The early production 500Es had Brembo front calipers as shown.

The reason MB replaced the aluminun 4 piston Brembos with 500SL cast iron calipers was to address a complaint from customers - as the pads wear, a vibration (or humm or growl) occurs between 30 - 50 mph. Litely tap the brakes and the problem goes away. This 'complaint' does not affect performance. I have experienced this 'complaint' twice ... both times when the pads were about 50% worn. We the pads where replaced, the sound went away.

Good luck.

__________________
1992 500E (Daily Driver)
2004 Porsche RUF 955 Dakara 550