MF5455 trailer brake bias

[flyonthewall]

Hoping someones come across this before....

Our 5455 has never had the most inspiring brakes since it was bought new back in 2006, and compared to our JD 6420s they are weak. On the JD the trailer seems to brake before the tractor. We have bled the pistons on the top of the trumpets and the valve by the side of the big oil pick up and discovered after the dyna 4 unit was replaced by MF dealer they hadn't been bled - now much better and like what they were, but I am still not confident compared to the JD. Someone did mention that our JD had the brake bias towards the trailer, is it possible to adjust the Masseys in this way? I just hate weak brakes with a 14 ton trailer behind me especially with idiots in cars.

 

[kill]

I had a new 5455 new in November 05 and that had the ability to combine both hydraulic systems via a blue switch to favour the loader but, when used it frothed the oil and the air would make the tractors brakes all but useless until they where bleed up again.
Very easy problem to sort tho as after repeated trip's back to my Massey dealer who was less than helpful and numerous promise's of a modification's that never came. So it had a one way trip to the local JD dealership.

 

[Simon Chiles]

Hoping someones come across this before....

Our 5455 has never had the most inspiring brakes since it was bought new back in 2006, and compared to our JD 6420s they are weak. On the JD the trailer seems to brake before the tractor. We have bled the pistons on the top of the trumpets and the valve by the side of the big oil pick up and discovered after the dyna 4 unit was replaced by MF dealer they hadn't been bled - now much better and like what they were, but I am still not confident compared to the JD. Someone did mention that our JD had the brake bias towards the trailer, is it possible to adjust the Masseys in this way? I just hate weak brakes with a 14 ton trailer behind me especially with idiots in cars.

How old is the tractor? EU regs state that later tractors can't have adjustable pre dominance valves. Many of the older JD's were quite high hydraulic pressure on the brake line. You can pressure test the brake line, the regs state that it should be a minimum of 100 bar, in reality they are at least 120 bar.

 

[flyonthewall]

JD is on an 02 plate. The MF doesn't have the twin pump option, I was told originally when sold it was 100/l minute pump, but when I came to trade it in (which I haven't) was told it was the billy boy basic 60/l minute pump. Wonder if an adjustable pre dominance valve could be fitted? Haven't had pressures checked, but may be next port of call.

 

[Chae1]

How old is the tractor? EU regs state that later tractors can't have adjustable pre dominance valves. Many of the older JD's were quite high hydraulic pressure on the brake line. You can pressure test the brake line, the regs state that it should be a minimum of 100 bar, in reality they are at least 120 bar.

The regs might say that but problem is at what pedal position is that pressure applied. If it's all when pedal to floor, tractor will have done most of braking before trailer brakes activate. We returned a tractor at 400 hours because dealer couldn't rectify this. Fine on air might I add.

 

[Simon Chiles]

The regs might say that but problem is at what pedal position is that pressure applied. If it's all when pedal to floor, tractor will have done most of braking before trailer brakes activate. We returned a tractor at 400 hours because dealer couldn't rectify this. Fine on air might I add.

I can't understand why the EU banned adjustable pre dominance valves as they allowed you to sort problems like this, after all it's not as though anyone is going to adjust them so that the tractor does all the braking!
If you stick a gauge on the brake line you should be able to see not only the pressure but at what stage of the pedal movement the pressure starts to ramp up. Normally it's between 1/4 to 1/3 of pedal movement, it should start at lower pressure first but quickly increase.

 

[Chae1]

I can't understand why the EU banned adjustable pre dominance valves as they allowed you to sort problems like this, after all it's not as though anyone is going to adjust them so that the tractor does all the braking!
If you stick a gauge on the brake line you should be able to see not only the pressure but at what stage of the pedal movement the pressure starts to ramp up. Normally it's between 1/4 to 1/3 of pedal movement, it should start at lower pressure first but quickly increase.

In your opinion what should brake first tractor or trailer? Workshop foreman was adamant it was tractor. I disagreed.

 

[Simon Chiles]

In your opinion what should brake first tractor or trailer? Workshop foreman was adamant it was tractor. I disagreed.

Ideally both at the same time but I'd agree with you if I had to make a choice. You want the trailer to slow the tractor but if the trailer brakes come on too hard and the wheels lock you would increase the chance of jack knifing. I would think this situation fairly unlikely though most modern tractors ( especially those with front axle brakes ) can hit up to 80% braking efficiency ( it's only the laws of physics that prevent them being any higher ) whereas older trailers are probably 25% and newer trailers with commercial axles 50%. Trailers with Ag spec brakes can be 50% on 18 inch rim sized tyres but as soon as you stick a super single on them you halve their braking efficiency.

 

[flyonthewall]

So do you think I could retrofit an adjustable predominance valve. The trailer brakes seem to activate at more than 50% of the pedal travel? I'm not sure what my expectations of my MFs brakes should be but as mentioned the older JDs are excellent on the different trailers we have. Having a small 100hp tractor on a heavier load I want the brakes to be in order and don't want the tractor doing all the work so the debris from the shoes is going in the g/box either!