1966 Cadillac's Question

[Bill Young]

My Friend Doug Bailey , Director of the Peach State Chapter has posed an excellent Question. On 1966 Cadillac's why under the hood on closed models are there steel tube arms that extend from the firewall on diagonal to both inner fender wells and secure with two bolts on each ,  however on Convertible models they are absent ?

[cadillacmike68]

That phenomenon goes out to 1970. The closed cars have the fender braces but the convertibles do not, except if one has ALC, in which case least the driver side has to have a brace.

[Bill Young]

Dougs 1966 Eldorado has level control but no braces

[chrisntam]

Dougs 1966 Eldorado has level control but no braces

Where's the compressor / tank?

[cadillacmike68]

I added two to my 1968 DVC many years ago. I thought that someone had removed them in the past. Anyway it runs fine at 90 & above.

[bctexas]

My Friend Doug Bailey , Director of the Peach State Chapter has posed an excellent Question. On 1966 Cadillac's why under the hood on closed models are there steel tube arms that extend from the firewall on diagonal to both inner fender wells and secure with two bolts on each ,  however on Convertible models they are absent ?

The steel top on a closed car is a major part of the structure.  Without it, the body and frame of a convertible is typically designed with significant additional internal bracing to make up for the lack of a roof.  That is why convertibles are significantly  heavier than their two door coupe cousins.  It seems likely that given the additional structure of the convertible it was found that the diagonal struts were not needed.  Just speculation though.....

Happy Motoring!

[Mike Josephic CLC #3877]

I had the same thought as the previous poster. 
Convertibles have additional bracing in the frame
that is designed to minimize body flex.  Therefore,
the bracing under the hood was likely not deemed
necessary.

By the way, my '73 Eldorado coupe does have the
two steel tube arms as described by Bill Young under
the hood.  I don't know if the '73 convertibles had this
feature or not.

Mike

[Gary McKinney]

Where's the compressor / tank?

For 1966, not sure of other years, the compressor and tank are mounted down low at the front of the engine.

[Bill Young]

The 1965 to '70 DeVille Convertibles perimiter box frames are not reinforced as with the earlier X Framed cars

[bctexas]

The 1965 to '70 DeVille Convertibles perimiter box frames are not reinforced as with the earlier X Framed cars

Thanks Bill, that's interesting.  Do you have any info on additional structure in the body itself?

[The Tassie Devil(le)]

I do know that earlier ones had reinforced sills.

Bruce.

[cadillacmike68]

The steel top on a closed car is a major part of the structure.  Without it, the body and frame of a convertible is typically designed with significant additional internal bracing to make up for the lack of a roof.  That is why convertibles are significantly  heavier than their two door coupe cousins.  It seems likely that given the additional structure of the convertible it was found that the diagonal struts were not needed.  Just speculation though.....

Happy Motoring! 

The 1968 DeVille Convertible has a curb weight of 4,600 lbs, while the 1968 coupe deVille has a curb weight of 4,595 lbs. That's only 5 lbs heavier.

There IS some bracing under the rear seat, possibly in the frame up around the front wheels as well, but no roof = lighter so any additional bracing minus fixed roof equals only 5 lbs.

[cadillacmike68]

For 1966, not sure of other years, the compressor and tank are mounted down low at the front of the engine.

Those are later years electric pump motors. The 1960-7x giant cylinder cannot fit down in front. I have not seen a convertible with the vacuum powered ALC, so I don't know where that cylinder would sit.

[Gary McKinney]

Those are later years electric pump motors. The 1960-7x giant cylinder cannot fit down in front. I have not seen a convertible with the vacuum powered ALC, so I don't know where that cylinder would sit.

The 1966 ALC pump and large tank are definitely mounted down low at the front of the engine, on brackets mounted to a cross member.  I have a 1966 Eldorado so equipped and have seen several others the same. 

[Bill Young]

Thank you Gary , that is interesting and verifies the position of the Automatic Level Control equipment on the Eldorado for 1966. We still have no clear answer as to why no support bars on the Convertibles ?

[Gary McKinney]

We still have no clear answer as to why no support bars on the Convertibles ?

Theories, but as far as I know, no definite answer.  All I know is that convertibles did not have the support rods installed.  There were plugs placed in the bolt holes where the rods would have been attached. 

[The Tassie Devil(le)]

Could it be that fitting support bars to convertibles accentuated the "Floppiness" of the Convertible body, and caused the front fenders to noticeably move as the cowl moved?

