Chassis leg, replace all or part?

[Chris Clarke]

I am replacing a rear chassis leg on a Mk2 Cavalier, it is rotten around the axle / suspension mounting (double skinned section) - the back 50% (single skin) is solid.
I have a full chassis leg (about 5ft long) from a donor car, but it was a bugger to get off and I did damage the floor in a few places where I couldn't find all of the spot welds!!
Question, am I best to cut the old chassis leg in half to remove the rotten part and join in that section fom the donor part - or, should I remove the whole leg and replace as a single complete panel?
Any thoughts please?

 

[CompoSimmonite]

Personally I'd change the whole leg but reckon just replacing half would be acceptable.

 

[BrokenBiker]

my view on this type of work is always the samem whether its chassis legs, sub frames, thicker components etc

if you can weld to a high enough standard that you can join the new part to the old part with atleast its original strength, then go for it...if not, its a full replacement becasue spot (plug) welds are generally easier to acheive to a good standard.

just my opinion though, i will say i havent done anything 'heavy' on a car in a good while, but i do fall on the side of just cut the rot out and replace that part

 

[Chris Clarke]

my view on this type of work is always the samem whether its chassis legs, sub frames, thicker components etc

if you can weld to a high enough standard that you can join the new part to the old part with atleast its original strength, then go for it...if not, its a full replacement becasue spot (plug) welds are generally easier to acheive to a good standard.

just my opinion though, i will say i havent done anything 'heavy' on a car in a good while, but i do fall on the side of just cut the rot out and replace that part

Thanks for that, I keep flik-flacking between the two, there's pros and cons to both... I like to keep as much original as possible but also, it's a chassis, so needs maximum strength... also, there's a chance of causing more damage (floors / boot etc.) the more I drill and chisel out... am slightly leaning toward chop and join but thought I'd get some other opinions.

 

[tom2207]

post a couple of pics

 

[dave h 2]

Cut the rot back till you find paint on both sides of the leg.

 

[Chris Clarke]

 

[Chris Clarke]

As you may notice, slight rust !! from the spring location forward... back from that not perfect but pretty strong...

 

[tom2207]

if the donor section is good , Id be cutting that out , not too bad either way though
but I would only be going as far as the joint where the bolt is , forwards of that will clean up ok rdrill half a dozen small holes say 1.5mm along the edge of the double skin so you have alignment marks for fitting the new section , just incase you have to take off both layers of the leg where it joins to the floor ,,, at least with marks you can decide and till know it will go back in the right place

 

[Pigeon_Droppings2]

I would also replace just to the factory joint I think if the rest is solid. I would imagine that joint is spot welded too so should be a nice neat repair.

As there's a natural factory joint I think just stop there as the leg is multiple pieces.

I've no idea if it's correct...but where I've butt welded chassis repairs I've plug welded a piece on the inside of the leg...makes the butt weld a lot easier as it's welding a double thick plate. There's a higher risk of corrosion but I fill the chassis with cavity wax anyway.

 

[Chris Clarke]

if the donor section is good , Id be cutting that out , not too bad either way though
but I would only be going as far as the joint where the bolt is , forwards of that will clean up ok rdrill half a dozen small holes say 1.5mm along the edge of the double skin so you have alignment marks for fitting the new section , just incase you have to take off both layers of the leg where it joins to the floor ,,, at least with marks you can decide and till know it will go back in the right place

Thanks for that, I did think about drilling a few 'alignment' marks... it should replace pretty well though positionally as it butts against the rear floor at the front, the inner cill to the outside and the wheel house along the outboard edge. The rotten section is where it's double skinned, I guess moisture gets in between the 2 skins and can't get out... so no chance to repair in situ for sure... and the outer reinforcement panel is very not available - hence the donor section.

 

[Chris Clarke]

I would also replace just to the factory joint I think if the rest is solid. I would imagine that joint is spot welded too so should be a nice neat repair.

As there's a natural factory joint I think just stop there as the leg is multiple pieces.

I've no idea if it's correct...but where I've butt welded chassis repairs I've plug welded a piece on the inside of the leg...makes the butt weld a lot easier as it's welding a double thick plate. There's a higher risk of corrosion but I fill the chassis with cavity wax anyway.

Yes, I love the idea of plug welding a reinforcement to assist the join, thank you... will also flood with cavity wax as well, lots and lots of cavity wax.

 

[tom2207]

Yes, I love the idea of plug welding a reinforcement to assist the join, thank you... will also flood with cavity wax as well, lots and lots of cavity wax.

gods no ,,, thats the worst thing you can ever do
google ACF50 ,,, I give a three year warranty on land rover chassis repairs , I can only do that because I usse acf50 ,,,, never never never use wax

 

[jo1010]

Replace the section back to the forward-most keyhole in the pics (that keyhole has been ravaged and is ripped - maybe bc its weak or maybe bc it's been brutalised but leaving it as is won't look good on a finished repair). Mark on the inner wheel arch the position where the double skin ends - that gives you alignment reference for the new part.
Structurally you don't need to puddle weld flitch plates inside the remaining U section but if you think it might help alignment of the new section do it (if it was a separate chassis then it's mandatory to have flitch plates, but this is just a U section welded to the floor).
At the forwards end of the leg are you joining the donor part forwards of where the double skin ends? That would be simplest

 

[Pigeon_Droppings2]

Personally I'd weld up a little jig to locate that top bolt hole so you get it back perfect.

Probably doesn't need saying...but the factory joint needs disassembling (peel off the top layer)...than should then allow you to plug weld in the repair....assuming it's a factory lap of course.

 

[Smallfry]

Good thing about doing this, is that the replacement is a factory part, so will be exactly the same as the part coming off, so you can see exactly were and how it was located.

 

[indykid]

Rest assured, whatever you do, it will be better than the last 3 years it was on the road. Geometrically, the axle bracket is the only thing that needs to go back with any sort of accuracy.

Nice to see someone else keeping Cavaliers alive. I'm assuming hatchback from the rear valance, but what body style is it?

I used to run this one at uni, it looked quite smart when it still had all the paint on the bonnet and the full calibre kit. My dad still has 4 and runs one as a daily.

 

[OJCar]

@Blobber to the rust coloured phone please.

 

[dave h 2]

As you may notice, slight rust !! from the spring location forward... back from that not perfect but pretty strong...

At least pretty strong till next year if you drive it in the rain

 

[Blobber]

If the "leg" is good change as much as you can, cut the old leg off leaving the flange behind which will make it easier to remove after, get as many spot welds from above and dont bother using spot weld drills as your not saving the old flange
The downside is its mostly lying on your back so good eye protection required, and as mentioned above you may also need to put the axle beam back on to make sure everything lines up before welding the replacement leg on
Looks like you could get 2 lengths of leg depending on repairs required which is where that joint is i guess