of AC's post-war 2 Litre Saloon
(early hydrastatic type)
Chassis up to EL1239 (1947-49) were fitted with Girling hydrastatic front brakes. These are self-adjusting and the linings remain in light contact with the drums. This reduces the pedal travel. The master cylinder has a 5/8" bore, and was only used by AC and Rover. It is hard to find any data or drawings of this cylinder, and at the time of writing (July 2021), new ones are not available. Repair kits, however, are readily available. The brake hoses are unique to this AC model. The wheel cylinders (1" bore) are the same as the rear ones on early Series 1 Land Rovers.
Later ACs changed to twin-leading shoe front brakes, with adjusters. The final brake system (EH prefix on chassis number), was all hydraulic, and the master cylinder changed to a 3/4" bore item.
Important note: If there is excessive slack in the rear mechanical brake linkages, the balance-link (near the pedal) will tilt too far to act as a balance-link. That is, it will act as a pull-rod, actuate the front brakes, while the rears might be doing little or nothing. Further down this page, I've explained how to set up the adjustments.
This is bolted to the chassis under the dynamo, and access is easier with the dynamo removed. It's held to the chassis with 3 bolts, 2 of which also help to secure the bulkhead. As always with hydraulic brake repairs, take care with the fluid, which is largely made of solvents. It will strip paint, and skin contact should be avoided.
The mechanical connection is to a balance linkage. With the system drained, it might be best to try and uscrew the large end cap, while the unit is bolted to the chassis. It takes a lot of leverage! Failing that, remove and dismantle the cylinder, and soak the end cap in penetrating oil. Normally, one would avoid getting oil inside, but if it's seized, then you have little choice.
On mine, the rubber belows are a slack fit over the push-rod, allowing water in, hence the rust seen in the photo below (bellows removed). Removing the circlip, releases the push-rod assembly. This should also release the piston, unless it is seized. Soaking in penetrating oil, followed by some persuasion from a mallet, will usually free it.
Clean parts thoroughly with brake cleaner (solvent). Install new rubbers, spring and copper washers. It might be worth annealing the copper washers, as it's hard to get a good seal (joints have to be very tight). Check that the joint surfaces are perfectly true. I found that the top surface where one of the pipe unions fits, was not quite flat. Also check that the end cap and its mating surface are perfect. I painted the master cylinder and reservoir with epxoy, as this resists brake fluid. I also painted the brake rods with epoxy, noting that one of them passes under the master cylinder.
Be careful to fit the piston seal the right way round.
A potential problem in this particular type of cylinder, is the aluminium cage that goes partly inside the end cap. It is supposed to press against the large rubber recuperation seal. It is made from soft aluminium sheet rolled into a barrel shape. Make sure that it is opened out enough to fit snuggly, and also, it should seat against a tiny ledge inside the end cap. If it slips too far into the cap, you will have problems!
When re-assembling, lubricate parts in clean brake fluid.
An odd quirk of this general type of cylinder, is that an air pocket can get trapped in the end cap. Fill the cap with brake fluid as you refit it. I installed the end cap assembly first, inserting a new recuperation seal into the body of the cylinder. Then insert the alumninium cage part way into the end cap, up to its seating and screw the end cap in (with new copper washer). From the other end, insert the spring and piston (with its new seal). Fit the little ball-socket piece to the end of the piston (some designs have this integral with the piston). Slide the heavy washer over the push-rod, smear the ball-joint with red rubber gease, and secure with the circlip. Pack more red rubber grease over this assembly, and into the new rubber bellows. With the bellows on, I added a washer to keep water and dirt from getting passed the push-rod. Other versions of this cylinder, have a collar on the rod for the bellows to locate on. Finally, the lock-nut and clevis yoke. I tightened up the end cap after fitting the cylinder to the chassis, so I could apply enough torque (I tried it at 90 ft-lbs).
If you are dealing with a different version of this cylinder, there might be a special shim that fits under the recuperation seal. The aluminium cage might be substituted by a plastic version.
Make sure that the pipe connections are tight, as fluid tends to seep out and get onto paintwork.
I obtained replacements for the unique hoses from Powertrack, and I received them the next day. I was a bit bemused to find that I needed a Whitworth spanner at one end, an AF spanner for the other (and the lock nut). Remember to place the copper washer at the cylinder end. I obtained wheel cylinders from Land Rover specialist Craddocks. These came with mounting studs with UNF threads, and the bleed nipple on one needed a Whitworth spanner and the other one, metric!
I dismantled the new wheel cylinders and packed the dust caps with red rubber grease. This is important, as any sticking, or partial seizure, plays havoc with hydrastatic brakes. They will drag if they don't operate freely. The red rubber grease keeps out dust and water.
My brakes had been fitted with the wrong type of bias spring. The photo below shows the correct version. There is a choice of 2 pairs of mounting holes and I found that the more slack fitting was correct. The linings should touch the drums, and the pedal travel should be short. In the photo, you can also see a small spring on the leading shoe. There is supposed to be a cut in the lining, allowing the spring to raise that spot, to prevent the leading edge "picking up". Mine has been relined without the cut. I don't fancy cutting the asbestos myself! I'll leave it for now.
Fitting and removing the shoes means pulling against the bias spring. I place some card over the cylinder to make sure I don't damage the dust covers (if the shoe slips). To remove them, pull one shoe back from the cylinder and slightly to the side, while using a large screwdriver to prise the bottom of it out and up from its pivot. To install the shoes, fit the bias spring to both shoes, install one shoe, and then use the hub as a fulcrum to ease the bottom of the second shoe onto its pivot.
