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I have a GRX400 groupset on my gravel bike. I've noticed that if I'm ridding in the low trim position and click on the shifter to move into Low, there's no movement from the mech. However if I over shift a little and start to move the mech, as if I were shifting into the big ring, but then release, the mech. drops back into its proper Low position a few mm outboard of L-Trim.
Equally, if I drop down into the Low position from the big ring, the mech. stops in the correct position. A click down from the correct Low position sees the mech. move a couple of mm inboard into L-Trim as expected.
So it's just shifting up from L-Trim that's problematic. It's not the end of the world as I can get into the Low position, but is there anything I can do?
I'm assuming that somethings a little awry in the shifter but I suppose that it might be cable tension (although this seems pretty good & I have no issues shifting from Hight to H-Trim). Any thoughts?
'Twas cable tension
Except it wasn't, or rather it was & it wasn't.
To recap, clicking up from Low-T to Low and there's no mech movement & some gears rub, but dropping down to Low from High-T & the mech stops a couple of mm further outboard (sorts rubbing). High-T & High seem to work.
Cable tension is correct according to Shimano (2 lines line up in High-T).
So, tweak the cable tension incrementally until the mech moves from Low-T to Low. Result!
Except that now, when I shift from Low to High-T the mech moves to its fullest extent (I can still click into High but there's no further movement). I've effectively lost High-T.
The work.around is to leave it as is & deliberately over -shift from Low-T to Low to put the mech in the right position (you can feel the resistance of the mech moving at the shifter).
So, not sure if this is a mech or shifter issue or just the way it is with GRX400 ;am I missing anything?
It seems an inordinate amount of faff just to get the gears adjusted. My XT 3x10 getup on my Swift has one mech position per ring & just seems to work. Adjusting it's a doddle.
I've noticed on my GRX400 that when I move to the 46T ring from the 30T, it seems to default to the outer position, resulting in a bit of front derailleur rub in at least the largest four sprockets (wouldn't use biggest ordinarily).
As soon as I've shifted up to the biggest ring, I then have to attempt a light tap of the shifter to move the derailleur in a fraction, which makes things all good. From time to time, I tap too hard and I end up back on the 30T and have to start the process again.
It probably needs tweaking, but for now I'm not going to touch it, because overall it's shifting far nicer than the brs505 brifters do on my '16 road bike!
FWIW, I've had no problems whatsoever with my GRX400 front mech but no end of problems with the rear mech (it never stays indexed for more than half a ride).
Frankly, it makes me hate riding the bike it's on so I'm minded to sell the bike and move to e-shifting on a newer bike.🤬
I never had any such problems with the Tiagra and 105 I've had on other bike 🤷
Yes I've been riding mine today and noticed this same thing. When you shift from small to big you get rub in the 4th from bottom. As I was also recently looking at converting to a single ring set up to make things a bit simpler. However getting the chainring and cassette and mech to get it done properly is a lot of money. With a single speed setup I would want the 812 mech to do it properly.
In the future I might give it a try when the mech is a sensible price but £70 is a bit steep I think. I've got cassettes already. Cand
Just to add the trim button from high to low is pretty delicate and I have found it can shift back to small ring pretty easily. You definitely have to feel it out.
As I'm new to riding a gravel bike I'm getting used to the lower level of comfort I had on my hardtail MTB. It's a lot bumpier front end without suspension and the tyres being thinner. Faster and more aero so it's pros and cons.
It's well reported that the tolerance in the grx 400 mech is a pain to say the least. It's nice shifting and performance at the back I thought so far. I may like a flat bar front end though if riding more bumpy stuff for control and comfort.
The new gravel bikes are starting to come with wider tyres and flat bars I see. Its matching what you want from the bike and the terrain and riding you are doing. I think in winter they will be great road bike substitutes with discs and slightly more relaxed position.
OP, I find what your experiencing to be the case with all Shimano road front shifters/mechs. Frustrating to say the least, especially when they've been setup to Shimano instructions.
My guess is there's just too much flex/play in the system to allow the tiny bit of tension you need for low trim without then effecting high
First question for me is how fresh are the cables?
But also this isn´t unique to RX400, I have a 4700 lever (probably has the same mechanism inside) that can seem a bit vague on triming down sometimes, it is a full outer run all the way from the lever to a stop just past the BB so about 1.1m (ish) with some lovely bends and a great positioning of that stop for dumping shite from the rear wheel directly into the outer.
So plenty of opportunity for additional friction to goose up those smaller increments of cable tension release.
What is the routing like on your bike OP?
It's as you describe, full outer down the outside of the downtube & around the bottom bracket to the cable stop on the back of the BB, then bare cable into the mech.
In the end I patched in a length of that extra flexy outer (usually used for rear mechs) as with SP41 I had to had an ugly loop under the BB. This gives a neater, smoother run around the bottom bracket but is a bit non-standard.
At present cable tension is set exactly as per Shimano's instructions (2 lines in High-T etc.). I get no mech. movement shifting up from Low-T to Low (but still have the mech. stopping a couple of mm more outboard when shifting down to Low).
However I seem to get minimal rubbing in the small chainring, so I can live with this (and over shift to nudge the mech on if I need to). It's always seemed to be the large ring that suffers with rub & I do get proper Trim positioning in High, so I think I'll leave it at that for now otherwise I'm going to spend forever fiddling with it.