Technical Subframe Rot

[jrkitching]

Is that even legal in the UK, it's changing a major component to something that has has no testing

There's no law against it, providing that the repaired beam has sufficient structural integrity to meet the construction and use regulations. In the real world, that judgement will be made by the MOT tester each year; if he's not happy that the repair is structurally sound, the car will fail. As has already been said, sill plate repairs must be seam welded; spot welding is not acceptable.

Personally I doubt the crashworthiness of many of these major corrosion repairs; there have been plenty of examples of older, structuraly repaired cars being deliberately crash tested, often with what would have been devastating consequences for the occupants.

Just my own opinion now, but I'd say what's acceptable in terms of safety depends on the use to which a vehicle is being put; whilst current MOT standards might be acceptable in an occasionally driven classic, I'd want something closer to factory level protection in a daily driver. Once the rust has taken a hold to this extent, I'd not consider continuing to use the car as my primary transport, regardless of the economics of repair. If the rear subframe is this badly corroded, then the integrity of the structural bodyshell must surely be highly suspect.

In the case of the OP's car, I'd send it to the scrappers.

 

[DaveMcT]

The big issue with body repairs is what's been done (or more correctly not done) under the repairs. Properly welded in all areas should be as good as the original, but they very rarely are. That said, this subframe looks like an ideal candidate for the repair to be at least as good if not better than original. None of it is high tech. The question is - what about the rest of it? Are we talking about an isolated area that can be fixed or a Forth Bridge that's endlessly needing work?

 

[jrkitching]

The question is - what about the rest of it? Are we talking about an isolated area that can be fixed or a Forth Bridge that's endlessly needing work?

My point exactly. If there's this much corrosion on the subframe, who knows what's going on with the parts of the underside that can't easily be inspected? Unseen structural corrosion won't get picked up at MOT time, but the car could still kill its occupants in a serious crash.

 

[mj2k]

My point exactly. If there's this much corrosion on the subframe, who knows what's going on with the parts of the underside that can't easily be inspected? Unseen structural corrosion won't get picked up at MOT time, but the car could still kill its occupants in a serious crash.

Guess it is more important for something as tiny as a 500 or Panda, but seems a shame to write the whole car off for the OP just because of a failed subframe. From the pics the subframe mount still looks rust free as does the spring hanger, so got to be worth checking over the common rust points you'd examine when buying one, surely?

On the other hand the MOT inspector might be a bit myopic so may have missed other areas of serious corrosion; that's a structural fail and no way that subframe mount's rusted that badly in the time between MOTs...

BTW I've no idea on how the entire 4x4 subframe looks, but is that bar completely different from the one on a standard Panda's subframe? If not the solution might be to buy a new pattern part, cut that bar off the new one and weld it in place of the rusted out bar, assuming the rest of the subframe's not on the way out. If it isn't possible I guess that might make the whole car beyond economic repair whatever the condition of the rest of the car, which means judging by all the other recent 'subframe rot' posts, 169 Panda 4x4s are going to become a rarity within a couple of years...

 

[koalar]

I agree with all above, about body shell rot

but I would point out this is a separate bolt on part

it looks to me as there is a weakness in the design and once water enter the tube it stays there and rots from the inside

as long as the rot is only in the subframe, i don't see any problem in replacing it, except availability. Just we do with the rear axle

As for welding. Unlike the example I wish I never gave as its complicated things. Its not a half hour job. To do the job properly a jig would be made to locate all the mounting points in 3d. Metal stretches and springs back while being bent and stresses bend and move metal while its being welded. A few tries will probably have to be made before it was correct. Insets and brackets would have to be machined and so on. Its going to the best part of a day.

Once set up, Replacing the same tube isn't such a big job probably 2 hours max

i Don't know how much a fabricator charges but people have charge between £50 and £150 per hour for my expertise in mechanical engineering and later electronics

its a fairly major part in rear end accident. If it was my car I would not be happy just patching it. Even though I said that on a previous thread. In retrospect I think I gave bad advise.

 

[vexorg]

That said, this subframe looks like an ideal candidate for the repair to be at least as good if not better than original. None of it is high tech.

I'd still take issue with what are effectively home made subframes being used. You dont know the original spec, so how can you say it would be ok. (admittedly, it's a fiat, so the standards aren't high for metal and rubber).

If you ask a dozen engineers to make one, then you'd have a dozen different subframes in terms of strength and fitting. You dont know the stress in it while corning at 70mph, and you dont want to find out they got it wrong at that point. Or as said, in a crash, the subframe is a fairly structural part for the body strength.

 

[chris3234]

There's no law against it, providing that the repaired beam has sufficient structural integrity to meet the construction and use regulations. In the real world, that judgement will be made by the MOT tester each year; if he's not happy that the repair is structurally sound, the car will fail. As has already been said, sill plate repairs must be seam welded; spot welding is not acceptable.

Personally I doubt the crashworthiness of many of these major corrosion repairs; there have been plenty of examples of older, structuraly repaired cars being deliberately crash tested, often with what would have been devastating consequences for the occupants.

