unibody frame

[SPAIN72MUSTANG]

hi can any one help, i have the mustang at the auto shop putting on shocks and the leaf springs and the shop called saying the car frame feels week, i know unibody frames have play in it and i have the convertible should i be worried or does the frame under lift pressure really flex alot ,any one have experience with this can help me thanks ron. called saying the car frame feels week, i know unibody frames have

[CZ-75]

It is not uncommon for our cars to flex on a lift, especially a convertible.

I'm getting ready to install sub-frame connectors on mine, and I'm going to have a shop that specializes in frames do it.

I'm going to have them put the car on a frame table (frame jig, whatever you call it), and be sure the frame is as staright and true as possible, then weld in the sub-frame connectors.

I'm pretty sure my car has some frame sag, because my doors are out of alignment (although, that could be just worn hinges or a mis-aligned job when it was restored).

Either way, I want to be sure the frame is true before welding in the connectors.

BTW, my mechanic buddy leaves the doors ajar when he puts my vert on his lift to help avoid undue stress on the latches when lifting it... all due to him expecting it to flex

[SPAIN72MUSTANG]

cz-75 thanks for the tip on the door being ajar.im going to order sub frame connectors this week, i been reading up on adding them and its al postive thanks again ron.

[luxstang]

We keep the doors shut on mine, so they keep it all together when we put it on the lift.

[Qcode351mach]

I think you need some more in depth definition of "feels weak" Ask them to be more specfic..

[matrixx]

Just about every unibody car will flex on a lift. Older cars make it more apparent due to 40+ year old automotive technology. I would especially expect a vert to show even more flex.

Hell my 98 coupe has flex. I jacked up passenger side front to replace a wheel and opened the door and realized it flexed. Its just something that happens. That's why cars have suspension. (Well one reason anyway haha).

I also agree with Q, you need more details before jumping to "frame is weak".

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[caspianwendell]

I think you need some more in depth definition of "feels weak" Ask them to be more specfic..

+1 What points are they lifting it from, how much flex indicates a possible problem, do they detect rust in the frame rails/torque boxes, and inner rockers?

[cudak888]

As Q said, not enough data. How do your door gaps look when the car is sitting? How do they look when it's on the lift? What type of "flexing?"

That said, I've seen a 4,500-pound 1979 Lincoln Continental on a lift with both ends drooping 2" lower than normal and the door gaps shoving together. Flex is usual, but a convertible is always suspect. If it was enough for your shop to mention it, you need to take a look (and report back with photos if you do not feel knowledgeable enough to diagnose the issue yourself).

-Kurt

[judge]

I believe we are only talking convertibles on this issue. I have worked on a few early ones up to a 71. Normal flex (depending on jacking point) is about 1/4-3/8" total. That's from the point of most compressed with door open to the other extream most spread (also door open). The flex is concerning but when on wheel points it's always back to normal. The above measurements are approximates of what I've seen. And were with good floors and frame rails....... flex is reduced when jacking one side at a time. Paint impacts during compression should be considered, but don't seem to be an issue if I keep doors latched, as the latch and pin keep door from hitting the quarters.

[SPAIN72MUSTANG]

we'll i looked at the car and the rocker panels are bad,worse on driver side than passenger side the floor pans are rusting away and crakeing ,so the auto shop is afraid of doing the leafsprings and shocks on the rear because too many week points when lifting up,i took it to a body shop by my house and got a estimate for the work.thanks for everyone for the feed back.