Rust Repair Plan of Attack!

[Coultl]

Hi All, I'm getting ready to tackle some rust on my new-to-me 84' 911. I've inspected everything, pulled the carpet, etc. and the car is actually pretty clean, but there's a few areas where the rust got in.

The front pan has bad rust at the low point under the battery. The rest of the pan is solid. The Rear wheel wells have rust at the front lower corners because of all the road dirt and crap the accumulated there. Still having a hard time understanding why these cars never had wheel well liners...

A few questions:
- Anyone replace just a portion of their front suspension pan?
- Any insights on the repair process for the wheel wells? I can't find good posts on it.
- Generally, any tips or resources on this work? I can weld and fab, but usually don't do exterior panels.

Suspension Pan Video: https://youtu.be/hlZ7PKqQNs4
Rear Wheel Wells Video: https://youtu.be/ku5UxEmxqQA
Project Spreadsheet (use tab "Body Repair"): https://docs.google.com/spreadsheets/d/1aclaL48tuu4xAWeoyl_vZEG102lp5ov-41GQbZDVHGI/edit?usp=sharing

[mepstein]

The suspension pans rust from the inside out. The inside of the pan collects moisture and water and it sits on the metal. So even though yours looks good on the outside (hard to tell until you remove the undercoating) chances are it's not so good inside. Most of the time the entire pan is replaced. Mine only had a small rust hole but the entire pan was toast when we started cutting. Most of the ones that come in to our shop with the same holes as yours, require entire new pans.
You can always cut out the rusted piece and peek inside.
The lower rocker/door jam area is a common rust area. Like you said, dirt collects there and holds the moisture against the metal. Again, probably will look worse once you start scraping away paint and undercoating and cut back to good metal.
All normal stuff on a 40+ year old car.

[Coultl]

Mepstein, makes sense on the suspension pan. I was hoping for something a little easier but that rarely works out.

Do you have advice on cutting the rear fender to get access to the lower door jam and rocker? Should I drill out the spot welds on the door jam or cut an inch or so off the seam? Thinking I’ll get these to replace the section I cut out: https://www.restoration-design.com/store/product/PP211R

[fallingat120mph]

Originally Posted by Coultl

Hi All, I'm getting ready to tackle some rust on my new-to-me 84' 911. I've inspected everything, pulled the carpet, etc. and the car is actually pretty clean, but there's a few areas where the rust got in.

The front pan has bad rust at the low point under the battery. The rest of the pan is solid. The Rear wheel wells have rust at the front lower corners because the PO never washed all the crap the accumulated there.

A few questions:
- Anyone replace just a portion of their front suspension pan?
- Any insights on the repair process for the wheel wells? I can't find good posts on it.
- Generally, any tips or resources on this work? I can weld and fab, but usually don't do exterior panels.

Suspension Pan Video: https://youtu.be/hlZ7PKqQNs4
Rear Wheel Wells Video: https://youtu.be/ku5UxEmxqQA
Project Spreadsheet (use tab "Body Repair"): https://docs.google.com/spreadsheets/d/1aclaL48tuu4xAWeoyl_vZEG102lp5ov-41GQbZDVHGI/edit?usp=sharing

Good stuff. Have the same exact issues on one of my 86's all hidden from normal "inspection" but looking closer need repaired. Subscribing and following.

[mepstein]

Originally Posted by Coultl

Mepstein, makes sense on the suspension pan. I was hoping for something a little easier but that rarely works out.

Do you have advice on cutting the rear fender to get access to the lower door jam and rocker? Should I drill out the spot welds on the door jam or cut an inch or so off the seam? Thinking I’ll get these to replace the section I cut out: https://www.restoration-design.com/store/product/PP211R

I'm not a metal guy but my suggestion is to starts small. Remove paint where it's already bubbling and cracked then cut back metal where it's compromised. Only cut back to good metal and cut the replacement metal to fit the opening as opposed to fitting the opening to the replacement steel. Of course you will have to enlarge the opening as you go deeper to get to the inner layers but you will figure it out. That's for the rockers and door latch panel. It's common to replace the entire suspension pan over patching in new pieces but I'm sure others have done it differently and you just have to research and assess what will be best for your situation.


Looks like you need to remove oil lines but also think about supporting the chassis and keeping track of dimensions as you cut away structural metal. It's not a targa or cab but cutting away metal and then welding new always has the possibility of changing critical dimensions. Better to keep track as you go than be surprised later.

[porsche930dude]

Maybe im not the one to answer but I would do the minimum. Theres no point replacing good metal. Especially since you will never get it as nice as the factory did it. So I would just do the underside of the rusted part of the pan. And honestly i wouldnt do the wheel well repair at all. Just neutralize the rust from the inside as much as you can access without disturbing the paintwork and seal it off from being exposed. It could last another 10 or 15 years before those rust bubbles grow. Then again my cars are drivers so they pick up new defects all the time. Cutting away the side of a perfectly good car to fix that seems crazy to me. Ask your mother if thats a good idea. She will say No Coulter put down those tools.

[Coultl]

Ha, I hear you Porsche930dude. Doesn’t feel good to cut into the car, but I’m not cutting into something that’s perfect from the factory. It’s rusted and needs repair. The car also NEEDS a repaint and there’s no sense in painting over rusted panels.

