Restoration of 1952 MG TD 2



Author: Bob McCluskey
First posted: 1 Sept 2000
Last amended: Dec 2015
Please email Bob McCluskey
Car No TD/11935
Engine No XPAG/TD2/12333
Body Type 22381
Body No 11301/78948






PRAKES In my opinion, the brakes would have to be counted amongst the best of Lord Nuffield's serious and successful efforts to keep development costs under control during the immediate pre-war and post-war periods. They are virtually identical to the brakes on my very first car - a 1937 Morris Eight two-seater tourer built fifteen years earlier - except that the separate steel reservoir also used on earlier Ts has been replaced by a totally inaccessible cast iron job integral with the master cylinder and hidden under the driver's floor. The only other difference I've been able to find is that the front drums have twin leading shoes.

There were a few problems, some of which, but not all, were due to poor materials, and were beyond reasonable control. The hydraulic fluid was hygroscopic, and eventually became acidic. This corroded both the cast-alloy cylinders and the steel pistons. The corroded pistons damaged the soft cylinders a bit more. The inspired location of the reservoir made it impossible to keep crap out while fluid was topped up. As the cylinder rubbers were replaced more and more often, the bleed-nipples were invariably over-tightened, with the result that eventually everything leaked to the extent that it was hard to keep the fluid up to the leaks.

Fortunately there is a solution: take all the cylinders to your friendly brake and clutch specialist and have them sleeved with stainless steel. At the same time have them reface the unions and make new pipes and swages in copper. They'll sell you modern hydraulic fluid and modern viton seals, and they'll even give you enough of the slimy red goop they use to lubricate the rubbers during assembly, so from then on you should have no further problem. For me, the only disappointment was that my guys said they couldn't sleeve the rear cylinders in stainless steel because of the slot that needs to be machined to accommodate the hand-brake mechanism, so they used brass instead on the rear cylinders; but I've since learnt that they could have done the whole job in stainless.

I was astonished how cheap all this was, and I think it's the best value I've had in the whole restoration. However, if you're amongst those who don't like my pragmatic approach to restoration, you don't have to use this cheap and effective improvement; but do make sure that the judges see and appreciate your leaky cylinders, because such commitment to originality really does deserve major points at concourse.

Just a note of caution, though: if you're planning an extended rehabilitation (like in excess of fifteen years), leave the brakes till close to the end. You don't want to leave the hydraulic fluid in the system longer than necessary, because even the best fluid is hygroscopic, and, as I have discovered, you certainly don't want to be leaving the rubbers unexpanded in the cylinders, because firstly they will get a set and secondly the slimy red goop turns out to be a chemical precursor for super-glue, and you will find it impossible to bleed the brakes and very hard to get the rubbers out. In my case, the holes in the master cylinder piston were also blocked, and the small hole - the bypass port - also looked suspiciously opaque. (Actually, it must be true about ill winds - I found that the reason the bypass port was opaque was that it had never been drilled out when the cylinder was sleeved, so the brakes would have come on, but never released. They could never have worked properly. The machine shop who had done the job originally had gone out of business - which may acount for why it had been so cheap - so I had to pay to have it done again.)

PASTER Cylinder Having complained about the master cylinder, I must now admit that it's a pretty sophisticated piece of technology (note however that my dictionary gives one of the meanings of sophisticated as "involved in sophistry, deprived of simplicity"). So I'm not sure whether the sophistication is the result of premeditated design or a series of compromises to make it work more or less as you'ld expect: it does seem to be much more complicated than you'ld think it ought to be.

To remove it, it's easiest to remove the floor board, even though this means removing the seats first. Alternatively if you prefer the brake fluid in your eyes and clothes rather than on your duco, you can struggle to undo it from underneath. In either case, undo the hydraulic pipe union and drain the fluid. The manual says you should disconnect the brake pedal return spring, and lift out the brake pedal with pushrod and rubber boot, but I prefer to undo the clevis pin on the brake pedal and remove the push-rod and boot with the cylinder. Undo the two bolts which luckily have captive nuts on the chassis bracket and you can remove the cylinder: if you're careful you shouldn't spill too much fluid onto your paintwork.

