Just as the caste system broadly categories Indian society into four castes and the outcastes, it also further categories every one of the four castes and outcastes into sub-castes .
As a result you have over 3000 sub-castes among the four castes and the sub-castes.
Among the Dalits you have several sub-castes, with each sub-caste being given its superior or inferior status on the basis of occupation of that caste.
Some of the sub-castes include Adi Andhra, Adi-Dravida, Badiga, Madiga, Mala, Cahmar and Dhobi among numerous others ( you can get a detailed list of the numerous sub-castes and detailed information about them on a state by state basis in the eBook The Truth About Dalits).
Consequently you see a system of discrimination at work even among the Dalits, which is one of the principal factors why the Dalits are dis-united and despite their numbers are unable to take advantage of it in a democratic political system.
Chamar (cobbler) is a Dalit sub-caste
Some effort has been made to unite the castes by Dalit leaders like late Kanshi Ram, which resulted in the formation of the Bahujan Samaj Party (BSP), but this is aphenomenon which is largely limited to the North India state of Uttar Pradesh.
No such fruitful association of all the Dalits sub-castes exists in the southern states though various efforts are being made and continue to be made.
In addition various Dalit sub-castes are up in arms for priveleges as has been accorded to otehr sub-castes within the Dalits.
NOTE: You can get very detailed and extensive information about Dalit sub-castes, including the sub-caste names in the eBook 'The Truth About Dalits'.