Mickmeister

I'm getting chain slips when I go uphill. Shifting into low gear seams to work okay, but after I'm pedalling uphill a little bit the chain will do a violent shift...like it's disengaging/re-engaging. The bike is a brand new Aggressor Pro; I've recently had it looked over and tweaked by a local bike shop and the tech said he test rode it and all was fine (though I'm not sure whether he rode up any hills).

I came across this video where a guy with the same bike and derailleur increases the derailleur tension by turning a screw (you can see the screw at the 2:28 point in the video). I wanted to see if that would help, so I gave it a quarter turn and did some loops around a big parking lot that has a little uphill stretch. All was good on the uphill stretches the first three times, but on the fourth pass the chain slipped. So I tried turning the screw another quarter of a turn. Three more tries with no problems, but then on the fourth uphill stretch the chain completely dropped off the front derailleur.

So...I don't know...do you think maybe I should tighten that screw some more, or is something else going on here?

BobbyG

These videos helped me.

terrymorse 

That derailleur tension screw is what Shimano calls a "B-tension adjustment" screw.

It is super easy to set correctly:

1. put the bike in its lowest gear (smallest ring on the front, biggest cog on the back),
2. adjust the B-tension screw so the rear derailleur jockey wheel just clears the rear cog's teeth without rattling against the cog,
3. you are done.

If the B-tension screw is too loose, the jockey wheel will hit the cog.
If the B-tension screw is too tight, the shifting will be worse.

From the Shimano Dealer Manual:

Koyote

I don't think the b-screw has any relation to the OP's problem. OP should probably put the screw back to it's original setting.

If the bike was purchased from a shop, take it back and ask them to fix it. If you bought it via mail order, ask them to take another crack at it. Ask them to check that the chain and cassette are compatible, check the chain length, and anything else that might cause this issue.

PS: You might ask a mod to move this thread to the Bicycle Mechanics subforum.

Barry2 

OP count yourself lucky...
My entire bike don't wanna go up hills!


Barry

On a serious note: Did the bike originally work and this is a new issue, or has it always been like this?

Mickmeister

Well, here's the history:
- Bought the bike from Dick's Sporting Goods a few weeks ago
- Tried it out...seemed to be doing weird things - pedals would lose resistance for a split second or so, then re-engage
- Took it back to Dick's...a tech put it up on a stand and shifted gears up and down...said everything was fine (he didn't test ride it though)
- Tried it out again...still didn't seem to be working right
- Took it into a local bike shop. He did some tweaking to the drive train then said all was fine...he said he had test ridden it for twenty minutes
- Did a bunch of test rides in a big parking lot that has a few steep inclines. It's working fine until I go uphill...then I get the chain issues detailed in my OP.

So to answer your question, I assume the problem was there from the start...but I've only started learning shifting and hill climbing a few days ago, so who knows. The thing that makes this such a huge pain is that this is the first time I've had a bike in fifty years...and the first time I've had a multi-gear bike - so I'm trying to learn shifting and diagnosing drive train issues at the same time. I don't even know what's normal and what's not (though I'm pretty sure my chain isn't supposed to jump ship when I go up hills!)

tallbikeman

Mickmeister I looked up the rear derailleur specification and the Shimano derailleur being used does not have a clutch on the jockey wheel chain tension take up arm. Derailleur bikes are terrible on rough terrain for shifting when hitting bumps. The derailleur manufacturers solved this problem by putting clutches on the jockey wheel tension arm assembly. The clutch does not let the derailleur shift unexpectedly when hitting a bump. An example is the Shimano Shadow MTB derailleurs with clutch. When the clutch is engaged the derailleur will not shift on every bump. Mountain bikes, gravel road bikes, and any bike being used on rough terrain will benefit from this derailleur clutch technology. The shifting can even happen on paved roads if you hit a big enough bump or pothole. I hope this helps you figure out what is going on. If you are going to be riding hard in the rough I would upgrade the rear derailleur to a clutch design. You will be much happier with its performance.

Noahma

Stick with me here. Are you sure its the chain? Do you actually see it skipping?

The reason I ask this. I had an issue with my Trek Checkpoint where the pawls in the rear wheel hub were not engaging or slipping. And it was MUCH worse under load. It took several videos while I was riding to nail down what was happening, And they replaced the wheel under warranty. And the problem has not been a problem since then. The symptoms were exactly as you were describing.

Rolla

Yeah, well... Dick's is not a bike shop.

Take it back, get a refund, increase your budget, save more money, get a bike shop bike.

kahn

I once had a bit of cable housing split or some such so that while the cable would move inside the housing, the split released the tension needed to keep it in gear and it would slip back out. If not tuned/adjusted right, the chain can sometimes not seat onto the gear teeth and it will slide without dropping into the gears gliding over the teeth rather than settling into place. When it does seat, it will finally turn the gears/chain.

But someone has to actually test ride it to know what's wrong.

good luck,

jay4usc

bring it back to Dicks for a full refund, they have a great return policy

jgwilliams

I've got to say I think this is quite unhelpful. None of my bikes have ever had a derailleur with a clutch and I've never had an issue like this, even on my mountain bike. Clutches are for bikes that you expect to take over rough terrain. If the OP is just getting back into cycling after 50 years I doubt he is going over terrain rough enough at a speed to trouble the derailleur. There is clearly something wrong with the set up.

Ryno317

I have the same bike and I haven't experienced any chain slippage yet. I have been on some pretty rough trails, up and down and the only slippage is from the crappy stock tires, slipping in the dirt while standing to climb a uphill portion of the trail. I have noticed on the front chainrings, that some of the teeth are not very uniform and look worn down. Not sure if it's poor casting or QA.

70sSanO

There is a lot to unpack here.

