[krowlands]

I've just had a 3 hour fight with the Astra to replace the knackered backbox, and once it fell off (and got chiseled,ground, and hacksawed to "de-sleeve" it) and I noticed a corroded bit on the rear chassis rail (i think?), where the back box looks to have been rubbing/knocking for many years.

Is this a known occurance? Of do I have something wrong here? I'm going to assume it will need welding..any advice? I've spotted a seemingly pointless bracket on the spare wheel well - is the exhaust supposed to be tethered to that, to hold it away from the rail?

Pics:

Bracket on wheel well - Cable tie is holding the box away from the rail now.

Chassis rail - not a good pic, but the corrosion looks like it's holed the rail parallel to the box..

I also spotted this surface (I hope) rust around the rear springs..any advice?

Here's the old back box..crumbly is not the word..

Many thanks..I'm now going to try and patch up the leaks I've sprung doing this..:lmao:

 

[Paul TD]

What year is it? Clean all the surface rust off with a wire brush in your drill or even better an angle grinder and then Waxoil inside and out.

Don't forget your safety glasses and get right in around the top of the coil spring mount. Plenty of Waxoil because it soakes into the metal/rust. Much better than underseal because you can keep an eye on it.

 

[dunkmeg]

The back box should be hung by 3 hangers, 2 by the tailpipe and 1 where it joins the middle. It shouldn't touch anywhere only in the rubbers, it could have the wrong type of rubbers (small 1's) therefore lifting it too high causing it to foul the chassis or it could be how the middle has been fitted

If you don't mind me asking but how much did you pay for the box

 

[krowlands]

The Astra is a '97 P reg..no rust on top, just the chassis spot and the spring seats underneath.

I have a large tin of waxoyl..I was thinking about trying to remove the spring, then the base in the shell, then wire brush/grind with the dremel or drill, then hammerite, put it all back together and waxoyl in and out..is it worth giving it a hammerite coat, do you think?

My backbox has 3 hangers..when I got it, I DID notice that the mid sections 2 hangers were cable tied to "squeeze" them..and the back box hangers aren't especially large..but I assumed they were all "standard size, factory fit" jobs..I take it they're not? I do know also that the cat rattles against its undershield at about 40mph..which is downright irritating in town.

I paid..ooh..about £23 for the back box with clamp from an exhaust wholesale place. They're quite good...I got the oil filter for £2.50 and a pollen filter for £7 at the same time.

 

[krowlands]

I've just stuck my fingers inside the box section chassis rail at the rusted/"may need welding" bit and had a feel about with my fingers..and I can't feel any rough or broken metal inside..so fingers crossed it's medium surface damage only..

I can see me getting under that car with tins of hammerite and giving it hell..heh. I've taken one of the rear hangers off and measured it..it's about a centimetre shorter than my PH2 "chipped" Astra ignition key.

Certainly doesn't seem to be very big..I never thought that maybe it had got the wrong size put on in the past. I always tended to re-use mounting rubbers when doing exhausts on previous cars unless they were shot, then I went and got one of the same size using the old one as a measure.

Hmm...

 

[Paul TD]

If you undo the top shocker mounts, 15/17 mill i think then when you jack the rear up you can get the springs and rubbers off. Just give it a good clean up. If you want to hammerite it you'll have to clean back to bare metal and I mean bare metal. I'd say your better off giving it a nice thick coat of Waxoil all around and just check it now and again.

 

[krowlands]

Thankyou all for the advice. Been back under it today, taken the box off again and opened my several year old can of waxoyl. No way could that spray..:lmao:

Anyway, I've wirebrushed/ground it all off, and it's not too bad. Medium surface rust with some pitting. So, I got out the paintbrush and painted the waxoyl on nice and thick..back axle, underbody, fuel tank, nuts, bolts, wheelarches..it's had the works. I would imagine waxoyl is ok to paint on?

I've reshaped the back heatshield to keep it away from digging into the chassis, and it's all back together again. I guess it's just 6/12 month checks really to keep an eye on the underneath.

I wish I had a car lift! :lmao:

 

[Paul TD]

Should out last the rest of the car now, lol.

It's nasty stuff but well worth the effort