Old Rear Derailleur Spring Tension (pic)
 

Hi,

I'm trying to restore/tune-up an old road bike.
It has the original shimano rear derailleur (see picture) which shifts really well.
However, it has no spring tension. I cannot pedal backwards, the chain becomes loose.

Does anyone know how to adjust the spring tension on this derailleur model?

Thanx

Larry

Attachment 48033

are you sure it's not more of freewheel problem than a deraileur problem?

Sheldon

Have you pulled the bottom pivot bolt out to look? Not sure on this model, but many RD have 2 separate holes to mount the spring, one providing more spring tension.

You actually have to unscrew & pull the lower pivot bolt all the way out to see that the spring is inside. You're right that just turning it some with an allen wrench does nothing.

it's a simplex derailleur, actually. what you're describing sounds more like

A) Sluggish freewheel
B) Misaligned derailleur hanger or cage
C) If it happens in the lower gears, the upper pulley may be sitting too close to the freewheel teeth to allow for backpedalling.

I didn't look at it that close - is this model worth anything?

Bumping this for help!!

I have an old 10 speed Puch, Shimano derailleur (not sure the model) that does more or less what OP described. Whenever I backpedal the arm of the derailleur that keeps tension pulls forward and causes the chain to slack up and fall off my chainring. I've given the chain a good cleaning and taken all the gunk off the cogs and it still happens. Could be that the little cogs need some more lube to turn, but i dunno.

The cables shift with friction shifters up on the stem, and I've noticed that the cable stop in the shift lever pops out a bit, IE there's not enough tension in the cable. I've tried turning the barrel adjuster where the cable runs into the derailleur counter and clockwise but I haven't seen any improvement.

Does the lack of tension in my derailluer arm come from my cable not being tight enough, the cogs being gunked up beyond what a chain cleaner can reach, or is the spring in my derailleur just gone?

That's the correct operation of the RD. If you pedal backwards in a gear that's doesn't have a perfectly straight chain-line, the angle of the chain will cause it to shift off the bottom of the chainring. This is actually worse with RD having strong spring-tension.

Why pedal backwards?

Would that be the cogs in the derailer cage you're talking about here? While giving them a clean and a lube probably won't hurt them it's not the most probable cause for your trouble.

As long as you can still get the chain onto the biggest sprocket/chainwheel, having the cable go slack when the der is in position for the smallest sprocket/chainwheel has no influence on function.
Usually the shifter can pull a bit more cable than what's actually required, and the der range of motion is controlled by the limit screws.
If you're really picky one could argue that it'll mean that you'll have to tweak the shifter a tad more before the der begins to move, and that a slack cable can slap and rub against the frame. Functionally it's a non issue IRL.
The easiest fix is simply to stop moving the shifter once you're in the right gear, and before the cable go entirely slack. Pushing it all the way against the stop isn't improving anything.

The only thing that would prompt me to do something about that is if the cable end got hung up on the shifter and didn't settle properly when the shifter was engaged again.

Forget about the cable. Spring is a possibility, as are guide & jockey pulley, but I'd check the freewheel first.

+1 :thumb:

That's my guess as well. An old gummed up freewheel will do what the OP describes. A weak derailleur spring would degrade shifting, which the OP describes as working "really well" still.

Remove the freewheel and soak it in solvent, then blow it clean with compressed air. Add a little oil and Bob's your uncle.

It looks like one of the all-metal Super LJs, with a long cage. One of these (in NOS condition) recently sold for $143.50 on eBay.

Well, I gave everything a good cleaning and took it out for my commute today and, as long as I don't cross the chain from smallest back to smallest front it is okay. I'm still not sure whey the derailleur pulls up when I'm on that combo as it was never a problem before. Also, could you explain why the freewheel would be the cause of this problem? EDIT: nevermind, I think I understand now... This weekend I'll pull it apart and try to clean the freewheel.

As for my cable issue, the problem is that I push my shift lever all the way up, so that it should be in the lowest gear in back, but the cable doesn't pull back with the lever and I don't shift into my smallest. So now my lever is as far up as it can go and the derailleur has stopped on up from where it should be. Generally if I run over a pot hole or do a little bunny hop it will pop into place. I think that I might just need to run some new cable.

There is some similarity to the SLJ, but that's an SX410. The arms are black plastic covers with thin metal and they have more steel parts. They're about 30 grams heavier than an SLJ. They work well, but don't sell for any thing near what an SLJ goes for unless the buy thinks he's getting an SLJ.

Simplex derailers have a little tab that has to hook onto the forward edge of the hanger. You can see it in this picture of my Super LJ. If it's not in that position, you won't have any spring tension.

http://inlinethumb40.webshots.com/40...600x600Q85.jpg

Sounds like an excellent suggestion!

This is a common symptom of too much friction in the cables and the RD's spring can't pull itself into the correct position.