When you get it onto the bench you can take off the boot and withdraw the pushrod, then push the piston far enough down the bore to remove the circlip. Now the pressure of the return spring should be enough to push the piston and rubbers out, and the valve and valve body should come out with it leaving only the valve washer still inside, which you must also get out. Carefully note the order of components.

Source: MG Midget Workshop Manual Iss 3 (H&E) 1/54
Have a look inside the reservoir: directly underneath the filler cap you can see two holes, one small (the "bypass port") and one larger (the "feed orifice") behind it. In its normal position, the piston is held back on the piston stop and circlip by the return spring, and the master rubber rests between the two holes. The master cylinder is filled with fluid, and so is the annular space behind the master rubber: this space is filled through the feed orifice. Fluid is prevented from draining out of the back of the piston by the secondary rubber which you stretch carefully over the end of the piston and into its groove.

When the brake pedal is pressed (the piston goes from right to left in the drawing above), fluid is forced through the holes in the side of the valve body, past the sides of the rubber valve itself and into the brake pipes where it does its job.

When the brake pedal is released, the piston is returned to its original position by the piston return spring (ie the piston and the master rubber are pushed from left to right by the spring). The fluid from the space behind the piston can flow past the sides of the master rubber allowing the master cylinder to fill quickly; to help this, the piston has a number of small holes in the head, and there is a dished washer between the piston face and the rubber (make sure the holes are clear, and make sure the washer is the right way round - concave side away from the piston head). If the brake shoes aren't adjusted ideally (and they rarely are), you can, as everyone knows, "pump" the brakes again quickly, and the extra fluid which has entered the system presses the shoes closer and more firmly against the drums.

reservoir exploded
Source: MG Midget Workshop Manual Iss 3 1/54
When you let the brakes off, the piston is pushed back against its stop by the return spring, and the bypass port is uncovered. The shoes are returned to their rest position by the shoe springs; the pressure in the system opens the valve against the pressure of the piston return spring and fluid is returned to the reservoir through the bypass port. When the pressure is about 8 psi, the pressure of the piston return spring closes the valve, keeping a small pressure in the system, which keeps the wheel cylinder rubbers expanded. Occasionally the bypass port becomes blocked with dirt, or covered by the piston rubber due to poor adjustment or softening of the rubber (or because your machine shop didn't drill it out in the first place - see above). In that case the fluid can't return to the reservoir and the brakes will bind in the "on" position. Solution: make sure the piston return spring is long enough, adjust the pedal free movement, clean out the port, fit new rubbers, get a competent shop to do the sleeving properly.

Here's a question: when you pump the brakes gently so fluid flows past the master rubber from the space behind it, why doesn't the partial vacuum also draw air into the system past the sides of the secondary rubber?

Oops
Q: Whats wrong with this picture?
A: Not much - good focus, good exposure, and and the resolution is at least good enough to show very nicely how the Micram adjuster on the top shoe is assembled back-to-front, which would have made it very difficult to adjust the shoe.
FRONT Brakes I don't think there are any tricks to the front brakes. When dismantling you have to be careful not to twist the flexible brake hose, so if you're dismantling that far you first undo the union nut on the metal pipe while holding the nut on the hose itself with a spanner, then undo the locknut on the flexible hose, and then the banjo on the brake plate (taking care not to lose the copper gaskets), which releases the flexible hose. I like to put the banjo bolt back in place with its gaskets, so they don't get lost.

Take off the grease cap, remove the split pin and undo the stub axle nut - there is a left-hand-thread on the left hand side of the car, and a right-hand-thread on the right side. Prise off the brake drum, taking the outer bearing with it. Remove the inner bearing using a hub-puller if you have one, or ingenuity and persistence if you haven't. Take off the spacer and grease retainer. Note that once you've taken off the drum, you must pull off the inner bearing etc, and reassemble them into the brake drum, because otherwise you can't reassemble it properly - the bearing will not fit properly into the drum when you offer it up, and the grease retainer will have nowhere to make the seal. Undo the four nuts and bolts holding the brake plate assembly to the stub axle, and remove.

