Technical Assessing rust - floor panels

[Twink80]

Good evening all -
Today on the project (1978 Spider restoration / resurrection) I uncovered the floors and removed the seats. My simple, naive question is: How do I accurately assess the rust damage so I know where I am going to need to replace metal?

Following are some lovely shots for your info and interest:

View attachment 459176
Passenger side

View attachment 459177
Drivers side


Looks like some fiberglass was applied at some point. The rusty cracks extend to the back - I have not yet removed the carpet.

Thanks in advance!

Hi There is already a lot of good advice posted. Pretty much all the steel on the car contributes to strength and stiffness especially between the front suspension / crossmember mounts, the sills (which are torsion boxes) and the rear bulkhead and rear crossmember
If you haven’t already buy a mig welder and high pressure gas cylinder (not the disposable ones) and learn to weld
If you have stone chip sprayed on the underside then remove that too. It delaminates on old cars and forms a water trap that you can’t see until its too late!
I would also recommend stitch welding all the main structural parts of the bodyshell and the engine crossmember. This will significantly stiffen the shell which will improve handling and reduce rattles and shakes later on
The Abarth rally cars were fully seam welded but for road and track stitch welding is fine.

 

[Twink80]

Back at it today: I’m clear that front and rear floor pans need to be replaced. I think I can salvage the seat supports (will need to do a little patching).

The tear-down continues; first look at the rear brakes - looks like someone put new calipers on. Also looks like an elec fuel pump retrofit?? Also am curious if you fine folk think I should replace the fuel tank. It has been sitting for a couple of years.
View attachment 459555

View attachment 459556

The silver can is a fuel filter, the OE ones are much bigger than the see through inline filters. To inspect the tank you can take the fuel guage sender out. You will be able to see the bottom of the tank and that’ll give you a fair idea. Stale fuel is no problem but if your fuel is mixed with ethanol when left water will separate out and cause rust. As long as the tank is sound you can stop residual scale entering the fuel system with a couple of in line filters.

 

[Slotman]

Regarding what metal to replace caused me to remember as a young car enthusiast watching an old body man testing out the floor in and old rusty nova, he had a craftsman Phillips screw driver he would try to punch thru the floor from the inside, if it went Thru the metal needed to be replaced...

 

[Twink80]

Regarding what metal to replace caused me to remember as a young car enthusiast watching an old body man testing out the floor in and old rusty nova, he had a craftsman Phillips screw driver he would try to punch thru the floor from the inside, if it went Thru the metal needed to be replaced...

Fortunately they have stopped garages doing that during the mot test here!
For interest modern cars use multiple different grades of steel, sometimes in the same panel called tailor welded blanks. For example around the door handle is stiffer/thicker than the main part of the door skin. The result is way more efficient structures but they no longer can be repaired to give the same structural integrity. Google a 2010 Audi A6 as an example.

 

[Slotman]

Thats very interesting! I retired from the aerospace industry as a cnc machinist and I do recall in my industry some aluminum skins similar to what you describe...technology...

 

[smahaley]

Hi There is already a lot of good advice posted. Pretty much all the steel on the car contributes to strength and stiffness especially between the front suspension / crossmember mounts, the sills (which are torsion boxes) and the rear bulkhead and rear crossmember
If you haven’t already buy a mig welder and high pressure gas cylinder (not the disposable ones) and learn to weld
If you have stone chip sprayed on the underside then remove that too. It delaminates on old cars and forms a water trap that you can’t see until its too late!
I would also recommend stitch welding all the main structural parts of the bodyshell and the engine crossmember. This will significantly stiffen the shell which will improve handling and reduce rattles and shakes later on
The Abarth rally cars were fully seam welded but for road and track stitch welding is fine.

Thanks @Twink80 - I have acquired a mig welder with a big (to me) bottle so think I am set for gear. I will read more and watch videos: as of yesterday I think I have a source for comparable sheet metal (~19 gauge) . I did wonder about the black stuff sprayed onto the underside: my thought was to a) cut away the truly unsalvageable areas b) clean the edges c) make a template d) cut and shape a replacement e) prep the replacement (clean) and f) stitch weld.

thoughts on that plan?

 

[Twink80]

Thanks @Twink80 - I have acquired a mig welder with a big (to me) bottle so think I am set for gear. I will read more and watch videos: as of yesterday I think I have a source for comparable sheet metal (~19 gauge) . I did wonder about the black stuff sprayed onto the underside: my thought was to a) cut away the truly unsalvageable areas b) clean the edges c) make a template d) cut and shape a replacement e) prep the replacement (clean) and f) stitch weld.

thoughts on that plan?

The black stuff is sort if rubberised and if it doesn’t fall off it is a messy nightmare to remove! I used 4ins angle grinder with scotchbrite type pad off ebay. Also tried hot air gun and paint scraper. Horrible job!
Your templating is a solid plan but you need to replicate all the features like stiffening reinforcements
I think Spiderpoint (also used to be Bruces Autoparts in the US) might do complete panels. $$$ vs time!
With the mig set up some sample jobs, start with current and wire feed on the highside then gradually reduce either one at a time. Inverter welders are very controllable but its also down to your technique. If you hold the torch in your right had then brace it or drape it over your left forearm to steady things up.When its running right you get a nice steady crackle.
Use a mix with 10-15% Argon, its more tolerant of paint/rust etc. BOC used to sell Argoshield TC that was great

 

[Twink80]

Thats very interesting! I retired from the aerospace industry as a cnc machinist and I do recall in my industry some aluminum skins similar to what you describe...technology...

