In Julius Caesar, Act IV, what are the issues that cause Brutus and Cassius to quarrel in their dialogue, or conversation, in Scene 3?

In Act IV, Scene I, Brutus and Cassius are the generals of
two armies set out to defeat the armies of Antony and Octavius for control of Rome. 
They are allies, but they argue over the pettiest of issues.  First, Cassius is upset
with Brutus because he punished Lucius Pella for taking bribes despite Cassius' wishes
to have him pardoned.  Brutus in return accuses Cassius of becoming greedy and corrupt
just like Lucius Pella.  They then engage in a bout of name calling where they argue
about which of the two is the better soldier.  Next, Brutus accuses Cassius of denying
him a request to borrow money.  Cassius denies this and credits it up to
miscommunication due to an incompetent messenger.  Cassius accuses Brutus of not
believing his good will based on their past friendship and Brutus argues that Cassius is
too hot-headed.  They go on in this fashion until calmer heads finally prevail and they
realize they must work together against the common enemy.