The original linings were fixed on with copper rivets.
The photo below shows the pedal assembly with the balance linkage and rods removed. If you are restoring the car, you might consider renewing the bush for the pedal arm pivot? Or at least oil it.
Below you can see some of the linkage parts including the balance linkage at the bottom.
A close-up of the balance linkage, installed (that split-pin needs bending). The brake-rod extends to the front of the engine bay.
The front end of the brake-rod (just ahead of the steering box).
The rear end of that articulated brake rod, where it passes under the driver's seat. You can see a barrel nut adjuster and the return spring.
Maintenance books say that the clevis joints need no lubrication. In view of the longevity of our classic cars, I think it is wise to grease them during overhaul. I applied some white lithium grease (I had left over from the wiper-motor gearbox).
Filling and bleeding the brakes
Fill the system with either DOT 3 or DOT 4 fluid. Try to stick to the same type and brand for topping up. Don't use DOT 5.
There seem to be a lot of different approaches to bleeding brakes, some being quite complex. It is fairly simple on the early ACs and can be done single-handed. Remove the panels on the back of each front wing, so that you can see what is going on. Get about 1/2 metre of 5 or 6mm bore clear tubing and place one end in a large glass jar containing a little fresh brake fluid. Push the other end of the tube onto the bleed nipple on the wheel cylinder furthest from the pedals. It's better if the jar is raised up so that the tube goes initially uphill from the nipple. That allows you to see bubbles in the fluid without using as much fluid.
If doing it single-handed, you will also need something to hold the brake pedal down, such as a plank to wedge against the driver's seat. Top up the reservoir to almost full.
Slacken the bleed nipple that has the tube on it (about half a turn). Then slowly press the brake pedal and hold it down, while you tighten the nipple. Then very slowly release the pedal. Repeat until fluid is seen in the tube without bubbles. Top up the reservoir. Then do the same for the other wheel cylinder. Then repeat on each cylinder. I find that this works better if the car is facing up hill. Keep an eye out for any fluid dribbling down the backplate. Also, after going for a short drive (to shake things up a bit), bleed the brakes again, as any trapped air will find its way to the wheel cylinders. Aim to have the reservoir about 2/3 to 3/4 full once finished.
After working on the brakes, be sure to press the pedal down while stationary, otherwise the pedal might sink right down when you first try to stop! The brakes should release properly without dragging, albeit with the linings touching very gently. Check for leaks and joint tightness. I repainted the drums with a POR-15 exhaust manifold paint, after removing rust and treating with phosphating solution. I used a blow-torch to dry the drum prior to painting.
Adjusting the linkages
The AC handbook emphasises that you shouldn't interfere with the linkage adjustments. It is a good idea to note the position of the adjusting nuts, etc. if you are restoring the car and have dismantled the brakes. But it is also possible that the adjustments are incorrect. I found that the clevis yoke on my master cylinder, was almost off the end of the thread, and once corrected, other linkages were found to be 'off'. I also noted that the rear brakes were very slack, causing long pedal travel.
Disconnect the handbrake cable at the front of the engine bay. If you have the later twin-leading shoe front brakes (identified by the 2 cylinders on each brake), then lock up those brakes using the adjusters on the backplates.
The first thing to check, is on the master cylinder. Measure from the mounting bracket on the chassis to the centre of the clevis pin. This should be 3 3/16" (81mm). If you pull the bellows back, and slacken the lock-nut, you can turn the push-rod with pliers. If the master cylinder is off the car, then the dimension from the mounting flange to the pin centre, should be 3 5/16" (84mm).
With the handbrake released, there should be 1/64" (0.4mm) of free movement at the lower end of the pedal arm, from its stop on the chassis. To adjust this, you need to remove the clevis-pin at the front end of the brake rod (front of engine bay), slacken the lock-nut, and screw/unscrew the yoke as required.
The next part to check is the large cross shaft under the centre of the car (see photo below). This has 2 arms coming down almost vertically. With all the brakes released, the clevis-pin centres should be 7/8" (22.2mm) behind the cross-shaft centre line. It's a bit awkward to measure. I parked the car on level ground, and made a plumb-line to sling over the cross-shaft. The shaft is 5/8" radius, so that the clevis-pin centre should be 1/4" behind the plumb-line. Adjustment is made with the barrel-nut under the driver's seat. Don't forget that one end has a left-hand thread, when you try to slacken the lock-nuts!
The rear rods might need adjusting. With the brakes released, tighten the brakes with the adjusters on the backplates. There are barrel nuts to adjust the left and righthand rods. These are hard to access on a fully assembled car (maybe it's AC's hint that they don't want us to tamper with them!). The right-hand one can be reached from under the car. If you have an early car with access panels (in the boot) for the dampers, then you can reach the left-hand adjuster from above. Otherwise it might be best to remove the boot floor. Tighten these adjusters until all slack is taken up (but not too tightly), then re-tighten the lock-nuts. Be careful not to confuse the shorter barrel nuts (attaching the rods to the brakes) for the adjusters. The photo below shows both, with the adjusting nut to the right.
With the rear brake drums still locked, take up any slack in the brake cable. Finally, slacken off the adjusters on the backplates, so that the drums are just free to turn. The brake pedal should now feel firm. For the handbrake, you can take up cable slackness by moving the position of the bracket on the steering column (that holds the end of the conduit). Then adjust the front end of the cable if needed. About 6 clicks of the handle should apply the rear brakes fully.