Foreword :- Most of you are aware of the MK1 3S-GTE
Turbo project I completed a few months back. In fitting that monster engine it
suddenly dawned on me that I had to stop this thing somehow…. Now we all drive
MK1's and apart from the main reason, we do this being they are fantastic fun to
drive it's also because they are cheap by sportscar standards, therefore not all
of us have £1000s to throw at them when we need performance upgrades such as
£1000 plus for Brembo brake conversions. I am a firm believer that if it can be
done cheaply but with maximum effect then all the better so with this in mind I
started to look for an alternative front brake set up to the standard and
woefully inadequate stock single piston caliper system we have on our cars. In
fact my reason for doing this was more motivated by the fact I didn’t want to
disappear over a hedge in my MK1 turbo! This conversion that I stumbled upon is
the first of its kind in the world and may prove to be the most effective and
simplest upgrade currently available to the MK1 owner.
Preparation :- This is without doubt the hardest part of the brake
conversion, sourcing the parts! For months I looked at alternative front
calipers from other vehicles in a bid to find something with nice big calipers,
multiple pistons and as big a disc as possible. In the end I found that the
Toyota range already had a big brother to the MR2 already fitted out with the
best brakes in the motor industry….Celica GT4 turbo (st205) calipers and brakes
are without doubt a serious piece of equipment. They feature solid aluminium
calipers with four pistons and a massive 315mm vented disc, in fact over 30mm
thick too! This is the hard part, these parts don’t grow on trees and it took a
few weeks to source the calipers and discs, neither of which came from the same
car. The total cost of them 2nd hand was £220 but expect to pay up to £400 from
Japanese breakers. When you compare this price to the cost of a four piston
Brembo conversion of the same quality it's easy to see it’s a cheap option. It
keeps it all Toyota too!
Method :- Once you have the calipers and discs its incredibly easy, in fact
it’s the least amount of modifying I've ever had to do to a MK1 to get the most
gain.
To start with remove the front wheels and clamp off the brake flexi hose,
undo it from the caliper and leave to one side, remove the old caliper by
unbolting it from the hub, next remove the old disc and also remove the disc
guard (if it still has one intact), mine crumbled away years ago and I'd be
surprised if the bolts actually come free on others. Chisel what's left of the
old guard off until happy.
You should now have a bare hub and nothing else. Believe it or not the GT4
caliper mounting holes line up in exactly the right place to the MK1 hub
holes….that’s right, no caliper brackets need to be made, here it is dummy
fitted a straight fitment! There is a little job to do though, on a GT4 the hub
has threads in its holes to bolt the caliper too, a MK1 does not as its threads
are in the caliper, so an M14 tap must be used to tap some threads into the MK1
hub holes and pop a 14mm drill through the caliper holes so the bigger M14 bolts
pass through, also when fitting the caliper place a 2mm washer between the
caliper and hub on each bolt, this centers the caliper on the disc, that is all
the modification the caliper needs to fit!
The disc however needs to be altered slightly more, for a start its now a
little too big to fit with the new caliper position so it has to be machined
down from 315mm diameter to 300mm diameter. Also it needs to have a four stud
Toyota pcd pattern drilled in its face (pcd 100), one of the 5 stud holes is
already in the correct place and the other three holes are drilled out in the
gaps. The last alteration is the centre hole, on a MK1 the centre hole is 54mm
diameter, on a GT4 its 55mm Now a 1mm spacer ring isn’t available so I had my
centre hole taken out to 3 mm and a 4mm ring inserted therefore making them
perfect. Here is the disc just after machining, just look at the thickness of
these things! This machine work can be carried out at any engineering firm but
its better if you know someone who can do it for you, my engineering work was
done by Mr Mac Sheavills who must take the credit for doing an absolutely
precision job on my discs he is a superb engineer and I am forever in his debt
(don’t drink all those cans at once Mac!), thankyou. The brake flexi must be
detached from the strut bracket so it will reach the caliper or alternatively a
set of GT4 braided hoses will suit perfectly.
After the discs and calipers have been fitted there's just the issue of wheel
to caliper clearance, now this I cannot judge on anyone elses car as we all have
different aftermarket alloys but obviously huge brakes like this need big
wheels, I run 17” rims on mine and there's good clearance but I do know 15”
wheels aren’t big enough for this conversion.
The finished conversion, as you can see there's about an inch between caliper
and inside rim edge. The rear brakes are now getting uprated too, I'm working
with Alan Jones on this using MK1 or MK2 front calipers that bolt straight onto
the rear hubs (trust me they do!) and are combined with a hydraulic handbrake
powered by a MK1 clutch master cylinder, no more seizing cables or linkages!
