HOW TO: Rear Disc Conversion Machining Process

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HOW TO: Rear Disc Conversion Machining Process

Post by PaulZ » Wed Sep 04, 2019 7:17 pm

Disclaimer: - I accept no responsibility if the information within this post is used but does not work as described or results in any damage to yourself or your vehicle.

I have endeavoured to ensure any information provided is as accurate as reasonably possible however any information is used at your own risk.

It is also advised that before undertaking this work you carry out your own research and assessment of the process to fully understand the work required. Upon commencement of work you accept that you are carrying out the modification at your own risk.

The machining processes should be completed by a trained and/or experienced machinist and fitting of components is carried out by a qualified and or experienced mechanic. Failure to properly prepare and fit the components may result in the modification not working, poor wheel alignment or in the worst case catastrophic failure.

Introduction: -
The instructions and information given below is the same information I used when I carried this modification out successfully on my car. I have covered around 500+ miles since its fitting and have experienced no issues to date, with the ABS working as expected.

The aim is to provide additional detail for those wishing to carry out a rear disc conversion with fully functioning ABS. The main detail of the conversion can be found in Wild E.Coyote guide found at the link (1) below so this guide aims to fill some of the gaps and give more detail for the machining processes. I also started a thread with the questions I had before starting this process which can be found at the link (2) shown below. Lastly a useful website for checking part numbers can be found via the link (3) below as well.

Link 1 – viewtopic.php?p=302532#p302532
Link 2 – viewtopic.php?f=20&t=32728
Link 3 –

When I carried out this modification I opted to use the second of the methods detailed in Wild E.Coyote guide. I decided this method because A) it is easier B) requires less machining and C) It appears the FRP solution used this method. I could not find anything documented to say that FRP ABS rings are different to standard or required modification to fit so they must have done something similar to option two.

Parts: -
Firstly the parts you require can be found below. The part numbers given are the Ford part numbers but you may wish to use these numbers to source alternative components due to the cost of Ford parts. Where possible I sourced new Ford components however a number of components I opted for good quality alternatives. The process should remain the same regardless of parts used.

Part (Part No.)
Rear hubs (1138512)
Rear LH spindle (1138520)
Rear RH spindle (1142082)
Rear LH callipers (1478337)
Rear RH callipers (1478419)
Rear calliper carriers (1075557)
Rear Discs (1780880)
Rear Pads (1075565)
Rear ABS Ring (7314843)
Handbrake cable (1502610)
Rear brake hoses (See Notes *1)
Rear ABS sensor (See Notes *2)
Miscellaneous bolts (See Notes *3)
Rear LH splash shields (1138516) (Optional)
Rear RH splash shields (1138517) (Optional)

*1 – Without rear spacers you may get away with retaining the original length hoses if you have coilovers fitted due to the reduced suspension travel but I fitted braided hoses that were around 5cm longer than standard to mitigate any risk. If you are using spacers or standard suspension it may be worth considering custom length hoses to suit your requirements.

*2 – A new ABS sensor to hand is advised as they are notorious for corroding and getting stuck in the existing spindle, at least if they do break during removal you have a new one ready to fit. Without spacers you should be fine to use a standard Puma sensor as I have done but if using spacers a straight ABS sensor may be required. The different part numbers can be seen below.

Puma Sensor – 1087770
Escort Sensor (Straight) – 1011582
InterMotor Sensor (Straight) – 60020

*3 – Some bolts may need to be replaced due to corrosion. You can use the Part No. link above to find the correct Part No. and then order them from Ford. Bolts are more complicated than most people would think so if you are not educated on the application of bolted joints get yourself down to Ford and order the right bits. Don’t forget to apply grease and torque to the correct specification.
P.S - In my instance I didn’t need to replace anything so you might get lucky and all will be fine.

*4 – I used Mk1 Focus parts however equivalent parts can be used from a Fiesta ST150 (See my questions thread link above for details) because the hand brake mechanism on the ST150 callipers requires some minor fettling of the rear beam to fit. Due to this my recommendation is to just source MK1 focus callipers and carriers instead.

Drawing Notes: -
The drawings included are provided as discussion points with a machining company to better describe the work required although I advise taking and supplying the actual parts to aid with the discussion and most likely the completion of work.

