Thread: Towing braked trailers

Originally Posted by No.3

Part of the reason for this is that the 2500Kg master cylinder is only rated to operate one braked axle or one set of disc's. A 3500Kg trailer is required to have both axles braked and the override coupling can't push that much fluid to operate all four calipers without making the WoF man think that the brakes are spongy and need bleeding... Ask me how I know this haha (oldmate thought it would be a 2 is good, 4 must be better in terms of numbers of calipers on his braked tandem boat trailer). It did stop well, I'll give it that but we could not get it past WoF once the little Indian inspector killed it for spongy brakes. The brakes passed in every other respect, good stopping power etc etc it just was too much fluid required to push out all four pistons compared to the available volume in the master cylinder. We actually looked at custom fitting a double master cylinder setup onto the coupling, but that wasn't allowed and also custom building a larger master cylinder but again not a goer. Ended up either needing to drop back to two calipers or only one braked axle or what we did in the end and fitting a US made electric/hydraulic actuator with wireless controller.

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.