Following the success of the GT4 front brake conversion on the MK1 turbo it
was time to start thinking about upgrading the rears to match. Not only is this
upgrade vital for my car but also useful for other MK1 owners who want to rely
on more than throwing an anchor out of the window for extreme braking
performance. I talked in some depth with our club technical guru (I am merely an
understudy in comparison) Mr. Alan Jones about the possibility of rear brake
modifications one of which was the possibility of a hydraulic handbrake set up
similar to those found on rally cars. The idea seemed simple enough, mate a
clutch master cylinder to the handbrake cable somewhere near the gearbox and
then “T” piece into the rear brake line. We had the theory well and truly worked
out as well as the mechanics of actually fitting it to the car, the stopper to
this idea was MOT law, it is illegal to have the handbrake on the same system as
the footbrake and our idea of ridding MK1 owners of seizing handbrake linkages
and cables came to an abrupt end, the only possible solution to this was fitting
and extra caliper to the rear that was dedicated as a parking brake but this is
just silly due to extra weight and mounting issues.
My early spec MK1 rear discs are a pathetic 239mm diameter and look really
small compared to the front brakes. Therefore I had to come up with an upgrade
that simply relied on the current system of rear caliper only bigger. After a
month of research the best “Toyota” caliper available turns out to be the MK2
turbo item, not really much of a shock upgrade as the front GT4 calipers but
they do feature a bigger piston and the ability to house a much wider disc, this
in turn allows a much bigger diameter disc with vents. The search began for a
suitable disc that would just plug 'n play and after talking to my fellow MK1.5
owners on the US forums (cheers Deno and Harvey) we found that the front disc
taken from a 1989 VW Corrado G60 model had the correct height and four stud
(4/100) pcd to fit. It was also a whopping 280mm diameter/vented and 22mm thick,
just enough to fit the MK2 turbo caliper onto.
These discs were bought from the motor factors for £30 each plus vat, and the
revision 2 MK2 turbo calipers are around £40 each second hand, a total of £150
for the whole upgrade, compare that to an aftermarket caliper and disc combo and
it’s a great idea. I hasten to add that a revision 1 MK2 caliper wont do as it
only accepts a 17mm thick disc so revision 2 turbo onwards must be used. All
that needs to be done to the disc is an insert made for the centre hub hole to
make it 54mm.
The MK2 turbo caliper has to be mounted further away from the hub than the
MK1 caliper naturally due to the new disc being 280mm and this is achieved by
cutting the mounting holes off the MK1 caliper carrier and also cutting a
section out of the MK2 carrier and welding it in. Here is the MK1 caliper with
its mounting holes removed.
The second pic shows the areas to be removed from the MK2 caliper so the AW11
pieces can be welded in. Below is the caliper cut and the new pieces clamped in
position to show how it's going to look. The hole centres need to be exactly
131mm apart so they are bolted to the hub ready for the caliper carrier to be
dummy fitted onto the disc.
Next the disc is fitted and the caliper carrier is mounted onto the disc with
its pads fitted, the pads are clamped solidly to the disc in the exact desired
position and they hold the carrier square to the disc. I also inserted four
steel plates between the carrier and disc on either side of it to centre the
carrier making sure it had the same gaps either side as seen in the pic below.
The carrier is now in exactly the right place and firmly secured ready for tack
welding onto the mounting holes. Once tacked the whole carrier is removed and
seam welded.
The carrier in position with spacer plates to centre it all and the carrier
tack welded and removed. Below you can see it all welded and ground off, good
welding skills are essential for this final weld and not to be attempted by a
novice.
The caliper can then be mounted now knowing it will fit perfectly and plumbed
to the brake flexi hose and handbrake cable. Still being MR2 the MK2 caliper
will fit the MK1 cable and brake flexi perfectly, isn’t it lucky for us that
Toyota don’t change absolutely everything with later revisions, marques or even
models (GT4 etc). As with the front brake upgrade wheel to caliper clearance is
again an issue and at least a 16” wheel must be used in conjunction with this
mod.
Hopefully this brake upgrade will prove valuable to another MK1 owner wanting
more stopping power. Sincere thanks must go to Deno Plumley and Harvey from the
US owners club message board, between the three of us we managed to discover
this upgrade and work through all of the problems, many thanks chaps. Feel free
to ask any questions on this or any other of the MK1.5 upgrades.
paulwoods.v6mr2@ukf.net
PAUL WOODS
Mk1 MR2 rear big brake upgrade:-
