1957-1964 Cadillac Tubular X-Frame question

[Huffstutler]

I am approaching this from two angles, one the designer posted in another thread and technical, posted here.

Everyone here knows that the tubular X-Frame design was initially developed for the Eldorado Brougham project and still seeking out which pre 1957 show cars may have had a prototype under it.  It was documented that one was tested on the streets for 3-years prior to production.

1) Why was there a difference with the rear "fork" of the X between the 1957 Eldorado and the standard Cadillac line?  The standard frame which was the "original" design and have seen SAE publications depicting the Eldorado drivetrain and suspension in this, was triangulated in the rear which also reduced trunk space and pushed the spare tire to the center.  While the Brougham was squared off in the rear like in the following 1958 model years standard line incorporated.  So, why two styles for 1957?  Both used leaf rear springs that year so doubt that was the reasoning?

2)  Why was the use of this frame all over the map with GM cars?  Chevy used it between 1958-1964 and Cadillac 1957-1964.  Pontiac dropped it in 1961 but Buick picked it up that year late in the game...why?  Especially if other divisions dropped this controversial frame due to side impact issues.... which is part of another puzzle, the Buick Riviera was the last to use it through the 1970 model year.  Oldsmobile never used it but had a variation with side rails.

One person mentioned in a Cadillac book that the frame was too stiff and caused too much thump and road noise.  Others like to blame the side impact issue for its demise but all cases I have seen involve either Chevrolet or Pontiac and mostly convertible models where the car was cut in half by side impact at high speed.  So one questions if that was a viable reason?

Maybe someone can shed some light on the development, the "why's" as to it being dropped yet picked later by Buick, and other bits and pieces you would like to share.

Thanks!
Eric

[Quentin Hall]

         A couple of things on the 57s. Remember the Brougham chassis was completely different to the rest of the line as the car had air susp and hence rear trailing arms instead of leaf springs. 58s went to coils on the rear. . . and of course Brougham was completely different dimensions to regular line as well.
        I too have wondered about the side impact issue as the sills are a structural member of the body and would offer some strength against impact. Look at any modern car.
        Obviously the cars were a design of the times and some has changed in body design but I am sure a 57 is as strong as a car with unibody design. The side rails on a 53 up to 56 chassis are also inboard of the sills so I can't really see how they would offer a great amount of side impact resistance anyhow.
        Hit anything hard enough and it will break in half. Just don't hit me. Q   

[Huffstutler]

         A couple of things on the 57s. Remember the Brougham chassis was completely different to the rest of the line as the car had air susp and hence rear trailing arms instead of leaf springs. 58s went to coils on the rear. . . and of course Brougham was completely different dimensions to regular line as well.
        I too have wondered about the side impact issue as the sills are a structural member of the body and would offer some strength against impact. Look at any modern car.
        Obviously the cars were a design of the times and some has changed in body design but I am sure a 57 is as strong as a car with unibody design. The side rails on a 53 up to 56 chassis are also inboard of the sills so I can't really see how they would offer a great amount of side impact resistance anyhow.
        Hit anything hard enough and it will break in half. Just don't hit me. Q   

Quentin,

It just seems a bit odd if the rear suspension was the factor, why was the 60 series on up style triangulated chassis was also slated for the Brougham in 1956 test shots for the air suspension?  Then it changed prior to 1957 production to the squared shape which was then used on all of the 1958 cars no matter of wheelbase?  It seemed like they were only to have the Brougham on that chassis and was even thinking going unibody with the other Cadillac's for 1957 but instead used the original design for the 1956 Brougham prototype and gave the Brougham a different shaped frame...

[Roger Zimmermann]

Eric, I cannot answer your questions. In my opinion, GM had so much money at that time that a different frame here and there had no impact on the financial situation. Another example: water pump. From 1949 to 1962, they are more or less identical; why has just 1957 a RH inlet when all other pumps have a LH outlet?

