Brake Upgrades for an Austin Healey 100 – BN1

Brake Upgrades for an Austin Healey 100 – BN1

We have had our BN1 back on the road since July 2008 having completely restored it over a 2 year period. This included modification within the manufacturers’ parts bins where we saw fit to suit our purpose. The engine was rebuilt by Denis Welch with ‘an adequate power increase’ which in turn was seen as a possible overload to the standard front drum brakes. To assist in this matter, I installed front stub axles and drum brakes from a 100/6. This increased the shoe width to provide better braking, and at the same time the stub axles are a larger diameter and therefore stronger.

As the years have gone by, my concerns have risen as the brakes appear slightly inadequate. This was put down to two things, I was getting more familiar with the cars abilities, and the modern saloon car braking has improved tremendously, and they can stop very quickly.

Roll the calendar forward another couple of years and I was the proud owner of a conversion kit for front disc brakes. This conversion job sounded very straight forward, and eventually my chance to install all these goodies came in the winter of 2015.

Now the tricky bit unfolds, so get yourself a coffee and read on (I will not use suppliers names, but point out the pit falls and workload that I experienced):-

It is not difficult to dismantle the front end, but keep your parts and put them aside carefully (you may need them). Now do not forget that I have 100/6 – 3000 axles, so mine stay on the car. If you need to up rate your stub axles, the job becomes larger and will involve taking the suspension to pieces to install the alternative axles (and of course more expense).

After a clean down and a grease-up, the first part to install is the conversion plate that holds the caliper (mine were original parts from stock, so no problems here). At the same time, (as they are on the same bolts, it is time for the dust covers to be fitted behind the discs). Lots of race boys do not fit these in favour of more ventilation, and there is not too much mud on a race track!!).

My new dust covers were pattern parts, but when installed were way off fitting correctly. The cover was about 12mm too far forward of the disc, therefore the caliper side was overlapped by the disc. This I believe is due to the brackets on the new parts being welded in the wrong place on the dust cover (another NFC member cut and welded his to make the correction). With great fortune, I secured a pair of original covers which did fit correctly with the required tolerance gaps. So off with the pattern parts and made ready for their return and credit.

The discs are bolted to the back of the hubs (ensure the bolts are long enough to fill the nuts, but not so long that they collide with the bolt heads behind), the bearings and oil seal are best installed on a press, but can be done with a good sized vice, but take care to get them centrally lined up to gain a good fit. With this all completed the hub goes on to the stub axle with bearings freshly packed with high temperature grease (the bearings should be adjusted to achieve a free spinning wheel, but still provide a small tolerance when the wheel is fitted and checked for vertical & horizontal rattle).

Caliper in place

Caliper in place

Now is the time that you discover the new pattern calipers are of Ford manufacture (Escort/Capri).

This means that the large special bolts holding the caliper to the conversion plate have to be a mixture of diameters.

The conversion plate is UNF as is the stud that takes the brake flexible hose bracket, but the shank that goes through the caliper needs to be 12 mm. So washer sizes are to be watched and the original dust cover plate brackets will be in need of opening out to get the 12mm bolt through them.

Do not forget to centralise the caliper about the disc, this may need additional washers as packers to get it as close as possible centrally. Now the pads can go in which are also Ford (the long wire clips in the pack are not required, only the short dimple clips).   Due the caliper bolts being newly made, also bear in mind that the studs to receive the brake hose brackets are also oversized and the brackets may need the holes increasing a little to allow them to fully tighten.

Flexi pipe with slack

Flexi pipe with slack

Now it is brake hose time. The hoses that were supplied to me were too short for this application in my opinion. I always place a small block of wood between the shocker arm and the tower plate before jacking the car up to avoid the suspension dropping fully (it also stops the rubber buffer from being squashed by the suspension weight).  In this configuration, there should be some slack in the hose for further movement downwards if needed. If too tight at this stage (I have had an MOT failure for that, as the engineer considered that the hose would snap on full suspension movement, and do not forget to check lock to lock on the steering for clearances). The short hoses are also back in the box for return and credit. I have actually fitted some of my shelf stock hoses, and they seem fine to me.

