Possible to strengthen or replace body spring Suntour rear mech?

On 7/22/2019 4:36 PM, Sir Ridesalot wrote:
On Monday, July 22, 2019 at 5:39:25 PM UTC-4, AMuzi wrote:
On 7/22/2019 1:37 PM, Sir Ridesalot wrote:
On Friday, July 5, 2019 at 9:30:13 PM UTC-4, AMuzi wrote:
On 7/5/2019 3:53 PM, Sir Ridesalot wrote:
Hi there people.

I have an old Suntour Cyclone rear derailleur that doesn't want to return to the two highest (smallest) cogs on my 8 of 9 speed cassette. I think it might be because the return spring inside the body of the rear derailleur is a bit weak. Is there anyway to either make that spring stronger by bending it or by replacing it with a similar spring from another Suntour rear derailleur? This is the normal derailleur with just one guide wheel and one jockey wheel. It is NOT the triple pulley version.

Thanks and cheers


No.
Your body return spring hasn't changed.

Undo a roller bolt, slip the chain out and disconnect the
gear wire. Remove th echanger from the bike.

Look closely in a good light for dings/scuffs on the outside
edges which indicate how many times and how hard it's been
smacked. Minor deformation of the parallelogram can
sometimes be freed by carefully flexing it back using padded
vise jaws. Sometimes not.

Look closely at the pivots from various angles to see how
much crud and dirt is lodged in them. A good cleaning and
oiling usually helps even smacked bodies- they aren't made
to exceptional tolerances.

Product plug- Rock-N-Roll is really great for this sort of
problem. It goes into tight spaces amazingly well.

Update.

YES the spring in this Suntour Cyclone rear derailleur is DEFINITELY weaker than when new. Compare to all other derailleurs I have here that return spring inside the body is indeed VERY weak. Fortunately I just got a NOS rear Cyclone derailleur body with just the outer part of the cage and missing the pulleys,, cable pinch bolt assembly, the low gear limiting bolt and the body to frame mounting bolt. I'll take all those needed parts from my old Suntour Cyclone derailleur and put them on this new body. Now I'll be able to shift into ALL of my high gears.


The lower pivot It may well be goopy or rusted inside. It
may have been disassembled then re set with the spring in a
less favorable position (six choices there) but springs do
not 'weaken'. Your symptom is real or you would not have
reported it. Twice. The diagnosis isn't weakened spring.

https://phys.org/news/2015-02-law.html

--
Andrew Muzi
www.yellowjersey.org/
Open every day since 1 April, 1971

Ah, but it's NOT the lower pivot of the cage that holds the idler and jockey wheels that's the problem, it's the spring inside the body that controls the side to side movement of the derailleur from high gear to low gear and back to high gear that's weak. It takes hardly any finger pressure to move the derailleur but on all my other derailleurs including the NOS Cyclone body it takes a lot of pressure to move that body.

I only did the update because it's so unusual to have such a weak spring there. I wonder if perhaps a bit of the spring has broken off at some point in time? A weak spring does show why this boy can't return itself to the high gear position though. Everything is adjusted properly, it's been tried with the cable disconnected and that spring is definitely far weaker than any other I've ever seen.

Once I get the needed parts swapped over to the NOS one I should send you this old body so you can see for yourself and perhaps tell me why it's so weak. It's been thoroughly cleaned and the movement is free but just very weak ie a very light touch is all it takes to move the body.

I have seen these same symptoms on a SunTour Cyclone "GT" rear
derailleur - original design, years ago. I also thought at the time
(less sure now) that the spring had somehow "gone soft," though I agree
that's hard to believe.

Symptoms were definitely the same - parallelogram pivots moved freely
(and perhaps loose), but the parallelogram spring did not have enough
"oomph" to shift to the small cog (even with cable disconnected).
Removed from bike, the parallelogram moved quite a bit (at least a cog's
worth) before resistance from the spring was felt.

I think I threw it away, but packrat that I am, it may still be in a
drawer somewhere, I'll take a look.

Mark J.