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Cadillac 59 tire pressure


Caddy59

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Hi everyone,

in the Cadillac 59 manual there is stated the recommended tire pressure of the std. 8.00x15 tires with 24 psi. I´ve put my tires just to make the car rolling without checking the pressure some months before. It looked even a bit flat, not too much, but now i checked the pressure and had 40 psi !!! I can´t really imagine how I should decrease the pressure down to 24 psi, but I noticed that the car runs after every ground waves. It feels a bit strange although all steering linkage joints are rebuilt, the idler lever as well, no clearance in the linkages. The toe-in is fixed at 0.5 degrees.

It´s my first old US car, is it normal such a strange behaviour or might it result from the big tire pressure? Or does everyone have some special advices?

Thanks much for help,

Udo

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Radial or bias ply tires?

24 PSI was recommended for the soft ride. This is too low. Try 32PSI. If the ride seems too hard you could go to 28PSI.

Your car might need a front end alignment. Caster and camber need to be checked as well as toe in. How old are the shock absorbers? They may look OK (not leaking oil) but if they have over 20,000 to 25,000 miles they should be replaced for best ride and handling.

Edited by Rusty_OToole (see edit history)
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I remember that when we got our first set of bias-belted tires, they did ride better and handle better (cornering), but I don't recall the flaky behaviour regarding pavement grooves and such (at least on our '66 Chrysler, at the time). I concur, the 24psi recommendation is for "best ride at normal loading" (which means a driver and a few passenbers with NO weight in the trunk). I had best wear and handling, in the same orientation, with 30psi front and 28psi rear. The front's heavier, so the tires on that end need more air than the rear ones (which have less weight on them).

With those narrower wheel rims and narrower tread widths, with 40psi and "no load", the tread ribs are probably spreading a little too much and WILL seek out grooves and such.

You might have rebuilt the suspension and linkage, but what about the adjustment of the steering gear? There are TWO adjustments . . . one on the top (which everybody knows about) and one on the input side of the gearbox (the "adjuster plug" adjustment). If the "input side" adjustment is not correct, it can let the steering wheel/column shaft turn and move upward in the column (a small amount) BEFORE the pitman gear in the gearbox moves to turn the car. If everything else is "to specs", then look at this adjustment, too!

Be sure to get the toe-in set to min. specs for the car! As the car moves against the roadway, this puts a rearward torque on the suspension, which then lets the steering linkage and other "joints" move rearward to get the desired "zero running toe" adjustment. Think of the static "toe-in" as the pre-load to ensure a zero running toe situation.

Some of the more modern steering gear set-ups use a more damped situation, via "high-effort" guts in the gear box . . . rather than the "zero effort" guts which many '60s luxury cars had in them. Therefore, a steady hand(s) can be more important to keep the wheels pointed where they need to be.

True, radial tires do tend to run "straighter" than other tire construction types . . . but it seems that when radial tire ply configurations were modified in the 1980s to ease impact harshness at lower speeds to better accomodate the increase inflation pressures of P-metric radials, that old "radial feel" was compromised somewhat. Rather than the outer belts running a very low angles to the rim's bead, they now look more "bias-ply" angled, more like the outer belts of the prior bias-belted tires of the later 1960s and earlier 1970s.

So, to have the best handlling/steering vehicle, you need "tight" steering system specs and adjustments to minimize the "give" of the suspension when the tires might seek to head off in other directions (other than the intended route of travel) on the roadway. EVERYTHING has to be "right" -- period. Even if it might be "new", you need to ensure the adjustments are "to spec". Harder rubber bushings are preferrable to "soft" ones, too.

ALSO, do NOT forget about the rubber bushings in the rear suspension!!! They deteriorate with time, too, and "rear wheel steering" can intensify any issues which might be present in the front end.

Just some thoughts,

NTX5467

Edited by NTX5467 (see edit history)
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