5

enter image description hereI've got a second hand bike. Doubt it ever had a chain replaced. Before I replaced the chain, it had an awful grinding sound. On replacement the machine worked perfectly and smoothly. (It's a Shimano altus 8 speed with a 3 chainring and an alvio rear derailleur) I thought it would be good to also replace the cassette. I bought the exact same model. Now it causes grinding sounds when not in the smallest cog. It always grinds in chainring 1 and 3. In chainring 2 it grinds in the larger cogs and had an awful vibration through the pedals in the smaller ones. My chainring looks okay I think ? What could be worth giving a go, I've tried to adjust the limit screws, and b is at its max. Any help would be great, just not sure what's going on and it worked great until I installed a new casette .

7
  • 1
    Intriguing. Please add some close-up photos of the chainring teeth (all three). The answer may be somewhat dependent on that information.
    – Ted Hohl
    Nov 5, 2023 at 6:44
  • Are the gears indexed properly and limit screws set to avoid the cage grinding on the chain? Nov 5, 2023 at 12:34
  • 1
    Did you tighten the cassette lock ring properly? Either way, if you have grinding in almost every gear then it sounds like poor indexing. You should not have needed to touch the limit screws. And what do you mean by B-screw at max? Fully inserted or fully out?
    – WornChain
    Nov 5, 2023 at 14:19
  • 1
    Can you determine what causes the grinding sound? Chain not aligned with the cassette properly (indexing issue), derailleur pulley wheels hitting the sprockets, chain not meshing with the cassette properly, chain not routed through the derailleur properly …
    – Michael
    Nov 6, 2023 at 6:10
  • I've put the b screw fully in because it was touching it on the lowest gear before. Nov 6, 2023 at 16:19

2 Answers 2

4

That really sounds like an indexing issue. The cable tension isn't as it should be. Barrel adjusters at the shifter or where the cable enters the rear derailleur can be turned to fine-tune how the chain runs on the cassette. Probably best to start over by releasing the inner cable from the pinch bolt, set the high limit screw--and there-by have the upper jockey wheel in the proper starting position. Reset the barrel adjuster(s) to one or two rotations out from full-in, and then route the loose inner cable properly through the pinch bolt area, taking up the slack in the cable and run in the pinch bolt firmly.

From there, attempt shifting up the cassette. Incomplete shifts call for increasing cable tension. Grinding in the gears after a shift means the cable tension isn't correct, but could also be too tight rather than loose. Adjust appropriately at one of the barrels. Generally the upper jockey wheel should run directly under the sprocket associated with a particular shift. Initial position of the jockey wheel has it running just under the outside plane of the smallest sprocket.

Obviously this all assumes correct installation of derailleur onto a straight hangar. The B-tab or B-screw needs to be touching the hangar's lip and eventually also set correctly when gearing is at its lowest. You'll need at least 5mm of clearance between the upper jockey wheel and large sprocket. Sometimes more, depending on size of largest sprocket.

An older bike with an Altus set-up may have non-indexed front shifters. Despite many of these models having click-detents, they are really just friction shifters. If the chain noise is heard it can mean the position of the front derailleur cage needs to be adjusted by manipulating the shifter. Worry about proper shifting/indexing at the cassette first. But if the chain noise is coming from chain rubbing on front derailleur cage, manipulate it out of the way via the left, front shifter.

Chain noise refractory to indexing can infer a bent hangar, derailleur cage, improper cassette install. The inner cable, ferrules, external housing are not infrequent areas where shift problems arise. This still sounds mostly indexing associated. Certainly should be tried very near first thing.

I'm assuming too that you didn't run the new chain on the old cassette for a long length of either time nor miles which can wear the chain abnormally making its interface with a new cassette compromised.

5
  • Thanks so much for the comprehensive response. I've just now pulled the slack out of the cable. when you say that the initial position for then jockey should be outside the plane of the smallest, should it not allign then? Nov 6, 2023 at 16:24
  • And I've only ran the new chain on that old one for a week or so . I miss how well it worked for that time ... I'll get back to you once I've given indexing a go, can't say I've had to do it before. Nov 6, 2023 at 16:25
  • It should align with the outside of the jockey wheel. Another way to say it is the jockey wheel teeth should be a hair outside of the teeth of the small cog. This is accomplished by manipulating the H limit screw. The chain should not rub on anything nor fall off to the outside when you shift on to the small cog. Also, this is set without the influence of any cable tension.
    – Jeff
    Nov 7, 2023 at 21:45
  • Indexing is fairly simple. Shimano states that cable tension is ideal when the chain is running on the second from smallest cog and the shift lever is thrown about ½ way to the next detent (click), the chain should begin to rub on the next, third from smallest cog. If the shift completes at a half throw of the lever the tension is too high and the barrel adjuster needs to be rotated clockwise to loosen inner cable tension. If the half throw of the lever does not result in chain rubbing next cog, you would rotate barrel adjuster CCW until it does.
    – Jeff
    Nov 7, 2023 at 21:53
  • A note about removing the slack of the inner cable: I use pliers pulling the inner cable with one hand and an Allen wrench in the pinch bolt with the other. I pull the slack out of the inner cable but not so tight that the derailleur starts to move inward as when shifting. The inner cable will appear nice and straight but at this point won't be super taut. The first shift usually completes and then you use the technique described above to dial in cable tension. If first shift doesn't complete, CCW rotation of adjuster increases cable tension then try the first shift again.
    – Jeff
    Nov 7, 2023 at 22:12
0

The old chain caused wear on the old cassette and chain wheels. So the new chain doesn’t exactly fit into the worn gears. Change the chainrings and the cog set. If this is too expensive, and it would be for me, ride as it is and the wear in will take care of itself. But I think you can see if it is properly adjusted as above, you still have an incompatibility with new and old. And a wear issue. HVAC

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.