Reassembly is quite straightforward. The back plates are quite clearly assymetrical in order to accomodate the wheel cylinders, so you can't get it wrong. Bolt the wheel cylinders into place, naturally using Loctite, noting that the Micram adjuster is going to go on the bottom on the front cylinder and on the top on the rear cylinder. Fitting the shoes is a bit tricky. First note that each shoe has one plain end and one slotted end; the slot is going to fit over the Micram adjuster. The two pull-off springs fit into the front hole on the slotted end, and the second from back hole on the plain end; they go between the shoe and the backplate, not outside the shoe. So: first fit the springs onto the shoes, then on each shoe, slip the slotted end over the adjuster. Then, first on one shoe, then the other, lever the plain end into the groove in the wheel cylinder. This will be easier if the Micram adjusters are turned fully anti-clockwise, ie right off, and it is probably easier if the back plate has been bolted into place on the stub axle (the bolts are inside the drum, and the nuts outside; as always, don't forget the Loctite).

New bearings are very cheap, so I made a point of using new bearings throughout. Pack the inner bearing with grease, and push it into place in the brake drum. Fit the spacer and grease retainer into the drum on top of the bearing, making sure it's the right way round (open side towards the oil or grease you're trying to retain), and push the drum onto the hub.

REAR Brakes Unfortunately nothing can improve the rear brakes, which have one leading and one trailing shoe both operated by one wheel cylinder which is supposed to be free to move in the backplate in order to equalise the braking force between the two shoes. The manual makes a virtue of this deficiency, claiming that it gives "the advantage of equal braking action when the brakes are used in reverse". In fact this is not exactly true: eventually the works become glued up with road dirt which stops the cylinder from sliding freely and makes the trailing shoe virtually useless, and they are if anything even worse in reverse when the one effective leading shoe becomes a trailing shoe (this is also the real reason why, in the words of the manual, the front brakes "take the greater percentage of the braking load" - not because the front brakes have twin leading shoes, but because more often than not the back brakes just don't do their job).


The pictures above show the front and back of the left rear brakes. These are a little more tricky than the front brakes, and I found a couple of pitfalls.

The piston is in two halves, and the inner half has a bevelled slot for the handbrake lever. You assemble the springs and rubbers in the normal way, then the inner half of the piston, and then you have to slide the handbrake lever into position and hold it in place with the pivot pin. Then you fit the outer half of the piston with the seal and dust cover. When you pull on the brake lever, it forces the outer half of the piston outwards, and when it's assembled in the brakeplate, it forces the leading shoe (ie the bottom shoe) against the drum. The cylinder is supposed to be free to slide in its slot, and it is held in place by the rubber boot. The idea is that the reaction of the pressure of the leading shoe against the drum makes the whole cylinder assembly slide upwards in its groove, thus forcing the trailing shoe against the drum. Inevitably it becomes glued up with road dirt, and doesn't work effectively. I know of no answer to this, except to clean it frequently. A little smear of grease on the back of the cylinder will help it to move freely initially, when it should work at least long enough, hopefully, for it to pass its rego. The other problem is that the cylinder is held in place only by the rubber boot; when it starts to fray, the cylinder isn't held exactly in place. Similar systems were used on other British cars, notably Standard Triumph, but - at least on those I've had the pleasure of working on - the cylinders were held in place by a spring clip rather than the rubber boot.

The other thing I found to be wary of is the backplate. At first sight they look symmetrical, but they are not, which means you must fit the plates to the correct side. The shoes are located by a shoe steady spring. You push this spring through the hole in the brakeshoe and twist it, where it engages with a little bracket welded to the backplate. This bracket is the source of the asymmetry: it is to the rear of the triangular plate pressing on the top, and to the front on the bottom. You can just see the spotweld in the second picture, where the bracket is welded. If you try to assemble the backplates the wrong way around, the bracket will be to the front on the top, and to the rear on the bottom. You will find, as I have, that you can assemble the steady spring, with difficulty, but the brake shoes have restricted movement.

