Okay, I was involved in another thread when the subject of rear end sag came up. I noticed my rear sagged over time when I had my car up off the ground working on the backup light switch and the rear trailing arms. So..... it sagged enough to worry me, I let it down and it realigned. I have a quick jack that lifts from the frame and I was wondering what everyone does to support their car when leaving the tires on.

I know about building blocks to set the car tires on, one possibility.

What about jacks on the rear trailing arms somehere or Dub said there is another frame rail back there I can use with really tall jacks on.

Can you guys post picks of what you did with the tires on. If I took the tires off I would do like Dub says and support the car on the disc brake rotor with the lugs installed.

Thanks for the posts and pics




Drivers gap while off the ground. Passenger side is the same






On the ground the gap is closed up.






It looks like the gap is openning a little




Hard to see anything in these pics but you get the idea

 

If im changing the oil maybe I can jack up the rear diff until the gap closes while I'm working on it

 

This is how I lifted mine with the tires on. Works well and very stabile.

 

I see you also have a hardtop, if my HT is on when lifting car, I always release the front hold down latches out of fear of flexing windshield posts resulting in glass breakage. Just a friendly reminder to all, Mark

 

This is all that matters. Nothing is going to bend from it being jacked up.

 

I never worried about it, frames flex like that, for over 10 years I would jack the car up in the middle of the frame to slip the jack stands under it.....make sure your jack stands are as far forward and back as they can go. some times I would use three stands per side but that was for up front. I never worried about the back

 

We have been though this in a previous post and I will respond to your comment the same way I did before. Due to you NOT ever having to repair one that did bend...and you are STILL not convinced due to knowing everything about metal...being mechanical engineer for 25 years as you stated) ...well... I HAVE...even though you STILL can not grasp the concept that metal can bend, rust and fatigue....THUS it can occur. But you still want to dispute this. Just boggles my mind.

https://www.corvetteforum.com/forums...der-bar-2.html

Post #34...post #49...post #76.

What is funny is HOW the hinges for a 1982 Collectors Edition bend ...and many owners of a Collectors Edition know this....ad this bending in the cast metal hinge is caused by a gas charged cylinder over time.

Convertibles are different than coupes...when we are referring to the door to quarter panel gap.

The frame is supposed to flex...or it would be stiff and bone jarring as all get out.....but also the design of the frame is to support the body and stay level...when weight is being allowed to pull down on the frame....the frame can distort. Some may feel I am full of crap...but when an owner can visually see the gap increase...it does not take a rocket scientist to realize that something is NOT RIGHT.....and IF the car goes back and the door work well....WELL GREAT....for at least THAT TIME it did. Because if it is done over and over...the possibility that if the rear clip is allowed to hang and sag for a long time...that this problem may NOT go back like it did before.

Rescue Rogers (Scott),
If you need anything more from me..let me know.

AS you can see in 'sullyman56''s photos....the concept is much like what I did but he left the wheels on. THUS..the frame can not sag.

DUB

 

DUB, if you bent a frame by only jacking it up, that frame had to have been rusted to the point that the car was not safe to be driven on the road anyway.

 

Dub, You are absolutely right. I had my 74 vert on a 2 post lift last night and did noticed the body flex, and the larger door gap. When I let it down the door gap went back to normal. My frame has NO rust and is solid, spent 33 years in a garage without being touched, and is like new...

 

I dont plan on using my spare so I may pull that out this weekend. That will be extra weight gone. And I will run the tank down, that definitely doesnt take long. Thanks guys.

The design of this frame obviously shows it is designed to keep itself level with the support at the wheels, and reversing the forces obviously flexes it in the opposite direction easliy. Any weekness in the frame at the kickups would definitely be prone to failure if pulled in the opposite derection. I guess when I use my lift it will go up quickly then get properly supported as quickly as possible. No sense in testing the laws of gravity.

Thanks for everyones input.

