The underframes of the trailer cars are basically as for any Mk3 coach but the MBLS underframe carries the traction equipment. Both sides of an MBLS are illustrated here.  Above on unit 2404 car 62939. The equipment groups left to right are (thought to be) rear of air-conditioning unit, circuit breakers, camshafts and switchgear.  Below on unit 2402 car 62938, where the equipment groups left to right are weak field resistances, EP brake unit, starting resistances, auxiliary equipment case and air-conditioning unit.

The MBLS has two motor bogies providing four traction motors - the motors being recycled from 4 Rep units.  This is clearly one of the motor bogies of unit 2402.

A trailer bogie with shoebeam and pickup shoe. Pickups are fitted to the 1st, 4th, 7th and 10th bogies in the formation, that is to the bogies under both driving cabs and on the bogies of the TS and TSW next to the MBLS.