In the process of my partial rear end lift project to replace my rotted out #4 mount reinforcement brackets.
They are - by far - the most rusted parts on my '69 (I hope!). I can break away the vertical flanges that came apart from their rivets to the body long ago.

Both #4 bolts snapped off at the head. I think I can coax the body off of the frame by whacking on the crusted-over spacers as I'm lifting.
The cage nuts up top just have the nuts remaining - as the cages gave up the ghost long ago and came out in rusty shards in my hands.
Any advice on how to proceed here, would be appreciated!

Also planning to replace the #3 mount hardware since I needed to remove those bolts as well to lift the rear enough.
Passenger side #3 came out the way it was supposed after several days of coaxing with penetrating oil on the threads.
Driver side started to act friendly as well, until about 4 or 5 full turns - now I can feel it spinning as if something (the cage nut) is spinning underneath.
Although I can't feel the actual square nut rotating when I stick my finger on the inside top edge of the frame rail, poking into what - I think - is the open side of the cage to feel the side of the nut. With my finger against this nut, I can jiggle the bolt head from up top, but can't feel any movement at the bottom (maybe I'm not feeling the nut?).
Anyways - was figuring on having to cut this bolt head off from the top and get access to the remains once I lift the body away.
I'm hoping the cage is still welded in place to the frame and just the nut rounded over to allow it to spin inside the cage.
Wondering if the "Square Nut" that the vendors sell for both Radiator and Body Mounts is able to be replaced inside an existing cage? Just slip it in from inside or outside opening of the cage?
Also - is the nut that's used inside the cage for the #4 Mount, the same nut that is used on #3? I already acquired 2 of those sets, but may end up using washers and lock nuts on #4s if I can't get enough lift for my rivet gun to stake the cages in there.

Thanks
The "Other" Leigh

 

Basically....do what you have to in order to get the bolts out.
A couple of mine unscrewed....
I drilled the heads off a couple....
I used aSawsall on a couple....
also used a Dremel with double cut-off wheels so they wouldn't break so easily.

While you're at it....you may as well inspect all the bolts/replace as needed.

 

Hey there "other Leigh,"

So odd that there's 3 of us on this forum... I've only ever met one other Leigh and she was a chick. And you're in Michigan, too. Small world.

Anyhow, I just did my #3 and #4 mounts within the last month for exactly the same reason. My #4 supports were toast.

I soaked the crap out of all body mounts with PB Blaster ever day for almost a week. The #3's broke loose and were turning fine until the area of the bolt below the nut hit the caged nut threads. Then... wait for it... anyone whose done that mount says with a sigh, "The damn caged nut broke loose and spun with the bolt." I'm told you can wedge a big punch into the cage along the frame rail, but I ain't buyin it. I ended up with enough bolt high enough in that little doorway to sawzall off the heads. In retrospect, when she was turning easily and seized, I should have stopped and soaked it with more PB ... OR ... I just discover this Locktite Freeze stuff that I could have used rather than going all caveman.

Another helpful item was the extractor sockets I borrowed from Hooah... oh and a longer socket with adjustable head. They are awesome help to keep bolt heads from getting slick on ya and getting enough torque on those little buggers. Good luck.

 

heads are off. drive them up out with a hammer and punch or socket extension. don't bother with the cages on number 4. they are to make it quicker to assemble when new. 2 hours fighting to rivet them in so you don't need a second person holding the other end of the bolt for 5 minutes... #3 cage actually holds the body down. this thread has some good pics. i just read it may be possible to drive a punch in between cage and spinning nut. but not easy to get to. https://www.corvetteforum.com/forums...unt-bolts.html

 

Thanks Stroh (Leigh) - I guess I'll be Leigh #3.
I still can't determine what exactly broke loose under my driver side #3 mount. The nut definitely feels loose with the bolt seized in it. I can not only turn the bolt by hand and hear the nut turning with it, I can make the pair wobble off-line from the hole.
Like I said originally, I can't actually feel anything that is loose underneath by putting my finger on it. If I knew the nut got loose within the cage, I could try the "wedge something in there" approach that was suggested. That would be the best option, allowing me to finish backing the bolt out properly, then replace the nut within the cage when I lift the body up. (hence my original question of whether the square nuts that come in the #4 cage nut kits (or the radiator mount nuts)).
Otherwise, I'm taking "Leigh #1's" approach of the dremel tool to cut off the head. Then I'm still stick with a half-bolt seized in a loose nut.
What I really want to avoid is having to replace the entire #3 cage nut unit, as I don't have access to a welder, and I'd rather not go the route of a back-up nut inside the frame to replace it.

