Bicycle Mechanics - time to replace rear derailleur?

Subject is a mid-80's era Raleigh Technium mtn bike. Derailleur is a Deore XT. I've been using this bike for grocery and beer runs. I think I'd like to restore it for easy trail use for my son.

Problem is something others in BF have called "lashing" - chain jumps or skips when peddling over bumps like curbs or bigger.

History of repairs so far:
- new chain
- new rear freehub (tiagra road at 130mm was the closest fit to the 126mm dropouts on this frame)
- new 7 speed cassette with 4.5 mm spacer
- new jockey pulleys

Gave up indexed shifting - using smooth shift mode.

There was this one time - in a fit of frustration before any of the above mentioned repairs - when I kicked the rear derailleur with my foot....several times maybe...I can't remember. The cage looks bent and has resisted my efforts to straighten it. When I remove the cage and pulleys nothing appears bent.

Should I throw in the towel on this derailleur?

Thanks

You've bent the RD and/or bent the hanger as well.

concerning rear derailler, i had a problem with mine too ,changed gears to go up and all of a sudden, the derailleur fuller retracted and went right between the spokes in the rear wheel (luckily i was just testing the bike because i changed the pads earlier in the day,or else i would have been pretty mangled up lol) what could have cause the problem ?

btw the derailler is all bent now but the wheel stayed true (weird) made a quick single speed mode to save the ride day!

Mike, it could also be a worn out front chain ring. Will it skip on any of the front chain rings or just one?

Mike, it could also be a worn out front chain ring. Will it skip on any of the front chain rings or just one?

I can't bear the thought of changing the Bio-Pace chainrings :). I only use the 2 of 3 largest rings. I haven't paid enough attention to that detail to report if the problem happens on one or both. I'll keep on eye on that.

The chain length is OK using "big-big idlers vertical to 10 degree" and "little-little idlers not touching" rules googled out of BF.

I wonder if I should change out the shift cables. Maybe stickiness in cables gets jarred loose going over bumps?

I'm going to see if some gentle bending of the hanger will straighten out the chainline.

I suppose that if none of the above helps then I can replace the RD with a salvaged or cheaper replacement. The oddball 126mm rear drop outs keep me from doing too much more to this bike. Other possibilities are to keep this bike for utility and convert it to single speed or fixed gear, or make it a 3-spd by keeping the FD working.

The oddball 126mm rear drop outs keep me from doing too much more to this bike.

If you wanted to get up to current MTB standards, you could always cold set the frame to 135mm and be able to use all modern stuff.

well it's fixed; here's what i did;

1. i removed 5 links from the chain because the when it was engaged on the little front and little rear cogs, the chain touched itself at the idler wheels; in the big-big configuration the idler wheel cage was pulled forward to about the -45 deg position; no more chain slap over bumps -but there needs to be many more test miles/km before closing this trouble ticket

2. i removed, cleaned and inspected the deore xt RD; the thing is built like a rock and all parts moved freely and smoothly, and had tension as good as other derailleurs; no excessive play in the joints; i concluded the derailleur was not a problem

3. i replaced the shift cable and housings with new parts

4. i figured out why indexed shifting did not work; closer inspection revealed the shifter was for a 6 speed freewheel and i was using a 7 speed cassette on a freehub; i had a shimano 7 speed index trigger shifter left over from some craigslist purchases, so installed it in place of the shimano 6 speed thumbie; voila! 7 speed indexed shifting working perfectly

This bike can continue a long and productive life as a street beater and will see many runs to the stores.