Rear pump / push startable auto transmissions?

[TJ Hopland]

Seems like I read that the early Hydra-Matics had a rear pump and could be push started.   It was mid into the controlled coupling version 58? that they dropped the rear pump and thus the ability to push start?

Was push starting the reason for the rear pump or just a happy side effect and selling point for early buyers that may have considered that important? 

[Jay Friedman]

I believe it is until 1955 that cars with early Hydra-matic can be push started.  You have to get the car going fairly fast in neutral, 35 mph or so, and then if put in drive the motor will turn and the car will start.  If I'm not mistaken, this is no longer possible beginning in '56 with the introduction of the Jetaway transmission, though you may be right and it was not dropped until 1958. 

I don't know what the thinking was at GM when Hydra-matic was developed, but I imagine they didn't want potential buyers thinking there were disadvantages associated with the new automatic transmission.  Until the mid-fifties most cars had manual transmissions, drivers didn't carry jumper cables in the car and if a battery went dead the normal way to start the car was by rolling it down a hill or pushing it. 

[Bobby B]

TJ,
Because of that, it's not advisable to "Hook" tow an early Hydra-Matic Car without disconnecting the driveshaft first. 
                                                                                                                                            Bobby

[m-mman]

Cadillac included hand cranks in the tool kit well into the 1930s. Not that a 1930s Cadillac owner was going to crank start their car BUT . . . . . just in case . . . . . ?

Buyers of new cars are always most familiar with 10 year old technology.
Hand cranking cars DID happen during the 1920s and push starting cars was actually common in the 1930s-40s. WHY??

6 volt electric systems that required 'amperage' to crank the engine (and was easily defeated with a little corrosion on the terminals) AND generator charging systems that dont full charge at idle AND (earlier) 3 brush generators that dont use a regulator and either undercharge a battery or boil it dry. Nothing in between. Read about 3 brush systems - lots of good articles out there.

Put all this together and push starting is the only thing that will guarantee you a running engine.
"Hey buddy, I cant get my car started. Can I get a push?"
"Sure Mac, get in, I'll pull behind you" (1930s bumpers had no problems with pushing)

Another under appreciated concept. A generator equipped car can be push started WITHOUT even having a battery under the hood. The generator has permanent magnets and will create electricity just by spinning. (it needs no 'priming' from outside voltage) This will then power the coil and spark the plugs. A carburetor is completely mechanical. As long as air moves through it an air/fuel mixture will be created.

So, push start a car that doesn't even have a battery? Yup! Done it many times.
But it doesn't work with an alternator or fuel injection. 

[Bill Ingler #7799]

Here is the procedure for starting by towing with hydra-matic that is on page 12 in the Cadillac Drivers Manual, provided with each new 47. Here also is a PDF file which is a little better reading than the JPG picture.    Bill

[dadscad]

The 58 CDV my dad owned could be push started. I was with him one night in the late 50's when the battery died, a good Samaritan offered to push us and that did the trick. Got it rolling in neutral, dropped it in drive and we were off and running. My 63 will not push start.

[Bobby B]

I believe it is until 1955 that cars with early Hydra-matic can be push started.  You have to get the car going fairly fast in neutral, 35 mph or so, and then if put in drive the motor will turn and the car will start.  If I'm not mistaken, this is no longer possible beginning in '56 with the introduction of the Jetaway transmission, though you may be right and it was not dropped until 1958. 

Jay,
Yeah......I was also under the impression that for the most part, '55 was the cut-off point for push starting an Automatic Trans car....
                                                                                                                                                 Bobby

[TJ Hopland]

So it was most likely something they specifically designed to work but dropped because of extra cost and people got used to the idea of 12v and jumper cables? 

[Roger Zimmermann]

The rear pump was installed the last time on the 1958 MY. On 1959 Hydramatics, the rear pump is gone.

[savemy67]

Hello TJ,

I am fairly certain that the rear pumps in GM transmissions were not there for push-starting cars.  As you said, this just happened to be a useful side-effect.

In GM's Powerglide transmission, once the rear pump developed sufficient pressure, the pressure regulator in the front pump would be affected, and much of the transmission's line pressure would be provided by the rear pump.  This was most likely engineered because GM knew that early automatic transmissions would get poorer mileage than manual shift equipped cars.

On the highway, engine horsepower could be spared from driving the front pump, because the rear pump would be driven by the momentum of the car, particularly during coasting (the rear pump was driven by the output shaft).  This may not have been a big deal when gas cost 20 cents a gallon, but automatics were marketed as an improvement over manual transmissions, and decreased fuel efficiency was seen as a negative.

