Packard Forum Index » V-8 (1955-56)

My 1955 Patrician with a 3.54:1 axle surges while under heavy throttle at speeds between 35 and 80 mph. It seems to usually occur while in high gear converter drive, but I have felt surging while in direct drive as well. I have never felt it surge in low gear. It's a slow surging. You don't hear it, you feel it. The car just sort of slowly lurches forward and back.

Climbing a long, steep grade at 65 MPH and roughly 3/4 throttle makes it surge. I do not know if the converter unlocks for that. If it does, I don't hear or feel it. I'm pretty sure it just grinds up in it in direct.

Rolling heavy into the throttle at 50 mph unlocks the converter and it surges the whole way on up to 80 MPH whether you keep the throttle steady or go ahead and floor it after you reach 60 MPH (flooring below 55 mph downshifts to low...don't do that). Again, I cannot tell if or when the converter locks at those speeds.

The engine has good power even while surging. It will continue pulling hard. It's not like the surging that I have experienced in other cars due to ignition or carburetion problems where they fell flat on their face if you opened the throttle more. I do not hear any misfiring. The engine feels and sounds strong, but you can feel the car surging.

Moreover, it does this regardless of the outdoor temperature. It is the same on a 20-degree day as on a 90-degreee day. It's not a form of vapor lock.

Sometimes when it's surging you can let off the throttle partially then roll back in and it's better.

I have:

1. Replaced the fuel pump.
2. Replaced the fuel line between the pump and carburetor.
3. Replaced the fuel filter.
4. Blown out the fuel line between the tank and fuel pump to make sure it was not leaking or restricted.
5. Checked the rubber fuel hose at the pump.
6. Rebuilt the carburetor (Rochester 4GC).
7. Rebuilt the engine ignition system. Coil, points, condenser, wires, plugs, all of it.
8. Driven without the gas cap in case it was sucking a vacuum.
9. Changed the transmission fluid (Type F), adjusted the bands, adjusted the shifter linkage, and adjusted the throttle linkage.

Not one of those things has altered the surging even the slightest bit.


I don't know. I'm starting to think it might be the transmission slipping, but I don't get any of the "groan" that people describe when their lockup clutch is going out. The lockups that I hear at lower speeds are always crisp and clean, but I cannot hear or feel what is going on with the clutch at higher speeds.

I'm at the "get over it and live with it" stage.

It could still be a fuel supply issue, such as a pin hole in the fuel line between the pump and the tank or any other sort of leak. A non-working fuel cap vent might cause it.

It's possible the vacuum advance could cause it, or a lack of lubrication on the distributor rotor or too much lubricant on it. Too much or too little fluid in the transmission could cause it. Some automatics are very sensitive to fluid level. Some cars have the wrong dipstick in the transmission.


Long shots: A problem with motor mounts or with the throttle linkage could cause a feedback effect.

A problem with the fuel flex line or fuel pump linkage might cause it, as could a defective fuel pump diaphragm or spring or valves.

A weak or broken valve spring might give a surging effect.

Clogged exhaust?

When I first purchased my 1956 Caribbean it was running a single Rochester 4-bbl and had the surging symptoms you describe. Ultimately, the solution was to replace the carburetor main jets with a set one step richer.

PS - I've still quite quite an assortment of those jets, let me know what # you wish and I'd be glad to check.

I had the exact same problem with a 1972 Thunderbird. Main jets one number richer eliminated the surge and improved performance.

Hooking up a tachometer would show you if the enngine speed is is fluctuating and help you in your diagnosis.

Quote:

As far as I know, not unlocking at 3/4 throttle is normal. Do you have the throttle lever extension on the transmission?

I don't think this is surging related, just commenting on the transmission. Transmission problems (for fairly obvious reasons) often happen at a certain RPM, certain gear, certain temperature, etc. Since it happens the same in all possible states I think the transmission is fine.

Try disconnecting the vacuum advance line at the carb and plugging the port.

Try driving it with the air cleaner off. I had running problems on my '51 when running at higher speeds, which I eventually traced to the matting inside the air cleaner. Took me four months to figure it out after doing a lot of the things you mentioned in Post #1.

The carburetor is definitely not lean. Rich, actually. I live at high altitude and left the standard jets in it because it's not rich enough to hurt anything and it allows me to drive to lower altitude without damaging the engine from being lean.

It's not the gas cap. I've driven with the cap off with no change.

It's not the vacuum advance. The old vacuum advance didn't work and it still surged the same as it does with the new vacuum advance.

It's not the points or condenser. I've been through several sets. No change.

It's not the fuel pump. Three different fuel pumps all acted the same.

Nothing is out of place or clogged in the air cleaner. I soaked that whole thing out with kerosene and thoroughly inspected it before I ever drove it.

No valve springs are broken. I looked at them all when I had the valve covers off not long ago.

The fuel line is not clogged. I can blow a high volume of air back through it. Pinhole air leak, maybe, but usually that makes the pump lose prime when the car sits and I do not have that problem.

Motor mounts are good.

Throttle linkage is good.

Exhaust is not clogged.

Carburetor bowl vent is sealing properly and adjusted properly.




I wonder if it's some sort of fluttering in the air cleaner or carburetor. I can imagine the oil in the air cleaner getting sucked up into the gauze then draining back and getting sucked back up again in a fluttering rhythm. Something similar could happen with the air and fuel flow in the carburetor as well. Some models of four barrel carburetor can get secondary flutter. I might switch a pleated paper air cleaner onto it or disable the secondary barrels of the carburetor and see what happens.


It is definitely a weird one.

Sounds like it is time to hook up a gauge to the DirectDrive port and watch the pressure. Also hook up a tachometer as bullish—ter suggested. If you don’t have someone to monitor and record the pressure, rpm, speed and surge, setup a video camera to record the test and look at the data after.