Improving Your Imperial for Towing

Ross Alexander

  In response to your question about the original factory service tips, I no longer have the advice from Chrysler in regards towing with the C/Y bodied cars. I most recently ran across a reference in the public library (main branch) in a couple of books on towing "lost" (not catalogued) in the Transportation Section. The author of this book on "How To Tow" (or some such) noted that although Chrysler limited the '67 Imperial in his possession to (as I recall) about 3,500 lbs due to 2.94 gearing, low output 440 (about 275 net SAE today), and overall vehicle weight, he nevertheless used his to travel the AL-CAN Highway past Anchorage with an over 6,000 lb trailer. He went on at some length in regards other Chrysler products and it had some good pictures of these locomotives under a full head of steam.

My maternal grandparents last tow car was a '68 Monaco with the 440-Magnum, 3.55 gears and 10 mpg solo or towing which they used to travel full-time until 1971 with nary a serious problem. From what I remember, a very general consensus was in favor among all the folks we talked with about the superiority of the driveline/suspension of Chrysler products as tow vehicles. (Although a friend used his '69 Imperial sedan to tow thru 1973 but experienced continual overheat problems, and switched to an Oldsmobile).

We used a '73 Town and Country (friends used a '72) for years, but my old man switched over to Cadillac in '76 (and ran up 190,000 before selling it to a car collector who still hadn't needed to replace the motor at 240K miles). Beyond the money and time to repair, modify and update the vehicle, I see no "good" reason not to do this. But a 3,000 lb boat under tow and a 6,000+ lb tow are worlds apart. I feel that to do a heavy tow with one of these cars requires good planning, and I hope the following will serve as a template:

I've been giving thought to and trying to research the problems you've been contemplating and am now considering the following: Given an "up" weight of 5,500 lbs with driver/passenger, a little luggage, full fuel and Class 4 hitch, what mechanical and suspension problems need to be modified to tow a 6-7000 lb trailer?

First, motor output has to be increased to 350-375 "at the wheel" horsepower with 3.23 gearing (my reasonable minimum; 3.31 to 3.54 is better) with 475 ft-lbs torque from about 1800 rpm up to near 4000. I am planning an engine rebuild utilizing the 4.15 "stroker" crank new from Mopar with -452 or -906 heads "flowed" (Hughes Engines, Muscle Motors, etc) to provide a 20% or better gain in the sub .450 lift range to optimize low lift and not loose the efficiency the engine was given by the factory. By increasing cubic inches - with a custom camshaft delivering a smooth idle and high vacuum to operate the power accessories - I believe I'll be able to very significantly broaden the performance envelope. Of course, the attendant systems of fuel and ignition delivery will have to be modified, but nothing outrageous.

Second, this will necessitate a stronger rear axle and transmission set-up. A Sure-Grip or a Detroit Locker-style traction device with 3.23 or better gearing (3.73 or better for mountainous roads) will be needed. Which in turn begs the question of drive shaft strength with (those quiet but, "hmmm, I wonder . . ?) constant velocity joints. The trans needs to be upgraded to current diesel truck strength bands and clutch plates with the Hemi 4-pinion carrier and shift lever, plus an auxiliary oversize (24,000 + GVW ) transmission cooler and auxiliary filter with a deeper pan and extended pump pickup (haven't yet consulted with Turbo-Action, TCI or Level 10 Transmissions on this for pricing, but I expect to spend around $1200 with a torque converter built for my particular application); and the stock motor and trans mounts will need converting to modern "locking" engine mounts coupled to polyurethane transmission mounts (Energy Suspension). C-body mounts are available, but I don't know for the Y-body.

The radiator ought to be replaced with a ultimate heavy duty piece from Griffin or US Radiator (preferably with 1.25 to 1.50 tubing); and a thermostat (Robertshaw HD) of about 180F should work. The fan shroud should be completely sealed to the yoke, and the fan clutch and fan itself need to be in best condition. Have seen this new EVANS non-aqueous propylene glycol coolant advertised as needing only 5-7 PSI to operate; anyone know anything yet? Otherwise, new hoses, clamps and a pressure check after professional back flush and refill with one of the new "silicate-free" coolants (Havoline DexCool). We like RedLine "Water-Wetter" as well.

Brakes should be rebuilt to highest possible standards and I intend to investigate with HPC and other providers the feasibility of having a true metallic-ceramic heat barrier applied to the calipers and drums (as well as the vented interiors of the disc).  I'll also check DOT-approved stainless steel braided brake line hose replacements, possibly all new stainless hard lines and a brass-sleeved master cylinder. Also riveted, not bonded, pads and shoes, but the material composition is not yet settled. A very careful brake job by an experienced professional shop who tests all components and system to provide "blueprint" application of front/rear and side/side hydraulic application. An imbalance virtually unnoticeable in a solo vehicle is a real problem under tow.

[A company called DECELOMATIC in Phoenix has for years advertised "exhaust brakes" for gasoline powered vehicles and I need to update my information concerning this, but the big truck "jake brake" evidence is convincing. Anything I can do to reduce panic stops and keep my attention outside the vehicle is warranted expense. (See Trailer Life magazine advertisers index)].

Replace all the rear suspension bushings with grease-able polyurethane or (better) spherical nylon (Global West; I don't know sizes or even availability) to keep the rear from tracking separately from the front. A rear anti-sway bar is mandatory if equipped without the Panhard rod. Yes, seven leaf springs (National Spring Co, or Detroit Eaton) with NEW u-bolts, double-headed nuts and front spring pack clamps (Competition Engineering). Check and re-weld or replace spring hanger axle attachments and box or re-weld body attachments. This will cost some solo ride comfort, but stability is improved even over superior Imperial setup. The front suspension should be rebuilt if much over 50m since last done and be sure to carefully check condition of front sway bar bushings. I have yet to find any replacements for these and would be grateful if anyone has a line on a source (69-71 C-body). As these rear springs are 2.5" wide, I'll be investigating as to whether the BF Goodrich "Velva-Ride" replacement rear shackles will fit our applications: they take the sting and the jounce out of rear axle movement under light/solo driving.

