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Windy101
Spa-Francorchamps


Joined: 05 Jun 2015
Posts: 306



PostPosted: Mon Jan 20, 2020 3:27 pm    Post subject: Chassis leg repairs - Good news and few issues Reply with quote

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.
 



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Rotten heat shield, bolts at the top firmly seized
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Dom B
Österreich


Joined: 10 Apr 2010
Posts: 976
Location: Wimborne

1996 Porsche 993 Carrera 4S

PostPosted: Mon Jan 20, 2020 6:02 pm    Post subject: Reply with quote

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.
 



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Windy101
Spa-Francorchamps


Joined: 05 Jun 2015
Posts: 306



PostPosted: Tue Jan 21, 2020 8:39 am    Post subject: Reply with quote

Dom B wrote:
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
 
  
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andyobro
Monza


Joined: 02 Nov 2007
Posts: 222
Location: Poole


PostPosted: Tue Jan 21, 2020 8:50 am    Post subject: Reply with quote

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.
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Windy101
Spa-Francorchamps


Joined: 05 Jun 2015
Posts: 306



PostPosted: Tue Jan 21, 2020 9:17 am    Post subject: Reply with quote

andyobro wrote:
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.
 
  
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Allan E
Monza


Joined: 17 Jun 2017
Posts: 158
Location: Rowlands Gill, Tyne & Wear


PostPosted: Tue Jan 21, 2020 3:46 pm    Post subject: Reply with quote

andyobro wrote:
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.
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2016 Macan DS
1987 Mercedes 300SL (R107)
 
  
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Dom B
Österreich


Joined: 10 Apr 2010
Posts: 976
Location: Wimborne

1996 Porsche 993 Carrera 4S

PostPosted: Wed Jan 22, 2020 7:05 am    Post subject: Reply with quote

Windy101 wrote:
Dom B wrote:
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


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
 
  
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Dom B
Österreich


Joined: 10 Apr 2010
Posts: 976
Location: Wimborne

1996 Porsche 993 Carrera 4S

PostPosted: Wed Jan 22, 2020 7:06 am    Post subject: Reply with quote

Welding would be a better option though.

Good luck Thumb
 
  
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Windy101
Spa-Francorchamps


Joined: 05 Jun 2015
Posts: 306



PostPosted: Wed Jan 22, 2020 11:39 am    Post subject: Reply with quote

Dom B wrote:
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.
 
  
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Endoman
Barcelona


Joined: 11 Apr 2011
Posts: 1435
Location: Bolton U.K.


PostPosted: Thu Jan 23, 2020 7:36 pm    Post subject: Reply with quote

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.
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Porsche 993 Coupe 9m RS Replica
 



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berni29
Indianapolis


Joined: 24 Oct 2009
Posts: 2335
Location: Kent


PostPosted: Sat Jan 25, 2020 9:41 am    Post subject: Reply with quote

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
_________________
993 C2 Tip 1994 197k miles. Black and Grey. M029 & Bilstein HD's, Elephant Racing RS bushes F&R, RS mounts, strengthened engine carrier, 100 cell cat inserts, HID's. Solid steering arms mod, top of the engine rebuilt, mapped by Wayne, suspension set up by Chris at CG.
 
  
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Endoman
Barcelona


Joined: 11 Apr 2011
Posts: 1435
Location: Bolton U.K.


PostPosted: Sat Jan 25, 2020 10:43 am    Post subject: Reply with quote

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
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Porsche 993 Coupe 9m RS Replica
 



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Windy101
Spa-Francorchamps


Joined: 05 Jun 2015
Posts: 306



PostPosted: Sat Jan 25, 2020 8:14 pm    Post subject: Reply with quote

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



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berni29
Indianapolis


Joined: 24 Oct 2009
Posts: 2335
Location: Kent


PostPosted: Sun Jan 26, 2020 4:15 am    Post subject: Reply with quote

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
_________________
993 C2 Tip 1994 197k miles. Black and Grey. M029 & Bilstein HD's, Elephant Racing RS bushes F&R, RS mounts, strengthened engine carrier, 100 cell cat inserts, HID's. Solid steering arms mod, top of the engine rebuilt, mapped by Wayne, suspension set up by Chris at CG.
 
  
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guards red
Hockenheim


Joined: 10 Jan 2008
Posts: 673



PostPosted: Sun Jan 26, 2020 2:44 pm    Post subject: Re: Chassis leg repairs - Good news and few issues Reply with quote

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 wrote:
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.
 
  
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