I worked in the car industry developing new cars. One had bonded aluminium structure, we were supported by Ford Research and someone doing a 2yr PHD on the bond interface with different anodising and adhesive options! Good luck trying to repair that lot!

 

[Slotman]

The aluminum panels I worked on that varied in thickness at certain locations had been chem- milled prior to my milling machine, that I did guage reduction on..again technology...I went to ase school in this country just because of my car hobby and I remember my instructor telling how the industry is constantly changing just like the job of being a doctor, you can never stop learning if you want to keep up ..

 

[Twink80]

The aluminum panels I worked on that varied in thickness at certain locations had been chem- milled prior to my milling machine, that I did guage reduction on..again technology...I went to ase school in this country just because of my car hobby and I remember my instructor telling how the industry is constantly changing just like the job of being a doctor, you can never stop learning if you want to keep up ..

Totally agree with that! I started out designing on drawing boards using film and ink, within 5 yrs CAD had arrived and went from a 30k workstation to being available on a home pc. Lots of very skilled trades like pattern making, tool making all disappeared and 5 axis machining centres worked 24/7. And now AI……. Still at the moment AI cant rebuild a Spider!! Ive been continually improving mine over 25years! I’m currently trying to build something similar to a Stradale! Its 1980 so changed the rear lights and door handles back to earlier model, and then a respray. I sprayed it with a rattle can years ago, looked ok but paint was too soft.

 

[Twink80]

Back at it today: I’m clear that front and rear floor pans need to be replaced. I think I can salvage the seat supports (will need to do a little patching).

The tear-down continues; first look at the rear brakes - looks like someone put new calipers on. Also looks like an elec fuel pump retrofit?? Also am curious if you fine folk think I should replace the fuel tank. It has been sitting for a couple of years.
View attachment 459555

View attachment 459556

Heres an idea while you car is in bits….how about a Monza type fuel filler? These were fitted to the Stradale models and you can replicate using all the existing fuel tank and fill pipe. You need to buy the Monza style cap (around £35)
You can delete the std fuel filler flap, which I never really liked, and get a much cleaner, more symetrical rear end. Here’s my implementation!

 

[smahaley]

Heres an idea while you car is in bits….how about a Monza type fuel filler? These were fitted to the Stradale models and you can replicate using all the existing fuel tank and fill pipe. You need to buy the Monza style cap (around £35)
You can delete the std fuel filler flap, which I never really liked, and get a much cleaner, more symetrical rear end. Here’s my implementation!

That's very cool - good work! I'll keep this in mind whenever I get to the body work...

 

[124BC1]

Regarding what metal to replace caused me to remember as a young car enthusiast watching an old body man testing out the floor in and old rusty nova, he had a craftsman Phillips screw driver he would try to punch thru the floor from the inside, if it went Thru the metal needed to be replaced...

Fortunately they have stopped garages doing that during the mot test here!

We don't have the MOT here, we have the NCT and it's even worse, being both fully computerised and dearer!

Our Testers, who all work in government operated and staffed test centres, (no independent garages, so no little favours will be done..) use MOT Hammer and Corrosion Assessment Tools. These are quite short and have a relatively soft nylon head, I believe the idea is the tool should be used to lightly 'tap' any suspect area to assess state of corrosion.

Here's a pic of such a Corrosion Assessment Tool (at the bottom of the pic is the Brake Pipe corrosion assessment tool :-

 

[Twink80]

We don't have the MOT here, we have the NCT and it's even worse, being both fully computerised and dearer!

Our Testers, who all work in government operated and staffed test centres, (no independent garages, so no little favours will be done..) use MOT Hammer and Corrosion Assessment Tools. These are quite short and have a relatively soft nylon head, I believe the idea is the tool should be used to lightly 'tap' any suspect area to assess state of corrosion.

Here's a pic of such a Corrosion Assessment Tool (at the bottom of the pic is the Brake Pipe corrosion assessment tool :-

View attachment 463402

It would be interesting to see how they recommend applying that! Different grades of steel are used in the structural areas of cars since the late 90’s. Aimed at saving weight and improving crash worthiness thickness was optimised against the cost of higher grades. Tailor welded blanks are used in door pressings, the steel around the door handle is higher grades and thicker than the main part of the door skin. If you shut the door by pushing on the main panel there is a good chance you will dent it!
Years ago I found an Audi A6 body repair guide on line. Basically a 2010 A6 cannot be structurally repaired by anyone other than a main dealer and even then there is no guarantee it will perform as the original. Noone crash tests repaired cars so there is little or no data on how effective the repair might be.
Another example is a small car called the Suzuki Swift, my wifes car rolled backwards into one on an incline at about 5mph, the car was written off! Unbelievable!

 

[124BC1]

It would be interesting to see how they recommend applying that!

Here's the relevant section from the Irish NCT (National Car Test) Tester's Manual.

 

[Twink80]

Here's the relevant section from the Irish NCT (National Car Test) Tester's Manual.
View attachment 463454

Love the subjectivity!
Other appropriate tools ??
Unwarranted force…..is that one without a permit?
Sorry for sarcasm wine has taken over
Unless measures are objective its really difficult for everyone
Your point in a previous post an experienced mechanic can feel when something is correctly vs a newbie who might not.
Whereas a specific torque everyone knows what is required.
However….tuning Twin 40’s is part science part art and experience!