Just my own opinion now, but I'd say what's acceptable in terms of safety depends on the use to which a vehicle is being put; whilst current MOT standards might be acceptable in an occasionally driven classic, I'd want something closer to factory level protection in a daily driver. Once the rust has taken a hold to this extent, I'd not consider continuing to use the car as my primary transport, regardless of the economics of repair. If the rear subframe is this badly corroded, then the integrity of the structural bodyshell must surely be highly suspect.

In the case of the OP's car, I'd send it to the scrappers.

That reminds me of the state of the chassis's I've seen on Nissan Navarros that people weld a reinforcement plate over and continue to use even after it has already split and cracked once and people even thing they are still safe like that.

 

[jrkitching]

as long as the rot is only in the subframe, i don't see any problem in replacing it, except availability.

No more do I; I'd agree with this.

But is it only in the subframe? There have been plenty of posts from folks who've found structural bodyshell corrosion, particularly in the sills. One concern with modern cars is that (for perfectly sound reasons) body panels are significantly thinner than in days gone by; they depend on galvanic protection to retain their safety as the car ages. But that protection only lasts for a finite length of time; once the protection has eroded, the underlying steel will rot surprisingly quickly, and there isn't as much of a safety margin as there used to be. So a car like the 169 could easily go from being perfectly safe to dangerously corroded in less time than the gap between MOT's.

Corrosion like this should be a 'red flag' to carry out a thorough inspection, including getting a borescope into the critical box sections; this isn't going to happen as part of an MOT.

One issue which has only emerged recently is that the substantially stronger used car market is encouraging folks to keep cars for longer than they otherwise might; a repair which would have been uneconomic before the pandemic could be justified today. These cars had a design life of perhaps 10-12 years; now that we're carrying out structural repairs to keep 15yr old cars on the road in daily use, the level of ongoing safety protection offered by these older vehicles does give me some concern.

 

[chris3234]

Found some pictures of the sort of thing someone was repairing and said they didn't see any issue with welding new section's in and putting strength plates over the top

Don't know about anybody else but for me that's fit for nothing but scrap no was that's in any sort of shape to be repaired with anything other then a whole new chassis's

f

 

[mj2k]

Found some pictures of the sort of thing someone was repairing and said they didn't see any issue with welding new section's in and putting strength plates over the top

Don't know about anybody else but for me that's fit for nothing but scrap no was that's in any sort of shape to be repaired with anything other then a whole new chassis's
View attachment 401154View attachment 401156fView attachment 401157

Wow, I'd certainly think twice about repairing a mess like that, especially as it appears to be a truck! On the other hand if the rest of the rail is intact it's a simple box section so welding in a new panel of the same gauge to solid metal with a suitable 'joddle' (actually joggle) to provide strength wouldn't be too much of an issue, assuming there was still some solid metal to weld to that is...!

Sticking a piece of tin over the top of the mess with a MIG welder might get it through the MOT, but I certainly wouldn't want to risk driving it, so I guess the best advice is do it yourself assuming you've got the skills (and trust your own workmanship, of course!), or give the welding to a 'real' pro who can weld the panel in properly, or has the cojones to say "no way that's ever going to be strong enough, you need a new chassis"

In terms of advice to the OP, that'd probably mean going to a well-respected classic car restorer (or maybe bodyshop) rather than Bob the MOT welder down the road (who might just slap baked bean cans'n'underseal over rotten Ka sills in exchange for a kickback to the local MOT tester), if trying to repair that subframe is a possible option, though it might well be cheaper just to replace the car.

 

[chris3234]

Wow, I'd certainly think twice about repairing a mess like that, especially as it appears to be a truck! On the other hand if the rest of the rail is intact it's a simple box section so welding in a new panel of the same gauge to solid metal with a suitable 'joddle' (actually joggle) to provide strength wouldn't be too much of an issue, assuming there was still some solid metal to weld to that is...!

Sticking a piece of tin over the top of the mess with a MIG welder might get it through the MOT, but I certainly wouldn't want to risk driving it, so I guess the best advice is do it yourself assuming you've got the skills (and trust your own workmanship, of course!), or give the welding to a 'real' pro who can weld the panel in properly, or has the cojones to say "no way that's ever going to be strong enough, you need a new chassis"

In terms of advice to the OP, that'd probably mean going to a well-respected classic car restorer (or maybe bodyshop) rather than Bob the MOT welder down the road (who might just slap baked bean cans'n'underseal over rotten Ka sills in exchange for a kickback to the local MOT tester), if trying to repair that subframe is a possible option, though it might well be cheaper just to replace the car.

Is a nissan pick up and they are known for severe rust on the inside of the chassis due to Nissan ***** Ing up the rust proofing


As for the pandas subframe is say its beyond saving as well given how it's a twist beam type there needs to be a degree of flex within it which would be very hard to match when patching it up

 

[mj2k]

Is a nissan pick up and they are known for severe rust on the inside of the chassis due to Nissan ***** Ing up the rust proofing


As for the pandas subframe is say its beyond saving as well given how it's a twist beam type there needs to be a degree of flex within it which would be very hard to match when patching it up

Ah, gotcha. I've got no idea on the 4x4 but assumed it'd be independent rear suspension (unlike the normal Panda / 500) to allow for more wheel articulation. In that case welding in a new beam's a definite no-no, it'd be like trying to weld a snapped spring...

