gv28953

Hi everyone. I have been removing all the under trays and sill covers on my 964 and several of the captive nuts welded to the body shell are badly corroded/snapped off.

Is there a recommended method of replacement?

Regards, Guy.

apanossi

If you are talking about the studs from the body, then you will either have to weld on a new stud or some have mentioned drilling the stud base out and putting in a rivnut. You would then use a bolt to hold on the covers instead of the plastic nut.

gv28953

Yes, I was talking about the studs from the body. So, no magic wand solution then!
Thanks for the suggestions. I am reluctant to pierce the body floor as (unlike other parts of the car) it is rust-free! Do you think I could have them welded without causing damage to the carpets (on the sills particularly).
Regards, Guy.

ALSPEAKE

Are the studs even available? They're a very course pitch thread to suit the plastic nut.

-nick

Maybe?
http://www.borte.com.cn/goods.php?id=2454

These are referred to as an M5x1.6 fir tree stud. I have no idea if these are correct, but that's as close as I've found.

JasonAndreas

999.503.094.00 is the part number for the M6 x 12 weld studs that attach the center cover to the body. To replace you cut them as close to the body as possible and then grind away the remainder with the tip of a 1" wide belt sander, the same type that you would use for removing spot welds.

robt964

During the refurb of my car, I replaced all these underbody studs with stainless riv-STUDS. These are like a riv-nut however they have a protruding stud. The underside was receiving the full treatment and so sealed and painted afterward. Those studs are never gonna rust now

-nick

Thanks for this! I didn't think that a part number existed for these.

gv28953

Hi Everyone,

Thanks for all the suggestions. Since posting this thread, I have found something that might be interesting. There is a firm called BigHead that makes captive bolt and nut plates in stainless steel.

https://www.bighead.co.uk/

They are for building into fibreglass or can be bonded/welded/riveted on.
I think I am going to try bonding these on. I will post the results (in a few weeks!)

Thanks again, everyone.

Guy.

HiWind

i think Rob's rivnut idea is better but even the new GT4 has the same captive bolts on the bottom (though far fewer)

-nick

Sorry folks, I thought that you were talking about the coarse studs that hold the bottom of the rocker/sill covers using plastic nuts. Those are the "fir tree" style. I measured mine as M5x20mm.

If anyone is in need of the rocker panel studs, I bought some "Opel Corsa wheel arch fender mounting screws" on ebay to try out. They're M5x18 with the correct fir tree thread, and they have a flat platform to bond them to the sheetmetal.

NineMeister

The studs are welded on using a single sided spot welder, so the issues you have are that:
a) you have not got a spot welder
b) you have to strip the interior to ensure the weld spot does not set the car on fire.

The inexpensive work around is to weld new studs onto some small plates, grind off the remains of the old stud flush with the body, then bond the plate onto the pan with body adhesive (or strong epoxy). Seal around the plate and you're done. Even with mild steel studs these plates should last another 25 years and of course can easily be removed if you want to effect a factory quality repair at a later stage.

gv28953

Hi everyone,

Thanks for all the excellent suggestions. I am sorry for not replying earlier, but I did not realise exactly how to get all the replies up. You are correct Nick, some are the fir tree type, but I was going to use the stainless "Big head" type and use conventional nuts to hold the sill covers on. Actually, I would imagine the plastic nuts would probably work with conventional M5 bolts as they are quite soft.

The other good thing about the "Big head" rivnut is that they have a small dent in the bottom, which allows you to locate them exactly, before grinding off all of the old stud. I have found so many other rust-orientated jobs that this one has been put on the back burner, but I will post results one day!

Regards, Guy.