How should I handle this suspension mount rust?
 

I've started a suspension refresh on my 70 911 and discovered some small rust through spots around the driver side front mount point for the front a-arm.

Here's the best picture...

http://forums.pelicanparts.com/uploa...1271556991.jpg

And here's the other pictures...

http://eludicate.com/~bolen/911E/photos/38.php

How should I address this situation? This is the first rust repairs I've made to this car myself. I had some rust around the battery tiedown strap mount (which is basically above this rust in the trunk) cleaned up, but that is it (ignoring the sheet metal rust I dealt with during the repaint of course).

The big hole is a little big smaller than my thumb.

How do I deal with whatever is going on inside the tub between the bottom of the car and the floor of the trunk?

thanks,

Britt

Well i'd use what ever tool you used on the underside on the inside ans see what's going on. It might be a simple as a small cutout and weld in new metal

x2

The rust has come through from the inside of the car so the damage would be worse from the inside. (Captain obvious?)

Have you removed the battery tray? (Assuming a 70 is similar to my 78)

I have a similar hole in my car and I'm planning to cut out the battery tray out to get to the top of the damaged area.
I'm dreading it big time because I expect to find more rust.

The plan is to remove most of the tray, leaving a 20mm edged all the way around... Then repair the rust hole by patching, paint, etc.
Then replace the tray with something I'll make myself from a plastic bread board or similar attached to the 20mm edge.

This is my battery tray right now... Yucky as! :(

http://forums.pelicanparts.com/uploa...1271576557.jpg

If I were you, I'd try to poke at it with some force with a screwdriver. That way you quickly discover how bad the rust is. Since it rusts from the inside and out, it is most likely worse than what you see now.

But, given that the structural integrity of the panel is intact (ie, the poking don't cause the holes to get very much bigger), I would just weld it up. And then afterwards drill some strategic holes, spray rust preventor into the cavity, and then plug those holes.

I had rust in this area also, but much worse than your case. The rust was also on the passenger side. I had to replace the entire suspension front pan, a job that is not fun doing. It takes a lot of time. :(

Almost certainly there will be fair amount of rust in the void between the suspension pan and fuel tank support, primarily due to battery acid damage.

I expect you will end up replacing the suspension pan (front half) and fuel tank support and repairing and/or splicing parts of the longitudinals.

I had to do a suspension pan replacement on an otherwise perfectly rust-free car. It is a big enough job, but more time consuming than hard (as long as you have the necessary tools that is). This was my thread on Rennlist that might give you some ideas:

Battery-area surprise! - Rennlist Discussion Forums

If you seach here you will find many other helpful threads on this topic.

PJO has a very good point that is many times overlooked. Welding over an enclosed area there is no access to do post weld prep cleaning or rust preventitive, the access hole(s) work.
I have tried some 3M weldable primers with very little luck, makes for a dirty weld and in doing test pcs it was burned off iside as well.
Freshly welded metal starts corrosion in the weld / heat effected zone almost instantly.

Regards
Oh I am not throwing off on the 3M products, they make great stuff, I just think anyone making something like that is a bit optomistic on results at the weld bead.

"poke at it with some force with a screwdriver"

bears repeating - this is a structural area - if it fails, you will crash

Ok I gave the area more screwdriver poking. The holes got bigger and a lot of rust fell out. Great...

how good are you at welding?

strip the top back way far from the first good solid - not at all thinned - metal you find and go for it

sorry to hear but you will be saving an important art object for future posterity

Oh I've got zero welding expirience. I can unbolt and bolt but the closest I've come to metal working was prying out a fender at LeMons with a jack handle!

It is definately repairable. I had zero welding experience and took a welding class at my local tech school 1 night a week for 8 weeks. I bought the best welder I could afford and did some rust repair my self.

This is the part I got from a supplier in Rocky mount, NC.

http://forums.pelicanparts.com/uploa...1271627387.jpg

You may want to get a section cut differently for your application. This is the portion I didn't need.

http://forums.pelicanparts.com/uploa...1271628288.jpg



This is not the end of the world,.........just the begining of a very educational journey.

This is a link to my work.

http://forums.pelicanparts.com/paint-bodywork-discussion-forum/498431-front-bumper-shock-support-rust-repair.html

Doing it yourself is possible. The majority of the labor is in dismantaling the front end so you can weld the new piece in, and then the re-assembly.

Don't get discouraged, If I could do it, any one can.

You can always do the tear down yourself and get some one more experience to do the welding for you.

Britt, I don't know if this will help or not, but here's my suspension pan replacement story...not a fun job, but absolutely necessary in my case.

http://forums.pelicanparts.com/porsche-911-technical-forum/399773-another-suspension-pan-replacement-post.html

Out of all of my projects...I disliked this one the most. AND I thought I bought a clean roller!
http://forums.pelicanparts.com/uploa...1271801341.jpg
http://forums.pelicanparts.com/uploa...1271801357.jpg
http://forums.pelicanparts.com/uploa...1271801386.jpg
http://forums.pelicanparts.com/uploa...1271801454.jpg
http://forums.pelicanparts.com/uploa...1271801500.jpg
http://forums.pelicanparts.com/uploa...1271801616.jpg
http://forums.pelicanparts.com/uploa...1271801729.jpghttp://forums.pelicanparts.com/uploa...1271801816.jpg

Well, that was easy!

2 years later I drove the car around the lot around my garage!

Things done...

Front suspension rust patched and fixed, didn't replace the pan, my mechanic advised against and just did a patch job in that corner.
New Bilstein struts with new shocks
Control Arms rebushed, new ball joints, and generally made pretty by Elephant Racing
Tarret sway bar
Elephant Racing upper shock mounts
New fuel lines up front
New fuel pump from Zim's to replace my MFI pump which dried out and started to leak (i'll post about that soon)
New rotors
New CarboTech pads
New wheel bearings
Pretty anodized hardware from DTW
Carrera torsion bars all around
New trailing arm bushings
New rear Bilstein shocks
rebuilt my original transmission (i have 2nd gear for the first time in 20 years!)
stripped and restored fuel tank
stripped and restored oil tank
new cv boots
repainted the muffler

Now I just need it aligned and I'm back on the road!

B

Love these follow-up posts....I replaced a nearly new battery with a Braille dry cell when I bought my car because battery acid sucks, glad your back on the road.

Nice follow up story, these things must not be rushed.

I did my suspension pan in 2 weeks ;) mind you I had just bought the car and was EXTREMELY motivated to get back on the road.

yeah, i didn't want this to be a 2 year project.... but life gets in the way... also a LeMons race got in the way for a few months...

I did pretty much everything except the rust repair and the transmission rebuilt myself, and I don't know anything :)

Car is being aligned today, so I hope to drive it this evening!

B