cleared up properly and that’s what remains (superficially it looks similar, but it seems an odd thing not to have cleaned up).

Does anyone recognise it?

Hi David,

very difficult to judge from just a photo, but that looks very much like the paint stripper effect of spilt brake fluid. Does it scrape off easily?

Ian F

Or maybe a stone chip type spray on underseal.

Richard: I did consider underseal as part of my rust prevention theory. But it’s solid (unlike many modern underseal types I’ve seen) and doesn’t resemble the (old) underseal used on the rest of the car.

Ian: Solid, and has been since I got the car back in 2019. I suspect I could chisel it off bits with a screwdriver or the such if so minded. The plan is actually to take a Dremel and some steel brushes to it.

Of course understanding what it is and whether there are risks involved first is useful (and the prompt for posting here).

Thanks

Why would brake fluid be on the inside face of that panel? Master cylinder leaks generally drip down from the aperture through which the pedals hang. It looks like some form of preservative coating to me. From the factory that would simply be painted in body colour.

However its worth checking out the behind dash area as it is double skinned and can rot right through.

Bumpa wrote: ↑Sun Feb 25, 2024 8:04 pm Why would brake fluid be on the inside face of that panel? Master cylinder leaks generally drip down from the aperture through which the pedals hang. It looks like some form of preservative coating to me. From the factory that would simply be painted in body colour.

However its worth checking out the behind dash area as it is double skinned and can rot right through.

I agree Mike, regarding the likelihood of brake fluid in that location. I was just commenting on the appearance of the surface which looks like blistered paint. Paint like this will harden again over time.
Could it be heat/fire damage causing blistering?
Clutching at straws here perhaps.

Ian F

It doesn’t feel like fire damage (I have some experience in that regard). I’ve added two more photos from slightly different angles. One backs up the consensus view emerging that it’s not not brake fluid (the incrustation would have come out of the opening closed off by the rubber cover). The other shows it doesn’t carry on back to the end of tbd footwell.

I’m starting to lean towards Richard’s thought it’s some sort of underseal. Maybe it was accidentally sprayed on when the car was renovated in 1989 and never removed.

Anyway: the mystery continues. I’m grateful for all thoughts offered so far though

It looks like seam sealant or stonechip treatment. Possibly factory applied but it could have been done by a previous owner if they happened to have the remains of an aerosol left over from coating the sills or inside the wheelarches etc..
I cant see anything here for concern, its not going to flake off and expose the underlying metal to surface corrosion. If you'd like to improve the appearance you could smooth it by rubbing it down with some 150 grade wet and dry, then a finer grade and spray over it with black or body colour.

The cream coloured section looks more concerning if it's filler that's not been smoothed.

Hi David,
My first MGB GT (1971) had a similar appearance with several areas covered with what I assumed was a sound proofing / rust prevention coating. Does yours have the same appearance in the battery wells? Mine also had both wells finished in the same way and even the underside of the battery cover lid! I'm pretty sure it's what yours has. - Possibly Zeibart rust proofing when new?

best Neal