Bicycle Mechanics - Whats going on when your chain locks up.

When riding my older road bike( which in the last year has had a rear dereileur and cluster along with a front middle ring replaced) ocassionally while shifting from the smallest to middle chainring, will totally freeze up...Luckily, I was sitting..But, I back peddled and the problem corrected itself..
Once in awhile while upshifting the dereileur will overshift from the smallest to the biggest chaingring and not stop at the middle ring..I then have to down shift to the middle ring.
I suspect the front STI shifter is in needed of being replaced due to old age. But that should not cause the chain to freeze up..If standing that can be hazardous to your health...Whats up..thanks.

When riding my older road bike( which in the last year has had a rear dereileur and cluster along with a front middle ring replaced) ocassionally while shifting from the smallest to middle chainring, will totally freeze up...Luckily, I was sitting..But, I back peddled and the problem corrected itself..
Once in awhile while upshifting the dereileur will overshift from the smallest to the biggest chaingring and not stop at the middle ring..I then have to down shift to the middle ring.
I suspect the front STI shifter is in needed of being replaced due to old age. But that should not cause the chain to freeze up..If standing that can be hazardous to your health...Whats up..thanks.

Sounds like the front derailleur is out of adjustment. Sometimes if the upper limit is set too far out it pushes the chain into the big chainring too fast and locks up the drivetrain. I doubt the shifter has anything to do with it in this case. Typically when an STI shifter wears it won't go into gear all the way and requires a little "finesse".

When riding my older road bike( which in the last year has had a rear dereileur and cluster along with a front middle ring replaced) ocassionally while shifting from the smallest to middle chainring, will totally freeze up...Luckily, I was sitting..But, I back peddled and the problem corrected itself..
Once in awhile while upshifting the dereileur will overshift from the smallest to the biggest chaingring and not stop at the middle ring..I then have to down shift to the middle ring.
I suspect the front STI shifter is in needed of being replaced due to old age. But that should not cause the chain to freeze up..If standing that can be hazardous to your health...Whats up..thanks.

Sounds like chain suck to me. Chain suck is when the chain actually rides up the back of the chainring and sticks on the chainstay. The common cause is a worn chainring which has a burr that catches the chain. Sometimes you can dress up the chainring on a bench grinder, but since the smallest ring is just a plain flat stamping, they aren't very expensive to replace.

When riding my older road bike( which in the last year has had a rear dereileur and cluster along with a front middle ring replaced) ocassionally while shifting from the smallest to middle chainring, will totally freeze up...Luckily, I was sitting..But, I back peddled and the problem corrected itself..
Once in awhile while upshifting the dereileur will overshift from the smallest to the biggest chaingring and not stop at the middle ring..I then have to down shift to the middle ring.
I suspect the front STI shifter is in needed of being replaced due to old age. But that should not cause the chain to freeze up..If standing that can be hazardous to your health...Whats up..thanks.

http://www.parktool.com/repair_help/howfix_frontderailleur.shtml
Besides what has been mentioned hee check the alignment of the der. itself. the chain needs to be in a straight line with the cage, and at the proper height.

Next time it happens, before backturning the cranks, look down and see where the chain is caught. That might offer some insight.