Chain slip

[plainlazy]

I have just given my commuter bike ( 1991 Cannondale mountain bike ) a service after completing 20000 miles.
I have replaced all the cables, taken the rear/front mech off and gave them a good clean. I also replaced a couple of the front chain rings and the chain.
I checked the rear sprocket and it seemed ok, as i replaced it about 4000 mile ago.
Now i have put it altogether and it works fine except that the chain slips when i put any type of pressure on the pedals.
This is because the rear sprocket is worn more then i thought ?
I noticed that the rear mech has alot of play in it, so i am looking at replacing this but i am having trouble finding a 7 speed one,preferably an Shimano XT.

 

[HLaB]

Yip, the cassette is more worn than you thought and the new chain isn't slotting smoothly into it.

Edit: PS, congrats on the 20,000 miles

 

[Moodyman]

I have just given my commuter bike ( 1991 Cannondale mountain bike ) a service after completing 20000 miles.
I have replaced all the cables, taken the rear/front mech off and gave them a good clean. I also replaced a couple of the front chain rings and the chain.
I checked the rear sprocket and it seemed ok, as i replaced it about 4000 mile ago.
Now i have put it altogether and it works fine except that the chain slips when i put any type of pressure on the pedals.
This is because the rear sprocket is worn more then i thought ?
I noticed that the rear mech has alot of play in it, so i am looking at replacing this but i am having trouble finding a 7 speed one,preferably an Shimano XT.

This thread - discussed earlier should answer your queston:

https://www.cyclechat.net/

 

[peelywally]

maybe spring in the rear dérailleur is tired causing chain slap and skipping are the chain stays marked by the chain ?

thats a sure sign ,

you can adjust the rear dérailleur to be more resistant and stop the chain skipping ,

failing that select larger gear to tighten the chain on rougher ground , tbh its not a big problem to fix theres a grub screw you loosen tighten its a matter of increasing tension feel tension before you start and give tighten screw about half turn try that and keep going till fixed ,

chances are this has never been adjusted in its life its often over looked

info here

http://www.wikihow.com/Adjust-a-Rear-Bicycle-Derailleur

 

[plainlazy]

Thanks for all your advice.
I have now brought a new cassette and have just done my first commute on it.
The chain did slip a couple of times when i put pressure on the pedals.
Hopefully it just needs bedding in and i will start to feel confident getting out of the sadle again.

 

[Glover Fan]

No it shouldn't slip at all.

 

[HLaB]

Thanks for all your advice.
I have now brought a new cassette and have just done my first commute on it.
The chain did slip a couple of times when i put pressure on the pedals.
Hopefully it just needs bedding in and i will start to feel confident getting out of the sadle again.

If its still slipping it sounds like something is sticking somewhere, perhaps the rear derailleur isn't adjusted right or the mech isn't smooth and perhaps more lube on the pivot points will help. I also had problems with an old bike when I cleaned/ replaced/ relubed things. I'd replaced the cable outers to the exact same length as old but replaced them again making the rear derailleur outer a few cm's longer it then run like a dream!