strengthening in convertables

[NO NAME]

no i am not going to build a convertable, not at present anyway but after a conversation with FC427 last night about the subframe/firewall/dash/A pillar area last night ive been thinking about it today, and i was just wondering, how do they make it all stay together in a covertable, were do they add bracing and reinforcement so the A pillars dont bend back?

[Glenn 'Stinky' Stankevicius]

The CRS kit would help out, as it ties the subframe to the welded/bolted main rails underneath

[NO NAME]

there must be more to it than that, that only connects the subframe lower legs to the rail going across the floor then two rails going to the leaf hangers, is there extra plating/bracing, rod etc around the A pilar, dash and subframe?

[ratbox]

the crs kit doesn't come close to being enough, i did an EK wagon years ago needed rails welded in simular to crs, then triangulate the sills which is a plate from the bottom of the sill to the floor, then a steel plate in the kick panel area, if it was a sedan it would have needed cross bracing behind the rear seat which would of consisted of the opening being welded closed, but because i used a wagon and welded the bottom tailgate closed that was enough also the back doors were welded shut
it was pretty rigid you could jack it up on opposite corners and lift all four wheels off the ground

[mcl1959]

John Wanner's convertible FE has a box member along the sills that extend under the subframe right up to the front crossmember. It includes plates similar to the CRS kit which tie the subframe legs to the chassis boxing. The whole body is stopped from flexing by having a giant "X" welded in from the A pillar to the rear spring hanger on the opposite side. There is also bracing behind the rear seat between the C pillars and bracing extending upwards into the B pillars and bracing in the A pillars. Even with all this, the car still flexes a little bit if it is raised on one corner with a jack. It reacts similarly to the way 60's Mustangs flex when lifted.

[JB]

The other way is to put a complete chassis under the car as Harko did a while ago with his Wagon.

[mcl1959]

I seriously doubt that Harko's attempt had any possible chance of gaining registration. Half the floor was missing and the ability to tie the shell to the new chassis was suspect at the best.
Chassis swaps are fine for pre-war cars where there was a removable chassis in the first place and the body is a strong unit designed to be bolted to a chassis. So and old Chevy can be dropped over a HQ one tonner chassis for instance with ease and it retains all its original characteristics.
BUT the FE FC is designed with an integral chassis in the body shell so to place this over another chassis means that the original chassis has to be cut from the body - you see the problems.

Far easier to build strengthening into the original chassis and much better chance of registration.

Ken

[FC427]

It would be up to the Engineer to advise you of what he required[non of us are quilified consultant engineers who are accepted buy the RTA ] to make it strong enough as it is head on the chopping block it would be very expensive and torsional test would have to be performed during and after the build to get the right amount of flex in the car . FCCOOL if you are looking to strengthen your car so you can weld the front guards on with out cracking do it once do it right and get advise from some one who is qualified to give this advice and capable of approving your work with the RTA .........FC427.....

[ratbox]

mine WAS done as per what the NSW engineer wanted, with none of the torsional bullshit you speak of, been a few years since i've seen the car but it was still rego'ed and going 6 years after i sold it, it had been all over the east coast of australia

[FC427]

Ratbox I made a simple suggestion as to what may be involved to have this type of modification approved TODAY and advised FCCOOL  he is better to consult some one who is not guessing what reinforcement would be required. In one sentence you say that you did what your Engineer wanted and then you say it did not have any torsional bullshit is it possible that your engineer knew how to advise you to build the car  because he had made some calculations or he had previous experience in this type of modification . Or are you the expert ??    X is there answer to the unknown question and a spurt is just a drip under pressure  .......FC427.........

[ratbox]

like i said i did what HE told me to do not what I thought was right, all engineers have different ideas, like the one who asked me what was done to mine and then used this bassis on a customers car that still gets around, mainly i was commenting that you need alot more than a crs kit
i think i'll let it rest with i've done one that has been engineer approved and registered in NSW that has done alot of miles and to the best of my knowledge is still going so i'm speeking from experiance, have you done one?

[mcl1959]

ratbox, as an experienced engineer building a lot of modified cars, including a number of Mustangs which we chopped the roofs off and made into convertibles, it is quite clear from your explanation that a great deal of torsional rigidity was achieved in your wagon by welding up the tailgate and rear doors - virtually making a tub of the body and making it very strong.

Each vehicle needs to be examined on its merits and each engineer will have his own method of evaluating what is acceptable and what's not.  Generally a beaming test is conducted nowadays to determine body deflection under load, but not all engineers use this test and a lot rely on examining an existing car such as yours and basing new cars on what they know to be successful.  Both methods work.

Ken

[ratbox]

yeah i know how engineers can vary
like V8 conversions some of the things people try to tell you you have to have
basically i was saying you need more than a crs kit, but i do know of a convertable where the owner said all he had was a crs chassis but he doesn't drive that car very much
and usually i would say the same thing to someone contemplating this to contact an engineer, but as FCCOOL was only curiuos told him what i had done which is what the engineer had told me to do

[FC427]

RATBOX i HAVE NOT MADE A CONVERTABLE FC STATION WAGON but I am a Panel beater and have been modifying cars for nearly 35 years and have been involved in many different modifications to cars. built HotRods Drag cars and circuit race cars . I know even the CRS chassis kit was  torsionally tested before it was approved . Since you have done this conversion why don't you help FCCOOL out with some  SPECIFIC  information with regards to the strengthening of the A pillar and sub frame to body which he may be able to draw upon to help him with his interned project . He intends to weld on the front guards on to the car and wants to make sure that the frame is strong enough so that the guard is not stressed from subframe movement and leads to fatigue  .........FC427........

[ratbox]

he asked about strengthenig for a convertable i said what i had to do FOR A CONVERTABLE
i don't want to know or care what you say you've done the specific question was early holden convertable

[RET]

A lot of heat and very little light being generated in this thread. I think the original question was answered quite a few posts back.