Jacking up C3 Front end or rear end in "one Shot"

[David H.]

Re: Jacking up C3 Front end or rear end in "one Shot"

This is one I have heard but truly do not understand. The body is mounted to the frame in a number of places. The frame is a strong steel structure supporting the body. ....

Keith

Not so strong.

C3 Targa Top originally was to be a single piece. Tests found unless car was absolutely on flat ground tops would not install as frame/body twisted.

A redesign was required. Result: two piece Targa - with center support from windshield header to rear bow - added necessary stiffness.

Redesign and production of two piece Targa top took time. For that reason, (I remember) in 1968 first ~12,000 cars were convertibles.

Dave

[Kenneth B.]

Re: Jacking up C3 Front end or rear end in "one Shot"

I am talking about a 4 point lift not a ramp lift. Trust me I saw it happen on a C-2. The C-3'S even had a pin & receiver in the top of the door to help stiffen the convertible up.

[Keith M.]

Re: Jacking up C3 Front end or rear end in "one Shot"

Keith

Not so strong.

C3 Targa Top originally was to be a single piece. Tests found unless car was absolutely on flat ground tops would not install as frame/body twisted.

A redesign was required. Result: two piece Targa - with center support from windshield header to rear bow - added necessary stiffness.

Redesign and production of two piece Targa top took time. For that reason, (I remember) in 1968 first ~12,000 cars were convertibles.

Dave

Disclaimer...I am an engineer and eternal sceptic. I still think there is more urban legend to this one and technical details are critical. Do you recall where you heard/saw the targa top design thing? It would imply part of the assembly line was not flat and resulted in twisted frame going down the line.

Further, not saying if you lift one corner the frame won't "twist"...the question is by exactly how much?? And to the don't open the doors point...the rear of the door is not locked into place preventing front to rear lateral play to some extent when closed. I am not saying all of this is a total non-issue...just think it is very overblown most of the time. If one has the car on four well placed jack stands...not much different than being on 4 wheels.

[Mark E.]

Re: Jacking up C3 Front end or rear end in "one Shot"

If one has the car on four well placed jack stands...not much different than being on 4 wheels.

That's not my experience with C2/C3. Door gaps change enough to see when on jack stands, and often the latch becomes misaligned enough to feel when latching or unlatching the door. Think about it... there's over 1,000 pounds of engine and other stuff cantilevered beyond the front jack stands, enough moment to cause deflection.

[Leif A.]

Re: Jacking up C3 Front end or rear end in "one Shot"

That's not my experience with C2/C3. Door gaps change enough to see when on jack stands, and often the latch becomes misaligned enough to feel when latching or unlatching the door. Think about it... there's over 1,000 pounds of engine and other stuff cantilevered beyond the front jack stands, enough moment to cause deflection.

And, therein, lies the difference between the car being on the ground (on it's tires) vs the car being in the air on jack stands with all that weight hanging/sagging down...simple physics.

[Timothy B.]

Re: Jacking up C3 Front end or rear end in "one Shot"

Same sag in the rear of the frame if not properly supported.

[Kenneth B.]

Re: Jacking up C3 Front end or rear end in "one Shot"

[QUOTE=Keith Michaud (67636);928828]Disclaimer...I am an engineer and eternal sceptic. I still think there is more urban legend to this one and technical details are critical. Do you recall where you heard/saw the targa top design thing? It would imply part of the assembly line was not flat and resulted in twisted frame going down the line.

Further, not saying if you lift one corner the frame won't "twist"...the question is by exactly how much?? And to the don't open the doors point...the rear of the door is not locked into place preventing front to rear lateral play to some extent when closed. I am not saying all of this is a total non-issue...just think it is very overblown most of the time. If one has the car on four well placed jack stands...not much different than being on 4 wheels.[/Q
So why did GM go to the trouble to put pins & receivers in the doors then. I will buy your story if the jack is under the engine.

[Keith M.]

Re: Jacking up C3 Front end or rear end in "one Shot"

In either this thread or another I mis-stated where my jackstands are located. Two are under the frame directly in front of the rear wheels. Other two are under the front crossmember spread as wide as possible. Now I know...some might take issue with the crossmember not being an integral welded part of the frame..but...

[Mark E.]

Re: Jacking up C3 Front end or rear end in "one Shot"

In either this thread or another I mis-stated where my jackstands are located. Two are under the frame directly in front of the rear wheels. Other two are under the front crossmember spread as wide as possible. Now I know...some might take issue with the crossmember not being an integral welded part of the frame..but...

I often place jack stands under the frame horns (locations shown in the service manual) or under the front shocks (not shown in the manual). Either causes less frame flex than the side rails; under the front shocks mimic load from the tires.