Ventilated Disc Brake Conversion
By Owen Williams
The problem started when I was taking my MkIII through
engineering in
The car in question is from 1963 and has a 327ci Chev
motor with 4 speed
The car was basically rescued from the crusher in
All the body mods were well made in the day but
buggered as found and not to my taste at all. I like old school sleepers. Clean
and neat but tasty underneath.
The front brakes were standard with a remote booster
fitted (not sure why) when I got the car and didn’t work at all. I stooged
around for months fitting new remote boosters of the same sort and eventually
realised they had probably never worked. In
As the Magnum mags are 14” there is not much room
inside them for the brake bits when fitting larger and thicker rotors. I was
doing up Holden 1 tonner for my son at the time so used that a guide to
clearances needed as it also has 14” wheels with ventilated disks the same
diameter as the Ford stud pattern ones I used.
I found a kit available from Castlemaine Rod Shop and
rang them to chat. The kit is number DB38 and cost A$175 at the time. It uses
slightly modified Ford ventilated disks from the XD-XF Ford series, PBR
callipers (same as my sons HQ Holden one tonner and popular amongst rodders)
and your own selection of master cylinder and booster dependant on the rear end
etc. For your money you got the following:
·
Two adapter plates (ZMF3) which are donuts cut from
plate steel and which bolt to the strut. The donut hole goes over the stub axle
·
Two dog bone adapters which mount the calliper to the
adapter plates
·
Spacers to get the correct lateral alignment of the
calliper when the dog bone is bolted up
·
High tensile CS bolts for the above
·
Inner and outer bearing adapters which are fitted to
the stub axe and allow use of standard wheel bearings for the ventilated disks
So overall it should have been pretty easy.
I found at the local wreckers a set of XE rotors which
were virtually new for $60 the pair including bearings. Bargain! I had the
outer bearing race machined about 3 mm deeper as per the Castlemaine Rod Shop
instructions so it would fit onto the stub with the nut and washer in place and
they were ready to go.
I bought off Ebay a set of PBR calipers which were
also pretty cheap, and rebuilt them with new pistons and seals and performance
pads, which are readily available. One of the Australian made pistons I bought
was the wrong diameter and I had a battle royal with the brake guy and literally
almost came to blows before he realised the manufacturing error was his. If I
had got it in I would never have got it out so watch out when buying “standard”
aftermarket components from arrogant “experts” (how could it be wrong, it is
mass produced…you must be fitting it up wrongly).
Then the fun began. I fitted the inner bearing adapter
to one side, no problem. You have to heat then and let them shrink into place
so rapid fitting is necessary. The second one jammed half way on and I could
not get it off without damaging the stub. Out with the angle grinder to cut the
adapter carefully and on the phone to the Rod Shop. Please send me another one,
which they did. The second time it went on OK.
So then I trial fitted a disk and low and behold the
clearances looked all wrong. When I jacked up the suspension the control arm
was actually binding on the disk (glad I checked in the up position). The tie
rod end was also almost touching the wheel rim inner and would have knocked the
wheel weight off. The Ford disks were not offset far enough on the axle by the
spacers supplied and there looked to be very little room for making them
thicker as then the stub axle becomes too short even with the already modified
disks. I made some spacer washers for
the inner spacers, and ground down the end of the control arms a bit to
increase the gap. This moved the disk out so the nut only just went onto the
axle so I then machined the axle nut down a bit until it all fitted back on the
stub with about ¼ gap between control arm and disk in the upper position. If
you use a rubber boot that is too baggy on the control arm ball joint it will
touch the disk also but I fitted some more snugly designed ones and they also
now have good clearance.
The disks now fitted OK. I sent Castlemaine Rod Shop
an epistle and got no the phone to them and to their credit they supplied a new
set of inner and outer spacers made to the new tolerances I gave them and I
removed the old (with difficulty) and fitted the new. Basically the revised
inner and outer bearing adapters spaced out the disk an additional 4mm on the
stub axle and got the wheel back to similar track width to when I got it. Track
width is a whole nuther issue with MkIII Zephyrs as the 14” mags are a long way
different to the skinny 13” steels originally fitted but that’s also another
story.
