Chassis leg repairs - Good news and few issues

Windy101 · 20 Jan 2020

I got round to a job I have been meaning to do for years at the weekend and stripped the rear bumper off to inspect the dreaded rear chassis legs.

Given the car is almost 24 years old there were a lot of seized fasteners, but I got there in the end and the chassis legs seem to just have surface corrosion.

I have a couple of snapped bolts where the lower bumper mounts go onto the body that will need dealt with.

I am however less sure whats the best way to deal with a couple of snapped studs that the side bumper stays/supports go onto. Should I just grind them flat and tack on a new stud or is there a better way to sort this.

Also you will see in the picture that the main heat shield on the rear of the exhaust is missing about 1 cm from the bottom and I can not get the bolts out from the top. What would the consensus be to do with them. I can keep at them with heat and penetrating fluid but they will probably snap anyway and need drilled out.

I can then drill them out and fit a new heat shield. I have also read that some people just throw away the heat shield. Another alternative would be to cut the rotten metal out from the bottom of the heat shield and fabricate a small section for the bottom bolts and rivet it on.

I know the answer is probably to keep going and get the bolts out and replace the heat shield with a new one, but just wondering on others thoughts/experiences.

Dom B · 20 Jan 2020

Regarding the broken bumper support stud, assuming you mean the one shown in the pic.
To save welding a new stud in place, as long as the steel is thick enough to do so, how about tapping a female thread into the arch and use a strong loctite or resin to bond a new stud in place. Alternatively you could drill it out and use a Rivnut Nutsert to take a new stud or cap screw.

Regarding the heatshields. While the rear end is apart I would keep going and replace them with new ones.

Windy101 · 21 Jan 2020

Dom B said:
Regarding the broken bumper support stud, assuming you mean the one shown in the pic.
To save welding a new stud in place, as long as the steel is thick enough to do so, how about tapping a female thread into the arch and use a strong loctite or resin to bond a new stud in place. Alternatively you could drill it out and use a Rivnut Nutsert to take a new stud or cap screw.

Regarding the heatshields. While the rear end is apart I would keep going and replace them with new ones.

The stud you are pointing to is the one I am needing to repair. I could use resin to locate a new stud, but I was thinking maybe drilling and tapping would be the way to go. Happy to hear from anybody with experience.

As far as the heat shields go I am just going to continue and replace them. No rush I suppose, its not 993 weather at the moment :thumb:

andyobro · 21 Jan 2020

I had one of the undertray studs pull out, havent fixed it as yet. I did find these stud rivnuts, but havent looked into cost and tooling as yet.

https://www.thorintl.com/RIVKLE-Blind-Rivet-Nuts-Rivnuts.shtml

I have some normal female rivnuts, was thinking of using those, a M6 grub screw and a half nut to secure in place.

Windy101 · 21 Jan 2020

andyobro said:
I had one of the undertray studs pull out, havent fixed it as yet. I did find these stud rivnuts, but havent looked into cost and tooling as yet.

https://www.thorintl.com/RIVKLE-Blind-Rivet-Nuts-Rivnuts.shtml

I have some normal female rivnuts, was thinking of using those, a M6 grub screw and a half nut to secure in place.

I have been looking at those rivnuts, they do seem to get used for a lot of applications.

I don't really want to disturb the main body of the car any more than is absolutely necessary.

Allan E · 21 Jan 2020

andyobro said:
I had one of the undertray studs pull out, havent fixed it as yet.

I had the same problem with two fixings on the undertrays, solution that worked fine, grind off what was left of the threaded stud, drill a pilot hole and insert a suitable size self- tapping screw, then grind off the head of the screw leaving enough length to put the undertray back and fix with the original or replacement plastic nuts.

Dom B · 22 Jan 2020

Windy101 said:
Dom B said:

Regarding the broken bumper support stud, assuming you mean the one shown in the pic.
To save welding a new stud in place, as long as the steel is thick enough to do so, how about tapping a female thread into the arch and use a strong loctite or resin to bond a new stud in place. Alternatively you could drill it out and use a Rivnut Nutsert to take a new stud or cap screw.