 

SERIOUSLY????? I HATE doing this...I REALLY DO....BUT.... HERE we go again. You might have been a mechanical engineer for 25 years (as you wrote) but you obviously skipped some classes during school. By you still not understanding the FORCES AT MOTION when this occurs. I have to wonder. I swear you are just trying to not provide good technical information from what you know so much about...but rather voice your views ....which in the past thread showed to not pack that much merit. Because here you are again...doing the same thing.

I DID NOT WRITE 'jacked it up'. I DID NOT damage this Corvette...I repaired the frame...due to...are you paying attention AGAIN....due to being left on a LIFT at ANOTHER SHOP over the weekend...and the rear clip of the convertible sagged....and thus...OBVIOUSLY...the frame did NOT straighten itself out when set back on the ground...because the doors would not close and latch I DO NOT know how many days it might have been on the lift BEFORE it actually came down. I was not told that. Does not matter...it happened.

You are aware that there are OTHER panels that come into play to make the car complete..and the FRAME and why these panels are joined do provide strength. I guess I am not 'telling' you something you do not already know....but just in case....it is a combination of many factors that can cause this.

BUT...regardless of that....for someone who states that they know metal WAY MORE than I do...I still can not grasp your belief that this can not happen to a convertible....it just simply amazes me.....UHHH...actually...no it does not amaze me. To date...when dealing with this issue....I have not read one thing where you shed some of your KNOWLEDGE of metal. Which just may conform that you KNOW that FATIGUE and forces applied to steel can cause it to distort and retain that shape...and all you want to do is stir up 'stuff'.

So...with you having your car up on stands for however many years you wrote and nothing happened....either you are lucky...or you might have gotten lucky and placed the jack stands so this potential problem would not develop...or you just have the BEST frame that GM ever made.

SO am I all ears on whatever wisdom you choose to provide....SUCH AS.....ACTUALLY...how much of the metal has to be actually lost due to rust to make it...as you put it..."not safe to be driven on the road anyway." Now that can either be holes in the frame or actual gauge thickness lost due to rust. When you figure that out..unless you already know it....let us know.

You want to still dispute this and yet you did not dispute the problem that occurs to the Collector Edition rear hatch hinges that bend over time....go figure.

AND then explain this....WHY did GM put the adjustment wedges in the door jambs BETWEEN the door and lock pillar???? And WHY did they use the same type of adjustment wedges on the inside of the hatch lid opening where it gets latched to make sure the convertible deck lid does not contact the rear upper deck area????

No matter how much I try to help...there are going to be days where I feel like I am wasting my time.

OH MY GOD!!!! Somebody who actually has a CLUE!!!!!! I LOVE IT... Isn't it amazing when a person can look at something and use the brain that the good Lord gave them and realize this. There are people out that that still can think and use deductive reasoning.

SCOTT...My hats of to you.

DUB

 

NEVER open the door of a convertible any time it is jacked up or on a 4 point lift. I have saw it many times even at Corvette shops. The doors act like a upper brace to keep the body from drooping. Corvette frames were designed to be on 4 wheels NOT on 4 jacks or pads.

 

AND if the car is raised in the manner you stated...the shop should have the tall safety stands that can be set under the frame to apply upward pressure so the rear clip and front clip can not be allowed to sag all by itself....

BECAUSE...if you actually stop and look. The head of your striker bolt where your door latch latches over...will move and stop against the latch IF the rear body is sagging....so now...there is tension on the latch and door assembly. And this can pull the door with the rear clip and now it has tension on it.

And so much this also depends on when you have your door closed...and look at how much of the striker bolts head is forward of the latch pawl...so...that means that the rear clip will sag. SO IF a four post lift is being used...when the tires come off the ground you can watch your door gaps and see what is going on.

There are times that I would LOVE to but a convertible up on my lift...but I can't due to the amount of sag the rear clip and or front clip is showing when the tires come off the ground. That is when I wished I had a 'drive over' pit. So no lifting would be required.

DUB

 

I agree. I have 2 lifts in my garage & both are the drive on ramp style.