richeydog

Okay, here goes. I have an older mtn bike. 1991/92 specialized rockhopper. Exage 400lx triple crank. 7 speed. Original chainrings, cassette, and until recently, derailleur. About a week ago the derailleur broke. I was tightening the bolt where the shift cable attaches to the derailleur and somehow the inside spring(?) broke from too much force.

Anyway, I had an older derailleur lying around from an unused mtn bike. A shimano deore lx, that is also about 20+ years old. I immediately put that on as a replacement. The first time I rode the bike I noticed that the chain was slipping on gears 5-7 in the middle ring, and only happens while standing up to pedal. So, I bought a brand new derailleur and it's doing the same thing.

So, after a bit or research, I took a look at my chain and cassette. The chain was longer than it should be. It is measuring 3/16" past the 12 inch mark. I know I know. I let it go too long. The cassette is a bit worn as well. (I'll take some photos tomorrow to show the wear of the cassette and chainrings)

My question is...since the chain is stretched and cassette is worn why didn't it slip with the original derailleur, but is giving me problems with a new one?

demoncyclist

I'm going to take a wild guess that when you reinstalled the chain, you changed its orientation. In any case, it needs to be replaced, along with the cassette.

cny-bikeman

You don't know that the derailleur is not the problem with slipping until you replace chain and cassette. It's possible the derailleur pulleys or body is twisted, which can cause inconsistant positioning of the derailleur and resultant skipping of the chain (you don't know why it was removed). Other than that a slightly off cable adjustment or pulley positioning could result in those symptoms when added to frame flex under high pedal pressure.

...whoops - somehow missed that OP tried a new derailleur and same thing happened. So now down to pulley positioning affecting skipping but chain still likely bad.

FBinNY 

The process that causes chain skip with worn chains or sprockets is often misunderstood. The chain doesn't disengage because of the tension in the upper loop. It fails to engage at the bottom, and when that section comes around you get the skip of a few links.

What happens is that the chain wears pockets into the back sides of the teeth causing a hooked profile. When the chain is pulled forward on the sloppy fitting teeth, the rollers can bump into the back corner of the prior tooth as they engage. If they bump and slip by all is good, but since derailleur bikes have very low tension in the lower loop, it's just as easy for the chain to use the bump as a step and ride the top of the teeth for a few links then drop back in.

Severe cases of wear will always skip, but a borderline case can be affected by the RD which may have more or less tension in the lower loop, or have the jockey riding closer or farther and be more or less assertive in guiding the chain onto the sprocket. Because of this you can sometimes solve borderline chain skip by adjusting the B screw. Beytyer chain lube also helps, but these are only short term fixes since more wear will make the skip unfixable.

demoncyclist

If it skipped on the replacement used derailleur and the replacement new derailleur, then I am guessing that the derailleur is NOT the problem, and that the chain and cassette are both badly worn, and swapping the chain's orientation exacerbated that wear. I am also assuming that the replacement derailleurs were both properly installed and adjusted.

richeydog

Thanks for all the replies. Makes sense. I ordered a chain and cassette. Will be installing this weekend.

I'm pretty sure I have the derailleur setup correctly. I've adjusted the hi and low limits as well as the b-screw. I'm no pro but am adjusting the best I can.

Here are some photos of my drivetrain. Let me know how it looks. Thanks!

FBinNY 

The cassette looks well worn, but looks are deceiving enough in the flesh that I don't trust photos.

Since you're replacing the chain and cassette anyway, try this when the new stuff arrives. A friend can help.

Talking old drivetrain, shift to a problem gear then cut the chain someplace in the lower loop and unthread it from the RD. Turn the crank until the chain dangles off the back but doesn't touch the ground. Arrange so the bike can't roll, either by tying a string around the lever to lock the brake, or setting the front wheel against a wall (I put a stick across the chainstays). Now here's the skip test.

Apply as much force as you can to the pedals, and the chain will creep forward on the sprocket, but it will hold. Tak the dangling free end and swing it under the sprocket as if it were winding on lower. If you feel the roller bump the tooth, it's a skipper.

Or you can do the test backward, by winding the chain around to the bottom with only a few inches to spare, before applying the pedal pressure. Then while under load, let go of the free end. A healthy chain will drop immediately to hang straight from the 9 o'clock position. A skipper will hang or not drop completely free immediately.

If you want, you can repeat the same tests after installing the new chain and cassette, and you'll see the difference.