If the freewheel/freehub pawls are disengaging it is a pretty quiet occurrence prior to the slip. Then the crank turns without any resistance and bam. You can duplicate this by riding on a flat area and shifting to a high enough gear that you need the same effort as climbing.

If it happens, it is a pretty easy fix if the bike has a freewheel, but not so easy with an unbranded hub running a cassette. In either case I would return the bike.

If the chain gets noisy and tries to jump to another cog under hard climbing and feels like it is slipping, it is probably not the freewheel/freehub pawls.

Another aspect to shifting while climbing is putting high stress on the components. The technique many people use is to back off a bit, or soft pedal, make the shift and then continue to grind up the hill. If you just force the chain over under high pedaling pressure anything from tweaking the rear derailleur/derailleur hanger to eventually breaking the chain can happen. But once things get bent poor shifting will happen.

I guess the last question is where you ride. If you are riding dirt trails a mountain bike is a good choice, although the longevity of a Dick’s offering may not be great. If you are only on pavement, an inexpensive mountain bike might look cool, but the extra weight, especially the cheap fork, is not a really good choice.

I would be more inclined to return the bike to Dick’s if you can, since you are having problems already. You can think of it as long demo ride to give you an idea of how much you enjoy riding and want to continue riding.

John

zweitesmal2

It may not be the bike. After 50 years off the bike you might just need to relearn shifting. If you're shifting under load you may not be all the way into the next gear and it's simply jumping back (or forth) into the next gear once the pedaling gets harder. I rode Ragbrai a few years ago and the violent chaotic shifting of people well into a hill was something to hear.

Bigbus

Based on the OP's lack of mechanical/bike experience, since he has already given the store a chance to correct the problem and even a bike shop a chance to diagnose and correct with no satisfaction from either, it's time to return it to the store and purchase from a legit bike shop that will stand behind their product and are concerned about having a happy customer, because I get the feeling that the OP will be a regular bike shop customer and there is nothing wrong with that. Not everyone gets joy out of tinkering on their toys, Good luck,

Mickmeister

I've just been assuming that the chain was slipping a tooth or two then re-engaging - but I could be wrong. This afternoon I'm going to try jerry-rigging a setup to hold my camera and get a video that might show what's going on.

What exactly needed to be replaced...the wheel plus the rear cassette?

I haven't been on any rough terrain...the issue is happening on a steep stretch in a paved parking lot...smooth as a baby's butt!

They gave me the distinct impression that once I wheel it out the door I've bought it. I guess I could return it if I could prove it's defective...but I still don't even know what the problem is. Keep in mind that I had already taken it back in once; they popped it up on a stand, shifted gears a bit, then said everything's fine...so I think returning it will be a tough nut to crack.

Noahma

The pawls are within the hub of the rear wheel. They are what engage the hub body so that you can move forward, and disengage when you say stop pedaling or pedal backwards. It is what is making the ratchet sounds when you are not pedaling but moving.

Some companies like Trek just opt to replace the whole rear wheel (minus the cassette), and some companies will replace the internals or cover the cost of a hub overhaul.

alcjphil

They still have an obligation to sell you a product with no defects. You have been very patient and have gone so far as to have the bike inspected by a real bike mechanic. This is a safety issue and you should be very clear about it. If the chain slips when you are pushing hard on the pedals you could fall and injure yourself badly. My guess is that your freehub isn't engaging its ratchet pawls properly. This happens quite often on bikes with cheap freewheels, but it can happen with more expensive cassette wheels. A friend of mine had a similar problem with a set of high end Campagnolo wheels. The local distributor completely rebuilt his hubs to correct the problem. At a minimum, Dick's should replace the defective part

Ryno317

As having bought the same bike from Dick's back in April. I looked into returning mine(2 weeks later), based on getting the wrong size. I checked my receipt and looked up there return policy on bikes and it's only a 24hr period and that's for size or if you don't like the color. They offered me a warranty at time of purchase, I declined, knowing I'll be doing my own maintenance or going to my LBS. Hopefully the OP got the warranty.

terrymorse 

There's another thing that can cause a chain to abruptly disengage, then abruptly reengage under load: a bent derailleur hanger.

A rear derailleur needs to be aligned with the cassette cogs about the vertical and horizontal axes to work properly.

It's hard to tell if a derailleur hanger is bent. Shops use a special tool to measure and align a bent hanger:

Mickmeister

I'm still not sure what exactly is happening...I tried rigging up my cellphone camera to get a video but I couldn't get it working.


Same with me...too big, so I returned it within the 24 hour period. The one I'm riding now is a size smaller, from another of their stores. Didn't get the warranty...for the same reason you didn't.

The other issue with trying to return it is that it's an intermittant bug. I just went back to the place where I've been test riding, and went up the uphill stretch eleven times in a row, and couldn't reproduce the bug...I can't imagine someone from Dick's test riding it, no less doing uphill climbs long enough to reproduce the issue.

Which brings me to another question: Could this all be due to bad technique...like maybe putting it under load too soon after shifting? During today's test ride I would shift just before the hill, then give it a split second or so before putting it under load...I'm wondering if that's why I haven't been able to reproduce the issue.

spelger

its not the "too soon after shifting" that is the problem. it is applying load during the shift. soft peddeling just means to lighten the load during the shift, reapply when teh shift is complete. this is of course, if shifting is the problem and w2ith rookie riders this can be the case.

(io'm a bad speller and i spelled shift incorrectly. good thing i cautht that.)

tornado60

Definelty try Spelger's advice.

Also, you might want to have someone watch you ride. See if they can see anything happening. Maybe they could even record it for you. If it is not actually changing gears, getting harder or easier to pedal, I'd say your initial shift isn't seating right on the cog. The jump you feel would be the chain slipping into the correct position.

gringomojado

I will give you a brake on the spelling!
gm