Mountain Bike Reviews Forum banner
1 - 19 of 19 Posts

·
Registered
Joined
·
9 Posts
Discussion Starter · #1 ·
Greetings,

I just bought a used 05 Prophet. I'm having problems with it skipping gears when I put a lot of pressure on the pedals going up steep hills. When it happens it jumps up 2 to 3 gears (to smaller cogs). I'm trying to figure out if I need to replace the cassette and chain or the rear derailleur (XT RD-750). The reason that I think it might be the derailleur is that the chain (Dura Ace) is within spec. (Well within the .75 mark on the park chain tool). The cassette doesn't appear to be worn a lot but I'm no expert in telling that by sight. I have put a new shifter cable on and have adjusted it so that it shifts smoothly. I have also checked for stiff links and haven't found any. The rear derailleur seems to be quite loose when I move it side to side, but again I don't know what is acceptable. Any thoughts on how to better troubleshoot this would be appreciated.

thanks, rick
 

·
Registered
Joined
·
3,061 Posts
It sounds like a worn cassette to me. You ought to check the chain rings too.

Edit: Oops, I replied after skimming your post and initially missed the part about it jumping 2 to 3 gears. In that case, it may well be the derailleur. But check the cable housing too. Gummed up cable housing can lead to some strange shifting problems.

Question: Does it shift smoothly when not under pressure?
 

·
Registered
Joined
·
9 Posts
Discussion Starter · #3 ·
Thanks for responding. Yes, it shifts fine when not under pressure. The skipping only occur on the steepest of hills when I'm using all of my body weight to push down on the pedals to make it up an incline.

rick
 

·
Registered
Joined
·
3,061 Posts
voithofer said:
The skipping only occur on the steepest of hills when I'm using all of my body weight to push down on the pedals to make it up an incline.
When it skips going up a steep hill... is the bike actually shifting on its own? Have you observed it changing gears? Do you end up in a different gear by the time you reach the top of the hill?

The reason I ask is that it's important to know whether you're experiencing unintentional shifting or whether the chain is staying on the same gear, but slipping under effort.
 

·
Occasional treat
Joined
·
197 Posts
Could be a hub problem either - does the cassette rock out & in from the wheel centre if you try & push it by hand? Does the wheel itself rock laterally back & forth if you grab it at the rim?
 

·
Registered
Joined
·
9 Posts
Discussion Starter · #6 ·
It's actually shifting on it's own. At the point at maximum effort the peddle lurches forward and the chain moves over 2 to 3 gears to a smaller cog. I tested it out a few times this morning and the same things always happens. After this happens, the rear derailleur is still lined with with the original gear. If I lift up the back wheel and turn the pedals it returns to the original gear without me shifting.

rick
 

·
Riding a Rig.
Joined
·
1,156 Posts
I think this has to do with suspension movement causing a change in cable tension.
 

·
Registered
Joined
·
3,061 Posts
voithofer said:
It's actually shifting on it's own. At the point at maximum effort the peddle lurches forward and the chain moves over 2 to 3 gears to a smaller cog. I tested it out a few times this morning and the same things always happens. After this happens, the rear derailleur is still lined with with the original gear. If I lift up the back wheel and turn the pedals it returns to the original gear without me shifting.
Which chain ring are you using when this happens?
 

·
Registered
Joined
·
3,061 Posts
Vulcan said:
I think this has to do with suspension movement causing a change in cable tension.
The OP has stated that the chain is shifting to a smaller cog and that he has a XT RD-750 derailleur, which, I believe, is a high-normal derailleur. Thus, an increase in cable tension (which might occur by compressing the suspension deep enough so that it begins to pull the cable housing out of its stops) would cause a shift to a larger cog, not a smaller one.

If there were some way for suspension movement to decrease cable tension, then this could indeed be the problem. However, I do not see how suspension movement could be responsible for a decrease in cable tension.
 

·
Registered
Joined
·
3,061 Posts
voithofer said:
It has happened mostly on the middle.
I'm going back to the "worn cassette" theory. When the chain is running from the middle (or even the large) chain ring to one of the large rear cogs and is placed under sufficient tension, it skips (due to wear on the rear cog in question) and then falls to one of the smaller cogs closer to the chain line.

If you were in your small ring and one of the large rear cogs, climbing a sufficiently steep hill, I would expect the chain to skip, but perhaps not shift due to the fact that the chain is likely better aligned between the front ring and rear cog.
 

·
Registered
Joined
·
9 Posts
Discussion Starter · #13 ·
That sounds reasonable. Thanks for going through the troubleshooting process with me.

Two quick follow-up questions: 1) I know it's standard practice to replace the chain and cassette at the same time, however, given the fact that the chain has less than .75 wear, should I still replace it? 2) SRAM vs Shimano cassette: Looking around the net it seems that most people prefer a shimano cassette all things being equal (above middle of the line shimano (e.g. XT) vs above middle of the line SRAM (e.g., 970/980) which would you recommend?

thanks, rick
 

·
Registered
Joined
·
3,061 Posts
voithofer said:
Two quick follow-up questions: 1) I know it's standard practice to replace the chain and cassette at the same time, however, given the fact that the chain has less than .75 wear, should I still replace it?
In order to maximize the life of the new cassette, I'd replace both the chain and the cassette at the same time. Hang on to the current chain though and consider putting it back on when you think you might be getting close to the end of life on the new cassette.
2) SRAM vs Shimano cassette: Looking around the net it seems that most people prefer a shimano cassette all things being equal (above middle of the line shimano (e.g. XT) vs above middle of the line SRAM (e.g., 970/980) which would you recommend?
My experience has been that Shimano cassettes last longer, sometimes even significantly longer. That's what I would go with.
 

·
Registered
Joined
·
832 Posts
I would check your quick release and make sure it is very tight. The prophet rear end has some flex to it and if the quick release isn't tight the problem worsens. I've had ghost shifting and brake noises before on my prophet because of a loose QR. Hope this helps
 

·
EDR
Joined
·
10,586 Posts
I totally agree with the worn cassette, middle ring theory. I'd bet money on it (not mine of course).

Also I'd get a new chain. Although the chain is in tolerance it may have been worn to fit the shark-toothed cassette. I have first hand experience with ruining brand new chains by using them with very worn cassettes. The result is that the 'good' chain (which is 'fitted' to the worn casstette) doesn't work well with the new cassette. This can cause you to go 'round-n-round' troubleshooting.

If it were me I'd do this:

1) replace middle ring (at least) if that's the one the chain skips in. If it skips in multiple rings then maybe start with step 2...
-ride bike, see if skipping is gone then, if needed:
2) replace cassette and chain at same time.
or
3) just replace all three at once and be done with it, money permitting.

Good luck.
 

·
Registered
Joined
·
974 Posts
I like the XT cassette. It lasts a long time and shifts well. There is one other problem that can cause this type of skipping. If either the derailleur hanger or the cage on the RD is bent. It may look all lined up but if the top pully is turned in due to a bend, it will shift when there is a lot of tension on the chain. But it will shift like butter when you put it on the stand. I've had this happen a couple of times, especially if you run shimano. The RD's don't take a hit very well.

Just something to look at to make sure you buy the right part. I'd hate to see you buy a cassette and chain, and on the first ride you get clickity pop. I hate that
 
1 - 19 of 19 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top