Chris Chicago

I have this suntour derailleur on an old mtb. when I shift to the bigger 3 cogs the jockey pulley is no longer engaged and if I shift to the biggest the chain rubs the cage and sometimes finds its way out if it.

it seems the derailleur should be pivoting forward more so that the jockey stays engaged with the frame. but the tab on the rd is flush up against the tab on the hanger so it cant pivot further.

here are a couple of pictures. axle wasnt all the way into the drops in these shots, fixing that helped some, got the pulley fully engaged on the 4th biggest cog, but problem still exists on larger cogs.

cyclist2000

It looks like you have two problems

1) there is not enough chain
2) the screw at the derailuer hanger is screwed too far in

I would start taking off the tension on the derailuer by unscrewing the screw at the top of the derailuer then if there isn't enough slack in the chain add some links.

look at the park tool site for some instructions on setting up a RD.

Chris Chicago

thanks!

the b tension screw is unscrewed as far as it will go, is that the screw you're referring to?

the chain lengthening helps..ie if i put it around the small chain ring up front then the jockey pulley is engaged on all cogs. but I was careful when I measured the chain for length, and it worked fine with a prior rd, so I want to make sure the problem isn't elsewhere before I put on a new chain.

MNRon

How did you measure the chain for length, and what was the previous RD?

KDC1956

Best way to check your chain is put the chain on the small cassette on the back and put the chain on the big chain ring on the front if all is well your derailleur should be straight up and down if not add more chain or take some out.Straight at 6 clock.Hope this helps.
Check this video out.https://www.wonderhowto.com/how-to-in...-chain-173237/

Ruffinit

Simple rule of thumb, when you are on the BIG BIG, your derailleur cage should be at a 45 degree angle.
You have too short of a chain by the number of the teeth difference in your 4th and final freewheel cogs judging by the pictures. IE; If your 4th is a 24 and your 6th is 34, you'll need 10 more links.

Chris Chicago

prior rd was cheap shimano rapid rise. c101 I think.

I used the sheldon brown method :"technique for setting chain length is to thread the chain onto the large/large combination, without running it through the rear derailer."

as far as the derailleur being vertical if the chain is on big small (which is the case in pic1)...I'm guessing this means the pulley wheels are vertical, not the chain line?

hopefully it's not a full ten links short though, bc I will need to buy an extra long chain.

Chris Chicago

does this rd seem odd in that the jockey pulley is towards the back/center as opposed to the front of the derailleur body (parallelogram?)?

operator

Lots of ridiculously incorrect advice.

1) The B-tension ('the screw at the hanger') should be set only after the chain length is verified to be correct. The present pictures show nothing.
2) The chain should be verified. Chain sizing is covered very well at https://www.parktool.com/repair/readhowto.asp?id=26 Big/Big +1/2 will reliably give you the shortest possible chain length for a given system

operator

Yeah, do it this way if you want to learn how to set the chain length improperly. Derailleur cage at 45 degrees? Where'd you come up with this?

Ruffinit

I've just read what Sheldon stated. I have to say I've never in 30 years heard of that technique. When speaking of the derailleur angles, it is always stated per the cage. By stating the derailleur is verticle that means that you are looking at the jockey pulley bolts and they are perpendicular to the floor. And remember you should never be running in the BIG BIG or SMALL SMALL combo.
I doubt if you're looking at 10 links unless you're running a 50 front 36 rear combo. It does look like you have a pretty large rear cog though.

Ruffinit

Been doing it this way for 30 years. Numerous shops and as a mechanic for quite a few teams. What's the beef? Show me how this wouldn't work.

Chris Chicago

the pics I posted, the chain was on the largest ring up front. big small in first pic. big 2ndbiggest in 2nd. seems like it is missing the obvious bend at the pulleys that the Park tool website talks about, which indicates it is too short. maybe i made a mistake measuring the chain, or maybe this rd is funky enough to throw sheldons method off.

cycle_maven

Yes, it looks like there something wrong with one of the two springs that balance out the derailleur. Looks like the one that rotates the derailleur inward is stuck or not doing its job. Mountech's had a real problem with the spring inside the guide pulley, IIRC. I have a Mountech I took off a touring bike a couple of years ago- I'll have to look at mine when I get home. It looks stuck rather than broken- a broken spring wold rotate the derailleur body the other way.

Ruffinit

+1 for reading up on the procedure first. One of the reasons for running it through the derailleur and the Big Big combo is that you are also taking into account the cage length/wrap of the derailleur also. I've never had a problem with the MounTech. The max cog size is 34.

Chris Chicago

if by inward you mean counter clockwise, or towards the front of the bike, I could be mistaken but I dont think that is the problem. it cant go any further forward due to the tab on the hanger.

here is a pic of another mountech, jockey pulley similarly mid parallelogram. but the parallelogram is straight horizontal where as mine tilts down.

not sure if that should concern me.

I know of the mountech issues. it was the oe rd and I ride this bike pretty casually...hoping it wont effect me.

thanks for the tip on the max cog. I will have to check that.

peripatetic

I had a Mountech RD on a bike, and the arm was bent. It seemed to be fairly weak metal. OP, did you perhaps disassemble the RD in order to clean/service it? It looks like the arm is on backwards/flipped to me.

Chris Chicago

did not take it apart. it's 2nd hand so anything is possible. do you see a difference comparing mine pictured in op to the one I linked to above your post?