Since the Dodge isn't using a WC51 brake reservoir, but an M38 type, the top of the fluid tank isn't sloped like the original. This restricts the amount of brake fluid and air space in the tank. This in turn leads to problems with brake pedal free play, fluid expansion space and enough movement to give braking. It's been a fine balance over the last few years, often affected by ambient temperature.

To try and help resolve this situation, I've added an additional brake reservoir expansion tank to the Dodge. This involved drilling the original fill plug and turning a hollow tube adapter. A secondary tank was purchased from Ebay. The reworked filler plug can be seen in the third picture, deep down in the engine bay. It's not been easy to reach in the past when bleeding the brakes. The rubber hose rises up from the adapter to the new tank which is currently wired to the firewall. Once I bring the Dodge home from storage, I'll make a proper bracket to support it.

I've now got a larger head of fluid and a much bigger air space for the fluid to expand into as the brakes get warm with use.