RE: Brake pedal failing to return fully.
Generally accepted practice is to completely flush brakes systems, replacing all brake fluid, every 4-6 years. Also, rebuilding or replacing master cylinders every 12-16 years. This is generally regardless of usage, although frequent, continuous usage favors longer intervals. Infrequent use and extended idle periods favors more frequent maintenance.
Springs in drum brakes and the nature of disc brake operation causes back pressure in the master cylinder, which is usually sufficient to cause full pedal return. If yours has a pedal return spring, it's merely there to assist master cylinder piston return. (I've seen loose, broken, or missing return springs in old trucks where the pedal was returning fully without the assist. These were invariably well maintained trucks.)
The seals on master cylinders tend to disintegrate with age, especially in older trucks like our motorhomes. In this case, the only option (short of abandoning the truck) is to rebuild or replace the master cylinder. (Worn or disintegrated master cylinder piston seals will prevent brakes from engaging fully and cause brake fade.)
In some cases, old brake fluid causes a gummy build up right where the piston seals were resting. (Especially common in trucks that have been 'stored' for extended periods.) Part of the gummy build up is from the early stages of piston seal disintegration. The build up can cause the piston to stick or jam, preventing full travel. Pedal return assist springs will not change the situation and could make things worse.
While rebuilding or replacing master cylinders is advisable, it is possible to free a sticky master cylinder piston, provided the seals are still in reasonable condition. At most, this is sufficient for one or two seasons of continued use. I strongly recommend not trying to extend this further.
The same situation may occur with wheel cylinders and calipers. Likewise, if your motorhome has separate brake boosters and associated slave cylinders. In these cases, you'll experience issues with the front or rear brakes, rather than the entire system.
The master cylinder is the key component and a single point of system failure. So, this is the place to start.
Something many people overlook is the brake proportioning valve. (This is where the 'brake failure' switch is usually located.) These also have a piston inside and can wear out. Most are not rebuildable.
Personally, in the case of brakes, any question of condition invariably means rebuilding or replacing components.
In my next post, I will describe the procedure for flushing brake systems and replacing brake fluid. ('Freeing' a sticky master cylinder is related so I'll mention that process as well.)
