Open all the doors to put on a lift?

[GTOger]

I was at a tire shop a couple weeks ago and 2 of the techs insisted that the proper procedure for putting a C4 on a lift was to pop the hatch and hood and open the doors. The reason was something to do with the rigidity of the car and putting stress on the fiberglass. This seemed odd to me, but I'm a relative C4 noob. Therefore, I thought I'd ask here before I get the car up off the ground. What gives?

[Scrrem]

I thought is was the exact opposite...I thought you wanted to keep the doors and hatch shut to keep the chassis from flexing and causing fiberglass damage. :icon_scra Am I off base here?
Rich

[hiperf406]

Discount Tire in Queen Creek Az did the same thing to mine, gave me the same answer. I don't personally know if it makes a difference or not. lorne #1748

[ZR1Vette]

When I first got my ZR-1 (about 3 years ago) I too also heard about the C4 "on a lift" issue. After researching (reading/talking to ZR-1 owners/and more research) I found there was indeed some cases reported of a C4 being jacked up on one lift point (such as using the jack to change a tire) and having the windshield crack or top misalign from racking the chassis. The common denominator was a door(s) being open.

Now, can I absolutely verify the validity of these reports?...nope. But I do know if you plan a do an asymmetrical lift you are to keep doors and hatch closed since in those positions there is added (how much do not know) structural integrity. Some have even suggested that in addition to door being closed you need the targa top screwed in place. Now if you are doing a 4 point (aka symmetrical) lift there is not need for the 'keeping the doors/hatch closed' etc. protocol since there is equal force being maintained on the chassis lift points. And obviously if using a four post lift (wheels on ramps) again makes not diff about doors open or closed. The C4 chassis is known for its less that stellar rigidity (chassis flex was somewhat addressed in the C5 and then more aggressively addressed in the C6).

I think the GM folks recognized the flex issue since in the MY90 ZR-1s (I think this was changed in MY91+?...I know in MY93+ was changed) since there was an additional door to body pin guide/pin guide receiver>>

This if from my MY90:http://i17.photobucket.com/albums/b79/MRBLU/ZR1doorinsidedetailwithpinkeeper.jpg

With this feature there would be 4 'anchor' points for the door (two hinges, door lock/striker and the pin/pin guide.

[Aurora40]

I was at a tire shop a couple weeks ago and 2 of the techs insisted that the proper procedure for putting a C4 on a lift was to pop the hatch and hood and open the doors. The reason was something to do with the rigidity of the car and putting stress on the fiberglass. This seemed odd to me, but I'm a relative C4 noob. Therefore, I thought I'd ask here before I get the car up off the ground. What gives?
That is what shops that believe wive's-tales do. If anything, opening the doors and removing the hatch make the frame more likely to bend.

The FSM has very clear jacking instructions, and it doesn't include popping the top or opening the doors.

[GTOger]

Alright, so in other words it sounds like a load of bull-patooey. With the body flex I have seen on the car with the top off vs the top on, I saw where there could be some plausibility to what the guys were saying, but sounds to me that it's better to keep the car as rigid as possible, and that means doors shut.

[ZR1Vette]

10-4

[Paul Workman]

Must be a Discount Tire policy. They use a 4-point lift under the frame, so I don't care if they "just hafta" open the doors, hood, and hatch - it isn't going to hurt anything. And, if it will keep them from making a fuss, I'll just :rolleyes: and keep quite.

P

[secondchance]

My experience in structural flexing of C4s:

I ordered and finally took a delivery of 1984 4+3 manual, Z51 C4 in early 84. This car flexed so much that with the roof off, going over a rail road track, stering wheel would shift left to right as much as 1/2". This car had the door pins ZRVette talks about.

Then there was a write up in a magazine that the Chevy engineers revised the fron "K" member (my guess is the cradle and diagonal bracing to the side rails) I believe for the MY 86. The fact that they introduced convertible may have had a lot to do with this - possible damage to covertible roof structure w/ so much flex. They also added "X" bracing (stamped "C" section" and reinforced bulkhead behind the seat backs.

My 91 ZR-1 I bought in 91 was a vast improvement over 84 in many ways - structural, NVH and above all, 375 hp.
This car still flexed with the roof off and living in Florida I use to drive a lot w/ the top off.
So, I went to Corvette Masters in Casselberry (right behind Roger's) and had Robbi cut a steel plate and stich weld and colse the convertible "C" section "X" member. This was a vast improvement in this member actually performing the way it was intended.
I can't recall exactly (been almost 20yrs...) but after bolting on the "X" member while the car was lifted on a 4 point lift, either the top couldn't be unbolted or reinstalled (I think it was the latter). He had to drop the car on the floor, loosen the "X" member attachment bolts, drive around a little and let the car settle and finally re-tighten 4 bolts.
After this mod, car most definately stiffend substantially even w/ the top off. However, the draw back was I could see the cross member while approching the car from distance and did not like this minor cosmetic wart - perhaps if not aware may never notice this. By the way, 91 had door pins also.

