From the article:
For the most part German armoured car designs during the Second World War were more than adequate for the roles they needed to fulfil. However, one very common complaint from armoured car crews was the lack of sufficient firepower when forced to engage the enemy.
In November 1944, Hitler ordered that the production of Sd Kfz 234/3 to cease and replacing it would be the Sd Kfz 234/4. While the Sd Kfz 234/3 featured the short barrelled 7.5cm KwK51 L/24, the Sd Kfz 234/4 was to be armed with the formidable 7.5cm PaK40 anti-tank gun.
The 7.5cm PaK40 complete with gun shield but minus its wheels was mounted on a pedestal mount centre of the fighting compartment; this effectively turned the vehicle into a wheeled tank destroyer. However, the design was not without its limitations; as with any hull mounted gun, the PaK40 was severely restricted by its inability to traverse.
Ammunition stowage was also an issue. Due to the size of the rounds, only twelve could to stow aboard the vehicle at any one time. If this wasn't enough, the open topped fighting compartment left the crew vulnerable to small arms fire and shell fragments. Despite these limitations, production of the Sd Kfz 234/4 didn't cease until March 1945.