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bmw e36 coupe rusted rear arches- what now?

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22K views 39 replies 11 participants last post by  Spirit 
#1 ·
Quick question really as if people haven't already guessed by now my rear arches are at the end of their life really and seeing as I'm hoping to respray it soon I have a few choices really what to do.

A local stainless steel co cuts them out and makes me new ones

Buy replacement panels but expensive by the time you redo it all

Buy aftermarket bodykit arches and cover it or replace originals if needed

Rub it down as much as possible and just spray it and be done with it

Every mod or time I wash the car its the rears my eyes get drawn to all the time and let's the car down so if anyone has replaced,fixed etc theirs how much and what did they do?

Money is very tight also which factors into all of this


Pics would be really helpfull too if you have fixed them yourself
 
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#2 ·
It's likely that if you do it yourself the rust will eventually come through again. Trying to blend in rattle can paint is hit and miss as well especially if you have metallic paint or the paint has faded over the years. If money is tight though you may not have any other option. Getting a pro to do it will be quite expensive as I'm sure you are aware.
 
#3 ·
Treated it before and went well even with a rattle can until the day after when I did the laquer and that night it dropped to minus 6 and the paint reacted with a teardrop effect.
Now the rust one side is def coming back though especially drivers side so need to sort it

Shame really as the car comes up lovely when clean but the rear arches let it down and I'm sure a lot of e36 owners say the same
 
#6 ·
i have just bought 2 new rear arches ,so to cut out the ones on my car and have a mate weld them back in for me.got them from ebay,there not oem,but they are fine,i will be putting how it goes on my project thread over the next few weeks.. if you have not done them by then take a look. will have pics of progress.:thumbsup
 
#9 ·
It depends how badly they've rusted and how much metal you have to cut out to remove the rot.
As long as you're not cutting out huge, hard to replicate/shaped panels, then you should be able to cut out simple templates to weld back in. If you're taking off a huge section however, then as said, get some replacement arch panels and weld them in. The trouble with pattern parts is they will need some fettling to get to fit properly and they will also be made of a thinner steel so prep is key! Weld through primer on the reverse side and plenty of cavity wax afterwards etc
 
#11 ·
Definitely butt them up flush, edge to edge.
Welding will have to be very slow, just tacks to hold in place then 'join the dots' waiting for things to cool between welds to try and stop it warping.
 
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#21 ·
The only thing I would say about filling pin holes (left from rust) with lead, is that the pin holes will have worse rust on the other side you can't see.
If the rust is bad enough to have eaten through, even just pin hole size, if you were to cut out that section you'd see the hole was just the part that had eaten though, the rest would be very close and you'd be better off cutting out at least a few square cm to make sure you got all the affected steel out.
 
#22 ·
^^ Good idea Tom but i've had a proper look at it and its only at the very surface from a stone chip the rest of the car is immaculate. So i'm leaning towards e36cuope328's idea of drilling the very top to remove rust and then filling with lead. I don't mind doing the whole arch but a <3mm pin hole of rust doesn't warrant major surgery :thumbsup
 
#26 ·
Might well have a look at that, reading is a great way to improve at these things.
 
#25 ·
You can, but unless it's groundhog day becoming a concert pianist on your first piano lesson, or in fact first couple of hundred is unlikely.


Not trying to dampen your spirits, and I don't know what your mates welding is like but realistic expectations help, i.e. if you go for gold and come up short the results will likely be a lot less cosmetically pleasing than planning for bronze and expecting to make good with lead or filler.


Put it this way I've been panelling cars up for MOT since I was 12, on the bench I can fold and weld clean steel into sump pans that will hold thinners (this is a good way to test COLD items for leaks as it is more searching than soapy water). On a good day I can weld a piece into a panel flush that once linished you can't see (until you have put a layer of primer on, yes paint tells a lot of tales) and I would dread trying to butt weld in an arch perfectly. It's a big piece to make a perfect fit and sustain a perfect weld all the way around. You couls have a couple hundred pulse or spot welds to make that distance and if you have a 1% error rate you could blow a couple of holes. Putt oo much heat in welding them up and, if you have gone into the vert, not the arch flare, large flat panels easily distort and you could be talking a whole load of time / filler / vorrection work to make good.

Then there is longevity, once ground the chances that the weld is watertight from the rear are slim, so unless clean sealed and treated you can easily get a bubble.

That said lap welds, if they get any water in, will suck the water all along the length via surface tension, can be combatted by a nick or stopping the lap before it meets other panels and corners.

However, they aren't all that terrible. 99% of the welds holding your car together are spot welded lap joints.
 
#29 ·
Dam!

E36Coupe328 - Fancy doing my arch or two :hihi

Great advice!
 
#33 ·
Well my drivers side rear I'm gonna have to butcher and literally cut away the whole inside lip part what's left as that's catching my tyre leaving just the outer wing thats on show externally left and hope it holds up till I replace them and cursing lowering it at the moment and running 235s is adding to the dilema but I will be at the pod even minus wings as I've worked too hard to stop now.

Friday will be d-day with my grinder
 
#37 ·
First off, excellent job and excellent cutting.

By going into the corner you will have risked losing the sharpness off the crease unless filler is done really well and welds really flat and you can see by the way the filler patch has an uneven top edge the distortion into the flat panel as the weld starts and stops with max heat in the middle of each run.

If you had made the cut 1/2" lower, the ridge would have stopped the flat side of the quarter distorting and kept all the filler in the arch.

 
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