TR8 4 Pot Calliper Vented Disc Upgrade

TR8 Lockheed AP 4 Pot Calliper Vented Disc Upgrade

The Factory fitted uprated vented discs and Lockheed 4 pot callipers to the development RHD UK spec TR8 NWK988W.

The story for this starts with the Austin Princess 1975 to 1981 and later an improved version, the Ambassador 1982 to 1984. As part of the drive to better position the Princess between the Ford Cortina and the Granada various engine options were offered along with various safety features. One of those was the Lockheed 4 piston callipers with a built-in dual brake system so if one system failed you still had a second system operating the other pair of brake pistons. This system used a 270mm diameter and 12.8mm thick solid disc. A normal solid TR8 disc at the time was 247.6mm diameter and 12.7mm thickness. In 1980 when Triumph was looking for a better set of performance brakes for the UK spec development TR8, with a view to the final production UK spec TR8’s having the same, a vented disc kit was developed by Brian Owen at Abingdon in conjunction with John Moore at Automotive Products (Racing) Leamington.

Excerpt from Richard Hurdwell NWK988W Memo BL Motorsport Dec 16th 1980.

A Ventilated Brake Disc Kit was fitted using Ferodo DS11 pads this has improved the standard braking significantly and is virtually fade-free from repeated high-speed stops. The kit was developed by Brian Owen at Abingdon in conjunction with John Moore at Automotive Products (Racing) Leamington. Automotive Products would be able to supply in quantity. These brakes will only fit the car with Alloy wheels.

What that actually translated into was an 8mm spacer between the two halves of the callipers and a 258 diameter and 21mm thick vented disc specially made by AP Racing. In addition a 2mm spacer on the leg to further centralise the disc in the calliper. (may only require 1mm on some cars)

Internally the callipers were ported and so they operated from just one of the two inlets with all four pistons operated together as one instead of independently.


On the TR7/8 alloy wheels UNMODIFIED callipers do just slightly catch the outer edge as shown here by the red line

The front bleed screw also catches on the keepax TR7/8 alloy wheels, and particularly stick on weights. It’s no longer needed if you port internally so that can be blocked off. If you port externally then you can take a few mm off that bleed screw as another option.
The ridges and lugs in the castings were filed away to allow use with the 13” keepax TR7/8 alloy wheels.

Note the area’s that need filing down on the new 4 pot on the left against how smooth the original is on the right by comparison. Also note the white marker on the original that was used to test the filing as they went against the alloy wheel. That is the main area in line with the ridges that catches.

After the development of this vented disc kit details quickly got out and kits particularly for Escorts and Capris were everywhere. FG Rallying supplied the kit for the TR8/TR7 but eventually AP Racing stopped making the discs and that came to an end for the TR8/TR7. How ever for the Escorts they continued with plenty of other suppliers making suitable discs. That means that almost all callipers you buy today will have a 10mm spacer to suit Escorts whereas the original TR8 has 8mm. So, more metal will have to be filed away to fit underneath keepax alloys. Best bet is to buy a kit at 8mm which is pretty straight forward to fit and easily available from eBay and the like.

They will fit easily with no casting mods required at all under 14” and above wheels. If you want to fit the alloys and don’t want to file the casting down, then there is another option and that is to fit a 3mm wheel spacer. Heavily powder coated alloys may require a bit more, check the clearance before you drive off!


The top and bottom pairs of pistons on a standard AP Lockheed Princess 4 Piston calliper are on independent circuits, which is why there are two inlet connections and the extra bleed nipples lower down (they are required for the lower pair of pistons). The second inlet connection and the lower bleed nipples cannot be blanked off unless a modification has been made to connect the two circuits internally. This requires the callipers to be fully disassembled; the halves separated and the pistons removed. A hole then needs to be drilled in the calliper inner half through the upper piston socket through to the fluid port for the lower socket. See yellow circle.

Original 4 pot callipers on NWK988W internally ported

This will permit the lower pistons to receive fluid from the supply port to the upper pistons. Only then can the lower bleed nipples be removed and blanked and the second feed connection be blanked. This internal modification has been made to the callipers on NWK988W by Abingdon/AP Racing. I remember being told once it had been modified with channels internally but wasn’t much the wiser to what that actually was, but this is what was meant, holes/channels drilled to make the calliper a single circuit system for all four pistons. It only needs doing to one half for each Calliper. Pretty straight forward but it will void your guarantee and may cause issues refitting seals and pistons.

Where to drill the hole to port internally

A simpler and much easier solution that won’t void the calliper guarantee is to use an additional cross over pipe to connect the lower inside bleed port to the second inlet port. This will allow fluid to supply the upper pistons from the lower pistons in series. With this solution, the lower bleed nipple on the outside is still required to bleed the outside lower piston. Note the inlet now feeds the bottom inlet. If you port internally then it’s only the upper inlet you need to use.

Showing the flow path for external porting


I did try to persuade AP Racing to remanufacture the discs but I got a flat no to that request as apparently all the plans, castings and dimensions have long gone. But they did put me in touch with another company who make bespoke discs for them. As I still had a set of original discs on NWK, I had them laser scanned and remade, but the cost because they are individually made and not mass produced, is high! I have a few I could provide to interested parties as I had a few spares made above my requirements, so please email me for details. If there is enough interest it may be possible to do a larger run and bring the price down, so again email me with your interest. These are exact copies of the originals albeit with some slight modification to allow the use of the larger pad plates now used on newer brake pads, PLUS they are double heat treated and made to a considerably higher standard than the originals.