AnkleWork

Looks like a CS-HG50, "G" cog set. IMO, the narrowed teeth on the 15, 17, and 20t cogs confirm the cassette is very worn.

richeydog

Here's a fun story.

A couple of hours ago I fine tuned the rear derailleur/shifting and took the bike out for a quick stroll. On the way out, chain slips like normal, get another taste of that delicious crunching noise.

About a 1/4 mile from home I come to a stoplight. Light turns green, I push off and stand up to pedal. Another big crunch! I try to pedal and nothing happens...so I look down and see the chain has come off the front chainring...or so I thought. After making it through the intersection and on to the sidewalk, I get off the bike and have a closer look. The sram powerlink that was on the chain had blown apart. I don't even know where it went cause it was too dark to look for it. I guess I need that new chain and cassette after all.

richeydog

You may be right. I'm not sure of the exact model at this moment. All I know is that it ranges from 13-30.

I just took a closer look at those cogs you mentioned. They really do have excessive wear. It's hard to see in the photos but it's there.

This is a question for anyone, how do my chainrings look? Anything to be worried about? I can try and take better photos if needed.

FBinNY 

The same test I described for rear sprockets works on chainrings. On the front, I prefer to use the second method, namely wind the chain around until the end is at the bottol. Then jam eht wheel and load the pedals before letting go. If it doesn't drop immediately it's a bad sign, though chainrings can be much more forgiving of wear than rear sprockets.

richeydog

Thanks FP. I tried to test the chain like your mentioned. Not sure if I was doing it right though. The chain would never grab hold of the chainring while I turned the cranks. I think I need to re-read what your said a few more times.

Here's the latest. Installed the new chain(kmc Z-72) and cassette(shimano hg30). I finally felt confident that my issues were over at this point. That is, until I went for a ride. I shifted into the middle chainring and a random cog in the back. Everything was fine until I stood up on the pedals and applied force. It is still slipping. I've tested the small and large chainring and have no issues. Although, I believe the large chainring is probably wearing/worn down but hasn't given me any symptoms yet.

So, I'm not sure where to go from here. Do I get a new chainring? If I replace the middle would it make sense to replace the large and small as well? From the looks of things, it appears that a set of chainrings would cost more than a new crankset. If that's the case, I would have no problem buying a new crankset. I have a small budget and don't need anything fancy. Just something that works. What say ye?

richeydog

Oh yeah. One more thing. The new cassette( shimano hg30, 11-28) I ordered has a lot of horizontal play in it. I can literally move the cog side to side a mm or two. From what I've read, I may need a spacer.

If it helps, I can shoot a video and try and post it here to show what I'm talking about.

FBinNY 

Sometimes what people report as slippage or skipping on the cassette is really skipping at the chainring. The effect is similar and the noise can be deceiving as to where it's coming from.

I took another look, and the middle chainring is pretty worn compared to the others. You might shift into it and use a screwdriver or something to lift the chain away from the ring at the /2 wrap point (3 o'clock). A bit of lift is normal, but if you can lift it clear of the teeth, that may be the issue.

As for the cassette being loose, the rule is simple. Cassettes MUST overhang the front of the freehub body by 1-2mm so the lockring can compress them without bottoming against the freehub. If you're familiar with threadless headsets, it's the same principle. If the cassette is too narrrow to overhang, you need spacers in back.

richeydog

I can lift the chain clear of the teeth on the middle chainring. So it's obvious that it needs replacing. I don't know where I can find a 38t that will fit my Shimano Exage 400lx crank.

My cassette has three parts. Cogs 15-18-21-24-28 are one piece. The 11 and 13 cogs are separate. The 11t cog overhangs the freehub like its supposed to. The 13t(or maybe it's the 15-28t) seems to be moving around too much. That, or the cassette is out of spec and I need another one. Have a look at the video below.

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FBinNY 

Is it possible that you have one of the last two sprockets lined up wrong? Make 101% sure that all the sprocket splines are in the correct freehub grooves, including the wider "key" splice which matches the wider groove. Also note that the spline grooves are very square, but some freehub also have tapered or angled grooves between the driving splines to save weight.

richeydog

It's possible. I don't want to rule anything out so I looked it over again. I've tried every combination just for the heck of it. Those last two sprockets only go on one way.