Regarding the heatshields. While the rear end is apart I would keep going and replace them with new ones.

Click to expand...

The stud you are pointing to is the one I am needing to repair. I could use resin to locate a new stud, but I was thinking maybe drilling and tapping would be the way to go. Happy to hear from anybody with experience.

As far as the heat shields go I am just going to continue and replace them. No rush I suppose, its not 993 weather at the moment :thumb:

Drilling, tapping and resin is what I was suggesting. Resin alone wouldn't be strong enough. The resin in the new tapped thread would help stop the stud from spinning in the new thread when tightening the nut over the bumper stay. Nutsert would also be worth considering :thumb:

Dom B · 22 Jan 2020

Welding would be a better option though.

Good luck :thumb:

Windy101 · 22 Jan 2020

Dom B said:
Welding would be a better option though.

Good luck :thumb:

Cheers for the input. I will drill the old one out when I get a chance and see what I am working with then.

New heat shields and bumper stays ordered from Porsche today as well as loads of miscellaneous fixings.

Endoman · 23 Jan 2020

I have used riv studs in similar applications but welding is still the better option. A decent body shop should be able to do weld studs, luckily I know a magic mobile welder. He replaced a large section of chassis leg and fitted stainless studs for me.

berni29 · 25 Jan 2020

Hi

While you are there, go in through the bumper support hole and spray a load of Tectyl ML, Dinitrol (not waxoyl) or similar in the chassis leg.

This is especially important if you have had a new section welded in as the back of the repair will rust. Of course the repairer may have done this. Not all do. Some say they have but haven't.

Berni

Endoman · 25 Jan 2020

The repair panel was made from galvanised steel , painted with epoxy paint externally and Eastwood Internal Frame Coating ( messy stuff) internally followed by Dinitrol.
As shown it was pretty bad

Windy101 · 25 Jan 2020

My car does not seem so bad. Been drilling out the lower bolts for the bumper mounts today as they both snapped.

berni29 · 26 Jan 2020

Hi

Mine had surface rust on the drivers side, and a 50p size hole on the passenger side. There really is no way of telling. Just have to have a look.

Sounds like your rustproofing technique is excellent!

Berni

guards red · 26 Jan 2020

Hi,

The studs for the bumper mounts are welded from the otherside of the panel and are actually a disc with a stud that is pushed through a hole in the shell the spot welded. The stud therefore is like a bolt with a flat round disc instaed of the hex. So the panel where the stud is mounted is quite thick and one can comfortably drill and tap it. It is a better solution in many ways as the new fixing will not rust given that the bolt is now screwing into the body and is protected.

If you choose to drill it and tap it, you can see the hole from the engine bay. You can also, if you wish, screw a bolt in from the that side giving you a "stud" in the wheel well.

If you look in the engine bay along the sides, you will see little discs welded to the panel. The studs are on the otherside of these discs.

Hope that makes sense....

Windy101 said:
I got round to a job I have been meaning to do for years at the weekend and stripped the rear bumper off to inspect the dreaded rear chassis legs.

Given the car is almost 24 years old there were a lot of seized fasteners, but I got there in the end and the chassis legs seem to just have surface corrosion.

I have a couple of snapped bolts where the lower bumper mounts go onto the body that will need dealt with.

I am however less sure whats the best way to deal with a couple of snapped studs that the side bumper stays/supports go onto. Should I just grind them flat and tack on a new stud or is there a better way to sort this.

Also you will see in the picture that the main heat shield on the rear of the exhaust is missing about 1 cm from the bottom and I can not get the bolts out from the top. What would the consensus be to do with them. I can keep at them with heat and penetrating fluid but they will probably snap anyway and need drilled out.

I can then drill them out and fit a new heat shield. I have also read that some people just throw away the heat shield. Another alternative would be to cut the rotten metal out from the bottom of the heat shield and fabricate a small section for the bottom bolts and rivet it on.

I know the answer is probably to keep going and get the bolts out and replace the heat shield with a new one, but just wondering on others thoughts/experiences.

Chassis leg repairs - Good news and few issues

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