RAMBLINGS AT RANDOM
By Dean Sprague
Many of us maintain our own vehicles, the classic ones anyway. Most of us have learned to change our own oil, lubricate the chassis, and check levels and so on. Some of us have even learned how accomplish our own restorations. Usually that doesn’t include doing our own bodywork and painting all though a few of us do but there is something about the gearbox and diffs that leaves most of us in wonder.
Several years ago Peter Egan wrote an article for Road and Track about gearboxes. He was most certain that aliens probably designed, built and left them here to be unearthed when needed. Man would surely have never built something so complex and convoluted.
Most strategies include ignoring the thing until it begins to emit strange noises, shifts poorly or turns quality hypoid into brown slimy metallic ooze. When any or all of these things occurs action must be taken.
The best thing to do is to remove the gearbox and take it to Yoda, Grand Master of the gear Jedi for only he truly understands the “order of the gearbox”. Seriously, if you must attack them they must be carefully disassembled and parts stacked as they were assembled, exactly. If you foolishly just rip them apart needle bearings fly in all directions, gears, shims and synchros scatter until the gearbox is nothing but a pile of random parts. Way back, when I used to work for a British car dealership, if someone brought a transmission in a box and it was not the one it came in they were charged by the hour. We abandoned flat rate charges. It’s amazing how difficult and time consuming it can be to put one of those back together. It’s a metallic jigsaw puzzle where everything begins to look alike. Trying to match the parts with the break-way diagram in the workshop manual can be a daunting task. Only transmissions correctly assembled with proper clearances using precisely machined parts in a clean environment will function properly. All others will be sub-standard in some way.
This is not intended to discourage the brave-at-heart who wish to tackle the “surreptitious box” but simply to serve as a warning; to be forewarned is to be fore- armed. In other words read the manual thoroughly. Make sure you understand all that you think you know about it. Then clean off the bench and have at it!
The differential however, is another matter all together. These “pumpkins” require special tools. Churchill Tool Company made most of them for British cars. They made tools for rebuilding the gearboxes as well but you can usually get by without them. Since they are out of business all these tools are getting very difficult to find. They made tools that set the pinion so it would mesh properly with the crown gear, measure the lash and preload and even to disassemble the rear itself. One of them is called a case spreader. Yes, it actually stretches the case so the gear cage will come out. The first time I was asked to get one I thought I was going on a Snipe hunt. You mean you actually have to “stretch” the cast iron differential case? Oh yes, well most of the time.
If you are changing the gear ratios access to the correct pinion tool is invaluable. You can “wag it in” but it can be time consuming and faulty. I have done Jaguar (Salisbury) rears where I did everything perfectly and they were still a little noisy. Then I would do one in a hurry and it would be quiet as a kitten. Beats me. Where is Yoda when you need him?
I have developed a strategy for dealing with diffs and tyrannies; change the seals and fluid, paint them if you want to but if they are relatively quiet leave the inside alone. I have come to the conclusion that the hidden secrets to anything that has gears is “if it still works don’t fix it!
Remember when driving British cars little noises, rattles and nuances should be expected and celebrated, then ignored. They are all part of the grand design just like oil emitting from most of the mechanical components. After all, driving a British car offers challenges not expected by other vehicles but that’s really just part of the adventure.
