Screw type bottle jack

I was teaching my son how to change a tire on the Tacoma... and had the pleasure of using the OEM screw type bottle jack. Actually, I was impressed by its travel... When I first saw it I thought "no way this will extend far enough."

I've never used a screw type bottle jack... Anyone know how the internals work on this? Is it mechanical or hydraulic? Has to be hydraulic, right? it more than doubled it's length.

 

Mechanical. Hence the 'screw'.

Hydraulics you pump. And they will eventually leak, so not the best choice for an OE jack/spare changer.

 

Yeah, I didn't know if there was an actual screw mechanism, or it was called that because of the rotary motion used to jack it up. I'm curious exactly how the internals are arranged... as what I know about a screw jack... the screw is a fixed length... how does this jack more than double its collapsed length?

 

Perhaps it is a screw within a screw. I believe the jack does extend in two stages.

 

There definitely are 2 sleeves... the first one extends... at that point I thought it wouldn't make it... then another sleeve extends. I thought it was a clever design and tried to Google it (I just like to know how stuff works)... but ended up empty. Thought I'd try here.

 

Correct. Double screw. While you don't get 3x closed length, you do get more than 2x, as you found. I've never seen the internals either. Maybe I'll pick one up at a junkyard and cut it open. In honor of dear old dad. He loved doing stuff like that.

 

This is the best I could find. Just Imagine that you are turning the center screw from below. When it tops out, the outer screw would start to turn.

 

Thanks for the replies. That's a good diagram... I suspect you are right in that the screw is just turned from below. I do like the idea of getting an old one to cut open. Clearwater Bill, If you don't report back in a couple of weeks, I may give it a try... "inquiring minds want to know!"