 

Thanks Derek.
I was considering passing on the #4 replacement cage nuts and go the route of good washers and lock nuts up top.
Especially if I can re-purpose the square nuts from them to replace the #3 mount's nuts.
I've tried driving the #4 headless bolts up from the underside with no success yet. More soaking this week.
What is really fugly, is the wad of corroded aluminum and steel that's melded together and is wadded between the body and the frame bracket. That's probably going to resist my attempts to separate one from the other. I'm wondering if pounding on this with a tie-rod separator fork might coax the body off the frame?

 

you sure the #4 cages are completely detached? might be able to get a piece of square tubing on them as a wrench. i think 1-1/4 or 1-1/2.

 

Derek. The cages are gone but the nuts remain.
The new parts I have, the nuts are 1" squares.

 

i was thinking putting sq tubing over what is left of the cage. once bolt head is off, bolt should be free. it may be siezed in a bushing. i think WD and a BFH are called for here.

 

Agreed - I don't expect the nut is fused to the inside of the fiberglass. But the bushing/shims/washers sure look like an angry lump not willing to let up on their grip of the bolt.
BFH and a good sized punch will be on the agenda for this afternoon.
Then, to lift the rear of the body off the frame, I need to undo all the bolts that attach the rear bumper to the frame.
Anything else? I'm not looking for more than 4" of gap at the #4's.
Maybe the negative battery cable?
I plan to actually support the body from its lifted position (currently up on my QuickJacks), and lower the frame and QuickJacks from the body.
I've seen threads that call for support under the battery and jack trays, but where else in the rear should I be holding the body up?

 

You are lucky to that you are working with a coupe and not a convertible. I had to be very creative to replace #4 body mounts on my convertible. When I replaced them on the coupe, and I have done four of them, I cut them out with a sawzall, then bought the new nuts with cage and put them in through the inside of the car in the well. I mounted new outer covers with small screws versus rivets, and buttoned it up. I would absolutely replace the #4 body mounts on both the frame, and the body, if they are in bad shape. The #3 body mount should also be replaced, and it isn't hard to do, but you do need to lift that body up off the chassis to do this work. When I discovered my #4 body mounts were toast, and my #3 and #2 were rusted, I lifted the body to fix them all and I am glad I did because lifting that body revealed other issues which have now been addressed. Anything worth doing is worth doing well. If I were closer I'd show you how this is done. My 74 restoration shows what I had to do with the #4 mounts.
Good luck with your decision.
David Howard
AllVettes4Me

 

I figured the third Leigh may as well chime in on this thread!
I just pulled my body a week ago. t wasn't as bad as I feared.

The #3 driver's bolt was the worse and just would not budge. I cut it off. Also #2. I only cut both #4s just cause they spun.
I include this picture so you can see all the galvanic electrolytic corrosion I had on this mount, it's the nearest to the battery ground.
Also when I did get it out the threads were still bone dry. The PB blaster never soaked in. I believe the blue-green corrosion effectively sealed the threads and the penetrant could not sink down from the top.

I tried to shoot PBblaster in from the side (blue arrow) (body on) and thought I got it in there. But upon dissasembly that area was so packed with dirt as to be solid. I had to dig the dirt out to see the bolt. The threads were dry.

The bolt does go thru the frame. I figured this out later.
There is a hole in the bottom of the frame near the red arrow. It is a long way to the bolt, but if you can reach it with PBblaster that is the most important section of the bolt that needs to thread thru the nut.Just spray "liberally" from below.

I just checked a nut in it's mount. They look like they are welded in. And there is a lot of extra room. So if the weld rusted off / breaks off, yes the square nut will probably have room to spin.
BTW once my body was off I was sure I was going to have to sawzall those two mounts competely off. But I got some PBlaster on the correct part of the threads easily now, and the leftover studs came out easily with vice-grips. I would never have predicted that.

 

Wait a minute - I thought I was Leigh #3!!!
2 of us are in Michigan - but I'm a born Jersey boy! Essex county and then moved the shore in Long Branch before moving the fam to Michigan.
Today was a good day in the garage. Was successful yesterday at getting the passenger #3 bolt out per plan. The driver side #3 came halfway out then the nut started spinning.
Today I cut the driver bolt head off with a combo of regular dremel and a sawzall.
The #4 bolts, which I snapped off both heads yesterday, today I was able to punch them both up through the body.
So, now all 4 rear mounts are free!
I proceeded to dis-mount all my rear bumpers, brackets, negative battery cable, and look for anything else that might have held the body to the frame.
I took 2 cinder blocks with sections of 4x4s on top and tucked them under the battery and jack compartments.
Started to lower the car on the Quick Jack until the compartments rested on the blocks.
I had my son coax the Jack down a smidge at a time allowing the weight of the body to be supported while the frame (was supposed to) drop.
I didn't want to stress the body to the cracking point, so we were being very ginger.
I was only able to get about 1/2" separation at the #4 mounts and about 1/4" at the #3s.
Called it a night when the dinner bell rang.
Will hit again (maybe literally) tomorrow when the quitting whistle blows.
Probably have to come to the realization that I'll have to at least loosen the #2 and #1 mounts to allow the rear of the body to separate more.
I could probably re-build the #4 mounts with the new brackets, spacers, shims, and bolts.
But the #3s need new square nuts (at least 1) and I need more access to the cage to get a new nut in there from the side.
I'm not looking forward to the #2s, since I'll need to remove the speakers I mounted in the kick-panel pockets which will have to be removed.

