Popular mythconceptions

[turnkey4099]

From what I understand it depends on the transmission. Some in the past had a pump in the tail section and could actually be roll started. If it does not, I don't think you can ever roll start it and make the flywheel move enough to spin the engine over. I think the old powerglide could be roll started.

Yea, that one was true back in the very early days of automatic transmissions. My brother is a professional mechanic. I told him one day of my experience with a dead battery on my manual tranny truck. I started it by coasting in reverse. Him: "you were very lucky" but didn't explain why.

 

[CobyRupert]

Yea, that one was true back in the very early days of automatic transmissions. My brother is a professional mechanic. I told him one day of my experience with a dead battery on my manual tranny truck. I started it by coasting in reverse. Him: "you were very lucky" but didn't explain why.

Did you ever find out why?
Maybe lucky that reverse was geared high enough?

 

[4570Man]

Did you ever find out why?
Maybe lucky that reverse was geared high enough?

I’ve roll started my truck by rolling backwards in reverse and going forward in forward gears. As long as you don’t use reverse going forward I’m not sure what the point is.

 

[Jstpssng]

In the olden days when many trucks with 4 speeds, like a NP-435, reverse was 8.20:1.
That could provide one heck of a jolt to the drivetrain.

A little bit different setup, but the six volt system in my father’s KB5 wasn’t very strong (were they ever?) so he would roll it backwards out of the barn, release the clutch and it would start right up. I wish that I was more mechanically inclined, when he got rid of it 10 years ago I would have grabbed it.

 

[k0ua]

Yep, I heard the same story (or joke, what ever it was).

Then there is the one about ummm starting a leaf blower..

 

[k0ua]

Did you ever find out why?
Maybe lucky that reverse was geared high enough?

One reason for being "lucky" is that there still has to be enough charge in the battery to energize the coil to create a spark to fire off that first cylinder. If the battery is flat enough, it won't fire no matter how fast you get it going. Old enough and an generator would maybe have a permanent magnet and create some electricity, but I think newer vehicles the alternator has to be excited by current to make any power.. I don't think they will self excite. I could be wrong, someone that works on alternators all day might want to comment.

 

[lilranch2001]

On this very old model, it takes a very hot gal to excite me.......

 

[4570Man]

One reason for being "lucky" is that there still has to be enough charge in the battery to energize the coil to create a spark to fire off that first cylinder. If the battery is flat enough, it won't fire no matter how fast you get it going. Old enough and an generator would maybe have a permanent magnet and create some electricity, but I think newer vehicles the alternator has to be excited by current to make any power.. I don't think they will self excite. I could be wrong, someone that works on alternators all day might want to comment.

You’re right based off my experience. My fuel injection gas truck doesn’t seem to like the idea of rolling off but maybe I haven’t tried hard enough.

 

[goeduck]

For years when I did not have enough money to buy a battery I parked at the top of hills so I could get my gear rig started. I would leave it running in parking lots while I was buying groceries, etc. those days are past :drink:

 

[dragoneggs]

I bet most of the world in which that term is used, doesn't know that actually.

You got that right. Ask 10 people 'not in the trades' what are the dimensions of a 2x4. My bet you won't get more than one with the right answer. Most will probably look at you and question your sanity.