The 109’s brakes suffered a partial failure a few days ago. Under light braking, everything was normal, but under medium or heavy braking, the steering pulled hard to the right and even if the steering was kept straight, the vehicle would skew and crab to a halt. It was quite evident that the front left brakes weren’t applying the proper levels of braking effort.
The left drum was removed and the cause was immediately apparent; the upper slave cylinder was leaking and the whole brake unit was heavily contaminated with congealed black sludge and dust. On inspection, the lower cylinder was also found to be lightly corroded and the seal scuffed, though it wasn’t yet leaking.
Both cylinders were replaced and new shoes fitted to both sides (never replace the shoes or pads on just one wheel – you must replace them as an axle set). There’s nothing really to show as far as that work is concerned, but bleeding is always a problem on these twin leading shoe systems. I tried bleeding conventionally with the units in place, but predictably it didn’t work, so I had to go through my usual and long winded bleeding method using an Ezibleed (a bottle pressurised by tyre pressure) and a draining jar with clear hose to the bleed nipple with as follows:
1)Â chock the rear wheels and apply the hand brake;
2)Â Â jack a front wheel up (start with the near side) and remove it, followed by the hub centre cone and the drive flange;
3)Â undo the wheel bearing nuts and remove them, carefully laying them out in sequence and with correct orientation to which way each side of the inner nut was facing (inwards or outwards – mark if necessary) ;
4)Â back off the shoe adjusters and remove the hub and drum as a complete unit (be careful not to drop the outer wheel bearing race as it comes off the stub axle);
5)Â undo the top two bolts securing the swivel seal retaining ring and the flexi-hose bracket and remove them;
6) undo the six bolts securing the brake backplate and stub axle to the swivel housing, using a tray or bowl to catch the oil that runs out of the two lower bolt holes. Note that later axles have an oil catcher ring too, secured by these bolts, as seen on my modified axle (I fitted late stub axles and hubs to use the more commonly available RRC/Defender wheel bearings, which also allowed the use of these oil catchers);
7) pull the backplate, complete with cylinders, shoes and pipework, clear of the stub axle and lay on top of the swivel housing. Don’t deliberately separate the stub axle from the swivel, but don’t worry if the gasket was greased and opens up – it’ll seal again when bolted back later.
8) bleed the brakes with the wheel unit held horizontally above the swivel, pipework upper-most, tilting it one way then another around an axis through both cylinders to ensure any air gap gets pressed against the aft end of each cylinder in turn, preventing air being trapped at the back of the piston. This tipping must be done slowly,pausing at each tipped position for a few seconds, several times to ensure that air expelled from the first cylinder is into the second cylinder is removed.
9)Â in true, traditional manual parlance, refitting is the reverse of removal, but remember to top up the swivel housings with EP90!
10) repeat on the other side, and once the work is complete, test the brakes at low speed in a safe location before driving normally. Keep a close eye on the master cylinder reservoir and Ezibleed levels throughout as you will need to start again if it drops too low. Wash any spillages off paint or plastic immediately as brake fluid will wreck either if left more than a couple of minutes.
Why not replace just one set of shoes? My 1973 88″ was leaking from the front left cylinder, and we thought it was coming through from the seal collar on the axle housing. So they were fixed, and new oil seals and shoes were fitted about three months ago.
However it turned out to be the brake cylinder. The shoes have had only a couple months of light use, and a half set is half the price.
You can never guarantee a match in the friction of the linings on shoes from different ages, even if they’re from the same manufacturer, but different brands use different friction linings and they have markedly different braking efficiencies. You also have to account for the manner in which using one set of fully bedded in shoes on one side that have worn in to match the drum diameter and become contoured around the drum scoring while the new shoes will only contact the drum surface on the ridges of the scoring and at each end of the friction lining (because it initially has a larger diameter than the drum) and you will see that the new shoes will have markedly less than 50% of the contact area the old shoes on the other side have. It could easily lead to massive braking asymmetry and a loss of vehicle control.
Never, ever replace the shoes on just one side – always replace the full axle set. The same appleis to suspension dampers for much the same reason, and also apples to matching tyres and wheels from side to side (you can use old ones, but the new tyre/wheel should match the dimensions, tread and compound of the old one on the other side).
hi nick im after a bit of info,im doing my series 3 88inch up,just found out the front axle is of a 109.the bleed nipple is on the bottom,i thought it should be at the top can you tell me where should it be top or bottom,thanks.
Hi Keith,
Sorry it took so long to approve your comment – I’ve only just returned from holiday and had an email box full of spam!
109 front brakes (twin leading shoe) normally have their bleed nipple on the bottom cylinder. Some people modify the system so that instead of the flexible hose entering the upper cylinder first, with the rigid pipe feeding the bottom cylinder with fluid that has passed through the upper, the system will feed the lower cylinder first and then the upper while retaining the original rigid pipe that connects the cylinders together. This has the disadvantage of needing a second rigid pipe to connect the fexi-hose to the bottom cylinder, with the incumbent extra risk of leaks or off-road damage this entails, but has absolutely no advantages for bleeding – the air that gets trapped in the TLS system is within the cylinders; unlike the rear brakes’ or 88″ front brakes’ double acting cylinders, the TLS slave cylinders have their ports at the middle position, so air becomes trapped above the bleed nipple in the lower cylinder and above the connecting pipe port in the upper cylinder. the only way to remove the air is by vacuum bleeding or by removing the hubs and brake back plates to pressure bleed them with the assembly laying horizontally with the cylinder ports at the 12o’clock position.
So, leave the bleed nipple in the bottom cylinder.
Nick.
I’m just doing TLS front brakes at the moment. It’s worth pointing out that each cylinder is on a slight wonk, so one port is higher than the other. Obviously, you need that port to be the “out” from each cylinder, whether going to nipple or the other cylinder.
You’re right about the insignificance of which cylinder has the nipple, but I’m going with the top, purely and simply to make it easier to access – that lower cylinder is a bugger to get at the back of, thanks to the bottom of the hub casting. Since I needed to replace the pipes anyway, it’s not much of a difference, and avoids the sharp angles in the original flexi-to-top cylinder pipe. Getting the bottom cylinder unions in, though…