This note is for information purposes. We own a 2002 Beaver Marquis 40FT motorhome, non tag version, on a Magnum chassis. We found a leaking rear air brake actuator (parking brake chamber), evident only with the parking brake released. It was very difficult to read the original PN which is stamped on a small metal plate on top of the actuator. The PN is 4431156 and was manufactured by MGM. I called MGM and obtained the current replacement PN which is a MJS3030ET051.

I was misinformed by MGM about this being an exact replacement. The replacement PN is the same 30/30 chamber size (30sq inches each) but uses a longer throw chamber at 3 inches as opposed to the current 2.5 inch throw chamber. The threaded rod, that couples the actuator through a clevis to the slack adjuster, will need to be cut to the proper length. The original rod was cut at 4 inches from the actuator mounting face with the diaphram fully extended (check yours to verify). The new one will need to be cut to 4.5 inches fully extended to compensate.  If you did not know about the change of stroke length you would duplicate the original rod length and end up short. Hope this saves someone else a headache or two. Also be forwarned that MGM advises that you will need to change both actuators to the same stroke length on the rear axle. There may be other options but the space is tight and MGM makes a replacement for the original which does fit. The replacement chamber provides more uniform actuator pressure at the longer stroke lengths, is recommended by MGM, and has no down side as far as I can see, except the price.

Regards Ed