[Huffstutler]

Eric, I cannot answer your questions. In my opinion, GM had so much money at that time that a different frame here and there had no impact on the financial situation. Another example: water pump. From 1949 to 1962, they are more or less identical; why has just 1957 a RH inlet when all other pumps have a LH outlet?

Maybe someone else will have the answer but reminds me of some other GM questionable actions.  Like why did the 1935 Chevrolet Standard model have a X braced frame while the other models the VK frame and that one car one year only?  Or the 1940 Chevrolet Cabriolet have a massive overkill chassis that no other car shared and again a one car one year only?   Or why did Buick go from a X braced frame in 1958 to a K frame for 1959-1960, then go to the tubular X for 1961 when other models were dropping it due to safety issues and lawsuits?

[Walter Youshock]

Eric,  the difference in the rear "fork" between the Eldos and the standard line--are you referring to BOTH the convertible Biarritz AND hardtop Seville or just the convertible?  The frames were slightly different on convertibles due to the lack of a roof and had to be bulked up in certain areas.

[Huffstutler]

Eric,  the difference in the rear "fork" between the Eldos and the standard line--are you referring to BOTH the convertible Biarritz AND hardtop Seville or just the convertible?  The frames were slightly different on convertibles due to the lack of a roof and had to be bulked up in certain areas.

Nope, it was the shape that is different, not steel guage which I knew was heavier

Attached are examples... one showing the 1956 Eldorado prototype frame air-suspension and note the triangulated rear frame as on the standard 1957 Cadillacs.  The other example shows the standard 1957 (triangulated) 1958 (squared) and the production Eldorado (also squared) frames.

Eric

[Roger Zimmermann]

Eric,  the difference in the rear "fork" between the Eldos and the standard line--are you referring to BOTH the convertible Biarritz AND hardtop Seville or just the convertible? 

In my opinion, Eric is doing a major mistake when he refers to Eldorado models: he should be more specific and write Eldo Brougham.

[Walter Youshock]

I'm a bit confused myself...  The series 70 was entirely different than anything else where the Seville and Biarritz shared the series 62 lineage.

[Huffstutler]

Sorry for the confusion of Eldorado versus Eldorado Brougham but the question still remains the same... as you can see the section of the frame behind the rear axle is triangle shaped to the rear bumper on the non Brougham cars for 1957 (also like the 1956 Brougham concept) and squared off for the Brougham for 1957 which carried over to all frames in 1958.  So my question is why did they give the Brougham a squared rear section and the standard models have the triangle for one year only?  Why the last minute switch which carried over the following year?

Maybe if I highlight the area I am asking about you will understand better along with the previous post of pictures....

[Quentin Hall]

G'day Eric,
        There are many things that make you wonder like Roger pointed out, the 57 water pumps. Why did they go back to the 56 treddlevac style brake booster on the 58 ?
Remember that the 57 models were probably all worked out three years prior for the sake of the argument let's say 1954. The Eldorado Brougham prototype may have had a much shorter development time and the chassis may have been developed with the 57 regular line in 1954. The production Brougham chassis was possibly  developed in conjunction with the standard 58 chassis development that was possibly happening in 1955 or even 1956, hence a year or more of development apart.
         The distinguishing feature of the Brougham being Air suspension, was available only on the Brougham in 57 but to all models in 58 . The 57 standard range used leaf springs and the 58's used coils/airbags.

[Walter Youshock]

The rear suspension is the answer.  '57 standard line was leaf springs and only the Brougham had air suspension so the frame had to be modified to accommodate the air domes.  In '58, air suspension was available across the Cadillac line, as well as most or all GM cars, so the "X" frame was used on many GM cars.  Rear suspension went to coil springs so the new frame could accept either air bags OR coil springs.

There was one slight difference on the '57 Biarritz and Seville frames--one extra body mount provision.

[Huffstutler]

The rear suspension is the answer.  '57 standard line was leaf springs and only the Brougham had air suspension so the frame had to be modified to accommodate the air domes.  In '58, air suspension was available across the Cadillac line, as well as most or all GM cars, so the "X" frame was used on many GM cars.  Rear suspension went to coil springs so the new frame could accept either air bags OR coil springs.