However, I'm actually enjoying this more than I usually do, despite the challenges.
Something about being home all day, every day, without any Vette events up ahead, and not great weather for driving, that allows me to take some time to pace myself without any pressure to get back on the road.

 

Too many Leighs here! LOL I have never seen this many in one spot at once ever.

 

You can loosen all eight of the body mounts bolts and then lift one side of the car to do the driver side first, then lower it and raise the passenger side to do that work. It is much easier to lift the car one side at a time than front to back. Do your #4 and #3 on the same side at the same time and you will find it much easier to do than trying to jack the back up high enough. Don't ask me how I know this one okay?
When you open up the #2 pockets to loosen those bolts give them a huge and repeated soaking with PB Blaster and wait. Then do it again. You will also see what condition your birdcage front section is in by the amount of damage, if any, are in that #2 pocket. If you have a lot of scaling rust sitting in that pocket then take a break and drink a beer to think about next steps. Trust me on this one. If it is minor or no rust then take a break and have a beer to celebrate. New #2 and #3 body mounts are readily available from Paragon Corvette Reproductions as are frame mounted #1 and # 4 mounts. They are not cheap, but body mounts are not the time to go cheap. I had extra's but I gave them away already or I would send you a set to replace yours.
Good luck and enjoy.
David Howard
AllVettes4Me

 

Thanks David from Easton.
BTW - I spent a few weekends in a Lafayette dorm room with a girl I was dating back in early '80s. Didn't last though. Did that commute from North Jersey to Easton one time too many, and we called it quits. Good times though.
Anywho - I was up during the night picturing exactly what you are describing - to go side-to-side instead of front to back. The Quick Jack is nifty, but the fore/aft slant that it lifts the car on, causes problems when trying to prop up the body by the battery and jack compartments.
I think I will lower the frame onto jackstands in the rear, and then use floor jacks to lift one side of the body.
What are the recommended lift points for one-side-at-a-time body lift? I was thinking just a 4x4 at the rocker just inside the frame rail? Basically the outer edge of the seat pan? I don't see a lot of purchase outside of the frame rail under the door sills, and I don't want to crack anything.
Now that I'm destined to hit all 8 body mounts, I'm thinking of upgrading the spacers from aluminum to poly. I ordered a full kit of aluminum spacers, shims, washers, and bolts. But also just put in an order for a poly bushing set to upgrade early C3s. I'm thinking it should reduce the ride harshness, but not sure about the resulting increase in body flex and its impact on the fiberglass - again, no cracks!

 

not poly. rubber. poly has a short life. splits cracks leaves. then "where did my expensive pretty bushings go?" i mentioned earlier, but now it is doable. drive a punch in next to the #3 square nut to stop it spinning to unbolt. not sure if you can slide a new square nut in without cutting cage off and welding it back on. THAT cage AND #2 cage actually hold the body down. #4 cage is a convenience for assy line.

 

David - Also - with this method, do I need to loosen anything up front or underhood? I've read that some advise the front Rad core support bolts should be loosened, as well as the column rag joint.

 

Not only are there three Leigh's here, but we're all basically doing the same thing at nearly the same time. Cue the Twilight Zone intro.

 

Yeah - Well, there's not much else going on. So now's a good time to tackle projects that will cause some vehicular down time, while we wait for the fog of this virus to lift. Finally going to be a little warmer to enjoy garage work more. I've been putting off replacing the fuel lines that I bought 2 years ago, because they require some separation of the body/frame to snake them into place. Also replacing the hardware for the spare tire cover, and also refurbished both halves of the cover clamshell. Also have a replacement alarm horn to hook up while I'm up in there. Will attend to diagnosing that whole system later on this summer.
I don't mind having the car out of commission for a week or 2 with the current state of affairs - no shows, group rides, etc., plus the weather has been more like mid-March than mid-May around here. Hoping for an improvement in the coming weeks.
Stay safe.