MOT questions - welding

[sdp]

My rear subframe is a little flaky in places but seems solid, but I'm still dubious as to it's road-worthiness. My driver's side sill has a rusty patch around the jacking point and I have a tiny hole (1cm across) in the floor where the front left arch joins the floor.

I'm trying to work out roughly how much it's going to cost because I've got a bit put away and the less I spend on the mot the more I'll have for go-faster bits

If the rear s/f fails I'll replace it myself, cos I've heard it's an expensive job (350quid) as it takes ages to do. So assuming it needs the floor patched and a new outer sill and nothing else needs done can anyone hazard a rough guess as to how much that bit of welding will cost?

[Jiff Lemon]

Essentially any rust within 30cms of a suspension point will require welding.

I'm presuming from rear subframe talk we're talking Mini? Essentially anything on a mini is going to be welding! Mercifully panels are plentiful in availability.

[Zak33]

/\ he's right and he knows /\

[[GSV]Trig]

Plus if its a main chassis type thing it has to be seam welded....
None of your spot stylee stuff....

[sdp]

Sounds expensive I'm glad I'm gonna be learning some welding this year.

Actually, I think if original parts are used the sills can be spot-welded because that's how they left the factory. That's what I've heard anyway.

[Jiff Lemon]

Ideed, if you're replacing a FULL panel, then remove the spot welds, and you can re-spot it back on.

If you were doing a patch repair, its got to be a continous seam weld.

Generally it's best not to try and cover any crappy attempts at welding with half an inch of underseal - the tester will simply refuse to retest it until it's removed.

[kaillum]

sdp m8e... if your rear s/f is bad.. replace it.. the parts are cheap enough to buy s/h and iirc there bare s/f is the same for models up to '91.. but confirm that before buying...

there are only 8 bolts and the shocks that hold it on.. so any rust around the mounting points is gonna weaken the rear end.. better to get the whole thing off, clean, patch paint and replace...

its expensive to get the rear s/f replaced by a garage, as its more the time it takes to do it than the difficulty...
main points of replacing rear s/f:

Remove Fuel Tank, Rear Brake Lines, Handbrake Cable, Shock Absorber top mounts, Exhaust, Battery Positive Lead undo the 8 bolts that hold it. 2 in front of each rear trailing arm and 2 rear most corners.

the only b@st@rd part of the whole job is that the 4 bolts in front of the rear trailing arms are into blind holes.. and as this is the point of the wheel arch that gets covered in road cack 9 times out of 10 they'll shear off... which means either using bolt extracters or drilling and re-tapping.. but if its rotten in that area then the panels are really cheap to buy.. and the replacement is easy once the rear s/f is out....

dont lie underneath the car as when the s/f drops its bleedin heavy!! and can cause some damage to knee's, feet and other bits left in the way!

wire brush, clean, repair re-paint and gererally make good any dodgy area...

As your s/f is now out of the car its a good time to replace the bushes on the rear trailing arms.. they always seem ok 'til the next MOT time and its so much easier to do out of the car...

its a time consuming job, but you'll feel so proud of yourself when its back on 4 wheels...

i've ended up doing this on most of the mini's i've owned... and its one of those jobs that dosnt get easier with time

jeez.. this must be my longest ever post!!!