There was one slight difference on the '57 Biarritz and Seville frames--one extra body mount provision.

Walter, I had heard that but the sticky in this line of thinking is the 1956 Brougham proto diagram shows air bags on the non-Brougham style frame.  They must have worked with that style frame to publish it and their technical finds in a SAE journal?  This is the second half of the puzzle.  Doesn't mean they didn't change designs mid-stream but there doesn't seem to be documentation about it?

Thanks!
Eric

[Walter Youshock]

Was the '56 proto ROADWORTHY?  They probably learned very quickly that the '57 X-frame wouldn't work on an air-suspended car.  With leaf springs, the weight is distributed over a broader area where the coil/leaf spring design is completely at the axle.

And Cadillac didn't make the frames.  A.O Smith was the jobber who supplied them.

[Huffstutler]

Was the '56 proto ROADWORTHY?  They probably learned very quickly that the '57 X-frame wouldn't work on an air-suspended car.  With leaf springs, the weight is distributed over a broader area where the coil/leaf spring design is completely at the axle.

And Cadillac didn't make the frames.  A.O Smith was the jobber who supplied them.

True, A.O. Smith manufactured the frame but various people worked on the design including an engineer that was assigned to this chassis - Harry Purdy.

[Huffstutler]

Quentin… bringing this back to the top because I am not sure if I had a epiphany or simply a speculation.

Going back to your idea of design being done well in advance…true, development goes as far back as 1950 and road tests around 1954.  Purdy’s chassis designs were developed and used by 1956 which is the triangulated style, not the one that 1957 service information book states “The main frame member has been curved outward at the rear to support the air suspension and to provide additional trunk capacity.”   

But this is a two-fold question.  Since the triangulated version was studied using the air bag system but at the last minute changed to the squared off style and “one” reason was trunk space, why not do it across the board? 

Unless… this was initially THE design chosen but as you said, the air suspension, which was rushed out the door anyway, was not roadworthy with this configuration and A.O. Smith had already tooled up or pressed these out, the lower volume production Brougham would have been a custom fix on the assembly line?  And the frames already geared up was used on the lesser Cadillac models?  I also note that a similar rear fork configuration was used on the 1958-1960 Pontiac’s.  A.O. Smith during these last years at this plant in Milwaukee was churning out 10,000 frames each day for various manufacturers so I am sure only a few Brougham ones with the small change would be no sweat rather than retooling that year â€" which they did for the 1958 year anyway across the board.

What do you think?

Eric

[Quentin Hall]

Eric,
     From my limited exposure to small scale manufacturing production runs I have learned that "The first is worst" ie it takes the longest to produce and it shows all the inherent manufacturing problems that need to be addressed before the regular run can start, but it also shows up the next generation of improvements that can be incorporated in the follow up redesigns and unless a large scale run follows it, it alone has to absorb the costs associated with all the tooling up. So always best to get all the ideas sorted out before you make the dies. After that first one is sorted a production run will follow like clockwork so long as you don't throw spanners in the works.
          As you say if AO Smith were punching out 10000 a day then in a mere 15 days of production they have done all of the regular Cadillac run. The first chassis would quite likely take two full weeks of preliminary setup, and two/three years of prior development so technically the first one is a very expensive item to produce.
           One thing you haven't addressed is design obsolescence. You didn't give them everything all at once. You gave it to them in dribs and drabs. So that every year there was a new development to grab the attention of the buying public. So the "extras special " Eldorado Brougham introduced air suspension to a limited few in 57 and GM gave it to the masses in 58. Q
             

[David King (kz78hy)]

The original concept was to use the space inside the frame rails as the air suspension accumulator tank.  Therefore, they were square tubing sections.  That concept was abandoned for various reasons.  The development had started at least in 55 and probably in 54.

David

[Huffstutler]

After further investigation I have come to terms that the chassis change was due to suspension but sure would like to see both the SAE Paper 580014 which discusses the design or see some early test designs.