serious phantom shifting

Again another post about her bike not mine, it's a couple year old Trek
crossover type bike, appears to have all "SRAM 3.0" components except
the front der is Shimano something or other. SRAM indexed grip shifts.
She was having lots of phantom upshifts on the rear going up hills,
and when I took the bike inside to look at it here the cables are all
inside a housing from the handlebars all the way to the derailleurs. So
what could possibly be the issue? I have no experience setting up
indexed shifters; all the bikes I've ever owned save for the Cannondale
I bought last week have all been friction. Not sure if that is even the
problem. She is neither light nor weak so I'm sure her bike is getting
a good amount of stress when climbing. Bike has been more or less
sitting for the last few years, unridden. Chain and cogs all looked
brand new (except for a nasty twist - see my other post. I would like
to rule out all other possibilities before telling her it's good to ride
though.)

Should I just tell her to take it to LBS for a "tuneup?"

nate

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On Apr 20, 4:35 pm, Nate Nagel wrote:
Again another post about her bike not mine, it's a couple year old Trek
crossover type bike, appears to have all "SRAM 3.0" components except
the front der is Shimano something or other. SRAM indexed grip shifts.
She was having lots of phantom upshifts on the rear going up hills,
and when I took the bike inside to look at it here the cables are all
inside a housing from the handlebars all the way to the derailleurs. So
what could possibly be the issue?

I'm no expert, but in light of the twisted chain...

Dan O wrote:
On Apr 20, 4:35 pm, Nate Nagel wrote:

Again another post about her bike not mine, it's a couple year old Trek
crossover type bike, appears to have all "SRAM 3.0" components except
the front der is Shimano something or other. SRAM indexed grip shifts.
She was having lots of phantom upshifts on the rear going up hills,
and when I took the bike inside to look at it here the cables are all
inside a housing from the handlebars all the way to the derailleurs. So
what could possibly be the issue?


I'm no expert, but in light of the twisted chain...

I agree it's possible, but during the ride the chain fell off the inner
front ring and partially sucked at the same time - so I don't know if
the chain is the cause or the effect. (I had to manhandle it pretty
good to get it out from between the ring and the chainstay, so it might
have twisted then.) I'm trying to just make sure I check everything
easy before telling her to take it to a pro to look at it.

nate

--
replace "roosters" with "cox" to reply.
http://members.cox.net/njnagel

nasty twist? WHAZZAT? before or after?

PS occurs inpart when cables stick in housings when bars are turned. A
yearly cable - housing cleaning with thinner and a spoke and or used
cable run in and out 10-20 times after thinner sits in cable as U
then dry under hot sun or infralamp
relube with Finish Line Wax with teflon also U soaked under heat
wipe cable clean, drip FL on cable, allow to set
place cable back in housing, fill with FL.

often, the PS happens during a temperature drop when drying lubes
cross thier threshold of no sick to stick.

Dan O wrote:

I'm no expert, but in light of the twisted chain...

I missed that bit. A twist in the chain can certainly cause
auto-shifting and/or skipping skipping behaviour.

John

You didn't mention if your wifes bike was a woman's frame, if it is,
that is partially the cause. The reason is the flexing of the frame and
pedaling hard is causing the cable to move through the plastic guide
under the bottom bracket. The solution is cheap, put some dielectric
grease on the cable where it goes through the guide (it works as a
lubricant and won't corrode plastic). You can get this stuff at any
automotive store for 4-5 bucks. It worked on my wifes womans frame. Good
luck.

John Henderson wrote:
Dan O wrote:

I'm no expert, but in light of the twisted chain...

I missed that bit. A twist in the chain can certainly cause
auto-shifting and/or skipping skipping behaviour.

John

Ron wrote:
You didn't mention if your wifes bike was a woman's frame, if it is,
that is partially the cause. The reason is the flexing of the frame and
pedaling hard is causing the cable to move through the plastic guide
under the bottom bracket. The solution is cheap, put some dielectric
grease on the cable where it goes through the guide (it works as a
lubricant and won't corrode plastic). You can get this stuff at any
automotive store for 4-5 bucks. It worked on my wifes womans frame. Good
luck.

John Henderson wrote:

Dan O wrote:

I'm no expert, but in light of the twisted chain...


I missed that bit. A twist in the chain can certainly cause
auto-shifting and/or skipping skipping behaviour.

John


It is a ladies' frame (hey, she picked it out, I wasn't involved in the
process) but there is no guide down there - the cable is all in housing.
However that's a good tip for *my* bike - I was going to use bearing
grease but if the silicone will work better I have that too.

nate

--
replace "roosters" with "cox" to reply.
http://members.cox.net/njnagel

Nate Nagel wrote:
Ron wrote:
You didn't mention if your wifes bike was a woman's frame, if it is,
that is partially the cause. The reason is the flexing of the frame
and pedaling hard is causing the cable to move through the plastic
guide under the bottom bracket. The solution is cheap, put some
dielectric grease on the cable where it goes through the guide (it
works as a lubricant and won't corrode plastic). You can get this
stuff at any automotive store for 4-5 bucks. It worked on my wifes
womans frame. Good luck.

John Henderson wrote:

Dan O wrote:

I'm no expert, but in light of the twisted chain...


I missed that bit. A twist in the chain can certainly cause
auto-shifting and/or skipping skipping behaviour.

John


It is a ladies' frame (hey, she picked it out, I wasn't involved in the
process) but there is no guide down there - the cable is all in housing.
However that's a good tip for *my* bike - I was going to use bearing
grease but if the silicone will work better I have that too.

nate


Hi, you don't want to use any petroleum based lubricants on plastic!
That is why the dielectric grease works best. PS, if your wifes cable
housing runs under the bracket, pull the steel cable or buy a new one
and coatit with the Dieletric grease, it is worth a shot.

Nate Nagel wrote:
Again another post about her bike not mine, it's a couple year old Trek
crossover type bike, appears to have all "SRAM 3.0" components except
the front der is Shimano something or other. SRAM indexed grip shifts.
She was having lots of phantom upshifts on the rear going up hills, and
when I took the bike inside to look at it here the cables are all inside
a housing from the handlebars all the way to the derailleurs. So what
could possibly be the issue? I have no experience setting up indexed
shifters; all the bikes I've ever owned save for the Cannondale I bought
last week have all been friction. Not sure if that is even the
problem. She is neither light nor weak so I'm sure her bike is getting
a good amount of stress when climbing. Bike has been more or less
sitting for the last few years, unridden. Chain and cogs all looked
brand new (except for a nasty twist - see my other post. I would like
to rule out all other possibilities before telling her it's good to ride
though.)

Should I just tell her to take it to LBS for a "tuneup?"

nate


Phantom shifts are usually caused by frame flex when the frame is used
as part of the cable housing (bare cable runs between stops). You
usually see this when climbing while standing. If it's not that, it may
just be that it's a shifting tweak that's needed. It may be a "slow
shift" problem: the cable pulls the derailer inward, the spring pulls it
back, if it gets draggy, the spring pull back may be slow.