BIG BRAKES MR2 MK1 - GT4 Front Brake Conversion and New Rear Brake Conversion

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Rodger Carpenter
5 years ago
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1 BIG BRAKES MR2 MK1 - GT4 Front Brake Conversion and New Rear Brake Conversion By reading this guide you are accepting you have also read the disclaimer at the end of the document. 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

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.

Believe it or not the GT4 caliper mounting holes line up in exactly the right place to the MK1 hub holes.

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

2 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

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

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

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

3 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.

4 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! Mk1 MR2 rear big brake upgrade:- 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.

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

5 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

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.

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

Here is the MK1 caliper with its mounting holes removed.

6 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

carrier making sure it had the same gaps either side as seen in the pic below.

mounting holes. Once tacked the whole carrier is removed and seam welded.

7 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.

everything with later revisions, marques or even models (GT4 etc).

Hopefully this brake upgrade will prove valuable to another MK1 owner wanting more stopping power.

8 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@mk1turbo.fsnet.co.uk PAUL WOODS

9 DISCLAIMER. This file was downloaded from twobrutal.co.uk and may not be altered in any way whatsoever without prior notification and permission given solely by the author. Neither the author nor the filehost accept any responsibility whatsoever should damage or injury occur to persons or property using information contained in this guide. For insurance purposes persons carrying out any modifications to a motor vehicle in the UK are required by law to divulge such modification details to their vehicle insurers and the DVLA.

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