Then to fitting the callipers. More dramas. The
adapter plates had obviously been hand made not cut on an NC machine and bolt
holes were so badly located that one calliper bound onto the disk and the other
onto the wheel inner. Also, because the disk had moved out 4mm, the offset
spacers for the dog bone had to be reduced that much to move the calliper out
the same amount and now one of the four bolts did not fit as the bolt head in
the back got in the way of the dog bone. Fortunately it was possible to overdrill
the adapter plate and tap a thread into one of the strut bolt holes and fit an
oversized bolt (7/16”UNF) which avoided the need for the bolt from the back. So
now I have three conventional 3/8” UNF HT bolts from the back tapped into the
adapter plate and one 7/16” bolt into a tapped hole on each strut (see photo).
All good and nice and strong with a whiff of Loktite on assembly.
The standard way the calliper mounts to the dogbone,
then the dogbone to the adapter is also a problem as the multiple spacers came
loose after a few heavy stops (just after the engineering brake tests
fortunately), so I removed the lot and welded the dogbone to the spacers and
the spacers to the adapter to make a single assembly. It is quite tricky to fit
but with a bit of shaping to the inner edge of the dog bone I can install the
entire assembly by slipping it over the axle and rotating it into place before installing
the 3 plus 1 mounting bolts. You’ll have to do it yourself to see what I mean
but once you work it out it works well. So the only mod to the suspension in
the end was tapping one thread into one mount hole on each strut. I can live
with that. Without this mod I would not have been able to weld the whole
assembly together into one piece and be able to fit it, so overall it is a much
better and stronger solution.
The badly drilled holes in the adapter plates I welded
up and redrilled until I had minimum clearance from disk to calliper and
finally it all fitted together.
I used a TE Cortina power booster (quite small
diameter so it fits in neatly between V8 and inner guard and I can still get
the plugs out easily) and HQ PBR split master cylinder with 1” bore and it all
works well with my brakes. Stopping is powerful, doesn’t fade.
So now if you do the same Castlemaine Rod Shop
conversion, hopefully the bearing and dog bone spacers will come as per the
revised design, but you should assume you will need to check the adapter plate
drilling and caliper clearances. Expect to do a bit
of fenagling unless CRS have gone to NC machining. I offered to draft the files
for them to cut the pieces to, but never heard back. Overall I think this
conversion is now a safe and worthwhile update to the standard Z car brakes if
you are putting any serious horsepower into the car or your engineer mandates
it, and replacement parts will be around for a long time to come for the
components used. A side benefit was that the front wheel studs are now ½”
diameter which matches those of my rear LSD axles, so I only need one size of
wheel nuts and the studs are all much stronger than standard Z car.
Hope someone gets something useful out of this
rambling. There are a few pics below of the bits and pieces and fitup involved.
Let me know if you want any more info.
This shows the ZMF3 adapter plate mounted to the strut
with dogbone at the back for caliper mounting. You can see the caliper sitting
on the control arm behind. Three holes in the adapter plate are threaded and
one drilled out and the strut hole tapped so the dogbone would fit on and still
get to the bolt. The dogbone is fully welded to the spacers and adapter plate.
I left the two mount bolts in the dogbone mounts even after welding as belts
and braces…the Irish principle. “to be sure to be sure”, as the welded assembly
is otherwise under a lot of stress under heavy braking and will want to twist
due the offset.
These are the two bearing adapters for each side. The
larger inner one is two piece in this picture (has a spacer ring I made while
getting the spacing right). The kit will come with this as one piece item. I
found the machining of these was well done and an accurate fit onto the standard
strut, so CRS’s machinist seems to know what he is doing.
This is the PBR caliper with kidney shaped pads. Strong, simple,
reliable, available.
A view of the disk in position with adapter plate and clearance to the control
arm knuckle and rubber boot. Compare the disk to your standard one and you will
see the obvious advantage in brake performance.
Disclaimer: The advice
and guidelines given in these articles are given in good faith. The owners
and managers of the Galeforce Zephyr site will
take no responsibility for any injuries or loss sustained while carrying
out the described tasks and procedures or any consequences arising.
Please read the Safety First Article
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