Undiagnosable brake issue

[ShazMcG]

Hi, Aussie girl, VM 2011 Manual Diesel. Having a huge problem diagnosing a brake issue! Vehicle starts to slow down no matter what speed you are travelling, foot flat to the floor on the accelerator, won’t pick up speed and continues to slow down. By the time you can safely coast off the road, the passenger side brake has locked on and the vehicle will not move! If you put your foot on the clutch and brake to go back in gears,it stops dead! It smokes and smells and sometimes is red hot by the time I can get off the road. Replaced Vacuum Valve and travelled a further 2000kms without an issue then it did it again? Have now replaced booster, hoses, pads, callipers, ABS modulator and master cylinder was replaced before I purchased the vehicle. It is very intermittent and sometimes the mechanic can drive it for about 100klms and it won’t do it, last 2 times I drove it I got 13klms and then only 7klms! Has anyone ever had an issue like this? There are absolutely NO error codes on the diagnostics when this happens?

[knobby1]

Hey "Aussie Girl"....an "Aussie Bloke" here..! And welcome

Whereabouts in Aus are you,?? If fairly local to me I could at least try to offer some help.

Looks like you've done your best to get it sorted. You mentioned the hoses were replaced. I assume you mean the brake pipes/hoses etc...?? Were all the front and rear flexible brake hoses replaced..?? They're known to fall apart inside and cause grief, allowing brake fluid to go to the brake caliper...but not allow it return, acting kinda like a one-way valve..... as the fluid heats up and expands, the brake comes on harder, eventually locking up the brake & wheel as you've experienced.....when cooled it allows it to work as normal.....till it all happens again. The only reason this can happen is if the brake fluid is not being allowed to return to the M'cyl....If the flex hoses are new.....Possibly the "return ports" in the M'cyl are blocked or the internal seals are not allowing the ports to open.

You also mentioned the master cylinder was replaced before you purchased the van....do you know if it was a genuine Ford master cyl?? We've experienced some issues with non-genuine ones in the past....Just thinking out loud.

Lord Knobrot

[ShazMcG]

Hi, thanks for the reply. I’m currently in Port Augusta SA. Ford have handed the vehicle back to me as they cannot work out what is wrong with it and it hasn’t faulted for the mechanic the last 2 times he has driven it. The front brake hoses were replaced due to them corroding inside. I’m not sure if it is a genuine Master Cylinder but the mechanic had that plus the booster and vacuum valve all pulled out at one stage to check if there were any problems with them. He didn’t find anything or mention it wasn’t a genuine part.

[MinorMatt]

I remember someone having this issue before...

But I can't remember who, when, or what the fix was

Is it only 1 wheel that has a problem? If so that points to either a flexi hose or ABS modulator fault...

[Nordic Blue]

I'm not sure if my story is relevant at all but years ago when I bought my second hand MK2 Transit, it had a similar issue. I would drive along and after a while the van would slow and the wheels would eventually lock up.

My dad (mechanic) helped me look into it.

It turned out that that previous owner had fitted a replacement master cylinder (I assume lifter from another Ford) and although it looked right and the blts lined up, the pin on my servo was too long and was not retreating fully enough for the master cylinder when releasing the brake pedal.

We probably should have got the correct replacement cylinder but my dad fixed it by grinding down the pin on the servo. It and the brakes worked fine after that.

So what am I saying? I would suggest that you try and get the current master cylinder verified as the correct part for your van, and if not it might be worth taking the hit and getting another one. It sounds to me like that is the only part of the system you haven't replaced yourself so far.

[littlefb]

Hi, I’m having the same problem with my mk7 2.4 rwd lwb transit. Every aspect of the brake system has been checked and double checked. My problem is with the modulator, it has been in for repairs/rebuild without any success. At first it was only locking on the front nearside, after the first rebuild all four wheels locked up after half hours drive. It has been in dock for four month now. I can’t find a used replacement and ford have quoted £2700 new one