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So.... my passenger side #4 body mount is toast. The car actually leans slightly that way on level ground, as a result. Pretty common I guess.
That's the passenger side. The bushing looks to be smooooooshed, and the knuckle above it is barely recognizable. I'd like replace them both, both I'm not about to do a frame off right now. Eventually maybe, but I'd actually like to drive my vette this summer, so I'd prefer to wait.
The driver side isn't much better.
My goal is to replace the steel "knuckle"/body mount reinforcement and the bushing, linked below. My question is: Can it be done without lifting the whole body as this next post suggests?
I found the following post on corvettec3.com and it got me to thinking. While I have the interior out, it'd be a heck of a lot easier to tackle this now if the meat of this post is true.
Here's the post from Eddie who suggests this can be done without completely separating the body from the frame.
This is for 68-72 Chrome Bumper Cars 1. start by placing the rear of the car on jack stands (rear wheels off the ground) and remove the spare tire carrier. You now have easy access to the rear bumper brackets. There are 2 in the center that go to the license plate area of the body, 2 that go to the innermost bumper mounts, and 2 that go to the outer bumper mounts. Disconnect the antenna grounding strap. Disconnect battery cable where it mounts to the frame. Loosen parking brake adjustment as much as it will go. The adjustment is in the transmission tunnel, before the cable splits off to the wheels. You do not have to completely disconnect the cable. Remove the top bolts from the shocks. If your rubber gas lines are run tightly from the tank to the steel frame lines, clamp them off with vice grips and disconnect them from the frame mounted steel lines. Make a check of anything that might connect the body to the frame in the rear, that will not give a few inches. There is an access cover in the forward portion of the rear wheel well. Remove the four bolts holding it on. This exposes the #3 body mount bolt. Now the best way I've found to remove the #4 body mount bolt is to grind off the head and push it up and out, or cut it between the mount support & spacer. You decide which way is best. You can try unscrewing it...but I fear it is futile! Do take note of how many shims are under the mount spacer also. You'll find the cage & nut for the #4 mount in a deep recess in the far corners of the rear interior. Might have to pull back carpet to find it.This is the hard part….you’ll have to loosen the #3 body mount bolt (front portion behind rear wheel well access cover) enough to get at least 2" of body travel off the frame. If it's badly rusted, soak the heck out of it. Don't disturb the #3 shims between the body & frame...no need to. I made long T shaped lift (picture an upside down T) out of 2"x8" (cross portion of T) and 2"x12" (long portion of T) lumber, long enough to fit under the fiberglass rear storage area lip. (just in front of rear cross member) I placed a floor jack under this T and it held the body up enough to be able to work on the #4. All you need is a few inches. If your sure everything is loose, and your ready to continue..lets. With the car up on jack stands, and your temp T lift holding up the body under the rear storage compartment, loosen the #3 mount bolt, and grind off that #4 bolt head taking notice of how many shims are present. Punch or pull the #4 bolt through from the inside of the rear deck, in the rear deck valley. Now give the floor jack a few pumps and watch if the body moves a bit off the frame. If not, that's OK...you'll only need a few inches to remove the #4 reinforcement. There is a cage nut & cage at the bottom of that valley. It might be in good condition...but I doubt it. Check it. If the cage is good and the bolt is rusted, you'll have to remove the cage (which is riveted to the fiberglass). The #4 mount reinforcement is riveted to the fiberglass all the way around., so to remove it you'll have to drill out the rivets. By the pix I've recently seen you may have to do some fiberglass work to repair the valley before trying to attach the new reinforcement cup. Check other sources for fiberglass repair. It's pretty easy in this case, especially since your not doing body work or painting. Only want to stiffen up the body so the reinforcement has meat under it for strength. Attach the new #4 reinforcement by either using pop rivets, or as I did, with #12 or #10 stainless steel screws , nylon lock nuts, and stainless washers. For those with destroyed cage & cage nuts, don't bother trying to re-attach the cage. It's near impossible without the body off. I used a large diameter stainless washer on the inside to retain the stainless mount bolt. Some guys have made square pieces of metal with a bolt welded to it, that fits perfectly down in that valley and accepts the mount bolt. Now..the mount bolts that come with the kits are grade 5 steel. A good quality stainless bolt is comparable to grade 5 steel. Since there is little to no stress on that bolt, I used stainless. Your call!!! Install the mount bolt, spacer, and shims. If all your shims were rusted away, you'll have a trial and error procedure trying to ad shims to even up the body . I took measurements between the body & frame through out the rear kick up (just in front of #4 mount) until the measurements were even. Mine took 3 shims on one side and two on the other. Take these measurements with the mount bolt tightened with spacer and shims in place, and the body lowered onto the frame. Well that's about all I can suggest. Hope I remembered everything...Good Luck... Eddie
Can this slight lift be done safely? Has anyone done it and what was the experience like? Troubleshooting? As always many thanks in advance.