BTW agree, it'd be a complete waste of time / money trying to weld up a known-rotten Nissan pick up properly; I'd only consider it worth the bother of repairing that level of rot if it was e.g. a classic ex-army Bedford 4x4 or suchlike.

 

[vexorg]

We've got 2 navaras at work, both have been back to nessan for the magic plate welded on that prevents this type of thing

 

[Yolanda]

Please forgive my ignorance here guys but how much would it cost to buy a replacement sub frame from eBay or the likes. New ones for the front wheel drive version are about £140.00 last time I looked. I do appreciate the sub frame is more sophisticated on the 4x4 in order to accommodate the rear axle. Or are they not available.

 

[koalar]

Please forgive my ignorance here guys but how much would it cost to buy a replacement sub frame from eBay or the likes. New ones for the front wheel drive version are about £140.00 last time I looked. I do appreciate the sub frame is more sophisticated on the 4x4 in order to accommodate the rear axle. Or are they not available.

availability is the problem. Not many 4x4 sold here in the UK. More sold in Italy I believe. As long as the rot is only in the subframe its a simple ish bolt job

 

[jonti]

going back to the OP, the box section it's bolted to looks fine. If older monocoque cars are rust-repaired repaired properly, i.e. metal selected of similar thickness, butt seam welded with good penetration, or spot welded if it was spot before, I don't see that crashworthiness changes. The weld is as strong as the sheet. If say 5% by weight is new metal (or whatever), given accident variables, and that the existing metal is only 0.9 or 1.2 mm, it isn't significant. That nissan is something else though.

 

[jrkitching]

New ones for the front wheel drive version are about £140.00 last time I looked.

Only because aftermarket beams are available. OEM beams for the 2WD Pandas are currently around £1100 including VAT.

I do appreciate the sub frame is more sophisticated on the 4x4 in order to accommodate the rear axle.

The 100HP rear beam is almost identical; just a small change to the hub attachment plates & clips, so it wouldn't be so difficult for an aftermarket axle supplier to retool for this (Beams for the disc braked 500's are already available). But the 4x4 is a completely different design, so it's unlikely that these suppliers will consider it worth the investment.

it's a twist beam type there needs to be a degree of flex within it which would be very hard to match when patching it up

The 4x4 rear suspension isn't a twist beam design.

As long as the rot is only in the subframe its a simple ish bolt job

The trailing arms for the 4x4 are available in the UK, but I can't find a UK supplier for the rear subframe.

If you could persuade someone in continental europe to ship one over, I'd expect the price of the bare frame including delivery and taxes would be close to £2000. If you need the trailing arms as well (quite likely when you consider the state of the spring pans on most 2WD rear beams), and also need to get the whole thing fitted, the job's going to be in the region of £3500-£4000.

I can't see anyone spending that on a 15yr old Panda. Even in the current crazy used car market, they don't make that sort of money; a quick search has turned up this 2010 example for under two grand.

If by chance one of these rear subframes does come up at a breakers, I'd expect the condition to be questionable, and the price will doubtless reflect the scarcity, and lack of any meaningfully useable alternative.

 

[mj2k]

The 4x4 rear suspension isn't a twist beam design.

Mmm, I did wonder about that, didn't look like a twist beam from the above parts diagram either, but I've never rolled about under a Panda 4x4 so have no real idea...

Does sound a bit like it'd be worth taking a big pickup over to Spain or Italy, doing a tour of the breakers to pick up good 4x4 subframes, and bring them back to the UK. It'd save at least some of the 4x4s which are soon likely to be crusher bound, and there'd prob enough money to be made out of that to pay for the impromptu Mediterranean holiday

 

[Yolanda]

There's a small company over in East Yorkshire ( I can't recall exactly where ) that make new chassis for Land Rovers. Maybe someone like them could do something. But I suppose the market would be small in comparison Land Rovers number wise.

 

[DaveMcT]

Is a nissan pick up and they are known for severe rust on the inside of the chassis due to Nissan ***** Ing up the rust proofing


As for the pandas subframe is say its beyond saving as well given how it's a twist beam type there needs to be a degree of flex within it which would be very hard to match when patching it up

2WD Panda's have a twist beam axle that costs around £120 for a new part. The rotten subframe under discussion is a 4x4 which does not have a twist beam. I still believe the rotted parts of this subframe could be replaced. Whether you'd want the cost is another matter entirely. We also don't know the state of the car body in general or the axle swing arms.

By the way has anyone looked at the later model 4x4 subframe? It's likely the wider axle track is given by different swing arms. The middle part (which has rotted here) might well be the same. I stress MIGHT. Check it out before going to the scrapyard.