Estranho ... mas eu fiz exatamente o oposto das recomendações do @Wild Man:
Eu instalei bcmwl-kernel-source e removi bcma & amp; brcmsmac , e eu tenho a minha velocidade normal: - \
[~]> lsmod | grep wl
wl 4207846 0
lib80211 14381 2 wl,lib80211_crypt_tkip
cfg80211 484040 2 wl,mac80211
[~]> lspci
03:00.0 Network controller: Broadcom Corporation BCM4313 802.11bgn Wireless Network Adapter (rev 01)
[~]> lsb_release -a
Description: Ubuntu 14.04.1 LTS
[~]> uname -a
Linux martin 3.13.0-32-generic #57-Ubuntu SMP Tue Jul 15 03:51:08 UTC 2014 x86_64 x86_64 x86_64 GNU/Linux