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Chicagoland MG Club: Driveline
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  Chicagoland MG Club:Driveline
Just a Simple Wrench
by Ann & Jake Snyder

Ann and Jake Snyder All Worn Out

The GT seemed to wander on the tollway more than could be accounted for by the cross-wind. And it positively leaped at the chance to dart for the edge of the roadway when the camber of an entrance ramp changed. And the car pulled mildly to the left when braking. None of this was the way our MGs have handled in the past unless something was wrong. Tire pressures were fine, and the tires looked good and were evenly worn. We greased the king pins, checked and topped off the shock absorbers, added gear oil to the steering rack and took out the thinnest steering rack shim. The tie rod ends looked fine, and there was no excessive play. But the steering and braking problems did not get better. In fact, in the weeks it took to check these items, the pull to the left when braking got worse.

So we checked the brake pads, and found a problem: The pads on the left side were worn crookedly, as if they had been cocked at an angle when they were installed. We put in fresh pads, on both sides, of course, and the problem went away. For a few hundred miles, at least.

The MG started to respond more sluggishly on turns, even the very low speed 25 mph S-bends that are found in residential areas. The slow turning response was even apparent to the passenger, who at one point, while a traffic light was red, ran around the car, checking to find which tire was half-flat. But the tires were just fine. Maybe this was tread separation, and perhaps we should buy new tires? Maybe we should take the car in for a professional front end alignment rather than rely on two straight pins and a setting jig as we had learned years ago from a club member? (A club member, by the way, who was racing hyrdroplanes at a time when both of us were learning how not to get hurt when bicycles without training wheels threw us).

The logical problem was wear in the tie rod ends, and we were set to replace them, even though there did not seem to be any play at all. We jacked up the car, and each of us took turns twisting a wheel from left to right while the other of us held the opposite wheel. Something gave a clunking sound, and we discovered the sound coming from the left side. Taking off the wheel, retracting the brake pads a bit, and shaking the brake rotor showed that there was a large amount of play in the bearings, easily enough to change slightly which way the left wheel pointed. We reasoned that this was the cause of the sluggish steering and the wandering at highway speed. And the loose bearings were also the cause of the crookedly-worn brake pads, as the new pads had already begun to wear the same as the previous set. The problem was not that the pads or calipers were crooked with respect to the rotor, but that the rotor itself ran at an angle. We tried to get away with adjusting the shim pack on the original bearings, but, given the proper end float, the rotor still could be pulled far more from side to side than was expected.

Needless to say, we abruptly curtailed our use of the car, which was a real inconvenience as it is our main transportation, until we could change the front wheel bearings on the left side. We have seen too many three-wheeled cars on the side of the road, and occasionally, the burned remnants of the sheared stub axle are visible. That is the price of bad maintenance.

The steel oil seal, the inner tapered roller bearing, the spacer, the outer tapered roller bearing, the toothed washer, and the nut with split pin. The paper washer shows where the shims will be placed. The brake caliper must be removed in order to remove the hub.

There are two tapered roller bearings in the front hub of an MGB, and the distance between them is controlled by a spacer and shims so that there is a few thousandths of an inch more space on the bearing assembly than between the outer races that are installed inside the hub. This arrangement gives a little space for grease and for expansion when the hub assembly heats up during use. We assembled the bearings with oil as the lubricant while setting the end float because it is very difficult to detect a few thousandths inch of movement with heavy grease. With oil, there is an audible “clunk” when the end float is acceptable. We also have a dial indicator, but this is really too much trouble to set up after you have set shim packs for an MGB a few times. The critical thing is that when the nut is tightened with a substantial portion of your body weight on a standard breaker bar (the book specification is 70 foot-pounds), the hub still spins absolutely freely, with just a hint of end float when the lubricant is the final, heavy grease.

Setting the end float consists of adding or removing shims between the front race and the spacer. The task can be made much easier by not installing the rubber oil seal until the final shim pack is established. That way, the metal oil seal (a ring with a chamfer on which the rubber oil seal rides), the inner bearing (the large one), the spacer and the shims can be left on the axle and the hub slides over this. The alternative is to pack the inner bearing, install the rubber oil seal, slide the hub into place, and then try to fit the shims into place using screwdrivers, mechanics picks or anything else that will reach inside. This is no fun at all, and the long splined hub that is used for wire wheels makes the job even worse. Having a selection of 2-, 5-, and 10- thousands shims along with an inexpensive one-inch micrometer makes every thing easier, though we set up shim packs for years with just a couple of shims and a tube of grease. A good place to start on the shim pack is (1) 25-, (1) 10-, and (1) 5- thousandths shims. This will probably be within 5-thousandths of the final setting.

The tooth on a toothed washer must be undamaged. This washer keeps the nut from tightening (right wheel) or loosening (left wheel).

Sometimes, a well-meaning soul who does not know about shim packs will set up the front wheel bearings just the way he did his old Ford or Chevy that had ball bearings instead of tapered roller bearings. This adjustment consists of slacking off the wheel nut so that only a few foot-pounds of torque are applied to the wheel nut. The problem with this approach is that there is a smaller effective diameter axle holding the weight of the car, and bearing wear will be faster because there is more end play. On the other hand, if the bearings are too tight, they will fail very soon. As far as we know, only the MGB uses shim packs. The Midget hub is not adjustable, and there are no shims to measure.

And what was wrong with the original bearings? We cleaned them up in our little parts washer filled with paint thinner (which will burn but will not explode under ordinary conditions) and blew them gently with air. We observed the standard warning that dry bearings must not be spun at high speed with air pressure or the rollers and races will gall, even though the used bearings would soon go in the trash can. We recovered the toothed washer, nut, and shims for later use. As far as we could tell by careful inspection, the bearings were perfect and the outer races were flawless. We had no way to check whether the rollers themselves were the proper shape or whether they had worn to a contour that permitted the excessive side play. And since a fresh set of bearings costs only about 25 dollars and lasts for many years, there was no pressing need to know much more than that they were just all worn out.

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