Shape of ridged pipe

Shape of ridged pipe

It is now time to recover the original ridged brake pipe that linked the two wheel cylinders in the front drums. These can be modified with a bit of care to create the strangely bent pipes needed from the caliper to the hose bracket (if they are past recovery, then get new pipes for a 3000).

As the manuals say, the other side is completed in the same manner!!

It does not stop there, the rear drum pistons on a 100 are 1 inch diameter internally, and on the 3000 which is what we are heading for, they are .75 inches diameter. We therefore have to strip the rear drum and change over the cylinder. It is only the bore size that changes, as they are the same to look at on the bench!

Whilst at it, I decided to replace the brake shoes, thereby starting with a fresh set of everything. The clips holding the cylinder into the back plate are a fiddle to split apart, but from then with the brake line disconnected, they will come away easily. I generally strip new cylinders and ensure they are swarf free before installation, and for personal satisfaction of cleanliness.

The assembly of the shoes and springs is straight forward, but ensure the shoes are supported by the back plate pins so that they are square to the drum to ensure full brake effectiveness. Check that the static adjuster is right off, and fit the drum. This needs to revolve freely.

At this point I removed the cotter pin to the handbrake cable and released the tension springs on the cross rods. This enables the rear hydraulics to work fully and not controlled in any way by the handbrake system.

Disc face on

Disc face on

Adjust the static adjuster until the drum stops revolving. So now with all brake lines re-connected, its fun time bleeding the system. Top up the reservoir with new fluid and work from the rear left corner to rear right, front left and then right front. Try the pedal and if it pumps up closer to you, it still has air in it. Bleed around the same route again. It took me 3 times around the four corners to clear the air out. Keep hands and tools clean, this fluid eats paintwork, and do not rush it!!

This ensures two major objectives, to remove the air and ensure the new fluid flows throughout the system. All the time keep the reservoir topped up. Once you are happy with the pedal and it does not pump up after a few pumps, then tighten all connections gently but firmly, and clear away.

Do not get the fluid on the paintwork, and all rags and paper towels go into the bin!!

Now with the system free of air the final adjustments can be completed. Connect the handbrake cable again, ensuring that the swivel link is approximately at 45 degrees to the axle. Reconnect the springs to ensure the rods return after use. Now go back to the rear drums and readjust the static adjuster. Slacken off at least 2 notches to get the drums free turning, and not dragging on the shoes (this may take more than 2 notches). Ideally the handbrake lever should not come up vertically before the brake is applied but settle the system in on the road and adjust as needed after a test run.

Now get someone to sit in the car and push the pedal when told. Go to each corner and spin the wheels and call for brake. This checks that all corners are completed. After this operation go back over the pipe connections to check for weeps and tighten carefully if needed. Clean up and you are done.

Note:- Over the next few days I took the car out for short trips bedding the brakes in still further. It took further adjustment on the rear drums on the shoe adjuster, until the notches were only two from locked drums. This also firmed up the pedal and created better braking at the discs as well.

I have attempted to outline the work involved and details needing to be understood, by those who consider attempting this job at home, in the solitude of the winter garage. I have been around Healeys for 40 years but I am still an amateur, so there will be other methods of working.

This article and pictures was written to describe what can be achieved at home, in a well kitted out workshop.

Just in case you are wondering, the master cylinder is still .75 inch bore as there is no servo. If you go to a servo system it needs increasing to .825 inch bore.

Having run these brakes for a season now, I can say that the brakes are such an improvement and offer great protection against the modern traffic conditions.

Good luck and if

you wish to chat, my email address is on the New Forest Centre website.

Synchronisation of Twin SU HS-type Carburettors


Before proceeding to synchronise your carburettors and for best results, some preparation is in order. Your carburettors should be in peak condition with no play in the throttle shaft bushings. If these bushings are worn, synchronisation is difficult or impossible to achieve since there will be a vacuum leak past the bushings. Additionally, the jet needles should be identical and correct for the application; adjusted to equal and correct seating in the piston and centred in their jet bores (if not centred, you will feel a bind when moving the piston up and down). If any of these conditions exist, the carbs should be rebuilt or at the very least torn down and thoroughly cleaned and inspected before adjustment.

