MG and Rover PG1 Worn Gearbox Bearings

[MGJohn]

Over the years, I've replaced the three bearings on several of these gearboxes which are prone to wear and run roughly. Wearing particularly if lubricant escapes via worn seals, runs low and the gearbox overheats. These gearboxes are sometimes described as weak. That's a little unfair. Any gearbox with insufficient lubricant will weaken.

Here's the three bearings ~ actually there's four that usually need renewal as there are in fact two 6208 bearings carrying the differential ~ that's the largest diameter one with nine balls shown on the left in this picture. The other bearings have seven balls. Each gearbox has two of these nine ball 6208s :~



Here's a close up of the worn out 6208 showing some pitting around most of the inner race :~



Here's an even closer close up showing the wear damage to the 6208's inner race :~



All these bearings ran rough when turned manually. Inside the gearbox with far more power applied it is easy to understand why they would be so noisey and rough running.

I have removed the nylon/plastic ball cages from each of these worn bearings. Incidentally, that plastic stuff is very strong. Almost as hard as metal as I discovered when I first tried to remove the plastic ball cages. It needed a cold chisel and a heft blow with a 4lbs Club Hammer to remove them. They are really strong.

There are two of the larger 6208 differential bearings. This is what it looks like on the differential :~



I have already replaced the original plastic caged bearing with a steel caged item on the differential. The other 6208 is unseen on the other side of the differential in the gearbox housing. The old plastic caged worn 6208 is just to the left.

Also in the picture is the Input shaft bearing housed in the ... bell housing. Again the steel caged new bearing is already in place with the old plastic caged item to the right. This is the smaller of the three bearings. Here's a closer view of the old and new Input shaft bearing :~



The last bearing is the one that sits on the other end of the Input shaft. A new steel caged version is shown here in its location :~



I have renewed these three bearings in about a dozen PG1 Gearboxes over the years. In this limited experience, they are usually the only bearings that are prone to wear seriously, often as a result of progressive loss of lubricant over the years and miles. There are other bearings in the gearbox but, these are less prone to wear even when lubricant levels have run low.

Here's a picture of a friend's PG1 where the differential bearing's plastic cage housing the nine balls has broken up through lack of lubricant from resulting overheating. Note how the balls have aggregated to the one side instead of being equally spread around the whole race and held in place by the ball cage before it broke up..



When I acquire a used Rover or MG with one of these gearboxes, one of the first things I check is the gearbox lubricant. I check for correct grade and quantity. One badly 'failed' gearbox did not have the required 2.2 litres of correct lunbricant in it ~ it had this ~ less than an eggcup full!



Here's my check on another gearbox which showed the correct volume and quality of lubricant :~



A few days after I bought the car with known faults, I found in the damaged gearbox car a chitty under the driver's seat. It showed a respectable 1/4 mile time down the strip at Santa Pod a week or so before I got it. No bluddy wonder the gearbox gave trouble with only an eggcup of lubricant and that level of abuse...