Handbrake won't hold MK 7 RWD Transit unless all 4 rear wheels are on the ground

Question

I have a motorhome built on a Mk 7 2.4l RWD Ford Transit (which has dual rear wheels, i.e. four wheels on the single rear axle).

When camping on a slope I use levelling ramps to level it (of which I have 2). They are only as wide as a single tyre, so if I'm nose up only one of each pair of rear wheels is on a ramp and the other 2 are free. For example, the outer LH wheel and the outer RH wheel.

In this configuration the handbrake won't hold the van. It rolls down the ramps (all 4 rear wheels turning together), then stops as soon as all 4 rear wheels are on the ground. The same thing happens whether I put the inner or the outer wheels on the ramps. Leaving the van in gear or using the footbrake will hold it on the ramps.

What's going on? Is this expected or is there a problem? I believe the handbrake on this van just operates the calipers on the rear discs - surely this should hold regardless of which wheels are on the ramps as the two pairs of wheels are just bolted together? It's recently passed its MOT so brake force with all wheels on the ground is fine.

Answer 1

The 2 versus 4 wheels on the ground/ramp is a red herring, there's no difference in how much braking you get. If it's rolling with the handbrake on it's because your handbrake isn't working properly. Ramps are smooth, the ground is rough so you have more natural braking action from friction, and with 6 instead of 4 wheels on the ground it's enough to stop it. A slight downhill gradient will be enough to get the van rolling. It's definitely not something you want to ignore, if the handbrake won't keep your van from rolling down a slight gradient it won't stop it in an emergency.

The handbrake shoes could be too worn, or it could be they just need some adjustment, which is normal as the shoes get thinner from wear. Once you get that fixed you should be fine. The good news is it's usually pretty cheap.

Answer 2

I agree with GdD that the 2 vs 4 wheel thing is a red herring. The bottom line is that if you get two more ramps and put a ramp under all four rear wheels, you will get the same result: with the parking brake engaged, the camper will roll down the ramps until it reaches the ground, then it will stop.

Here's why --

I don't know anything about UK vehicle classifications, so for the purpose of this answer, I'm assuming that the MOT inspection that your camper must pass is shown in the "Heavy Goods Vehicle Inspection Manual." If your camper follows a different standard, suggest you find the proper manual.

Page 186 of the above manual lists the Parking Brake Efficiency Requirements, which is shown as 16% of DGVW (Design Gross Vehicle Weight). For a fully loaded vehicle, high school physics-level vector analysis shows that this force can be generated by a 16% slope.

I just measured the slope on a set of mechanic's ramps in my garage at 28.5%. Your situation is complicated by not having the front wheels on ramps, but I think the ultimate fact is that you are asking the parking brakes to hold the vehicle on a slope that is beyond the brakes' design capability. Your vehicle passed inspection so the brakes should hold on a 16% slope, but you've exceeded that.

You may get the ramps to work if you can get a second person to insert rubber chocks under the wheels on the ramps while you hold the camper with the service brakes, then ease off the brake onto the chocks and apply the parking brake.