Safety First, Safety Last, Safety Always!

All credit to Tom D., Frederick, and 'funola', and many others who are working/thinking about this, for the benefit of all.  Great work!

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I have compiled a little of what you guys have done, and I want to post it here--- and a bunch of other places, too---- in case anyone missed it.  It is important stuff to know, and too important to miss.

OK Boys and Girls, we have some of our Best Guys working on this, in the interest of keeping everyone safe.  Please read it:

From ‘funola”, Peachparts Mercedes Shopforum Diesel Discussion

I dug out my Craftsman ratcheting jack stand and gave it a close look and a quick test. Mine is the 3 ton and I assume the 4 ton is of simillar design. I raised it halfway, crouched, stood and balanced myself on it, reached down and yanked upward on the handle. To my surprise, it (and I) dropped all the way to the bottom! That was very sobering! Jack stand with pins will never do that! I was expecting it to catch on the next tooth on the rack but not so. The handle only needs to be raised upwards 3/4" to release the rack for it to drop. I'll try to find the owners manual and see what warnings/ instructions are provided.

With the car's weight (let's say 3000 lbs) on the jackstands, how much force is required to hit the handle at such an angle and cause it to go up 3/4"? Any mechanical engineers here want to take a stab at it? The jack release handle is 4.5" long.

From Tom D.... bimmerforums E21 1975-83

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it's actually just a simple machine and the mechanical advantage can be calculated. however, one factor is missing, the small section of the lever on the other side of the fulcrum. lets assume it's 1 inch. the handle is 4.5 inches. the car is 3000 lb.. and has a 50/50 weight ratio. each corner carries a load of 750lb. the mechanical advantage is 4.5 therefore it would take a total of 167 lb. of force to release the lock.

3000/4 = 750
750/1 * 1/4.5 = 167

keeping in mind that work in is always equaled to work out, so in order to raise 750 lb. 3/4". you would have to exert 167 lb. on the lever for a distance of 3 3/8 "

4.5/1 * 1/.75 = 3.375

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This also assumes no damage to the ratchet or pawl and a full engagement... If you saw the pic of the junk stand I found IN USE you have to question yourself... Whiskey Tango Foxtrot are you thinking????

Thanks Tom D.

fjk, jr.  (Frederick J. Klorcyzk, jr.)

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From Tom D. again bimmerforums E21 1975-83

i finally got a chance to look at my ratchet stands and my calculations although are correct, the operation of the ratchet is not like i imagined it.

the corner weight is still 750 lb.

the lever is 5.5" on one side of the fulcrum and 1.5" on the other. that makes the mechanical advantage 8.25

the pawl only needs to lift the weight 1/16" and move sideways 1/8" to disengage.

so without allowing for friction it would only take 90 lb. of force to lift and 1/2" of travel on the handle to move it off it's perch.

not good!

Tom D

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From ‘funola”, Peachparts Mercedes Shopforum Diesel Discussion

I couldn't find my owners manual so went to Sears to look it up. I told the salesman about the accident in CT and he knew about it. He was very helpful and made a copy of the manual from a jack stand on the shelf for me.

Here it is. There's no warnings about not bumping the handle or positioning it with the handle facing away from the car.

http://www.peachparts.com/shopforum/showthread.php?t=295591&page=5

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I am going to post this all over the place, and I encourage everyone else to do the same.  There was another report of a guy killed under his car in Texas last week.