The viscoelastic properties of filled elastomers (uncured styrene-butadiene rubber filled with carbon black) were investigated with two shear rheometers specially designed for the characterization of complex polymer systems. A torsional strain-controlled rheometer [i.e., a rubber process analyzer (RPA)] was used in dynamic and relaxation modes for measuring the storage and loss moduli and the relaxation modulus. A stress-controlled sliding cylinder rheometer (SCR) was operated for the measurement of the creep compliance. Both devices could be operated on a large scale of imposed strains or stresses ranging from the linear viscoelastic regime to the nonlinear viscoelastic regime, and they were complementary in supporting the original viscoelastic behavior of filled elastomers for a wide experimental time range. Moreover, when the measuring ranges of the two apparatus overlapped, a cross-check of the material functions obtained with the RPA or SCR could be successfully carried out. This validation of the data was performed not only in the linear domain of viscoelasticity, with the classical approach of a generalized Maxwell model, but also in the nonlinear domain, with a viscoelastic integral model of type K-BKZ.