My current car, a 94, after a discussion w/ RKreigh, I installed the "C" beam plates and w/ the top on, I could definately tell an improvement - car feels the front and the rear are finally not independent of each other. I never removed the top since install so I don't know how this feels w/ the top off. This car does not have the door pins.

I know some cars, when lifted w/ 4 point (wheels unsupported) lift with the doors closed, would not let you open the doors due to tension pulling on the striker. I experienced this with my 79 Trans Am. This concern may have been passed down the road w/ yonger mechanics and over time the reason for this procedure forgotten.

If you think about it C4s, as flexible as they are and at worst, are basically front structure and rear cage (quite strong actually) connected by 2 parallel box members (weakest point). When twisted (driving around w/ the top off would introduce more torsion then jacking up one corner, I think) flexing occurs between these box members which is covered by the sill trim - flexible piece - and never heard of paint/fiberglass cracking from stress on any part of the car.

Just wanted to share my experience and thoughts.

[GTOger]

Must be a Discount Tire policy. They use a 4-point lift under the frame, so I don't care if they "just hafta" open the doors, hood, and hatch - it isn't going to hurt anything. And, if it will keep them from making a fuss, I'll just :rolleyes: and keep quite.

P

Good call, Paul. And yeah, it was Discount Tire and a 4-point lift.

And hey, Secondchance... good share! Thanks, man!

[LancePearson]

I have a 76 l48 four speed and a 91 zr-1 and the 91 is infinitely more rigid than the 76. When you jack the 91 up with the floor jack just behind the front wheel at the correct jack point it lifts both front and rear equally. Driving the car it is so much more rigid than the 76 it's not even close. I now infinitely prefer driving the 91 largely because it is more powerful and so much more stable on a road, lower and bigger than the 255 tires on the 76. So far I still have kept the 76 but I drive it rarely now. I'll probably sell it in a year and if I do I might just go ahead and buy another Zr-1. I keep my tops off though the bronze colored one is in the back in its clips in case of rain so all my observations above are with it out, not in.

Lance P.

[scottfab]

Absolutely. All doors and hood and back hatch should be open. Otherwise the sky will fall. [-X
I heard it on the "internet" :thumbsdo:

[efnfast]

Maybe the thought at the tire shop is, make sure the doors are open before you lift the car, because you won't be able to open them once in the air?

[GOLDCYLON]

Good call, Paul. And yeah, it was Discount Tire and a 4-point lift.

And hey, Secondchance... good share! Thanks, man!

My thoughts as well. GC

[ZR1North]

My thoughts as well. GC


Ditto for me, Secondchance. Appreciate it when people take the time to support arguments with this kind of useful detail - many thanks!

[Kevin]

I have a 76 l48 four speed and a 91 zr-1 and the 91 is infinitely more rigid than the 76. When you jack the 91 up with the floor jack just behind the front wheel at the correct jack point it lifts both front and rear equally. Driving the car it is so much more rigid than the 76 it's not even close. I now infinitely prefer driving the 91 largely because it is more powerful and so much more stable on a road, lower and bigger than the 255 tires on the 76. So far I still have kept the 76 but I drive it rarely now. I'll probably sell it in a year and if I do I might just go ahead and buy another Zr-1. I keep my tops off though the bronze colored one is in the back in its clips in case of rain so all my observations above are with it out, not in.

Lance P.

while it maybe stiffer then your 76, it's not a stiff car at all unfortunately

[Gunny]

I have the "C" beam plates installed. In addition I installed the R&D Cross Bar which uses existing shoulder belt install points so no drilling required. I think the Cross Bar provides for harness install (I've not done that) plus a camera mount (I do use that) and maybe one other thing (can't remember) ... but the Cross Bar stiffened everything considerably so that, with the top off, I no longer experience the body flex as before. That was an unexpected "feature" that I'm really happy to have.

[Blue Flame Restorations]

It certainly doesn't HAVE to be done but the earlier models 63-82 cars do flex quite a bit when on a two post lift with adjustable positioning points. I would do it on these models. No reason not to. It wasn't a bad idea back in the day but not critical then either. Nothing was going to break or crack.

Since this was the case for so many years, I would only assume that the practice or belief has carried on to today.