The book gives no guidance about assembly, which can be tricky if its done on the car (but quite straightforward if you've taken the backplate off). So: first wind the Micram right off, then assemble the piston into the cylinder, and rotating the piston until the slot for the handbrake lever engages with the lever. Fit the Micram, and hold it all in place with the lower shoe while you fit the lower shoe steady spring. Note that, as with the front brakes, the slotted end of the bottom shoe fits over the Micram adjuster; the other end of the cylinder has a groove, and the plain end of the other shoe engages in it. Now the return springs: these go behind the brake shoes. Once again, the manual gives no guidance: I figured that the return springs were strong enough, so I fitted them into the first hole of the doublet (ie the easiest hole!). Fit the front spring first, engaging it in the lower shoe. Engage the upper end of the front spring into the front hole on the upper shoe, then fit the front edge of the top shoe into the slot on the top of the cylinder. Now engage the bottom end of the rear spring into the rearmost hole in the bottom shoe, and lever the top shoe into position, engaging the spring as it goes. I found that bracket for the top steady spring wasn't in exactly the right place, which is a bit surprising. On the other hand, on the right hand side there was only one (lower) spring, and so, shrugging slightly, I consigned the left hand side upper spring to the spares box. Now, make sure the whole assembly is free to move up and down to the limit of the cylinder in its slot, then fit the brake-drum over the shoes, tighten the nut and use a fresh splitpin.

Now as discussed above, these brakes were never very efficient, but particularly the handbrake is hard to get on with. There is less movement in the handbrake piston lever than you might expect, and that means that although you may be pulling on the handbrake itself with considerable force, you cannot bring the shoes into contact with the drums unless both sets of shoes are adjusted properly - just skimming the brake drum when the brakes are off. In my case it was even more difficult, because the effective range of the handbrake lever was restricted (what had happened, one day, before its long rest and while it was still in daily use, and when it was parked outside my home, just around the corner from the pub, two patrons, each as sharp and bright as a bagfull of rusty hammers, had parked their car right up against mine while they went to refresh themselves. Some time later, when they were fully refreshed and ready to leave, they found themselves parked in by another car which had parked right behind their's, and had thought the easy solution was to let my handbrake off and push my car forward. Unfortunately they didn't know about fly-off handbrakes, so with two beefy idiots pushing on the button while trying to release the brake, something had to give. What gave was the pawl, which now has only two teeth, and the ratchet itself, which now has a very limited effective range. I was not able to source cheap replacement parts, and drew back from the impossibly expensive solution offered by my parts supplier. Note to self: Future precaution: don't leave the car outside a pub, don't leave it uncovered, and do leave it in gear with the handbrake off!).

So, first undo the handbrake adjuster nuts until the handbrake lever (confusing naming system - everything seems to be the handbrake lever. In this case it is referring to the operating lever, at the cylinder) is completely relaxed (no tension on it at all). Then adjust each Micram adjuster through the hole in the brakedrum until the brake pads are just skimming the brakedrum. Possibly undo the Micram one notch. Then adjust the adjuster nuts, both sides together, until the brakes come on fully, ensuring once again that they are fully off when the handbrake is released.

Friction in the hand-brake cable is another thing that makes the brakes inefficient. Because I don't remember ever having greased mine, and any residual grease from the manufacturer had long since reverted to the rocks from which it had been extracted, this was a problem in my case. I cleaned it all by soaking in mineral turps, working the cable backwards and forwards inside the outer, then flushed it through with clean turps. When it had dried, I covered the cable with heatshrink plastic,then worked molybdenum disulphide (Molyslip) into it by hanging it up from one end and dripping the molyslip in at the top until it came out from the bottom (hint: don't do this before an important meeting: your nails won't come clean until they have grown out!).




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