Replacing the front brakes on the 12/4
Iíd known for months that the front brake linings on our 1931 Heavy 12 needed replacing very badly. They had been saturated in grease for a long time and now they were down to the rivets as well.
I had been putting the job off because I couldnít figure out how to remove the brake shoes with their pivot pins at the top held in with split pins front and rear.
I eventually worked out that the brake backplate would have to be
moved backwards as far as it would go after removing the four set screws that
hold it to the hub assembly. Only after Iíd come to this conclusion did I
think to look at my 1930 ownerís handbook where it says to do exactly that
A warning about grease and the front hubs is needed here.
When I bought this car I noticed that all the original grease nipples were still in place, and many had been painted over, so obviously had never had any grease near them for a long time. This is one of the few points where I sacrifice originality on my Austins. I replace all the old grease nipples so that I can be sure of pumping grease properly with a modern grease gun into all those important places where itís needed. What I didnít realise for a long time with this car was that I was forcing grease into the king pins and brake cam levers so well that the whole brake drum was filled with the stuff. I now use the grease gun very sparingly on the front hubs with the brake drums off so that I can watch the grease coming through and wipe off the excess if necessary. Thus the greased up brake linings which had already been subjected to washing with petrol and wire brushing many times already.
I fully expected the set screws holding the backplates to be rusted in solid, but fortunately they had been well painted over and came out with no trouble. I used a suitable wooden wedge to hold the backplate as far back from the shoe as possible, which gave me enough working space to remove the split pin at the rear of the brake shoeís pivot pin. The pivot pins could then be levered out forwards and with the return spring at the bottom of the shoes removed, the two shoes can be removed.
The same pair of shoes should obviously be kept with their own hub. On my car, the brake shoes are the aluminium type, but iron ones were also used. On my car the shoes were marked with an F and an R for front and rear, but if not they need to be marked.
After all the shoes were removed, I next used a screw driver to
chisel the old rivets off and remove the linings. I have used a drill to do
this in the past, but on these soft aluminium rivets and aluminium shoes it
would be very easy to drill too far and damage the holes in the shoe. Next
the shoes were thoroughly cleaned. I found that the rollers at the bottom
ends of the shoes had a flat worn on them. I guess the system of a wedge acting
on two rollers doesnít work as well as it was intended to, probably because
thereís too little movement for the rollers to roll. They can just be turned
round when re-fitting.
I hit a snag as soon as I came to fit my new linings from the VAR, ordered for a 1931 car with aluminium shoes. They were not the right ones for my shoes. I now know that Austin changed the shoes in 1930 such that the later shoes take linings with smaller rivets, and the spacing of the rivet holes is different. To make life confusing, both the shoes will fit early or late cars so could be interchanged. Any mixture could be found on any car, but the right linings must be obtained for your shoes.
The early shoes used rivets with ½ inch diameter heads and
¼ inch stems, but the later shoes as fitted to my car were drilled
for 3/8 inch heads and 3/16 inch stems. If you are supplied with linings with
the larger rivets and your shoes have the smaller holes, it would be tempting
to just drill out the holes in the shoes because they look as if the holes
might line up, but they donít. The spacing is slightly different.
The part nos. are AT/8/1 front and AT/2/1 for the rear linings of the early type with larger rivets and AT/8/2 front and AT/2/2 rear for the later linings with the smaller rivets.
They can be supplied by BRAKE AND CLUTCH LININGS 1900 to 1980, Mr. M. Pugh on 0113 258 3533 who is a brake and clutch lining supplier (and expert), and supplies the VAR.
So after a delay while I was lucky enough to be put in touch with Mr. Pugh, the man who knows, another set of linings was with me the next day, this time with copper rivets that Iím more familiar with, and holes that lined up properly with my shoes.
Fitting the linings is a fairly simple job. I use a steel drift or flat nosed punch clamped in the vice facing upwards. Line up the lining on the shoe, putting all six rivets through to locate them accurately and then start at the centre and work towards the ends. Place the shoe and lining with the rivet head located on the punch in the vice so that the end of the rivet stem is pointing upwards. As these rivets are hollow, I started them off with a Philips screwdriver which splits the rivet four ways and then hammer them down with a flat punch. Having three hands would be useful, but itís not too difficult to hold it all in line while you hammer the rivets down. Make very sure that each one is fully seated as far as possible before moving on to the next. These modern linings seem much tougher than some of the earlier asbestos ones Iíve handled, so thereís not much chance of cracking them by hitting the rivets too hard.
