Thread: Towing braked trailers

Originally Posted by Mathias

Standard override has a 3/4" master cylinder, you need to fit a 7/8" mc to drive 4 calipers effectively. Though its bloody hard to bleed every last bit air to get rid of a bit of sponge. Still only rated to 2500kg on override, with 4 wheel braking.

No, was running 7/8 and still not good enough. I know what the recommendations are - don't know why it didn't work in this instance. Properly vacuum bled and fully backfilled system with the front of the trailer lifted into the sky and any air traps were straightened to release all air from the system - but it just couldn't move enough fluid without the piston in the master cylinder having to move to the amount that gave the inspectors the spongy feel. There was nothing 'wrong' with the system, no leaks, no air, no mechanical problem and it passed the test just fine in terms of braking effectiveness - it just literally didn't move enough fluid ina short enough distance to make the inspector happy with the operation of the master cylinder. Needed to go to a full 1" we reckoned to get it to the point of success which is a foreign product - but in the end of it to strengthen the trailer to the point of not killing duratorque axles every other year and fix a few other issues it basically went past the 2500Kg rating limit of the override coupling, so with all of those other issues in the mix it was a case of "lets use the ton" and fix everything including a electric/hydraulic actuator. Went from spongy to locked up in f-all and a WoF inspector that tried to fail it because he'd never seen one before and couldn't drive it (facepalm). Was good after that though.