Is this possible?

How expensive is it?

Has anyone done it?

 

Cheers

It's probably not that different from the same conversion on the MK2.5, I'm in the process now myself of sourcing the relevant parts. I have bought two nearly new calipers with  pads off eBay for £20 each, pair of new discs of eBay £35, two new hydraulic hoses £20 and a new handbrake cable £30 ish and some new caliper mounting bolts from Ford's £6. Only thing left to get is the backing plates and they're £20 each. So without labour I'm going to be spending about £170 on parts. 

Retrofitting the rear disc brakes to a Focus MK3/MK3.5 can be done without any problems. The procedure to retrofit the rear disc brakes is for 99% the same as for the Focus MK2/MK2.5. Only all of the part numbers needed are different.

I made a guide for retrofitting the rear disc brakes to a Focus MK2/MK2.5. This guide can be downloaded from the following link:

https://www.dropbox.com/s/ohmuy84xvkq3pz3/Drum brake to Disc brake conversion.pdf?dl=0

Apart from all part numbers retrfitting the rear disc brakes is identical for the Focus MK3/MK3.5.

 

Note that rear drum brakes are really rare on a Focus MK3/MK3.5. Most European countries do have rear disc brakes as standard for all Focus MK3/MK3.5 versions. Even in the Netherlands where I live (with no hills at all) rear disc brakes are standard. Also note that the Focus mK3/MK3.5 only has 1 size rear disc brakes. Both the 278 mm and 300 mm front disc brakes are combined with 280 mm rear disc brakes. 

 

You will also need to use Focccus to tell the car it has disks now

I would imagine the brake bias needs changing as well as the algorithm1 for ABS

Thanks for the info guys.  So not ridiculously expensive then?  Yeah, my neighbour (who's into his cars bigtime but likes his Vauxhalls) was like "They still put drums on in 2014?!"

I think with it being brakes, I'd have to get the garage to do it...

I've always thought converting rear drums to disks has always been an aesthetic thing as it doesn't improve braking anymore in my opinion.

 

I'm sure the rear only has a max of 20% of braking anyway (i could have just made that up!) haha

If it can be done cheaply and easilly enough then why not :D

Rear disc brakes are not only aesthetics. 

In my opinion upgrading the rear drum brakes to disc brakes is definetely worth both the effort and money. I retrofitted the original rear disc brakes to my previous Focus MK2. After retrofitting the rear disc brakes the braking performance has increased significantly. During braking (especially at higher speeds) the car was much more stable with the rear disc brakes. An additional advantage is the parking brake which with disc brakes is a lot more powerful which is pretty useful on steep hills.

 

 

Remember to declare it to your insurance company though!

Are they likely to hike the premium despite the obvious safety improvements?

2 hours ago, JW1982 said:

Rear disc brakes are not only aesthetics. 

In my opinion upgrading the rear drum brakes to disc brakes is definetely worth both the effort and money. I retrofitted the original rear disc brakes to my previous Focus MK2. After retrofitting the rear disc brakes the braking performance has increased significantly. During braking (especially at higher speeds) the car was much more stable with the rear disc brakes. An additional advantage is the parking brake which with disc brakes is a lot more powerful which is pretty useful on steep hills.

 

 

I think for everyday use you wouldn't notice a difference though.

On my track car i did convert both cars to dsic brakes though.

If you just add disks and don't change the bias, then it will feel initially as you have more braking, as the disks rears will grab more initially when at speed, but as you slow down, then you are loosing braking as drums are more efficient at slower speeds and as hand brakes (and in the rain)

This also means you are more likely to lock the rears up during emergency braking. You need to tell the car it now has disks fitted via Focccus, as I suspect they have a different bias map, that doesn't brake the rears as hard initially and increases the bias to the back as you slow down at a different rate than when drums are fitted

My old landy had computer controlled bias that would automatically transfer braking to the axle that had the most weight on it in real time, as you nosedived during braking it would lower braking on the rear axle and as the car leveled would transfer power to the rear to help prevent slippage (As well as the ABS systems). Doubt the Focus is that clever but drums and disks definitely need different bias rates if you don't want the rears locking up too easily

Drums are not that bad either, my main enduro bike was drums only and the front line ambulance I drove for 12 years was drums only, They lack the initial grab that disks give but provide more force as the wheel slows and are better at heat transfer so fade less

1 hour ago, madmole said:

If you just add disks and don't change the bias, then it will feel initially as you have more braking, as the disks rears will grab more initially when at speed, but as you slow down, then you are loosing braking as drums are more efficient at slower speeds and as hand brakes (and in the rain)

This also means you are more likely to lock the rears up during emergency braking. You need to tell the car it now has disks fitted via Focccus, as I suspect they have a different bias map, that doesn't brake the rears as hard initially and increases the bias to the back as you slow down at a different rate than when drums are fitted

My old landy had computer controlled bias that would automatically transfer braking to the axle that had the most weight on it in real time, as you nosedived during braking it would lower braking on the rear axle and as the car leveled would transfer power to the rear to help prevent slippage (As well as the ABS systems). Doubt the Focus is that clever but drums and disks definitely need different bias rates if you don't want the rears locking up too easily

Drums are not that bad either, my main enduro bike was drums only and the front line ambulance I drove for 12 years was drums only, They lack the initial grab that disks give but provide more force as the wheel slows and are better at heat transfer so fade less

Yeah, but you're missing the most important, nay, fundamental aspect of the discussion. 

 

 

Discs look better.

 

=D

Lol, you can buy stick on fake disks and calipers if you're that sad

 

1 hour ago, madmole said:

Lol, you can buy stick on fake disks and calipers if you're that sad

 

Lol I'm not quite that sad thankfully.  Honestly I thought that brake performance was better with discs.  That and replacement costs in a few years, no?

Sorry, wasn't calling you sad, sad is those that buy the stick on fake disks!

Disks are far better for active driving at speed, drums are great for about town and parking

Plus drums last a lot longer and are cheaper to run, you'll rarely ever need to replace a drum, and the pads last forever on the back wheels

Mind you my front pads have done 30K now and are just about to be replaced with Brembo ones, but I'm old school and use gears to control speed. impresed with the standard OEM setup on the Mk3, it's actually better than the 6 pot Setup I had on the old works BTCC Mondeo!!!!

 

anyone know wich cable i have to buy to swap ? I will be removing all parts from focus st-2 65 plate.

The centre cable from the handbrake to the second cable should be the same, the cable that runs to each wheel is the one that's different.

I made a guide on changing my rear drums to ST discs conversion on my mk6.5 fiesta. 

Yes the handbrake cable is different for the rear drums and discs. The end of the cable is different so it can attach to the drum / disc caliper