The last job to be done with the newly lined shoes before fitting them back on the car, is to chamfer the leading edge of each lining with a rasp or coarse file to reduce the chance of brakes grabbing. I actually chamfer both ends.
Re-fitting the shoes to the hubs is straight forward, but setting
up the brakes was a pig of a job. Obviously as the linings had worn down over
the years, the slack had been taken up in the adjusters and everything would
need backing off as the brake drums would not go on over the newly lined shoes.
I started by backing off the large brass Ďtap-handleí adjuster below the brake
pedal which is the overall brake adjuster. This is slackened off by turning
anti-clockwise when viewed from the rear and increases the length of the rod
connecting the pedal to the brake cross-shaft. This didnít make nearly enough
slack, so I started unwinding the adjusters at the brake cable fork ends at
the cross shaft end. With these wound out nearly all the way, the drums still
wouldnít go on. So I wound out the rods from the threaded hexagonal blocks
too, but it was leaving so little thread engaged that it was feeling unsafe.
The offside drum was much tighter than the nearside too, which made me wonder
about the lengths of the cables. I had assumed that the cables were of fixed
lengths, but when I measured them, they differed by several centimetres. Then
I checked the front fork ends which connect to the brake levers on the brake
unit and realised that these were adjustable with a clamping nut and bolt.
They had obviously been trimmed off to suit the individual brakes when they
were fitted over four years ago before we bought the car. I remember being
told that new cables had been fitted. Fortunately there were a few centimetres
spare to play with where the cables had been trimmed off, so I slackened off
the fork ends and re-tightened. I could finally get the brake drums on and
could now wind the screw threads in at the rear end of the cables and rods
so that a reasonable amount of thread was engaged.
Slackening off the overall adjuster so far had left the rear brakes completely inoperative with the front ones binding so badly that the drums could barely be turned by hand, so now all four brakes had to be set up from scratch. I decided the best way to do this was to jack the car up and put it on four axle stands and work with the road wheels on, which gives a better feel for how much friction there is at each brake drum. I started by making sure that the overall brake adjuster, the tap handle, was more than half way out to allow for future taking up of the slack as the linings wear. Then it was a laborious process of adjusting the fork ends of each brake cable, (inner ends) with the brake pedal held partway down, using a piece of wood wedged against the seat, so that the front wheels were almost locked solid with the two rear ones not quite so full on, because the front brakes need to come on first. At each adjustment I had to check that equal effort was needed to turn the two wheels on each axle. When the brakes seemed reasonably balanced with the front ones coming on harder than the rear, itís time to release the pedal and check that the shoes arenít binding badly. A little bit of binding is OK as the new linings have to bed in anyway.
Next the car is lowered back down and the wheels tightened, and itís time for a gentle trial, reversing the car out of the garage and braking while going backwards and forwards on the drive to see if everything feels right. Now some people recommend getting up speed and jamming the brakes on while on a gravel surface to see if the skid marks are equal on both sides, but I donít like wasting rubber. My preferred method of checking for balance in the brakes is to run the car on the road for a couple of miles using the brakes hard and frequently, then to stop and feel the brake drums. If the brakes are working efficiently, all the drums should be hot with the front ones hotter than the rear. If one brake drum seems to be cooler than the rest, the shoes are not doing their job and more adjustment is needed. This time I seem to have got the adjustments right because all the drums were getting equally hot and the car didnít seem to pull to left or right when braking hard.
Job done, but when the car has done a few miles to bed the new linings in, the slack will probably need taking up with the overall adjuster.
|Brakes before dismantling||Closeup of the shoe pivots||Closeup of the expander end|
|Showing wedge between shoe and backplate||Pivot pin being withdrawn||Front shoes after removal|
|Hub with shoes removed||new linings with rivits||Shoes with lining fitted|
|Shoes with the new lining refitted onto car||The master brake adjuster||The offside front brake rod with adjuster|
|The nearside rear rod adjuster||Rear offside brake rod adjuster||The Finished product|
I am indebted to Tom Stapledon of
the UK for sharing his brake lining job so that we all benefit for his experiences