I’ll share progress here.

[Coultl]

Sheet metal ordered!

[3literpwr]

I've done the rockers before and it's not too terrible, but a fair amount of work. Drilling spot welds is the biggest challenge and finding good alignment after you've got all the parts. Well document repair for sure.

[3literpwr]

I recommend taking it apart piece by piece. A lot can be repaired normally, as I find the replacement panels from Restoration Design, not always that great.

[Coultl]

3literpwr, very helpful to see some photos. Nice work and thank you! I’m hoping to keep the door frame in place but I will remove the fender and was planning to cut right across to the wheel opening as you did. I’m dreading welding that back up… no second chances on that one.

I’ll spit the lower section at the leaded joint. Hoping everything ahead of that join is in decent shape. Do you remember if the seam between the door frame and the fender was leaded or did they just use filler? It’s perfectly smooth so there’s something there!

[Coultl]

Sheet metal arrived from Restoration Design! Suspension pan will be first. There’s a lot more info on that job out there and I’m feeling good about it. The rust in the rear seems way more complex…

[E Sully]

Mine was slightly different parts being a '73, but fairly the same process. I cut back to solid metal and trimmed the new pieces to fit. I found quite a bit of hidden rust as stripping progressed and needed quite a bit of work in my duel battery boxes. I fabricated a few pieces to avoid paying for full sections. I painted the inside surfaces before welding and put seam sealer on after.
One day I'll get to the kidney bowl area behind the doors.

[Coultl]

Nice work! Love seeing the photos. I always learn a ton from seeing how people approach this.

No question I’ll find more rust as I dig in. Just part of it…

[Loz]

I've done the suspension pan, kidney bowls and bothe inner and outer sills. I documented it on my Instagram zuffen_911. You might find the photos useful.
If I could offer any advice it would be to only cut away one area at a time. You need the car to keep it's integrity and strength the best it can while in surgery.
The front suspension pan in particular is critical. Restoration Design have a good YouTube video and the schematics for getting all your measurements and datums are on their website. Good luck 👍🏼

[Coultl]

Just followed you on Insta. Awesome work and helpful for me to see your process. Started pulling the car apart last night. I’m not planning to go bare shell like you did. Hoping to keep dash and whatever else possible in place.

[Coultl]

Progress. Removed the suspension and got to work on the front of the car.

The channel above the bumper bracket on the drivers side was full of crud and rust. This channel is a comically bad design for collecting crap. I see this and wonder how any of these cars are still on the road. On the drivers side it’s less likey to wash out bc there are some hoses in the channel too. My passenger side channel was less loaded up and corrosion looks minimal.

Rust wasn’t horrible but it did warrant a repair and I figured it was good practice. Drilled two locating holes and then did a 3D scan of the area. This was used to 3D print a jig that mounts to the locations holes I drilled and to the bumper bracket. Feels more than precise enough for when I weld the new one on.

Then got to work drilling out the spot welds. Took about an hour bc there’s a zillion spot welds and the bracket is thick metal. It’s also welded in a couple spots and that needed to be ground off.

The inner fender is Swiss Cheesy in the channel area and needs repair. Complex shapes in that area so rather than try to form sheet metal, I’m just going to get a replacement panel from restoration design and use what I need. Already have the replacement bumper bracket which I sourced from Porsche.

[Coultl]

I’m getting ready to start the suspension pan I have a question on locating the new pan. The car has never been wrecked so I’m confident everything is where it’s supposed to be now. I thought about welding up a jig but I think I will use the suspension to locate the pan.

The one issue is that the axis perpendicular to the floor of the car will not be well controlled. If I bolt the suspension to the rear mounts, the length of the lever arm makes is easy to push/pull the front of the suspension up and down. So, I need some other reference to make sure the height of the front suspension mounts are correct when I install the new pan. Any ideas?

[Loz]

Originally Posted by Coultl

I’m getting ready to start the suspension pan I have a question on locating the new pan. The car has never been wrecked so I’m confident everything is where it’s supposed to be now. I thought about welding up a jig but I think I will use the suspension to locate the pan.

The one issue is that the axis perpendicular to the floor of the car will not be well controlled. If I bolt the suspension to the rear mounts, the length of the lever arm makes is easy to push/pull the front of the suspension up and down. So, I need some other reference to make sure the height of the front suspension mounts are correct when I install the new pan. Any ideas?

You need to locate the zero datum line to get the pan in the correct up and down position. These are a available on Restoration Designs website. It runs approximately just under the battery boxes. There is a jig specifically for this purpose. I made my own and it can be done with careful reference to the schematics.
RD show the installation using the suspension rig. Maybe watch the video on YouTube first.

[Coultl]

Watched the video and, correct me if I'm wrong, but it looks like they just put the pan in and then double check by bolting the suspension up. I don't see anything to assure the up/down position is correct. Video here: https://youtu.be/2QtzA1Fj9Vc?si=DdoLk_uJ_uNeV0Dm

I have the chassis technical drawings and I am using a homemade trammel gauge, but locating the up/down off the datum line seem far from straightforward given the angles involved. I think I'll build a jig off the current pan which is not damaged and the car has not been wrecked. The coating on the strut towers has not even been removed.