Well the number 4 is out in the elements. Even my CA/AZ lifelong car, gave me a fit removing the bolts from both sides. they were the only bolts I had to cut out. My car had surface rust only. Its just the nature of the beast. To just replace the 4, I dont see how you can do it without at least removing all of the other body mount bolts, the bumper bracket attachments etc. Just as if you were to remove the body. But hey, I could be wrong. Even to try and re shim the body once it was back on the frame required I had to remove most everything. Then I just lifted the body enough to move a few shims around. But everything was new at that point and I did it in a few hours.
Last edited by Sunstroked; Apr 15, 2020 at 09:49 PM.
the problem with #4 is the cage around the nut. it is held to the car with a couple of rivets. a piece of square tubing around 1-1/4 to 1-1/2 should go over it and hold it in place with a pipe wrench. easiest is to put a socket on the bolt head and break the cage from the body. then drill the bolt head with successively bigger bits until head pops off. then drive bolt up into the car. the mount can be riveted-bolted to body without removing the 1-2-3 mounts. it flexed down. it'll flex back up. or get really bubba and shim body with a hunk of wood. once you get the height right, epoxy the wood between frame and body.
Edzred72 posted this here on the forum in another thread:
"The rubber body mounts found on 73-82 Corvettes vastly improved noise and ride over the solid aluminum mounts used on the 68-72 models. It is possible to retrofit the later rubber mounts on 68-72 and reap the benefits of a better ride, less road noise and less risk of fiberglass stress cracks. I recommend buying a body mount kit as it also comes with all new bolts, washers, nuts and shims."
Any thoughts on the substitution of the later parts?
Aside from needing some additional clearance to do the replacement, what other complications am I bound to run into? (I'm doing a restomod, so I could care less about it being an exact substitution.)
The shims that were on your car are probably still there and ok, It's the tin box that rots out, you'll need a new bolt (most likely) and you may or may not need the caged nut, If you're isn't salvageable there's no real reason it couldn't be replaced with a normal hex-nut and large washer, it's hidden behind the carpet back there in a pocket,
M
Edzred72 posted this here on the forum in another thread:
"The rubber body mounts found on 73-82 Corvettes vastly improved noise and ride over the solid aluminum mounts used on the 68-72 models. It is possible to retrofit the later rubber mounts on 68-72 and reap the benefits of a better ride, less road noise and less risk of fiberglass stress cracks. I recommend buying a body mount kit as it also comes with all new bolts, washers, nuts and shims."
Any thoughts on the substitution of the later parts?
)
I wanted to say there was a slight difference in thickness that someone had brought up, (the rubber was thicker ?) I briefly thought about it then when I though of the things that could go wrong as I tried to remove the #2 and #3 bolts I told myself if I wanted a smoother ride I should be driving my KIA LOL
M
I replaced the solid mounts in my 72 with the rubber or poly mounts...16 years ago. They are still working great. Was not easy and I do not remember all the details, I did loosen all the body mounts at the same time but did not remove the body. I did have to cut the #4 mounts and replace them. Much improved quality in ride and road noise. Then I installed side pipes...so much for road noise.
The caged nut was a convenience item so an employee didn't have to lie behind the seats to hold the nut while it is tightened from below. Not designed to come off 50 years later.
The caged nut was a convenience item so an employee didn't have to lie behind the seats to hold the nut while it is tightened from below. Not designed to come off 50 years later.
No doubt mine are rust fused, but I think I'm gonna try the switch anyway. Thanks fellas. ... Ordering the kit tomorrow. I'll post pics.
#4 is open at the top, fold back the carpet ears in the rear and you can get to it.
#3 I think the little cover plate at the front of the rear-wheel well will let you shoot in,
#2 you need to remove the kick panels and
#1 in through the side grills
M
Is there a way that Stroh can get PB Blaster or something like that on those bolts to help loosen their grip?
Yes access is relatively easy , but with the size of the thread and the amount of corrosion , just spraying stuff at it isn't really going to help much . The caged nut is only held to the fibreglass with 2 small rivets . so it would go together easy . Easiest way to get it out would be to climb in there with a small drill and just drill those rivets out straight away . get back outside and cut the steel cup away , to get to what's left of the steel bushing insert and grind that to pieces ,until you get to the bolt shank and cut that as well . If you just cut the head of the bolt off and start hammering it upwards , you run the real chance of driving the steel bush through the fibreglass.
Number 4 Body Mount Question