Eventually, the need for a rear pump was eliminated as engine horsepower increased and automatics became more efficient.  The Powerglide rear pump was eliminated for model year 1967.

Christopher Winter

[TJ Hopland]

Would the rear pump have helped with or been part of engine braking too?  Seems like earlier transmission had more of that going on too but it eventually disappeared.

Interesting about the powerglide having a rear pump.  With only 2 gears you would have think they would have been going for the minimum number of parts.   

[Lexi]

The 1956 owner's manual states on page 7 that 1956 Cadillacs may be push started with the vehicle in neutral at speeds between 30 -35 mph; then turning on the ignition and placing the shifter in either of the forward drive ranges (but not low). Clay/Lexi

[savemy67]

Hello TJ,

The rear pump would not have helped with engine braking per se - neither would the front pump, as engine braking works quite well on manual shift cars.  In other words, engine braking is a function of road speed, gear ratio, engine RPM, and throttle position.  At a given road speed, shifting to a lower gear makes the transmission "encourage" the engine to rev higher, but without the application of the throttle, engine compression provides engine braking whether the car has a manual or automatic transmission.

Christopher Winter

[Philippe M. Ruel]

Because of that, it's not advisable to "Hook" tow an early Hydra-Matic Car without disconnecting the driveshaft first. 
                                                                                                                                            Bobby

I read somewhere just the opposite is true.

Most cars with an automatic transmission may be towed at low speed (less than 20-30 mph on N) for short distance without disconnecting the shaft, provided the failure does not involve the transmission itself.
The rear pump will turn and lubricate the transmission by towing the car with the engine off. A transmission with a rear pump may be towed at low speed for as many miles as you please.
The absence of a rear pump will damage the transmission by lack of lubrication in a few dozen miles. Even putting the selector on N on a long downhill is not recommended as the front pump only will not provide enough lubrication with the engine idling and the car running fast.

without the application of the throttle, engine compression provides engine braking whether the car has a manual or automatic transmission.

The clutch on a manual transmission, being a purely mechanical linkage, transmits all of engine braking.
Torque converters on most automatic transmissions transmit only part of it, and none at low speeds - release the gas pedal at 40 mph with a TH400 on D, you get no engine braking at all.
Early Hydra-Matics had neither clutch nor torque converter, but a fluid coupling which transmits a larger part of engine braking than a torque converter.


No direct relationship to the presence or absence of a front or rear pump, which provide hydraulic pressure and lubrication and absorb little power.

[savemy67]

Bonjour Philippe,

"release the gas pedal at 40 mph with a TH400 on D, you get no engine braking at all."

I agree.  All you get is slowing engine RPM and a slowing vehicle.  However, if you release the gas pedal at 40 MPH and you shift from D to D2 or L, you will get engine braking (or an engine breaking  ) as there is enough of a connection through the torque converter, between the transmission and engine, for the former to affect the latter.

"No direct relationship to the presence or absence of a front or rear pump, which provide hydraulic pressure and lubrication and absorb little power."

"The rear pump would not have helped with engine braking per se - neither would the front pump..."

Nous disons la même chose.

Cordialement,
Christopher Winter

[TJ Hopland]

On the towing side of things in the manual that was posted above it did say that under normal conditions it could be towed without disconnecting anything.    I took that to mean as long as a transmission fault was not the reason for the tow you were fine. 

It just seems like the rear pump was extra parts but I guess compared to a manual, especially a non synchronized one an auto already had a lot of extra parts so a few more would not hurt. 

My engine braking question was flawed from the beginning,  I was thinking that when you took you foot off the pedal the front pump would have slowed way down but its always direct coupled to the engine so even though the engine may slow down its still not so slow that there would be a lack of pressure available from the front pump. 

[miketx]

Engine braking is not a feature of the engine but of the transmission. Automatics appear to coast when you left off the gas because the one way clutches they have overrun, or freewheel. Pull the lever down to two or one and you will apply an overrun clutch or band, which does not work in D, which will allow the engine braking effect.

[bcroe]

Bonjour Philippe,

"release the gas pedal at 40 mph with a TH400 on D, you get no engine braking at all."
Christopher Winter

There are a couple bands in the TH400, and they are only used
for decceleration.  When you pull the lever into a lower gear, bands
engage to prevent the car over riding the engine.  They are also
used for reverse, as I found with a trans that would not back up. 
Bruce Roe