I used brand new components so the drawings are completed based on the parts I used. If using second hand dirty or corroded parts please make an allowance for this or have them cleaned up in preparation.

Rear Hubs & ABS Ring: -
So for this part the rear hubs need turning down in a lathe slightly to accommodate the smaller ABS ring from the Puma. You have two options for this bit. The hubs can be machined so that the ABS rings are lightly pressed into place. This is probably best described as a ‘Transition Fit’. A transition fit means that there is sufficient friction to prevent movement however in order to remove them will require some amount of effort. Alternatively you can go for a looser ‘Clearance Fit’ and then glue the ABS rings in place. The ABS rings I used came with glue for this purpose.

Personal Experience – When I had the parts machined I asked for it to be machined to suit a transition fit and provided the ABS rings for them to work to. I also provided the glue and pointed out that if they needed to the rings could be glue in place instead. The parts I got back where pressed onto the hubs with no glue used.


Rear Spindles: -
These parts need to have the ABS sensor hole enlarged to accept the Puma sensor whilst also relocated slightly so it becomes central to the new Puma ABS ring. This then requires the ABS sensor mounting hole to be relocated to suit the new sensor location. Finally a pocket needs to be machined so that the spacing between the sensor and ABS ring are approximately 0.6mm. The rear spindles are easily the more complicated bits to machine and particularly for the pocket depth it is far easier if you can provide all the parts for them to assemble and calculate the depth for the pocket. It is also beneficial to take along some pictures of a standard spindle and a modified FRP spindle to show more clearly the results you are after. I have included the two I used with the drawings below.

Personal Experience – A few tips.
1) From memory the depth of pocket into the back of the spindle was only around 0.5mm. I used brand new parts so allow for corrosion/dirt etc if using second hand items.

2) Ask for the depth of the pocket to be slightly deeper so that the sensor gap is less than 0.6mm. This makes the sensor closer than required however you can use a DIN 988 shim washer with a 21mm OD and a 15mm ID of either 0.1mm or 0.2mm thickness to space the sensor back out. The benefit of doing this means that once bolted to the car you 100% won’t have to remove it all again to machine off additional material if the sensor is accidently too far away from the ABS ring.

3) Not essential but if planning to fit splash shields they can be used to provide a template for where the sensor mounting hole can be placed so it does not clash with the splash shield. Alternatively just fettle the shield to accommodate.


Rear Splash Shields: - (Optional)
If using splash shields be mindful that they will partially cover the new ABS sensor hole so before attempting to fit to the car offer it up to the appropriate spindle. Align the bolt holes then fettle away till the ABS sensor car fit without being obstructed.

Conclusion: -
There you go then. Finished components ready for fitting


That is everything you need to modify mk1 Focus parts to fit onto a Puma for a rear disc conversion. After this just fit them as you would expect, making sure to grease and torque bolts correctly.

Thanks to Wild E. Coyote, Tuonokid and XAF for helping me with my initial questions and special thanks to Wild E.Coyote for his initial guide which covers 90% of the conversion anyway.

If you have any questions feel free to comment below and I will try my best to answer or will add them to the post.

For those still not sure on carrying this out I can do it for you for a fee. Just get in touch to discuss, send me the parts and I will return them machined up for you.

Admin - If you want me to email you copies of the pictures, drawings etc to prevent them being lost should the image sharing website I am using disappear or start charging let me know and I will get it all across to you.

Paul Z
Last edited by PaulZ on Tue Sep 24, 2019 8:07 am, edited 1 time in total.
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HOW TO: Rear Disc Conversion Machining Process

Post by Orphan » Wed Sep 04, 2019 8:51 pm

Great How-to Paul.

It's on my future plans, if i ever get a Puma, even if here in Spain is quite difficult and expensive to do it legal.
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HOW TO: Rear Disc Conversion Machining Process

Post by red » Thu Sep 05, 2019 8:22 am

Great guide. You can feel free to email them to me, or they could optionally be uploaded to the gallery here.
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FRP#0201 (2000) 2009-2011
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HOW TO: Rear Disc Conversion Machining Process

Post by Wild E. Coyote » Fri Sep 06, 2019 7:19 pm

Great documentation Paul! :ok: :ok: :ok:
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HOW TO: Rear Disc Conversion Machining Process

Post by XAF » Sat Sep 07, 2019 7:51 am

Brilliant guide!
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