1) Remove the air cleaner and take the time to clean the area in which you will be working. Check the throttle linkage for free movement and unscrew the throttle adjusting screw on each carb until it is just clear of the throttle lever with the throttle closed. Turn the screw clockwise one full turn on both carbs. Using the elevating pin, raise the piston in each carb and ensure that it falls freely onto the bridge when released.

2) Remove the suction chamber assembly from each carb (Don’t mix them up! Do them one at a time if necessary!) and, by turning the jet nut, position the jet tube flush with the bridge in each carb or as high up as it will go. Regardless, adjust the jet tubes of both carbs so that they are the same. Check that the sintered needle guide of each piston is flush with the underside of the piston.

3) Turn the jet nut two turns down. This can be checked by adjusting it so that the top of the jet tube is .125″ (1/8- INCH) below the level of the bridge using a vernier or dial caliper.

4) Back the fast-idle adjusting screw well clear of the cam.

5) Reinstall the suction chambers and recheck to ensure that the pistons fall freely onto the bridge (see step 1, above).

6) Check the damper oil level and top up with suction chamber oil (GGL9035) or 20wgt motor oil.


1) Loosen both clamp bolts on the throttle interconnect mechanism. Likewise, loosen both clamp bolts on the cold-start interconnect mechanism. This allows the two carbs to operate individually.

2) Using a “Uni-syn” or other vacuum synchronising meter, balance the carbs by altering the settings of the throttle screws until the proper idle and balance is set. You can also use the time-honoured “HISS”-method: using a length of tubing as a listening device, insert it into the carb throat and listen to the air flow while you adjust the throttle screws. Adjust both screws until you hear both carbs “hiss” at the same pitch and volume (this works better than you might expect, but can make you crazy).

3) After making the above adjustment, set the mixtures by adjusting the jet nut on each carb down/clockwise (rich) or up/counter-clockwise (lean) until you achieve the fastest idle speed. Now turn each nut up/counter-clockwise (lean) until the engine speed just starts to fall off. Then turn each nut very slowly down/clockwise until the maximum speed is re-established.

4) Recheck the idle balance with the synchronising tool and adjust as required.


1) With the fast-idle cams of both carbs hard against their stops, adjust the cold-start connections so that both cams begin to move simultaneously.

2) Check and adjust for 1/16″ free-play in the choke cable before the cable can move the cams.

3) Pull out the choke cable knob until the linkage is just about to move the jet.

4) Using your synchronising tool, adjust the fast-idle screws to give the correct idle speed.

5) Tighten the clamp bolt on the throttle arm and choke mechanism.

6) Replace air filter assembly.

Taken from an Article date: Jan 29, 2000 

Make your own high intensity rear flasher lamps

Make your own high intensity rear flasher lamps


Use the standard reflectors for the body and rim.

For the amber lens I used 16099 Amber lens from  I turned them down on the lathe to fit the rim.

The light units are ordinary 12v MR11 domestic halogen down lighters (they are 20 watt so flash rate is about right) which you can get for less than £1.

Healey_flashers2010_0212(015)It is also necessary to bypass the Stop / flasher relay and run a new wire to the rear. Connect a new cable to both of the existing stop elements of the stop/tail lights; remove green and purple cable from terminal 5 on the brake / flasher relay under the bonnet and connect to the new cable. Connect the cable removed from the original stop elements of the stop/tail lights and connect to the new flashers. Provide earth connections to new lights.


You will need to fit other reflectors under the bumper.

Whilst I was at it I also carried out a halogen headlight conversion using headlights with built in side lights which meant I could replace the front side light bulb holders with a single 21w bulb holder fitted with an amber colour bulb inside the clear lens. Vehicle Wiring Products also do the headlights.