New gears fitted working fine except when I stand up!

[Tobyturnips]

Gears are working surprisingly well for my first time fitting a set.
The only problem I have is that when I stand up on the pedals and push hard the gear slips - any suggestions what I need to do?

[cyclerUK]

What have you fitted?

[Tobyturnips]

(05-11-2011, 08:36 AM)cyclerUK Wrote:  What have you fitted?

I fitted new deraileurs, new inner and outer cable and new shifters.

[RBurrelli]

Were the new items compatible with your current cassette? Was it necessary to change the chain (length) to work with the new deraileur?

[Tobyturnips]

(05-11-2011, 11:10 AM)RBurrelli Wrote:  Were the new items compatible with your current cassette? Was it necessary to change the chain (length) to work with the new deraileur?

I replaced a shimano deore gear set with a shimano deore gear set. I measured the new chain against the old one and they are both same length

[cyclerUK]

New chain skipping on an old cassette is indicative of a worn cassette. If a new cassette then possibly just needs tuning of the dérailleur but check that the rear dérailleur is in line with wheel/cassette sprockets. (Hanger alignment?)

[Tobyturnips]

(05-11-2011, 01:39 PM)cyclerUK Wrote:  New chain skipping on an old cassette is indicative of a worn cassette. If a new cassette then possibly just needs tuning of the dérailleur but check that the rear dérailleur is in line with wheel/cassette sprockets. (Hanger alignment?)

Thanks for the help.
Much appreciated