NEW AP Racing discs made in 2024

Original 1980 AP Racing discs refurbished

There is a cheaper and simpler solution and it comes in the form of a current Rimmers uprated brake kit disc P/N 7117A, and that is the discs they use with an adapter they provide fitted, work perfectly. The are almost exactly the same size as the originals at 258mm diameter with 20mm thickness just 1mm thinner than the original AP Racing discs. Picture above with the link pipes fitted is using those discs and as you can see it’s a pretty much perfect fit. Those discs are initially more costly because you get the TR7/8 adapter with them, but from there on in you can get the Toyota/Celica RA61/Supra 2.8 MA61 82-86 vented discs at a more reasonable price. As can be seen with the original AP Racing disc on the left and the Rimmers version with the adapter on the right they are almost exactly the same height. Point to note is the Toyota/Celica RA61/Supra 2.8 MA61 82-86 vented discs are now getting quite hard to get hold of so when you find some its worth buying a few sets! There are a lot of low grade quality versions of this disc out there from China or where ever so beware!

Supra disc showing the adaptor Rimmers make for the TR8/7

This is a cross reference list of other part numbers for the discs with no adapter. (Please double check as in reality some may not be exact!)

KAVO: BR9316
ASHIKA: 60-20-226
JAPCO: 60226
A.P: BG2401
AE: ADT34322, ADT34313
BENDIX: 333722
BOSCH: 0 986 478 795
BRADI: 1.5220.2.4
BRAKE PARTS INC.: 85734, 951910
BREMBO: 09.5027.10, 9502710
FTE: BS3604
JURID: 561300J
LPR: T2291V
METZGER: 1.5220.2.4
NIPPARTS: J3302026
NK: 204536
PAGID: 53617
SBS: 1815204536
SEBRO: 5639
TEXTAR: 98200 0437 0 1, 982000437
TRW: DF1928


Other Options

In 1992 the MGRV8 calliper vented disc setup was actually conceived from the earlier work in 1980 on the UK spec development TR8 by Brian Owen at Abingdon in conjunction with John Moore at Automotive Products (Racing) Leamington. That setup was meant to go on the production UK spec RHD TR8’s when they launched in 1982, but they never saw the light of day. So, it got shelved until the MGRV8. This version is available in two versions, an alloy light weight (no coating so will not do well in winter) or a cast one. It is internally ported as per the original one on NWK988W but goes a step further in that the second inlet is completely blanked off in the casting and all but one of the bleed screws are removed.

The MGRV8 used a 12.7mm spacer which is too big for our use as their discs are 24mm thick, but they also supply one for fords with the 9.7mm spacer fitted which is fine for use on wheels 14” plus but not for 13” alloy wheels unless you fit 8mm spacer as above or use a wheel spacer.


The one thing that has been found to be critical is alignment of the disc central in the calliper. It was once thought lack of air flow under 13″ Alloys was the reason for discs warping and having problems because cooling was restricted but it is far more likely to be alignment that is responsible. The disk below was in a set of callipers with the 10mm spacer but they weren’t central being nearer the outside edge. As a result this most likely contributed to a warp on the outside edge and pad imprint when hot and stationary. Had the disc been central I doubt this would have been an issue. Equally the poor grade discs certainly didn’t help either.

The callipers need a shim washer to align central. On NWK988W the factory fitted 2mm washers between the leg and the calliper to move it further inboard and central. Marked with RED outline

On my Silver EFi TR8 it only needed a 1mm shim washer so each car will be a little different. Time and care getting this right will pay dividends, so take the time to do so.

This is with 10mm calliper spacer fitted and 2mm spacer and clearly off to one side

This is with 8mm calliper spacer fitted and 2mm spacer and pretty much central the RED line indicates the correct position. See the closer in photos below to see the space that leaves. Not a lot,

Too far over

Just right with 8mm spacer

Once pads have worn down this becomes a lot less critical but with new pads it can and does cause issues if they aren’t central.


Having tested a few different pads I have found either the EBC yellow pads

Or the FEROD DS2500 pads to be the better choices for fast road use.

EBC Yellow Is below the DS2500 so you can see the EBC has a mm or two more pad plate.


For an uprated brake and vented disc kit to fit under factory 13” alloys this is pretty much still the best. Having driven my green 8 with the original AP/Lockheed brake kit still on it and my silver Efi 8 with the more up to date version as above, it really does make a world of a difference over standard. If you fit new Goodrich flexi hoses and add EBC yellow or Ferodo DS2500 pads the car start’s braking with just the gentle weight of your foot on the brake pedal. So, the fact this vented disc kit was originally conceived/designed for and tested on the TR8 in the first place, comes as no surprise as it just feels so right for the car. It is such a great shame the final version of RHD UK spec TR8 never went into full production because with a version of the Vitesse engine and these brakes it would have been one heck of a car to drive in 1982. I know first hand, because that is pretty much what the RHD UK spec development TR8 NWK988W is. These brakes can of course be fitted to the TR7 as well no problem at all, particularly if you want to retain factory alloys and have a V8 variant. FG Rallying were the first to offer this brake kit as an upgrade option for the TR7/8, presumably via contacts at Abingdon/BL Motorsport where they were first told about it, but once the vented discs from AP Racing ran out late 80’s it sort of faded out from view. That however didn’t stop it becoming extremely popular with Ford Escort/Capri owners who used different discs and have continued to use it, that and the MGRV8 version has essentially kept the callipers in production for the benefit of all! You can of course pimp them up a bit as I have with the originals from NWK988W, more to ensure they last another 40 plus years than anything else!

Lastly thanks to the following for helping with photos and information. Dave Redfern, Steve Willcox, Russ Cooper, Andy Salter and Robert James Clark.