This Cadillac has been a real challenge to prepare for towing, and I wouldn't have attempted had it not been for the fact that I purchased nearly a year before I purchased the Airstream. On the surface it looks like a great tow vehicle:
500 cubic inch V8, 190 Horsepower (net), 360 ft. lbs. torque
Turbo Hydramatic 425 Trans Axle with 2.73 (approx.) final drive
Shipping weight of 5, 120 pounds, wheelbase 126.3", overall length of 224.1", treadwidth front 54.1" & rear 54.5"
The wheel and tire issue is actually the last thing that must be addressed before I feel that the car will be truly roadworthy. It has already had (in the last 2,000 miles):
New, custom 4-row core radiator.
New, 12,000 pound rated auxilliary transmission oil cooler.
New Cargo Coil coil springs (30% stiffer than standard)
New Monroe Air Shocks (recommended replacement by my regular Cadillac mechanic).
New Monroe gas filled front shocks (recommended replacement by my regular Cadillac mechanic).
New heavy duty water pump.
New heavy duty fuel pump.
Front End rebuilt in 1998 (4,000 miles added since)
New bushings in rear suspension
The issue has been with the original style wheels that seem to self-destruct if they hit potholes or are curbbed too often - - the rim itself remains true, but the inner "spider" gets knocked out of alignment with the wheel and vibrations and wobble results causing ride and handling quality issues. It has been a problem with the original wheels since day one, and there are 12 pages in the factory service manual dealing with diagnosis of problems with these wheels.
When checked after new tires were purchased and installed on my car it was found that three of the four wheels were bent enough to cause the a pronounced shake at speeds in excess of 50 MPH. The first route was to try to get new wheels from GM or another OEM source - - the wheels on this car were only used from 1968
to 1978 and were shared only with the Oldsmobile Tornado of the same vintages - - no new wheels were available from GM or other OEM sources. The second route was trying salvage yard wheels - - after eight with only one more good one, I wasn't anxious to continue to make multiple trips to yards more than 100 miles from home only to find the wheels to be worse that what I had. The third route was to try aftermarket wheel manufacturers -- trying to find a 15" wheel with 5 bolts on 5" center, with a 6" rim width, an offset of 3.31 and a load rating of at least 2,600 pounds" immediately narrowed the possibilities to three at one store and none at two others.
I chose to go with the wheel that came the closest to the factory specifications - - the only place where it was slightly off was in offset - - it was 3.4 rather than 3.31, and it had a 3,600 pound load rating. The net result is that the wheel is slightly repositioned within the wheelwell which places the tire such that the sidewall will contact the lip of the wheelwell if the springs compress or deflect more than 1.3" with trailer or 2.3" without trailer. Fortunately, Cadillac switched to open wheelwells in either '73 or '74 so I don't have to worry about fender skirts or this wheel would not have worked.
The AirLifts/Firestone Air Springs or ShockWave 9000 are to help insure a stable ride height when towing more than anything - - I don't think that there will be a particular problem when solo. We have tried all of the measurements using the already installed air shocks, and while they may be sufficient I like the idea of having a little additional insurance and feel that the combination of an air bladder device in addition to the shocks will result in a less objectionable change in ride quality - - kind of like the quad shock setup currently utilized on some of the GM sport utilities.
So far, I have had the most positive response from the AirLift dealer. He has inspected the car and has advised me that the system will work as it is currently equipped. He was of the opinion that the best ride/towing situation would be to run the air shocks at the same inflation that I do for regular daily driving and then use the AirLifts to compensate for attaching the trailer.
His suggestion was to get the hitch setup just the way that I want it prior adding the AirLifts. Then (as per manufacturer's recommendation) inflate the AirLifts to maximum pressure (this step is necessary to be sure that the air bladders properly inflate and don't get pinched in the springs) and hitch the trailer using the spring bar adjustment determined in the first step. With the trailer hitched and car loaded for the trip; decrease the AirLift inflation until the car is level. The system of hitchig up is basically the same as that recommended for the level-ride system that I had in a previous tow vehicle.
The one last option that my tire/wheel dealer is looking into is whether there is a 60 series tire that would have the same load carrying ability as the 75 series tires that I had initially purchased - - this would increase the available clearance by more than an inch - - but load rating will be the determining factor and the dealer wasn't too optimistic when I last spoke to him.
I am seriously considering going with the AirLifts as they are only about 1/3 the cost of the other two options - - and I wouldn't have to find a fabricator willing to customize the installation kits. If this doesn't work, I may end up selling the Eldorado and looking for a '70 DeVille Convertible with the more traditional rear wheel drive.