Solution for coasting an automatic transmission: external oil pump

[MetroMPG]

I had the chance to talk to a transmission expert (works at a repair shop) at the EV association meeting last night.

I described engine off coasting with an automatic transmission. Not surprisingly, he strongly advised against doing it unless the manufacturer specifically says the vehicle can be flat towed. I asked, "even for short distances - say a hundred feet?" His reply: the damage is cumulative.

However he did offer two potential solutions:

1) One was significantly overfilling with transmission fluid (maybe he was joking about this...)

2) The most sensible option was adding an electric pump inline in the tranny oil cooling line return from the radiator. He says RV drivers who flat tow "non-flat-towable" cars sometimes do this, and power the pump from the RV's electrical system.

[aerohead]

Question? If they can make a 100% electric lock-up torque-converter,can they make a 100% electric "unlocked"torque-converter,which allows the flywheel to "free-wheel"against the torque-converter? And could they unlock the transmission's tailshaft electromagnetically to allow the transaxle or differential to "free-wheel" eliminating the lubrication requirement for the auto-trans during "coast"?

[metromizer]

I worked on an gasoline-electric hybrid project, '81 Chevy Citation for Bill Brobeck and Associates.

In electric mode, we were running the motor through the GM 'slushbox', and pumping oil to get the required line pressure was a challenge for the team. For a differrent purpose I know, but we did something similar to what you suggest. I mated an OEM power steering pump to a 12v electric motor, and Bill figured out where to tap into the throttle body. I can't remember all the details, I was just the 19yr. old kid who machined the castings, set up the test bench and did what Bill told me to do. BIll stayed up late with the GM manuals and figured out the fluid logic for the project.

I wondered if while flat towing and automatc, a guy couldn't just run the engine, idling in neutral to save the transmission a slow and painful death? I'm guessing the RV guys have already figured this out.

[Andyman]

Originally Posted by MetroMPG

I had the chance to talk to a transmission expert (works at a repair shop) at the EV association meeting last night.

I described engine off coasting with an automatic transmission. Not surprisingly, he strongly advised against doing it unless the manufacturer specifically says the vehicle can be flat towed. I asked, "even for short distances - say a hundred feet?" His reply: the damage is cumulative.

However he did offer two potential solutions:

1) One was significantly overfilling with transmission fluid (maybe he was joking about this...)

2) The most sensible option was adding an electric pump inline in the tranny oil cooling line return from the radiator. He says RV drivers who flat tow "non-flat-towable" cars sometimes do this, and power the pump from the RV's electrical system.

The pump idea seems like a good one but it has to send the oil to the right place, which is the internal bearings. I'm not so sure that the oil cooler return line will feed any oil to the bearings. It would be a good idea to look at a manual to find out how the oil circuits work in the transmission you are interested in. I remember reading that there is sometimes a bolt that screws into the transmission case which leads to the main oil passage at the output of the pump. It is there to connect a gauge for pressure tests. I think that the pressure at this port is called "line pressure".

I think that the way to pump oil to this is to connect a hose to a pipe added to the side of the transmission pan, connect it to the inlet side of a pump, and connect the outlet side to a fitting screwed into the line pressure test port. It would be smart to add a filter before the pump to make sure the pump is protected from little pieces of gears and clutches. I don't think it is necessary to have much pressure from the pump. It should be good enough just to keep oil in the bearings. Maybe 5 PSI would be enough.

Aerohead, I'm sure the two modifications you mentioned are possible but I'm not sure why you would want to freewheel the torque converter. Maybe if you wanted to power something besides the wheels with your engine, you would want to eliminate the drag of the transmission oil pump. Unlocking the tail shaft is a good idea for coasting since it would minimize drag and protect the transmission when the engine is off. It could be done either internally or externally by using a synchronizer from a manual transmission.

Metromizer, you said "Bill figured out where to tap into the throttle body". You probably meant "valve body" instead of "throttle body", right? I have heard of a throttle valve in a transmission but not a throttle body.

One modification I would like is to have the torque converter clutch engage in all gears and to stay engaged even when using high loads. I don't understand why it couldn't be engaged whenever the transmission input shaft reaches a reasonable speed such as 1500 RPM. A lot of power is lost by letting the torque converter slip while climbing hills. Maybe the manufacturers are trying to extend the life of the clutch by using it only occasionally and only for light loads.

For flat towing with an automatic transmission, I did exactly what you suggested (keeping the engine idling and the transmission in neutral) when pulling one of my cars at highway speed to a new storage place using a tow bar. The transmission still worked fine when I finished the towing. The transmission oil pump should keep the oil circulating as long as the engine runs. Other ways of protecting the transmission are disconnecting the driveshaft or axle shafts and overfilling the transmission with fluid. If the fluid level is higher than the bearings then they should stay oiled.

I had one car that had both front and rear pumps in the transmission. It could safely be towed for a long distance with the drive wheels turning. The transmission was the two speed GM Powerglide which was made until about 1970.

If you want an introduction to automatic transmissions, you may like to check this web site.
What The Heck Is A Transmission Anyway?

[MetroMPG]

Andyman - thanks for the thorough reply on the issue. It's that kind of info that helps build EM into a great resource. Good stuff.

[Tourigjm]

has anyone tried this, any off the shelf products that people have had success with.

I EOC all around town in my 'rolla, but never on the highway. I don't want to end up damaging it in the long run... but im addicted to EOC now

[BBsGarage]

Something like this.

Remco Transmission Fluid Pump - Camping World

A bit pricey.

[Tourigjm]

new transmission is cheaper... i think ill keep doing what im doing and cross my fingers

[Formula413]

Originally Posted by Tourigjm

new transmission is cheaper... i think ill keep doing what im doing and cross my fingers

FWIW, I am getting similar FE to you with a similar vehicle, using neutral coasting rather than EOC. Auto trannys are very complicated and very expensive, why take chances? Read the link a few posts above for some good in depth info on slushboxes.

[MetroMPG]

Formula: I just noticed your user title and LOL'd! "I can has ecomodz?" Thanks for the chuckle.