I decided to tackle replacing the old rusted out #4 rear body mount brackets on one of my C3's. The brackets were so bad that they literally fell apart as I pulled them off the frame mount. My challenge was doing it without removing the body off the frame. After extensive pontification and engineering analysis, I came up with the following approach:

I decided to cut off the rear tab of the new bracket (the one with one rivet hole) and slide it into place from the front.




I was then able to rivet the remaining three sides per design, slide the metal body spacer back into place and bolt the assembly back together. My thoughts were the rear tab added little structurally and wasn't worth the work to jack the body up high enough to insert the bracket without modification. This worked great for my first attempt on the drivers side.



Every thing was progressing along to good to be true. Murphy always steps in just when you think you got him beat. On the passenger side, it appears the inside captive welded nut broke loose from #4 body mount cage located inside the rear compartment. From what I can tell there is no way to get anything on the nut to hold it from turning while wrenching the bolt out. I'd like to meet the engineer that designed this one.







The only thing that comes to mind is hacksaw the bolt out. Drill out the rivets holding the cage in place. Remove the cage and nut and reweld. Then replace with new TBD rivets.

Anyone have any better ideas on how to proceed?? Help

Bullshark

 

I would swear there has been a thread here in the last 3 months talking about replacing the rear #4 body mount when it just it spinds in the mount. The answer was to get someone inside the car in the far rear area and get somthing to hold onto the top of the bolt. There were even pictures I think.

I might be halucinating, but I do remember reading it. I will try searching the archives and if I find it before someone else chimes in...I'll post it.

 

I thought about that but, you can't get to the nut because it is spinning inside the cage.

Bullshark

 

I think that this is the thread I was think of.

http://forums.corvetteforum.com/show...ody+mount+spin

Sounds promising, but a decent bit of work.

 

Thanks Marty, sounds like from GDaina and lars input, the only way is to proceed here is as I feared. It looks like I can hacksaw the bolt up close to the body. I have room because the bolt did loosen up some before the nut weld broke loose. And of course the rusted out bracket is gone so it looks like I have room to get a sawzall or hacksaw up there and cut it out. Not sure but if I am able to drill or chizel out the rivets holding the cage I will then be able to remove the cage from inside (Big if???). After that, the rest of the bolt and nut should lift right out. What type of rivets are needed to repace the cage? By the way, it's a coupe so I don't have to deal with the rear deck mounting hinges, but there is very little head room to operate from the inside.

Bullshark

 

I do not know what the 'type' of rivets they are, but in the ZIP catalog they are listed as part# M-2510. They are $8 and include the #4 body mount nut cage and rivets. I honestly do not know that much about it from first hand experience. I try and read everything on the forum here everyday so my help is just comming from remembering that someone else here knew the answer and I know how to find it.

I knew NOTHING mechanically about cars 3 years about when I got my 84 Trans Am, but have been learning everyday. I got the vette almost a year ago and have been learning MUCH more since I joined the forum here. I bubba patched my #4 body mounts with JB weld since they were cracked and rusted in a few areas so I have been paying attention to body mount threads. I hope your progress goes well and I will be keeping track and when I finally get my full garage built here in the next year or so I will be doing a full bodyoff restorarion so I need to learn up

 

This is on my dreaded list. Mine are rusted solid. Will a zip cut blade get up in there.

 

Can you see the factory tag on top of the #4, it reads "Not User Friendly"

 

Bud,
That's a good idea, worth trying.
If you do tackle it soak those nuts inside the rear compartment alot more than I did

Bullshark

 

mine were so bad i didnt know there even was a support for #4...it was so far gone the mount went thru the fiberglass!

 

Bullshark,

I had to cut mine as well after they broke loose on both sides, it is impossible to get a spanner on the nut from the inside. (nd I have all my car gutted)

The kit with rivets, nuts with new bolts worked fine as my brackets were good.

 

Is there some overwhelming reason why I should go to the trouble to rivet in a new captive nut/cage, other than NCRS Seems to me, a big plate washer and new nut would be easier and work better for the next poor bastard that want's to do a frame off.......after I'm long gone

Bullshark

 

I had to take a saws-all to mine, because the bolt, shims and mount were one rusted/fused mass. While cutting along the mount bracket on the body, the rivets went away as well. Then I just knocked everything out with a hammer and punch.

 

power options...sawz all ( my favorite and fastest), a dremel or Roto Zip, drilling the bolt head ,then chisel-pop the head, like you do rivets and an air/electric grinder or cut off tool.There are also 4 and 4 1/2 inch cut off blades that will chuck up in a drill.wear eye protection.

 

I have done this to both a 69 and 79, the 79 was easier with access behind the rear speaker. I cut the head off the #4 bolt on the outside with an oxy-acetelene torch and pulled the threaded end out from the inside. Ferget the cage for the nut on the inside, replace with a washer and nyloc nut.

As for the fiberglass body support, the aluminum rivets come out rather easily. If yours doesn't just pull out with some effort, cut the rivet heads with a chizel and off she will come. As for the two rivets between the rear splash shield and mount, you can drill two 1 inch holes through the fiberglass splash shield for access and later plug them with caps. This is not necessary as pop rivets can be placed from the inside or eliminated.

 

One of these days I have to post a picture of my passenger-side splash shield. It has a nice, straight cut out of it on the fender side. Doesn't look like there is any damage to the body or anything else...just a piece cut out of it. Totally bizzare.

 

I posted a thread about this a while ago with pics.
I did this same thing on both # 4 mounts and created my very own custom upper reinforcement since my bushing broke right thru the fiberglass. My nut was spinning also, I drilled a small hole in the corner of the nut cage and put a flat head screw driver in there and jamed the nut so it couldn't spin, then just losened the bolt. Worked on my pass side #4, both #3 mounts.
Worth a try if you want to salvage your nut cage.
I ended up buying new nuts and cage.
I welded those bad boys before putting them back as to avoid this headache in the future...but i won't let those mounts get that bad every again. I want to strangle the previous owner!!
Good luck, e-mail me if you need pics.
doogie1101@hotmail.com
-B

 

I posted doing mine a while back... Used replacement pieces unmodified...

I ended up replacing the 1/4 inch pop rivits i used initially with 1/4 inch Closed end rivits...

Some joker used resin to "Glue" the old mounts to the body....

 

This is a bit off topic, but is there a good way to get penetrating oil on 1, 2 and 3 body mount capture nuts? I'd really rather not have them start spinning - especially #3 in it's blind little spot.

This is my passenger-side rear well splash shield. The fender doesn't look like it's ever had any damage - I can't imagine why there is a piece missing.

 

I think you may have a problem getting to #2 and #3 cage nuts, #4 can be hit from inside the car, and #1 from under the car.