However, I noticed the last cog(11t) was overhanging the freehub much more than I previously thought. I can't push it any further down the freehub. I can turn the lockring by hand about 1 time before it starts to ratchet/click. In contrast, I just put my old cassette back on(it has one separate 13t cog), and it sits nearly flush with the end of the freehub. I can turn it's lockring by hand about 1 3/4 to 2 turns before I hear a ratchet/click sound.

FBinNY 

Yhe last sprocket isn't on all the way. It's hanging on something. If it's on right you can push it fully against the one before and compress the cassette with hand pressure. BTW- please tell me that you don't have the last one on upside down.

richeydog

Nope. Not upside down. Once I slide the last sprocket onto the freehub, it won't go past a certain point. There are notches in the sprocket preventing me from pushing it up against the 13t cog. Here's a photo of what I'm talking about. BTW thanks for all your help so far.

FBinNY 

The 1st sprocket can only go as deep as the dead-end channels allow. The sprocket matches the freehub on the right in this photo (borrowed from Sheldon Brown) where the raised channels end short of the face. If your freehub is different you might need a 1st sprocket where the channels are cut clear through.

It sounds like it might be a generational issue, but I'm not a Shimano expert. OTOH, you might try the sprocket on the freehub alone, and seeing if when pushed on all the way it would allow a chain to wrap and come up below the locknut face by over 1mm. If so, then all is good, except you need a spacer in back to bring the main parts of the cassette out to where the 1st sprocket can meet them and still have room to press down and compress the stack.

BTW- hopefully a true Shimanophile might step in and clarify the compatibility issue. See these images Shimano Hyperglide & Sram

Andrew R Stewart 

I suspect that the 11 t cog is bottoming out on the end of the freehub body BUT this is not enough tightening movement to fully press against the rest of the cassette. Shimano did change the freehub body length a few times over the years. Some times to allow for more cogs. Also the end of the splined body got a short section where the splines are removed to allow a smaller (11 or 12) cog to have enough meat on it to not break with the chain forces. Your nes cassette has an 11 tooth high gear. I bet your freehub body either is too long for the cassette or doesn't have this last bit of splines turned down (removed). An additional spacer behind the low cog will place the rest of the cogs further out and allow the high gear cog to press on the rest, tightening all down. Your comment about 1 mm of play fits this model.

Since this freehub body is almost 20 years old don't expect to get a cassette that fits like the old one. Instead head to a LBS that's been around for 20 years and see if they have a spacer. The younger wrenches probably haven't had to deal with this yet. Have fun educating them. Andy.

02Giant 

In case someone already mentioned this I apologize...the outer and middle chain rings on the crankset are completely worn out, they need replaced at the same time.

HillRider

Yes, Shimano introduced the "Hyperglide-C" freehub body with the ends of the splines shortened to allow an 11T cog to seat securely. If your freehub body splines go all the way to the very outboard end of the body, an 11T cog will not seat all the way. You either need a replacement body or a cassette with a 12 or 13T smallest cog. Here is sheldon Brown's article on the subject: Shimano Cassettes & Freehubs Scroll down to the "Hyperglide-C" discussion.

I agree your middle chainring is very badly worn and must be replaced. That crank has the very common 110 mm BCD 5-bolt pattern so replacement chainrings should be easy to find, just not Biopace replacements.

richeydog

+1 to Andrew and HillRider. You guys have given me some valuable information. I do have the older, non-compact freehub body in the link you provided. The splines go all the way to the edge.

In that article Sheldon says you can add a 1mm spacer to the body before installing the cassette. Last night I remembered that I had a spacer from the old cassette. I transferred it to the new cassette and it tightens everything up.

However, the 11t, with or without a spacer, still isn't fully seated(overhangs) on the end of the cassette. Is it safe to run like this or would it be advisable to go with a 12 or 13t minimum?

richeydog

No worries. You bring up a good point. It's probably wise to replace both rings at the same time. Do you or anyone know of an inexpensive source for 5 bolt 110mm BCD chainrings? I've looked online and can't find anything cheaper than $25 to $30 each for the 38t and 48t.

Don't want to spend a mint fixing up an old bike. If I cant find a low cost set of rings I may order a new crankset. I can get one of those for $25 or so... Amazon.com : Shimano M131 Crankset (170mm, 48/38/28) : Bike Cranksets And Accessories : Sports & Outdoors I know its cheap but the bike isn't in tip top condition anymore. This would be sufficient for me.