MikeD72

I have an issue with my 1972 Corvette transmission crossmember. Upon doing the "routine" underbody nut and bolt check, I found that two of the four bolts securing the crossmember to the frame one on the passenger side and one on the driver side was missing . Further inspection showed that the bolts that were missing was because of the weld fastener nut on the frame rail were broken , so when I try to fit a bolt it spins on empty . I'm not too comfortable driving it because I feel that can be a safety issue . What would be the proper way to fix that issue ?? Is it to remove the crossmember and re-weld the nut fastener or can I just put longer bolts that goes through the top of the rail ?? Thanks!

CSX66

I think you will need to have some fasteners welded in there.

I have a similar issue on mine. There are no bolt holes in the chassis or bolts installed on my cross member. It has either been repaired at some point and the inserts never re installed or they were never put in from the factory. There doesn't seem to be any evidence of repair so maybe the later. I'm going to have to machine up some threaded inserts, drill the chassis rails and weld them in place.

I'll try and take a pic so you can see what I mean.

Cheers

Mike

MikeD72

Hey csx66 thanks for Ur reply . That's very odd that u don't have any fastener on the frame rail ?? I read that some years the crossmember was just welded on but it must of been hard if u had to work on the trans . Do any corvette sites sell a remedy for this issue ?? I will need to have someone do it because I have 0 welding experience . I was thinking just to drill a hole on the upper rail and put a long bolt that will go through both side of the rail through the crossmember and put a nut ?? Please if u can send me some pics so I can show a welder what to do . Thanks

929nitro

I don't know if all years were but manual transmissions had a crossmember that was welded in not bolted.

emccomas

C3 Corvettes with manual transmissions has welded in cross members, auto trans C3s had bolted in cross members.

Dustup7T2

I know this to be consistently true. Yup.

c69vete

At some point in time, all C-3s have bolted in cross members. Not sure when that happened, but the early C-3s could be either as stated above.
To the OP, just find a flat spot near the existing holes, drill a new 5/16ths. in hole, tap it 3/8 threads, insert a bolt and tighten. All good!(drill and tap thru member and frame) This will hold till you get around to your Frame off restoration. LOL

CSX66

Since I have no bolt holes in my chassis can you see any problems with just welding in the cross member? Mine is an auto (TH400). Alternatively I can drill the chassis and weld in some inserts.

Anyone got any pics of a welded in cross member?

Cheers

Mike

Tim 1973

I would use a THREAD NUT RIVET and replace the old threads in the original spot.

This type of thread hold well. You might need to rent the tool to install it or maybe your local fastanall will lend you one. If you are not familer with this type of insert here is a link to the tool similur to the one I have.

http://www.ebay.com/itm/New-Astro-Pneumatic-13-Nut-Thread-Hand-Riveting-Tool-Kit-with-Case-1442/251573202216?_trksid=p2047675.c100005.m1851&_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D1%26asc%3D21249%26meid%3D8342688842152325982%26pid%3D100005%26prg%3D9374%26rk%3D2%26rkt%3D6%26sd%3D161364844640&rt=nc

c69vete

Because the case of an auto tranny is one piece with the bell housing, welding in the cross member will make removing the tranny difficult, but not impossible. My car has the welded crossmember and a 700R4 auto. The tranny had to be partially disassembled, the bell housing modified slightly, and the flex plate removed for the install. If I ever have to remove the tranny myself, I will most likely cut and modify the crossmember for easier removal.

MikeD72

Hey Tim , thank you a thread nut rivet sounds like this would be the way to go . I will have to check under the crossmember if the rail frame is not too badly damage to accept the rivet . Also I checked some auto store and hardware store and they don't carry that tool , I need to find someone that will have that tool to place the the thread rivet in LA or will just need to order it .

69Vett

they are called Nut-Sert, drill the correct size hole, they install like a rivet.
the Automatic has 2 main horizontal cross bolts, and 2 on each side secondary bolts from underneath for mounting.

MikeD72

69vett thanks for Ur reply that's exactly what I needed to know , now I would rather have it done but if I can't get anybody will have to do it myself . My crossmember is holding with one bolt in each side and is a driver , I hope maybe i can't wait on it a couple weeks to fix it . Thx

emccomas

I should have been more specific...

80-82 all used bolt in cross members, regardless of transmission type.

68-79 - manual trans is welded in, auto trans is bolted in.

Note that the 80-82 bolt in cross member is not the same as the earlier bolt in cross members. There are significant differences.

loup68

CSX66, You probably have a manual frame. GM sold the brackets separately that hold the long horizontal bolts. Someone probably cut off the welded cross member and added the two side brackets and never did anything about the other four smaller bolts. Do you work for CSX? Lou.

CSX66

Thanks for the feedback. I'll have a closer look at it this weekend. Trip the paint in that area and see if there's any evidence of repairs etc.

CSX-66 is the plate on my Cobra replica. All the original Cobras had chassis numbers starting with CSX. I thought it would be a cool number plate that Cobra people would get but be fairly anonymous and understated to everyone else.

Tim 1973

You can find the threads nut inserts on ebay or fastenal if you have one in your area. I use mine all the time but live in Central Texas.

Good Luck on the repair.

Tim

MikeD72

Thx Tim , so ya I have seen them on eBay , I'm just going to get the tool and some thread nuts . Thx

Tim 1973

If you are going to purchase a set I would stay away from the short handled ones and the hand squeeze ones. The longer the handles allows you to have more force with less muscle power. I'm getting old and need as much leverage as I can get... LOL

CSX66

I've got a nutsert tool that I use for all sorts of things on my project cars. I reckon they are great. The tool I've got looks like a pop rivet tool but it has threaded arbors that pull the nutsert against a matching anvil. I'd say the biggest one you could comfortably pull up with this tool is 6mm or 1/4" You would need one of those larger tools to set a nutsert large enough for the 3/8" cross member bolts.

The other thing to consider is the hole for the nutsert has to be pretty closely matched for size. Too large and it won't grip well and will fall out or come lose.

Cheers

Mike