Bruce.

[cadillacmike68]

The 1966 ALC pump and large tank are definitely mounted down low at the front of the engine, on brackets mounted to a cross member.  I have a 1966 Eldorado so equipped and have seen several others the same. 

I believe you but how did they fit it? I have a fellow member here locally with a 1966 Eldorado Convertible, Next time he has that car out I'll ask him. 

[J. Douglas Bailey]

Thanks for the conversation Gentlemen. You too, Bill... ;-) 

Easy stuff first: My '66 Eldo has the leveling tank up front, mounted on a frame member below the radiator support, just as Gary said. There's a pump or other device mounted out back, on the underside of the rear floor pan (passenger side). Mine's never worked, was bypassed by a previous owner. I installed Monro-matic Air Shocks with a filler valve mounted behind the license plate. Seems to work just fine, although I went through a period where it leaked down and I was always worried about bottoming out. Was a bad hose.

This topic was part of a string a couple of years ago, brought up by me. Ralph Messina weighed in on the matter then. (He's a guy I respect a lot because of his work on a perfect '66 Eldo.) The resolution back then, as I recall, was that the GM Body Manual indicates the Cadillac convertibles (both DeVilles and Eldorados) had the same frames, with some structural additions in the area of the rear seat/quarters. The closed bodies did not have those supports in the quarters. I was satisfied with that explanation, which handles the question about flex in the open cars. But the Authenticity Manual says nothing about the struts under the hood, and that caused me some heartburn at the Louisville GN. I was quite certain the convertibles in '66 did not have those struts, as I have seen dozens without them. The '66 SDV with 30k miles I owned five years ago (I was the second owner) definitely HAS them. In Louisville the judge said that her '67 Deville convertible HAS the struts so therefore mine must have been removed... Bill Anderson intervened.

I spoke with Knellar and Shively, who authored the Authenticity Manual, and they're aware of the gap. I was ready to put this aside until I heard from a fellow '66 Eldo owner on FB who claims his has the struts! Apparently it was a mid-year change? My car was built on May 1, 1966, among the last 10-15% of Cadillacs that year (by Body Number) and not long before they shut down the line to re-tool for the '67 Eldorados.

Thanks for your thoughts. I'm waiting to see what the next edition of that Authenticity Manual has to say about this!   Doug
 

[Ralph Messina CLC 4937]

I just saw this topic and wanted to add a few points.

First, Doug thank you for the kind words. I recall that discussion but could not locate it, which is quite common when ever I search for something. FWIW,  I’ll repeat it.

The braces being discussed are shown in the ’75 MPL as “Rod, Front Fender” Group 8.141. Two rods, forming a “V” from each inner fender to the center of the cowl,  were used from ’65 through ‘70. During those years, they are listed for all models except convertibles. They are also excluded on the ‘65 series 75  and 1967-70 Eldorados. If there had been a mid -year change, the ’75 MLP would reflect that which, it does not. If someone claims otherwise,  with respect including a judge, ask for a Cadillac publication supporting that opinion.

I have not been able to source any information as to why the rods were not used in convertibles, but believe Bruce captured the essence of the reason. When addressing the ride characteristics, the engineers design the body and suspension to eliminate noise, vibration and harshness â€" NVH. Looking at a convertible as a structure you have a bolted assembly from grille to cowl and a welded assembly from the rear edge of the door opening to the rear bumper. The center section where the door opening is located is the weakest part of the structure because there is no roof connecting the cowl to the rear body. The front and rear sub-assemblies are constructed to be rigid to eliminate noise and drumming from loose assembly. The springs and shocks are a compromise of handling and road motion transmission. Those motions always exist but become noticeable when visible. Bolting the fenders to the cowl would transmit those motions resulting in visible dash board and windshield shake. On city streets, My last Eldorado, a restored 140M mile car, had  all the road noise and creaks associated with a convertible but little or no cowl shake. My first Eldorado was an original 22M mile car that had these cowl braces installed by the previous owner. At the time I didn’t know they were not supposed to be there. That car had an annoying amount of shake.

The compressor and tank were located below the radiator in ’65 and ’66. It was moved to the strut rod in ’68 for ease of service. The ’67 tank is shown below the radiator in the SM but many have the tank on the rod. Service techs have told me they decided to relocate them because of the frequency of service……seems like the factory learned from the techs.

Hope this helps