So far as the unibody is concerned, once you tow a big load there ain't no way around the fact that it'll never quite be the same. So be it. Just gonna have to investigate those welds THROUGHOUT the car and repair 'em. Even body-on-frame is affected. But a "pickemup" just ain't gonna get it for this boy . . . so a careful check of BODY HEIGHT is warranted. (This entails more than just front height adjustment, and you may have to align and realign before it is right. Be sure you have the weight representing the driver and passenger IN THE CAR when it's on the align rack). Once the front end is up to par, a measurement of body height with a half-tank of fuel and, note, again, the proper amount of weight in the vehicle representing the normal towing conditions (if the vehicle is used 40% or better for towing miles); a check with and without the trailer of the points the factory service manual shows as "level" (or see FWD Toronado 67-70 manual for the idea) to arrive at the best compromise between tow and solo. Mainly, don't head down the highway "nose up". Your steering/braking control is compromised badly. Expect that you may have side-to-side imbalances which will need to be corrected. Air shocks ain't worth a nickel (shock mounting points were never meant to hold the weight, just to dampen the motions), but my experience with KYB's (Just Suspension) on my C-body are good. Can't pay too much for the handling/accident-avoidance improvement here. What is ya'lls experience with either Koni or the new, rebuildable, adjustable HAL Corp shocks?

As many of you are aware, the A, B, and E body guys have for years used sub-frame connectors to tighten up the body. Has anyone out there had the same made for their C or Y body and, if so, could you share the details? I expect to have to cut into and re-weld the floors, but at what front point did you attach said connectors. (Of course, for b-o-f guys, new body to frame bushing are in order.)

As for the hitch, we for many years used a guy who has since grown old and "retired" to shoeing mules and horses to customize our hitches (if this gives you an idea of what a good "hitch" man needs for patience). It is either right so far as distributing weight is concerned or it is not. I expect to have to first find someone with a lot of experience and then pay for the dead-on correct relationships here. It may be that I set up the sub-frame connector and weight-distributing hitch relationship in a to-be-specified manner barring anyone else's experience, (my granddaddy has "pulled through" that caravan park in the sky, and my daddy won't get back out of his "burban nor does he "remember how it was done", the old snake). There is a regular "shelf full" of books on this and other related how-to's of towing. See "Trailer Life" magazine.

The area that you may find most discouraging is the electrical system. You'll need a fatter alternator, the biggest battery, and, unless you rewire the car, regular wiring problems are EXACERBATED by the stress of towing. But you're already a "whiz", right? (I ain't, but I get a little better every so often). You'll want to replace both the turn signal and emergency flashers with modern xtra-heavy-duty ELECTRONIC ones.

I'm considering having the different wiring harnesses rebuilt using one-grade heavier marine-grade tinned wiring with a polyethylene coating and GM Weatherpak connectors, but have shied thus far from quotations. Also, gauges for trans temp, voltage, oil temp and vacuum are a good idea. Jacobs makes a great ignition system and wires and I'm very fond of Bosch Platinum spark plugs. Anyone?

Bob, I've about worn you out now, but I like the CB to keep me abreast of what's happening beyond the city limits. Join AAA , Good Sam, and carry a cell phone I guess, and pay lots of close attention to those very correct adjustments you've had made throughout your car (you did have the rear axle bearings serviced on the 8-3/4 didn't you?), and keep up those synthetic lubricants you've switched the Imp to. (Right?). Be aware that there are no easy solutions in pulling a big trailer, the forces generated are tougher even than drag racing on the driveline/suspension.

Now for steering. Mine is loosened up and I will be investigating the Dodge truck replacement shaft from Borgeson as well as a blueprinted gear box from Lares or Lee or someone for a blueprint version that will fit my C-body (69-71). Also, the pump: Does anyone know of a preference between the .94 and 1.06 pumps? An external cooler is also warranted; a Q-code 428 Ford I once had had this mounted on one of the hard lines. Any ideas here?

As for tires, I will fit the largest 15" radials with the best handling design I can find. At this point I lean toward the Goodyear Eagle GT+4 (whitewall available in up 235-R70/15), but am told that Avon and Pirelli stock some tall & wide tires. Anyone? Our family experience with tires and towing (since the 1940's) has always been: Five new to start with and never rotate the spare out if the replacements come in 45-60,000 mile intervals. Then, another new one in the trunk.


From Wayne Jorgensen, 12/2006:

I have been emailing John Corey off line in my quest for a hitch for my 1966 Imperial.

I have finally been successful, and I thought I would share the outcome with the list, in case the question comes up again. 

The hitch that John has installed on his Imperial is a Hidden Hitch, model 82200.  It is a universal fit hitch designed for motor homes with frame rails between 31" and 46" wide.

The hitch is still available from JC Whitney, but if you ask for a hitch for a 57-66 Imperial, they will not be able to help you.  However, if you search their site, you will find it listed as an adjustable motor home hitch.  You can also find it on Hidden Hitches web site, where you can download installation instructions.

Thanks to everyone who offered suggestions.

Wayne Jorgensen

1966 Imperial
1971 Imperial

10 Jan 2007

According to the 1975 Parts book, the original REESE TOW BAR KIT part number is 3837-658.  This is the weight distribution and frame bolted structure WITH a square receiver opening. It does NOT include the tongue and ball.  I am not sure which class it is, but the description says it is 7000 lbs max weight and 700 lbs max tongue weight.

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