new diff crossmember bushings are in - Q

Belgian1979vette

Belgian1979vette

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I got my new Paragon crossmember bushings and these were the right size.

This is how they fit on the frame.

Now I'm asking myself if the top of the bushing should touch the frame. The frame was zinc and powdercoated, so could be that this causes the bushing to sit lower than normal

IMG_2214.jpg
 
Yes, it should make full contact. Did you lube it before trying to get it seated?
 
I removed the bolt inside the bushing, the tab of the frame is seated in the cup of the bushing. I don't think it can go any further. I also checked the inside depth of my original bushing and compared it with the bushings i took out(the ones that were to small) but the inside cup of the bushing has the same depth.

At most there maybe a 1mm layer of powder and zinc coat in between, but that's it.

1194e33f74a62c4c.jpg

It looks strange this way, but there is no possible way to get it seated any higher.

Also when looking at the height of the iron cup in the bushing. this is a maximum of 2-3 mm below the rubber edge. If you look at the frame tab, this bends out, so I think the tab would start to ride on the edge of the cup when it would have mounted any deeper.
 
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I would bet when the full weight of the car is on there, it will seat just fine. Might need to tighten it later.:noworry:
 
what a memorable day it is.... i have to agree with Turtle..... :D

there should be alttle "give"between the crossmember and the frame, otherwise the crossmember would simply be welded to the frame.

this brings up a question that Ii have been wondering about for a while: are these cushions really necessary? why not just have a solid welded crossmember ???
 
turtlevette said:
Twin_Turbo said:
Yes, it should make full contact. Did you lube it before trying to get it seated?
Click to expand...

I thought that was suposed to be a wedge interference fit. So you should not have metal to metal contact, otherwise what's the point of the rubber/poly bushing?
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it's a cone and cup fitment, the outer flange on the rubber should sit against the flange on the cup It's meant to isolate ibrations, not to sit loose and allow the crossmember to tilt under load. Look at the gap he has there.
 
this brings up a question that Ii have been wondering about for a while: are these cushions really necessary? why not just have a solid welded crossmember ???
Click to expand...

wouldn't the vibrations be bad?
 
Twin_Turbo said:
[it's a cone and cup fitment, the outer flange on the rubber should sit against the flange on the cup It's meant to isolate ibrations, not to sit loose and allow the crossmember to tilt under load. Look at the gap he has there.
Click to expand...

Yep, The cone wedges very tight into the cup. If i remember right the cone part is rubber or poly. If it's bottomed out metal on metal that means there is no tight fit between the cone and cup.

With all this being said, i'm still not sure by looking at the picture what is going on. Is the connection tight? It doesn't look bottomed to me. I'm just going by what he's describing to us.



Moonsteel said:
this brings up a question that Ii have been wondering about for a while: are these cushions really necessary? why not just have a solid welded crossmember ???
Click to expand...

wouldn't the vibrations be bad?
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No, It'd just be noisey in the cabin. I have those aluminum disks that provide a connection in case of complete failure of the bushing. You can hear the rear end make its whirring sound a little.
 
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I went out and looked at the differential crossmember of my 1970. I purchased the car in 1992. As far as I know, the differential crossmember has never been removed.....can't be sure, this car has a whole lot of surprises that are surfacing as I dismember it.

The bushing does not touch the frame on this car. Eyeballing it, it looks like there's about a 3/8 inch gap between the bushing face and the frame.
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Surprises. The right quarter panel in front of the right wheel and underneath the bumper is a bondo sculpture. The front clip has been replaced, a sheet metal screw used to hold two panels together during repair penetrated the vacuum tank, making it very difficult to remove...it took me a long time just to realize the tank was attached to the body by a screw. Laying underneath the car, using a handheld long hacksaw blade, I was able to run the blade between the body and the tank and tediously saw it intwo. The windshield wiper door bracket on the right side of the car was cracked. Removing the original windshield wiper door caused the attaching bolts to shear, leaving parts of the threads inside the door. Bought a new (used) windshield wiper door from J&D Corvettes in Bellflower, Ca and a new (used) wiper door mechanism from Paragon. ($$$$$$ and time). Sent my wiper motor assembly to Paragon to be restored. They said it was not a 1970 Corvette wiper motor. Back to the front clip. It's really awful. It's been pieced back together from panel fragments. There's a lot of bondo that can be seen underneath. I really need to replace the entire front clip if I'm going to make this a whole car again.
 
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MYBAD79;85507 this brings up a question that Ii have been wondering about for a while: are these cushions really necessary? why not just have a solid welded crossmember ???[/QUOTE said:
I believe some of the drag racers have done this. Differential gear noise will be connected to the frame. These guys will probably never hear this noise.....well maybe if the diff grenades.
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turtlevette said:
Yep, The cone wedges very tight into the cup. If i remember right the cone part is rubber or poly. If it's bottomed out metal on metal that means there is no tight fit between the cone and cup.

With all this being said, i'm still not sure by looking at the picture what is going on. Is the connection tight? It doesn't look bottomed to me. I'm just going by what he's describing to us.
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I didn't mean metal to metal, there's a lip on the perimeter, that shoudl sit flush to the metal cip, the thickness of this lip is the distance you want between the 2 metal faces when fully seated. You can see it in his pic. His is not even close to being fully seated.
 
Well, the cup is tight, since there is no rock (which surely would exist if the cup would have any lateral movement when it is bottomed out).

I asked the same Q over at CF.

There were some guys that sent pictures of an untouched frame.

Apparently the gap is there originally as well.

http://forums.corvetteforum.com/c3-...67-rear-differential-crossmember-bushing.html

I'm with Marck, that it might have been better if the top of the bushing would touch the frame, but apparently this is the way the factory designed it for one or the other reason (i assume for vibration reasons).

On the other hand. Those trying to raise the diff, might get it 3/8 " higher when they have a suitable metal spacer installed...
 
On my 68, I was upset the rubber flange didn't touch the frame. At that time I assumed with was just another flawed repro part. I used a flapper sand wheel and smoothed down the frame socket (male) and also the socket hole in the bushing. I was able to get the rubber flange pretty close to the frame. It was about that time, I went out and looked at the 70 and saw that a gap appeared to be OK.
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It really helps to have another car around that's about the same vintage! Many times working on one, I go out and look at the other. For instance, that little spring on the back of the accelerator pedal. I just could not get that little sucker on. Finally, I went out and felt the one on the 70. (I couldn't see it so I had to close my eyes and go by feel). Once I could imagine in my mind how it was orientated, I went back and quickly installed the spring on the 68.
 
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